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Anim. Behav., 1988, 36, 44-54

T h e e f f e c t o f a g e a n d v i s u a l c u e s o n f l o r a l

p a t c h u s e b y b a n a n a q u i t s ( A v e s: E m b e r i z i d a e )

J O S E P H M . W U N D E R L E , J R * & D . J E A N L O D G E r

* Department o f Biology, U niversity o f Puerto Rico, Cayey, P R 00 633 , U.S.A .t Terrestrial Ecology D ivision, Center fo r E nergy an d Environment Research, G.P.O. 3682, San Juan,

PR 00936 , U .S .A .

A b s t r a c t . T h e f o r a g i n g a b i l i ti e s o f n a i v e , h a n d - r e a r e d j u v e n i l e b a n a n a q u i t s , Coereba flaveola, w e r e

c o m p a r e d t o t h o s e o f c a p t i v e w i ld a d u l t s f o r a g i n g i n a n a r ti f ic i a l f l o w e r p a t c h c o n t a i n i n g e i th e r o p e n o r

c l o s e d f l o w e r s . F o r a g e r s r e m o v e d t h e t o p s f r o m c o v e r e d f l o w e r s i n o r d e r t o f e e d , t h e r e b y m a r k i n g a l l

v i s i te d f l o w e rs . O p e n f l o w e r s p r o v i d e d n o c l u e s a s t o p r e v i o u s v i s i t a t i o n . A d u l t s s e a r c h e d t h e p a t c h m o r e

t h o r o u g h l y a n d m a d e f e w e r f lo w e r re v i si t s d u r i n g e a c h f o r a g i n g b o u t t h a n d i d j u v e n il e s. F l o w e r

r e v i s it a t io n s b y j u v e n i l es w e re m o r e t h a n e x p e c t ed b y c h a n c e w h i l e t h o s e m a d e b y a d u l t s w e r e f e w e r t h a n

e x p e c t e d b y c h a n c e . T h i s w a s t r u e f o r b o t h o p e n a n d c o v e r e d f l o w e r t y p e s . T h e i n c r e a s e i n f o r a g i n ge f fi c ie n c y w i t h a g e i n v o l v e s s e v e r a l d i ff e r e n t c h a r a c te r i s t i c s. O n o p e n f l o w e r s , a d u l t s a n d j u v e n i l e s d i ff e r e d

i n t h e f re q u e n c y o f t h e i r p a t c h d e p a r t u r e s a n d r e t u rn s , a n d i n t h e i r p a t t e r n o f t u r n i n g i n t h e p a tc h , t h u s

r e s u ! t in g i n a m o r e c o m p l e t e s e a r c h o f th e p a t c h b y a d u l t s . O n c o v e r e d f l o w e r s , h o w e v e r , t h e t w o a g e

c l a ss e s d i f f e re d p r i m a r i l y i n t h e i r p a t t e r n s o f t u r n i n g , a n d a d u l t s m a d e a m o r e c o m p l e t e s e a r c h o f t h e

p a t c h . B o t h a g e c l a s se s u s e d t h e p r e s e n c e o r a b s e n c e o f f l o w e r c o v e r s a s a c l u e t o p r e v i o u s v i s i t a t i o n .

F o r a g e r s f r e q u e n t l y e n c o u n t e r f o o d i t e m s i n

c l u m p s o r p a t c h e s ( G i b b 1 95 8; T a y l o r 1 9 61 ; W i e n s

1 97 6). T h e f r e q u e n t o c c u r r e n c e o f t h i s r e s o u r c e

d i s p e r s i o n p a t t e r n a n d t h e p r o b l e m s f a c e d b y

c o n s u m e r s a s t h e y f o r a g e i n p a t c h e s h a s f o s t e r e d

n u m e r o u s t h e o r e ti c a l a n d e m p i r i c a l i n v e s t ig a t i o n s

( f o r r e c e n t r e v i e w s see : K r e bs e t a l . 1983 ; K r e b s &

M c C l e e r y 1 9 8 4 ; P y k e 1 9 8 4 ; G a s s & S u t h e r l a n d

1 98 5). M a n y o f t h e s e s t u d i e s h a v e f o c u s e d o n

n e c t a r i v o r e s w h i c h t y p i c a l l y f o r a g e i n f lo w e r

p a t c h es . N e c t a r i v o r e s m a y o b t a i n i n f o r m a t i o n

a b o u t t h e q u a l i t y a n d v a r i a b i l i ty o f r e w a r d s i n a

p a t c h a s t h e y f o r a g e ( P y k e 1 9 7 8 a , 1 9 8 1 ; H o d g e s

1 98 1). A s a n e c t a r i v o r e c o n t i n u e s t o f o r a g e , h o w -

e v e r, t h e p r o b a b i l i t y o f r e v i s i t in g a f l o w e r in c r e a s e s

( e .g . P y ke 1978b , 1981, 1982 ), t h e r e b y de c r e a s in g

p a t c h q u a l i t y . W h i l e v a r i o u s m o d e l s o f p a t c hc h o i c e a n d p a t c h d e p a r t u r e h a v e b e e n t e s t e d ( e . g .

K r e b s e t a l . 1 9 7 4 ) , t h e r e h a v e b e e n n o p r e v i o u s

s t u d ie s o n t h e o n t o g e n y o f p a t c h - u s e b e h a v i o u r .

F o r n e c t a r i v o r o u s b i r d s , n e c t a r i n fl o w e r s r e p r e -

s e n t s a f o o d r e s o u r c e t h a t i s e x h a u s t e d o n a s i n g l e

v i s i t a n d r e q u i r e s t i m e t o b e r e p l e n i s h e d . A n e c t a r i -

v o r e r e t u r n i n g t o a r e c e n t l y e m p t i e d f l o w e r w o u l d

h a v e a l o w e r r a t e o f n e t e n e r g y g a i n t h a n a n

i n d i v i d u a l m o v i n g t o a n o t h e r , a s y e t u n v is i te d

f l o w e r . B i r d s s h o u l d t h e r e f o r e a v o i d r e v i s i t s t o

f l o w e rs d u r i n g a f o r a g i n g b o u t . F i e l d s tu d i e s h a v e

c o n f i r m e d t h a t s u n b i r d s ( G i l l & W o l f 1 97 7) a n d

s o m e H a w a i i a n h o n e y c r e e p e r s (K a m i l 1 97 8) a v o i d

f l o w e r r e v i si t s. L e a r n i n g e x p e r i m e n t s h a v e f u r t h e r

d e m o n s t r a t e d t h a t w i l d a d u l t h u m m i n g b i r d s ( C o l e

e t a l . 1 98 2) a n d b a n a n a q u i t s (Coereba flaveola;

W u n d e r l e & S o t o 1 98 7) c a n b e m o r e e a s i ly t r a i n e d

t o v i s i t a f l o w e r in a n e w l o c a t i o n t h a n i n a l o c a t i o n

j u s t v i s i t e d e v e n w h e n t h e b i r d s a r e r e w a r d e d f o r

r e v i s i t s . I n t h e s e e x a m p l e s , a d u l t b i r d s m a y h a v e

l e a r n e d t o a v o i d r e v is i ts t h r o u g h p r e v i o u s e x p e r-

i e n ce , b e c a u s e r e v i s it s t o e m p t y f l o w e rs i n t h e w i l d

w o u l d r e s u l t i n r e d u c e d f o r a g i n g e f fi c ie n c y .

I m p r o v e d f o r a g i n g e f fi c ie n c y h a s b e e n c o r r e l a t e d

w i t h e x p e r i e n c e f o r a v a r i e t y o f b i r d s p e c ie s , e . g.

b r o w n p e l i c a n s (Pelicanus occidentalis, O r i a n s

1969 ; B r a nd t 1984 ; C ob le n t z 1986 ) , o l i va c e ous

c o r m o r a n t s (Phalacrocorax olivaceus, M o r r i s o n e t

a l . 1978 ), l i t t l e b lue he r ons (Florida caerulea,R e c he r & R e c he r 1969 ), c a t t l e e g r e t s (Ardeola ibis,

S ie g f r i e d 1972 ) , m oor he ns (Gall inula choropus ,

S u the r l a nd e t a l . 1986 ) , oys t e r c a t c he r s (Haemato-

pus os t ra legus , N o r t o n - G r i f f i t h s 1 9 6 8 ) , B o n a -

p a r t e ' s g u l l (Larus philadelphia, M a c L e a n 1 9 8 6 ) ,

r i n g - b i l l e d g u l l (L. delawarensis, M a c L e a n 1 9 8 6 ) ,

h e r r i n g g u l l s (L. argentatus V e r b e e k 1 9 7 7 ; M a c -

L e a n 1 98 6), g l a u c o u s - w i n g e d g u ll s (L. glaucescens,

S e a r c y 1978 ), r oy a l t e r n s (Sterna max ima, B u c k l e y

& B uc k le y 1974 ) , s a ndw ic h t e r n s (S. sandvicensis,D u n n 1 97 2), A m e r i c a n r o b i n (Turdus migratorius,

G o c h f e l d & B u r g e r 1 9 8 4), n o r t h e r n m o c k i n g b i r d s

44

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Wunderle & Lodge." Floral patch use by bananaquits 45

(Mimus polyglottos, Breitwisch et al. 1987), and

starlings (Sturnus vulgaris, Stevens 1985). In these

species, the improved foraging efficiency of adult s

results from more successful searches or more prey

captures.Whereas previous work suggests that adult

bananaquits should be more efficient foragers than

juveniles, it has not yet been shown in what manner

the foraging behaviour of bananaquits differs

between adults and juveniles. Impro ved patch use

due to experience could involve more efficient

movement patterns, the ability to recognize pre-

viously visited flowers, and decisions regarding

when to leave a patch, all of which may be partial ly

dependent on learning. In this study we investi-

gated these possibilities by comparing the foraging

patterns of captive, wild adult bananaqui ts (experi-

enced) with those of hand-reared juveniles (naive)

as they foraged in a patch containing a random

distribution of artificial flowers. We compared

juvenile and adult foraging abilities on open

flowers, which provided no external clues as to

previous visitation, versus covered flowers, which,

because they must have their tops removed by the

forager, provided potential visual clues as to

previous visitation.

We deliberately chose to compare revisitation

rates to open flowers versus closed flowers in aneffort to mimic field conditions. Bananaquits leave

no evidence of visitation on flowers with short

corollas, since they enter the front of the flower to

extract nectar. In contrast, bananaquits pierce the

base of the calyx or corolla of long flowers, thereby

providing a potential clue for subsequent bouts or

visitors. Such clues might be used by bananaquits

in selecting flowers or patches, just as sunbirds can

discriminate between open and closed mistletoe

flowers (Phragmanthera dshallensis, Gill & Wolf

1975).

M E T H O D S

Nestling bananaquits were collected and hand-

reared in Cayey, Puerto Rico during June and July

1984. Once fledglings were capable of feeding

themselves, their solid food mixture (Wunderle &

O'Brien 1985) was placed in a shallow dish at the

bottom of their cage. Twenty bananaquits were

housed in two cages (1 x 0-5 x 0.5 m) that received

indirect sunlight and a natural photoperiod(approximately 12 h of light and 12 h of darkness).

All juveniles were at least 45 days of age at the time

of the experiments and were capable of sustained

flight. Prior to the experiments, the hand-reared

juveniles had neve r fed from flowers. Ten juveniles

were used for these experiments, five for the openflowers and five for the cove red flowers.

Wild bananaquits were captured in mist nets in

Cayey, Puerto Rico in January and February 1985.

All wild birds were in adult plumage, indicating

that they were at least 1 year of age. They were

placed together in a cage and kept under the same

conditions as the hand-reared juveniles. Ten adults

were used for the experiments, five for the open

flowers and five for the covered flowers. At the end

of the study, all adults were released.

The experiments were conduc ted in a flight cage

measuring 1 × 1 × 3 m with a floral board, measur-

ing 1 × 1 m, til ted 20 ° from the vertical at the back

of the cage. The flight cage was covered with a

black plastic sheet, except for the front, where a

one-way mirror measuring 35 x 60 cm was located

for observation. A fluorescent light was affixed to

the interior cage-top for illumination of the floral

board. The floral board contained a random array

of 85 red and 85 yellow artificial flowers inter-

spersed within a grid of 19 vertical and 19 horizon-

tal perches. Two flower colours were used in our

experiments because the results are intended toserve as the basis for future wo rk on the response of

bananaquits to differences in food rewards between

the two flower colours. As in previous work

(Wunderle & O'Brien 1985), we found that the

bananaquits showed no colour preferences when

both flower colours provided the same rewards.

Each flower consisted o f a straw floral tube l cm

long x 0"6 cm in diamet er at tached with a plastic

sealant to the centre of a numbered coloured tape

background (3-5 x 3"5 cm). The distance between

the closest flowers was 4-5 cm. For some experi-

ments, the floral tubes were left uncovered (desig-

nated open flowers) while in other experiments all

floral tube openings were covered with a coloured

tape disk (designated covered flowers), which the

bird had to pry off prior to feeding. To train the

birds to feed on the board, all flowers were filled

with a 15% sucrose solution (the same solution,

henceforth called nectar, was used in all experi-

ments). A group of birds was placed in the flight

cage, and within 45 min all individuals had learned

to feed from the open flowers. Once an individual

had learned to feed on open flowers, it was trainedto feed on covered flowers by presenting it with

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46 Anim al Behaviour, 36, 1

partially covered flowers on the edge of the floral

board and covered flowers in the centre. Each

flower was filled with 10 #1 of nectar for the

experiments. We measured the quantity of nectar

remaining in flowers following a single feeding visitby probing the flower with a micropipette. Five

visited flowers were sampled for each individual

(five juveniles and five adults; N= 50) and no

remain ing nectar was detected. Thus , we assume

that all nectar was removed dur ing a forager's first

visit to a flower.

Once it became accustomed to feeding on the

board, an individual was released into a flight cage

containin g no food or water. After an adjustment

period of 1 h, the bird was presented with the floral

board. All behaviour was recorded by an observer

watching through the one-way mirror. The bird

usually flew immediately to the floral board, and

the sequence of numbered flower visits was entered

on a computer. The board was removed after the

bird ceased to forage for 1 min; most foraging

periods were 10-15 min. Foraging periods were

separated by a 1-h interval in which the bird

received no food. Each ind ividual was given three

consecutive presentations (designated as runs) in

the morn ing (0600-1130 hours). Exper iments with

juven iles with open flowers were ru n in the first

week of October followed by experiments withjuveniles with covered flowers in the second week.

Experiments with adults with open flowers were

run in the first week of June followed by experi-

ments with adults with covered flowers in the

second week.

In these experiments a probab ility of type I error

of 0-05 or less was accepted as significant, but we

show greater values for descriptive purposes.

RESULTS

F l o w e r R e v i s i t a t io n s

To compare flower revisitation rates for adult

and juvenile bananaquits foraging on open and

covered flowers, we calculated the total number of

flower visits and revisits during each foraging

sequence. The numbers of visits and revisits were

greater in juveniles (open flowers: )(-+_so = 172.0 +

61.2 visits, with )?+SD=77.7_+56-7 revisits;

covered flowers: .(±SD = 112-4_+ 30'0 visits, with

)? + SD = 49-2 + 22'8 revisits) than in adul ts (open

flowers: .('+SD = 138"4+40.9 visits, with ) ?+so =30'5+22"2 revisits; covered flowers: )?+so=

102.1+26.1 visits, with )~-I-SD=17.7+ 15-8 re-

visits). A two-way analysis of covariance

(ANCOVA) with repeated measures was used to

analyse the relationship of revisits with two treat-

ments, bi rd age (juvenile or adult), and flower type(open or covered), while removing variation due to

the total number of flower visits (the covariate).

The total num ber of flower visits was foun d to co-

vary significantly with revisits ( F= 146.99, df= 1 ,P < 0.0001). The ANCOVA indicates that age had

a s ignificant effect on revisitation, after vari ation

due to the total number of flower visits was

removed by the covariate (F=22-27, d f = l ,P=0-0003). Juveniles made far more revisits per

total n umber o f visits than adults. Flower type also

signif icantly affected revis itation (F= 10.54, d f= 1,

P = 0'005), and the birds were more likely to revisit

in the open-flower than in the closed-flower treat-

ment. Although the data suggest that juveniles

behaved similarly regardless o f flower type, adults

revisited covered flowers less fr equently than open

flowers. No significant interaction was found,

however, between age and flower type in the

ANCOVA (F= 0.10, d f= 1, P = 0.76). Differences

in revisitation behaviour between runs were only

suggestive (F=3'00, d f = 2 , P=0-06), but there

were no significant interactions with either age

(run x age: F= 0.84, dr= 2, P= 0.44) or flower type(ru n x flower: F= 1-90, d f = 2 , P=0.17). This indi-

cates that overall revisitation behaviour differed

only slightly between runs, and that behaviour over

runs was no t related to age or flower type.

To examine the patterns of flower revisitations

further, a frequency distribution (tabulating the

number of flowers receiving zero visits, one visit,

etc.) was calculated for each bird during the third

run (run C). If each visit to a flower was indepen-

dent of all other visits by the same ind ividual, the

observed distribu tions should approximate a Pois-

son distribution. The frequency distributions for

each individua l differed significantly from a Pois-

son distribution (goodness-of-fit test with a G-

statistic), regardless of the flower type or age. Data

were then pooled within age classes when no

significant heterogeneity among individuals was

indicated by a replicated goodness-of-fit test with a

G-statistic (Sokal & R ohl f 1981). The pooled

frequency distribution for juvenile visits to open

flowers was signif icantly different from the

expected Poisson distribution (P<0.005), with

juveniles revisiting more flowers than expected bychance (Table I). Similarly, the distribution of

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Wunderle & Lodge: Floralpatch use by bananaquits

Table I . Observed dist r ibut ions of visi t s and revisit s by fo raging juveni le and ad ul tbananaqu i t s com pared w i th the Po i sson d i s t r i bu t ion

47

Age* F lower t ype Di s t r i bu t i on

N u m b e r o f v i s it s t

0 1 2 3 > 4 G-value

Juveni le Op en Obs erved 609 150 66 22 3Pois son 557 236 50 7 1 68.255

Ad ul t O pen Obs erved 517 293 38 2 - -Pois son 547 241 53 9 23-255

Juveni le Cov ered Obs erved 600 154 74 20 2Pois son 550 239 52 8 1 188.17,

Ad ul t Cov ered Obs erved 510 305 35 0 0Poisson 547 241 62 - - 40.82*

* Each grouping i s poo led for f ive individuals dur ing runt No te tha t two or m ore visi ts i s equivalent to a revisi t.

* P < 0.005.

C .

j u v e n i l e v i s it s to c o v e r e d f l o w e r s w a s s i g n i f i c a n tl y

d i ff e re n t f r o m e x p e c t e d ( P < 0 . 0 0 5 ) , a g a i n w i t h

r e v is i ts h i g h e r t h a n e x p e c t e d . A l t h o u g h a d u l t s a l s o

s h o w e d s i g n i f i c a n t d i f f e r e n c e s f r o m t h e e x p e c t e d

P o i s s o n d i s t r ib u t i o n ( o p e n , P < 0 - 0 0 5 ; c o v e r e d ,

P < 0. 0 0 5) , t h e y m a d e f e w e r r e v i si t s t h a n e x p e c t e d .

Overal l Coverage of the Patch

T o q u a n t i f y t h e p r o p o r t i o n o f p a t c h a r e a v i s i t ed

b y a f o r a g e r d u r i n g e a c h r u n , w e d i v i d e d t h e p a t c h

i n t o 3 6 s e c t o r s a n d c a l c u l a t e d t h e t o t a l n u m b e r o f

s e c t o r s v i s i t e d b y t h e f o r a g e r . E a c h s e c t o r w a s

1 5 x 1 5 c m , s i nc e (1 ) a f o r a g i n g b a n a n a q u i t c o u l d

r e a c h f l o w e r s f r o m a c e n t r a l l o c a t i o n w i t h o n l y

m i n i m a l m o v e m e n t , a n d ( 2) t he 1 5 -c m d i m e n s i o n s

a l l o w e d e q u a l d i v i s i o n o f t h e f l o r a l b o a r d a l o n g

h o r i z o n t a l a n d v e r t i c a l p e r c h e s . S t a n d a r d

A N C O V A p r o c e d u r e s w e r e u s e d t o a n a l y s e t h e

r e l a t i o n s h i p o f t o t a l s e c t o r v i s it s w i t h a g e a n d

f l o w e r t y p e u s i n g t h e t o t a l n u m b e r o f f lo w e r v i s i ts

a s th e c o v a r i a t e . T h e n u m b e r o f s ~J cto r v i s it s d i d n o t

c o - v a r y s i g n i f i c a n t l y w i t h t o t a l f l o w e r v i s i t s i n a

f o r a g i n g s e q u e n c e ( F = 0 . 7 9 , df= 1, P = 0 . 3 9 ) . A g e

s i g n if i c a n tl y a ff e c t e d th e n u m b e r o f s e c t o r s v i s i t e d

( F = 4 . 4 1 , df= l , P = 0 . 0 5 ) . J u v e n i le s v is i te d fe w e r

s e c to r s e v e n t h o u g h t h e y m a d e m o r e f l o w e r vi s it s

t h a n a d u l t s . F l o w e r t y p e a l s o s i g n i f i c a n t l y

i n f l u e n c e d t h e n u m b e r o f s e c t o r s v i s i t e d ( F = 6 . 1 7 ,

df=l, P = 0 - 0 2 ) , w i t h c o v e r e d f l o w e r s e l ic i ti n g

m o r e s e c t o r v i si t s t h a n o p e n f l o w e r s . N o s i g n i f i c a n t

i n t e ra c t io n w a s f o u n d b e t w e e n a g e a n d f l o w e r ty p e( F - - 0 . 0 1 , df= 1 , P = 0 . 9 3 ) . I n a d d i t i o n , t h e r e w e r e

n o d i f fe r e n c e s i n b e h a v i o u r b e t w e e n r u n s ( F = 0 . 3 1 ,

df=2, P = 0 . 7 3 ) , n o r w e r e t h e r e a n y s i g n i f i c a n t

i n t e r a c t i o n s w i t h r u n s ( r u n x a g e : F = 0 . 4 2 , df= 2,P = 0 . 6 6 ; r u n x f lo w e r: F = 0 . 1 3 , df=2, P = 0 . 8 8 ;

r u n x a g e x fl o w e r : F = 1 .2 8 , df= 2, P = 0-29) .

S t r o n g e v i d e n c e f o r s y s te m a t i c p a t t e rn s o f m o v e -

m e n t b y a d u l t s i s i l l u s tr a t e d b y s i g n i f i c a n t p o s i ti v e

c o r r e l a t i o n s b e t w e e n t h e n u m b e r o f s ec t o r s v is i te d

a n d t o t a l f lo w e r v i s it s f o r b o t h o p e n a n d c l o s e df lo w e rs ( r = 0 . 8 1 2 , P < 0 . 0 1 ; r = 0 - 8 9 3 , P < 0 . 0 1 ,

r e s p e c t i v e l y ) . I n c o n t r a s t , j u v e n i l e s s h o w e d n o

s i g n i f ic a n t c o r r e l a t i o n s b e t w e e n t h e n u m b e r o f

s e c t o r s v i s i te d a n d t o t a l f l o w e r v i s it s f o r e it h e r o p e n

( r = 0 . 1 2 7 ) o r c o v e r e d fl o w e rs ( r = 0 . 4 6 7 ) . T h e s e

d i f f e r e n c e s b e t w e e n a d u l t s a n d j u v e n i l e s e x p l a i n

w h y s e c t o r v i s i ts d i d n o t s i g n i f ic a n t l y c o - v a r y w i t h

f lo w e r vi si ts in t h e A N C O V A a b o v e .

P o s i t i o n e f f e c t s w e r e p r e v i o u s l y o b s e r v e d i n

b a n a n a q u i t s f o r a g i n g i n a f lo r a l p a t c h ( W u n d e r l e ,

u n p u b l i s h e d d a t a ) a n d g i v e n a c h o i c e o f fl o w e r s in

t w o d i f f e r e n t p o s i t i o n s ( W u n d e r l e & S o t o 1 98 7). T o

q u a n t i f y s u c h a p o s i t i o n e f f e c t , w e c a l c u l a t e d a l l

s e c t o r v is i ts a b o v e a n d b e l o w t h e h o r i z o n t a l m i d -

l i n e o f t h e f lo r a l b o a r d ( T a b l e I I ) , a n d a l l s e c t o r

v i s it s o n t h e l e f t a n d r i g h t o f t h e v e r t i c a l m i d - l i n e .

S i g n i f i c a n t p r e f e r e n c e s f o r t h e u p p e r p a r t o f t h e

b o a r d o c c u r r e d w h e n ju v e n i l e s f e d o n o p e n f l ow e r s

( t w o - t a i l e d , W i l c o x o n s i g n e d - r a n k s t e s t , T = 1 18 .5 ,

P < 0 . 0 0 1 ) a n d o n c o v e r e d f lo w e rs ( T = l I 4 . 0 ,

P < 0 - 0 0 2 ) . A d u l t s s h o w e d a s i m i l a r p r e f e r e n c e f o r

t h e u p p e r p a r t o f th e p a t c h w h e n p r e s e n t e d w i th

o p e n f l o w e r s ( T = 1 0 2. 5, P < 0 . 0 01 ) , b u t s h o w e d n os i g n i f i c a n t p r e f e r e n c e w h e n f e e d i n g o n c o v e r e d

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4 8 Animal Behaviour, 36, 1

Table I I . Pos i t ion preferences of juveni le and adul t banan aqui ts foraging in an ar t i f ic ia l f lower pa tchwi th op en and covered f lowers for a ll individuals and a l l runs

Nu mb er of sec tors visi ted (Mean_+ SE)*F l o w e r

Age type Up pe r ha l f L ower ha l f P :~ R igh t ha l f L e f t ha l f P

Juveni le Op en 17.0- t-0 .3 11.2_+ 1.2 < 0 . 00 1 1 4. 6 _+ 0. 7 13.7+0.9 NSAd ul t 16 .9+0 .3 13"8_+0"7 < 0"0 01 15" 0_+ 0"6 15"7+0"5 NSJ u ve n il e C o v e re d 1 4 . 3 _ + 0 . 6 8 . 5 _ _ _ 0 . 9 < 0 .0 0 2 1 1 - 3 - t - 0 . 9 1 1 .3 _ + 0. 9 NSAd ul t 13.5+0 .8 11.9 _+0 .8 NS 13"0+0"8 12"4+0"9 NS

* The n um ber of 15 x 15-cm sec tors visi ted by foragers on each ha l f of the f lora l boa rd was used to testfor posi t ion preferences ( tota l numb er of sec tors = 36) .

:~ W ilcox on signe d-rank s tests, two-ta iled.

r " - "3 ADULT/

0 . 28 "~ m J U VEN ILE

IO. r 6 ~

0.12

0.08

0 .04

0.12

0.08

0.04

-135" -900 -45 " (7 45* 90* 135" 180"

A N G L E

Figure I . Dist r ibut ion of turning angles for adul t andjuven i le bananaqu i t s f e ed ing on op en (A) and cove red (B)flowers in an art ificial floral patch. See text for anexplanat ion of turning angles.

f l ow e r s ( T = 4 6 - 5 , P > 0 . 6 0 ) . N o e v i d e n c e f o r a

r i g h t / l e f t p o s i t i o n b i a s w a s f o u n d f o r e i t h e r a d u l t s

o r j u v e n i l e s f e e d i n g o n e i t h e r f l o w e r t y p e .

M o v e m e n t P a t t e r n s i n t h e P a t c h

A n i m p o r t a n t f a c t o r r e s p o n s i b le f o r d i ff e re n c es

i n a f o r a g e r ' s c o v e r a g e o f th e p a t c h a n d a s s o c i a t e d

f l o w e r r e v i s i ta t i o n s m a y b e t h e p a t t e r n o f t u r n i n g .

T o q u a n t i f y t u r n in g , w e m e a s u r e d a f o r a g e r ' s t u r n

a n g l e t o a th i r d f l o w e r f r o m a l i n e o f m o v e m e n tf o r m e d b y t h e t w o p r e v i o u s f l o w e r v i s it s . F o r

e x a m p l e , w e m e a s u r e d t h e a n g l e f r o m f l o w e r o n e

a n d t w o t o f l o w e r t h r e e , t h e n t h e a n g l e f r o m f l o w e r s

t w o a n d t h r e e t o f l o w e r f o u r a n d s o o n . O n t h e

f l o r a l - b o a r d g r i d , t h e s e a n g l e s c o u l d r a n g e f r o m

f o r w a r d m o v e m e n t w i t h n o c h a n g e ( 0° ), f o r w a r d t o

t h e r i g h t b y 4 5 ° , p e r p e n d i c u l a r t o t h e r i g h t ( 9 0 ° ),

b a c k t o t h e r i g h t ( 1 3 5 ° ) , o r a c o m p l e t e r e v e r s a l o f

1 80 ° C o r r e s p o n d i n g t u r n s t o t h e l e ft o f t h e d i re c -

t i o n o f m o v e m e n t w e r e - 4 5 ° , - 9 0 ° , o r - 1 35 °. W e

r e c o r d e d a l l t u r n i n g a n g l e s i n e a c h f o r a g i n g b o u t ,

e x c l u d i n g t h o s e e n d i n g i n a fl i g h t d e p a r t u r e , b e g i n -

n i n g w i t h a f li g h t r e t u r n , a n d t h o s e w i t h f l o w e r s

a l o n g t h e f l o r a l - b o a r d p e r i m e t e r . T h e f r e q u e n c yd i s t r ib u t i o n s o f t u rn s a m o n g t h e ei g h t tu r n i n g -

a n g l e c a t e g o r i e s w e r e a n a l y s e d f o r h e t e r o g e n e i t y

a m o n g r u n s w i t h i n i n d i v i d u a l s , h e t e r o g e n e i t y

a m o n g i n d i v i d u a l s w i t h i n a g e c l a s s e s , d i f f e r e n c e s

b e t w e e n a g e c l as s e s , a n d g o o d n e s s - o f - f i t t o a n

e q u a l d i s t r i b u t i o n u s i n g r e p l i c a t e d g o o d n e s s - o f - f i t

t e s t s a n d G - s t a t i s t i c s ( S o k a l & R o h l f 1 9 8 1 ) .

T h e d i s t r i b u t i o n o f t u r n i n g a n g l e s in t h e o v e r a l l

g o o d n e s s - o f - f i t t e s t i n d i c a t e s t h a t t h e f o r a g e r s d i d

n o t t u r n e q u a l l y i n a l l o f t h e e i g h t p o s s ib l e d i r e c -

t i o n s ( G - s t a t i s ti c s , P < 0 ' 0 5 ). A g e a n d f l o w e r t y p e

w e r e b o t h a s s o c i a t e d w i t h d i f f e re n t p a t t e r n s o f

t u r n i n g ( F i g . 1 ). B o t h j u v e n i l e s a n d a d u l t s d i s -

p l a y e d s i g n i f i c a n t h e t e r o g e n e i t y a m o n g i n d i v i d u a l s

w i t h i n a g e c l a s s e s w h e n f e e d i n g o n o p e n f l o w e r s

( juven i l e s : G = 71 .05 , P < 0 -005 ; a du l t s : G = 46 .38 ,

P < 0 . 0 2 5 ) . F u r t h e r m o r e , s i g n i fi c an t h e t e r o g e n e i t y

a m o n g r u n s w a s f o u n d f o r t w o j u v e n i le s w h e n

f o r a gi n g o n o p e n f lo w e rs (G = 2 5 . 7 2 , P < 0 . 0 5 ;

G = 3 2 . 8 3 , P < 0 .0 0 5 ) , b u t n o a d u l t s s h o w e d h e t e r o -

g e n e i t y a m o n g r u n s . T h e s e r e s u l t s s u g g e s t t h a t

a l t h o u g h a d u l ts v a r y i n th e i r m o v e m e n t p a t t e rn s ,

i n d i v id u a l s h a v e c o n s i s t e n t p a t t e r n s o f t u r n i n gw h i c h m a y h a v e d e v e l o p e d t h r o u g h p r e v i o u s e x -

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Wu nderle & Lodg e: F loral patch use by bananaquits 4 9

p e r i e n c e w i t h o p e n f l o w e r s . O v e r a l l , t h e t u r n i n g

m o v e m e n t s o f a d u l t s ( a l l r u n s p o o l e d ) w e r e s ig n i fi -

c a n t l y d i f f e r e n t ( G = 1 6 4 . 7 6 , P < 0 - 0 0 5 ) f r o m t h o s e

o f t h e j u v e n i l e s ( a ll r u n s p o o l e d ) w h e n f e e d i n g o n

o p e n f l o w e r s (F i g . 1 A ) . J u v e n i l e s a s a g r o u p t e n d e dt o m a k e a l i n ea r p r o g r e s s i o n a n d r a r e ly t u r n e d

w h e n f e e d i n g , w h e r e a s a d u l t s t u r n e d e q u a l l y i n a l l

d i r e c t i o n s e x c e p t 1 80 ° ( F i g . 1 A ) .

W h e n f e e d i n g o n c o v e r e d f l o w e r s, j u v e n i l e s a n d

a d u l t s s h o w e d n e i t h e r h e t e r o g e n e i t y w i t h i n i n d i -

v i d u a ls ( a ll i n d iv i d u a ls , P > 0 . 0 5 ) , n o r h e t e r o g e -

n e i t y a m o n g i n d i v i d u a l s w i t h i n e a c h a g e c l a s s

( j u v en i le s : G = 2 7 . 0 8 , N S; a d u l t s : G = 3 9 . 5 5 , M S ).

T h u s , a l l j u v e n i l e s c o n s i s t e n t l y t u r n e d i n t h e s a m e

m a n n e r a n d a l l a d u l ts c o n s i s t e n t l y tu r n e d i n t h e

s a m e m a n n e r w h e n f e e d i n g o n c o v e r e d fl o w e rs . W e

t h e r e f o r e p o o l e d a l l th e i n d i v i d u a l j u v e n i l e t u r n i n g

r e su l ts f o r c o v e r e d f lo w e r s a n d c o m p a r e d t h e m

w i t h t h e p o o l e d a d u l t r e s u l t s ( F i g . 1 B). T h e a n a l y s i s

i n d i c a t e s a s i g n i f i c a n t d i f f e r e n c e ( G = 6 0 . 6 6 ,

P < 0 . 0 0 5 ) b e t w e e n a d u l t a n d j u v e n i l e t u r n i n g

a n g le s w h e n f e e d in g o n c o v e r e d f lo w e rs . T h e m a j o r

d i f f e r e n c e b e t w e e n t h e t w o a g e c l a s s e s i s i n t h e

d i s p r o p o r t i o n a t e l y h i g h f r e q u e n c y o f 1 80 ° t u r n s

m a d e b y j u v e n i l e s , s in c e e l i m i n a t i o n o f t h is c a t e -

g o r y a n d a n a l y s i s o f t h e s e v e n r e m a i n i n g c a t e g o r i e s

i n d i c a te s n o s i g n i fi c a n t d i f f e re n c e ( G = 6 . 4 2 , M S)

b e t w e e n t h e t w o a g e c l a s s e s . T h u s , j u v e n i l e sr e v e r s e d t h e i r m o v e m e n t p a t h m o r e o f t e n t h a n

a d u lt s w h e n f e e d in g o n c o v e r e d f l o w e rs .

T h e p r e s e n ce o r a b s e n c e o f c o v e r s o n t h e f l o w e r s

w a s a s s o c i a t e d w i t h d i f f e r e n c e s i n t h e p a t t e r n o f

t u r n i n g w i t h e a c h a g e c l as s . S i g n i f i c a n t d if f e r e n c e s

i n t u r n i n g p a t t e r n s w e r e f o u n d b e t w e e n o p e n a n d

c l o s e d f l o w e r s f o r j u v e n i l e s ( G = 2 1 3 . 5 4 , P < 0 . 0 0 5 ) ,

a n d a l s o f o r a d u l t s ( G = 2 1 . 44 , P < 0 - 00 5 ). T h e r e -

f o re , t h e p a tt e r n o f t u r n i n g a n d m o v e m e n t t h r o u g h

t h e p a t c h d i f f er e d , d e p e n d i n g u p o n b o t h a g e a n d

f l o w e r t y p e .

Pa tc h D e p a r tu r e s an d R e W r n s

F l i g h t s o f f t h e f lo r a l b o a r d t o a n e a r b y p e r c h

f o l l o w e d b y re t u r n f l ig h ts w e r e i m p o r t a n t c o m p o -

n e n t s o f th e f o r a g i n g m o v e m e n t s o f al l b a n a n a -

q u i ts . D u r i n g e a c h f o r a g i n g s e q u e n c e , w e r e c o r d e d

t h e n u m b e r o f t i m e s a b i rd d e p a r t e d f r o m a n d

r e t u r n e d t o t h e f l or a l b o a r d . U s i n g t h e n u m b e r o f

f l o w e r v i si ts as a c o v a r i a te , w e u s e d a n A N C O V A

a n a l y s is o n a l l b i r d s a n d a l l r u n s t o e x a m i n e t h e

e ff ec t o f a g e a n d f l o w e r t y p e o n t h e n u m b e r o f t i m e sa fo r a g e r d e p a r t e d f r o m t h e f l o ra l b o a r d d u r i n g a

Table I I1 . Average number ( )?+SE) of ful l and emptyflowers within a 10 cm radius of a flower at t ime ofdepar ture are compared w i th those wi thin a 10 cm radiusat si te of return

F l o w e rFlower

Age type Behav iour Fu l l E m pty Ar t

Juveni le Open Depar ture 2.7__+0.3 4 .9+ 0.3

Re tu rn 2 -5+0 .4 4 -3+0 .3 25P* NS NS

Adul t Open Depa r tu re 3 .3+0 .4 5 .2+0 .5Re tu rn 5 .4+_ 0-5 3 .8+0 .6 29

P <0 .01 <0 .05Juven i le Cove red Depa r tu re 6 .0+0 .8 3 .7+0 .5

Re tu rn 7 .2+0-5 1 .4+0 .3 27P <0 .02 <0 .001

Adul t Cove red Depa r tu re 2 .9+0 .8 6 .1+1 .1Re tu rn 6 .4+0 .7 2 .9+ 0 .6 23

P <0-001 <0-02

* P-values are given for paired t-tests as explained in thetext.

t N represents the numb er of pa i red depar tures andreturns.

f o r a g i n g r u n ( T a b l e I II ). T h e n u m b e r o f d e p a r t u r es

d i d n o t s i g n if i ca n t ly c o - v a r y ( F = 0 . 0 2 , df= 1,

P = 0 .9 0 ) w i t h t h e n u m b e r o f f l o w e r v i si t s d u r i n g a

f o r a g i n g r u n . A g e w a s s ig n i f i c a n t ly a s s o c i a t e d w i t hd i f fe r e n c e s i n t h e n u m b e r o f d e p a r t u r e s d u r i n g a

f o r a g i n g s e q u e n c e ( F = 8 . 0 2 , d f = l , P = 0 . 0 1 ) .

F u r t h e r a n a l y s i s d e m o n s t r a t e d s i g n i f i ca n t c o r r e l a -

t i o n s b e t w e e n f l o w e r v i s it s a n d f l ig h t d e p a r t u r e s f o r

adu l t s (open : r = 0 -814, P < 0"01 ; co ve red : r = 0 ' 736 ,

P < 0 "0 1), b u t n o t f o r j u v e n i l e s (o p e n : r = 0 . 1 9 0 , y s ;

cov e red : r = - 0" 139, NS). F l ow er t yp e a l s o s i gn i f i -

c a n t l y in f l u e n c e d t h e n u m b e r o f d e p a r t u r e s

( F = 9 -9 9, df= 1 , P = 0"007), an d b i rd s l e f t t he pa t ch

w i t h o p e n f l o w e r s m o r e f r e q u e n t l y t h a n w i t h c l o s e d

f l o w e r s . N o s i g n i f i c a n t i n t e r a c t i o n o c c u r r e d

b e t w e e n a g e a n d f l o w e r t y p e ( F = 3 . 3 5 , df= 1,P = 0 . 0 9 ) .

E x p e r i e n c e o b t a i n e d d u r i n g t h e t h r e e p r e s e n -

t a t i o n s ( r u n s) s i g n i f ic a n t ly a ff e c t e d t h e n u m b e r o f

f o r ag e r d e p a rt u re s ( A N C O V A , F = 5 . 3 8 , d f = 2 ,

P = 0 . 0 0 9 ) , b u t t h e e f fe c t o f e x p e r i e n c e w a s c o m -

p l e x . T h e r e w a s a s i g n i f i c a n t i n t e r a c t i o n b e t w e e n

a g e a n d r u n ( F = 3 " 2 8 , d f= 2 , P = 0"05) , and adu l t s

t e n d e d t o d e c r e as e t he n u m b e r o f d e p a r t u r e s w h i l e

j u v e n i l e s te n d e d t o i n c r ea s e t h e n u m b e r o f d e p a r -

t u r e s o v e r r u n s . A s i g n if i ca n t in t e r a c t i o n b e t w e e n

f l o w e r t y p e an d r u n w a s a l s o o b s e r v e d ( F = 5 - 1 1 ,d f= 2 , P = 0 . 0 1 ); f o r ag e r s d e p a r t e d m o r e f r e q u e n t l y

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50 Animal Behaviour, 36, 1

from the open-flower patch than the closed-flower

patch with each run. The suggestive (F=3-09,

df= 2, P = 0-06) interaction of run, age and flower

type indicates that these factors together may

influence patch departures by the foragers.To determine whether the foragers consistently

left depleted areas and flew to unvisited sites, we

calculated the number of full and empty flowers

within a 10 cm radius of both the last flower visited

prior to departure and the first flower visited on

returning. We selected 10 cm as a distance over

which a forager could reach other flowers without

flying, and with a minim um o f hopping movement.

A paired t-test was used to compare the full flowers

near the sites of depar ture and return; the analysis

was repeated for empty flowers. Lower local

resource availability near patch borders would be

reflected in fewer full flowers within the 10 cm

radius. The distribution of empty flowers was not

simply the inverse of full flowers since much of the

floral board contai ned no flowers. If the birds were

flying from the patch edge or depleted areas to

unvisited areas in the patch, we would expect

differences in the numbers of full and empty flowers

near the site of departure and return.

For juveniles feeding on open flowers, the patch

departures and returns were unrelated to local

resource availability. This was evident from thealmost identical numbers of full flowers within 10

cm of the points of departure and return (Table

III); similar results were found for empty flowers.

These data indicate that juveniles did not

remember where they had previously fed. Covered

flowers, however, may provi de clues enabling juve-

niles to leave depleted areas for richer sites in the

floral patch. For instance, there were significantly

more full flowers at the return site than on

departure (t=2.59, P<0-02), and significantly

fewer empty flowers on the return (t=3"86,

P<0.001) when juveniles foraged on covered

flowers. Thus the juveniles were able to use the

covered flowers for locating richer areas of the

floral patch, but were unable to do so when the

flowers were open. Yet, despite the finding that

juveniles were able to use covered flowers for

locating richer areas of the floral patch when

departing and returning, they still displayed similar

revisitation rates fo r open and covered flowers. We

attribute this to the previously mentioned tendency

of juveniles to reverse their path of movement to

revisit flowers while moving across the patch withcovered flowers.

Adults departed from areas with low resources

and moved to richer areas, whether foraging on

open or closed flowers. For instance, with covered

flowers, more full flowers were at the site of return

than at the site of departure (t= 3-93, P< 0.001),and more empty flowers were at the site of

departure t han at the site of return (t =2-76,

P < 0.02). This same trend was found with open

flowers in which more full flowers were at the site of

return than that of departure (t=3-12, P< 0.01)

and correspondingly fewer empty flowers were in

the area of return than near the site of departure

(t=2. 38, P<0. 05) . Thus, adults were capable of

remembering the areas of the patch in which they

had fed even without clues, while juveniles did no t

do so unless provided with visual clues.

D I S C U S S I O N

As expected, adults searched the patch more

thoroughly (i.e. visited more sectors) and made

fewer flower revisitations during each foraging

bout than did the juveniles. Flower revisitations by

juveniles were more than expected by chance while

those made by adults were fewer than expected by

chance. This was true for both the open and

covered flower types. The adults were apparentlyable to re member the locations of previously visited

flowers, even though the open flowers may have

provided no information about previous visi-

tations. Hence, it appears that an increase in

foraging efficiency with age involves several differ-

ent characteristics.

A major difference between adults and juveniles

foraging on open flowers was in patch departures

and returns. The frequency of adult departures was

correlated with the number of flower visits, and

adults tended to fly from dep leted areas and the less

productive patch edge to unvisited areas of thepatch. This was not characteristic of the juveniles,

which departed and returned to the patch in a

ran dom manner. A second age difference, seen with

open flowers, was in the pattern of turning: juve-

niles tended to probe the flowers directly in front of

them, while adults turned widely to feed on nearby

flowers. The overall forward mov ement pattern of

juveniles frequently resulted in open flower revisits

when juveniles reached the patch edge, reversed

direction, and revisited all the flowers along the

same horizontal perch.Covered flowers have the potential to provide

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Wunderle & Lodge: Floral patch use by bananaquits 51

foragers with clues regarding previous visitat ions,

and it was evident that these clues were used by

adults and sometimes by juveniles. Under these

circumstances, the patterns of turning differed

between individuals within each age class but wereconsistent for each adult and most o f the juveniles.

When vis iting covered flowers, adul ts differed from

juveniles primarily in the patter n of turning, espe-

cially in the frequency of 180 ° turns. Adults rarely

reversed their direction of movement, while juve-

niles frequently did so. Yet, juveniles, as well as

adults, departed from nectar-poor areas of the

board for nectar-rich areas, suggesting that both

used flower covers as a clue.

Whereas the flower covers used in our experi-

ments are certainly more obvious visual clues than

flower-punctures in nature, the speed with which

both captive adults and naive juveniles responded

to them suggests that wild banana quits probably

also use available visual clues which indicate

previous visitation. This is supported by observa-

tions that bananaquits (Wunderle, unpublished

observations) and other nectarivorous species may

use flower-punctures in assessing resources in the

wild. For example, orchard orioles, leterus spurius,

feeding on Malvaviseus sp. flowers puncture the

corolla near its base and remove nectar. Flowers

punctured by orioles produce no more nectar, andhummingbi rds avoid visiting such flowers possibly

by using the oriole punctures as clues (Montgo-

merie 1979).

Previous experimental work by Hainsworth et al.

(1983) indicated that three-dimensional inflores-

cences resulted in fewer revisits by hummingbirds

relative to total flower visits than did two-dimen-

sional infloreseences. In our study the two-dimen-

sional patch may have cont ributed significantly to

flower revisitations, even by experienced adults.

While foraging on the board, adults occasionally

revisited a flower as they moved towards an

unvisited area. A three-dimensional patch might

reduce this tendency. Thus, by perching off the

floral board they may have obtained a better

perspective of the patch that was useful both for

remembering areas of previous visits and for

locating new areas.

Memory plays a valuable role in the foraging

behaviour of a variety of animals (Shettleworth

1984). For example, memory is particular ly impor-

tant in many parid and corvid species that store

food and recover it at a later date (Balda 1980;Shettleworth & Krebs 1982; Vander Wall 1982;

Sherry 1984a, b; Kamil & Balda 1985; Bunch &

Tomback 1986). In avian nectarivores, memory

undoubtedly is also important in reducing flower

revisits by foragers (Gill & Wol f 1977; Kamil 1978).

In our study, the importance of memory is sug-gested by the departure of adults from depleted

areas of the patch and their movement to unvisited

areas when they foraged on open flowers (i.e.

flowers with no clues indicating previous visi-

tation). It seems likely that a particular pattern of

the random array of red and yellow flowers in one

section of the patch is remembered by the depar ting

bananaquit and thus avoided on its return. Simi-

larly, wild hummingbirds remember the location of

resource patches relative to one another (Miller &

Miller 1971). On a finer scale, however, it may be

impossible to remember numerous individual

flowers within a patch during a foraging bout, and

thus revisits are inevitable. Even wild humm-

ingbirds revisit some flowers during the same

foraging bout at frequencies of 5-10% (Pitelka

1942). In this instance, natural selection may be

unab le to 'fine tune' memory for recall of individual

flowers within a dense patch, because the time and

energy costs of occasional revisitation are probably

quite low.

The movement patterns of foragers in response

to variation in resource density can affect netenergy intake (e.g. Tinbergen et al. 1967; Croze

1970; Cody 1971; Smith 1974a, b; Char nov et al.

1976). For example, bees show greater turning

angles upon visiting flowers or inflorescences with

higher rewards than after visits to flowers contain-

ing lower rewards (Pyke 1978b; Heinrich 1979).

This area-restricted searching has the net effect of

keeping bees in food-rich areas, but allows them to

pass through areas with less food. The turning

angles of adult bananaquits in our floral patch fit

the pattern of area-restricted searching, as evi-

denced by the lack of a strong modal turn ing angle

for the frequency dist ribut ion of turning angles for

both open and closed flowers. Furthermore, the

juveniles resembled adults when foraging on

covered flowers since they also showed no strong

directional preference, with the exception of rever-

sals. In the open-flower patch, however, the juve-

niles showed little evidence of area-restricted

searching (less consistent than adults) and they

mostly probed the flowers directly in front of their

path of movement, as indicated by the modal

tur nin g angle of 0 ~. Thus it is possible that the cluesprovided by unopened flowers help inexperienced

7/28/2019 8802483-mainyhj


52 Animal Behaviour, 36, 1

b a n a n a q u i t s l e a r n t o p r o b e a l l f lo w e r s w i t h i n

i m m e d i a t e r e a c h , r e g a r d l e s s o f d i r e c t i o n ( a n g l e ) ,

b e f o r e m o v i n g o n t h r o u g h t h e p a t c h .

F o r a g e r s m a y l e a v e a p a t c h b e c a u s e th e y h a v e

d e p l e t e d t h e r e s o u r c e , o r b e c a u s e t h e y h a v ea s s e s s e d t h a t r e s o u r c e s a r e l o w . T h e c u e s o r

i n f o r m a t i o n u s e d b y f o r a g e r s h a v e b e e n s u m m a r -

i z e d i n a d i v e r s i t y o f p a t c h d e p a r t u r e r u l e s

( r e v i ew e d b y P y k e 1 98 4). T h e s e d e p a r t u r e r u l e s c a n

i n v o l v e t i m e p e r p a t c h , f o o d p e r p a t c h , o r g i v i n g -u p

t im e . A l t h o u g h o u r e x p e r i m e n t s w e r e n o t d e s i g n e d

t o d i s c r i m i n a t e b e t w e e n t h e v a r i o u s p a t c h d e p a r -

t u r e m o d e l s , w e s u g g e s t t h a t f l o w e r r e v i s i t a t i o n s

c o u l d a f f e c t a n e c t a r i v o r e ' s p a t c h d e p a r t u r e d e c i -

s i o n s u n d e r s o m e c i r c u m s t a n ce s . F o r e x a m p l e , t h e

h i g h f l o w e r - r e v i s i t a t i o n r a t e s o f j u v e n i l e s c o u l d

a d v e r s e l y i n f l u e n c e t h e i r a b i l i t y t o a s s e s s t h e d e g r e e

o f r e s o u r c e d e p l e t i o n w i t h i n a p a t c h a c c u r a t e l y ,

c a u s i n g t h e m t o d e p a r t p r e m a t u r e l y . T h e r e f o r e ,

j u v e n i le s m a y b e l e a v i n g p a t c h e s b e f o r e t h o r o u g h l y

s a m p l i n g o r c o n s u m i n g t h e a v a i l a b l e n e c t ar . C o n -

s i s t e n t w i t h t h i s a r e o u r o b s e r v a t i o n s t h a t j u v e n i l e s

g e n e r a ll y s t o p p e d f o r a g i n g w i t h o u t s a m p l i n g

f lo w e rs in t h e l o w e r p o r t i o n o f th e p a t c h , a n d t h a t

t h e l e n g t h o f t h e i r f o r a g i n g b o u t ( i n t e r m s o f t h e

n u m b e r o f f lo w e r s v i s it e d ) w a s n o t c o r r e l a t e d w i t h

t h e n u m b e r o f s e c to r s v i si te d . F u r t h e r m o r e , j u v e -

n i l es d i d n o t s y s t e m a t i c a l l y l e a v e a r e a s w i t h l o wr e s o u r c e s a n d m o v e t o a r e a s w i t h h i g h e r r e s o u r c e s

w h e n f o r a g i n g o n o p e n f l o w e r s . T h u s t h e h i g h

f l o w e r - r e v i s i t a t i o n r a t e s o f j u v e n i l e s n o t o n l y

r e d u c e f o r a g i n g e f fi c ie n c y b y r e d u c i n g t h e r a t e o f

e n e r g y i n t a k e , b u t m a y a l s o i n t e r f e r e w i t h t h e i r

a b i l i t y t o a s s e s s r e s o u r c e d i s t r i b u t i o n s w i t h i n a n d

a m o n g p a t c h e s .

A s n o t e d p r e v i o u s l y ( W u n d e r l e & O ' B r i e n 1 98 5),

n a i v e j u v e n i l e b a n a n a q u i t s t e n d t o r e v i s i t f l o w e rs

i m m e d i a t e l y f o l l o w i n g t h e i r f i r s t v is i t. I n o p e n

f l o w e r s , t h i s o f t e n i n v o l v e d t u r n i n g a t t h e p a t c h

e d g e a n d t h e n m o v i n g f o r w a r d t h r o u g h t h e v is i te d

a r e a a g a i n , w h i l e i n c o v e r e d f l o w e r s i t i n v o l v e d

f r e q u e n t t u r n i n g r e v e r s a l s t o r e s a m p l e a p r e v i o u s l y

o p e n e d f l o w e r. A d u l t s t e n d e d t o m o v e a w a y f r o m

p r e v i o u s l y v i s i t e d f l o w e rs . T h i s a d u l t p a t t e r n o f

f l o w e r v i s i t a t i o n w a s c o n s i s t e n t w i t h p r e v i o u s

s t u d ie s o f a d u l t b a n a n a q u i t s ( W u n d e r l e & S o t o

1 98 7) a n d a d u l t h u m m i n g b i r d s ( C o l e e t a l. 1 9 82 )

w h i c h i n d i c a te t h a t t h e y s w i t ch m o r e r e a d i l y f ro m a

l o c a t i o n w h e r e i n i t i a ll y r e w a r d e d t o a n e w l o c a t i o n

( w i n - s h i f t ) , r a t h e r t h a n r e t u r n t o t h e e x a c t l o c a t i o n

w h e r e o r i g i n a l l y r e w a r d e d ( w i n - s t a y ) . H o w e v e r ,h a n d - r e a r e d j u v e n il e b a n a n a q u i t s l e a r n e d w i n -

s h i f t a n d w i n - s t a y p r o b l e m s w i t h e q u a l f a c i l i t y

( W u n d e r l e & S o t o 1 98 7) . T h e s e r e s u l ts s u g g e s t t h a t

j u v e n i l e s a r e f l e x ib l e i n t h e i r s p a t i a l l e a r n i n g a b i l i -

t i e s a n d t h a t t h e a d u l t w i n - s h i f t b i a s r e s u l t s f r o m

p r e v i o u s e x p e r i e n c e w i t h e x h a u s t a b l e r e s o u r c e s .T h i s j u v e n i l e l e a r n i n g f l e x i b i li t y ( i. e. n o p r e d e t e r -

m i n e d w i n - s h i f t r e s p o n s e ) m a y a c c o u n t f o r t h e i r

h i g h l e v e l o f f l o w e r r e v i s i t a t io n s . I n t h e e a r l y s t a g e

o f l e a r n i n g t o f o r a g e i n p a t c h e s , a j u v e n i le b a n a n a -

q u i t m a y r e t u r n t o t h e l o c a t i o n o f sp e c if ic f l o w e r s o r

p a t c h e s w h e r e i t w a s i n i t i a l l y r e w a r d e d ( e ve n

t h o u g h i t is n o t r e w a r d e d f o r s u b s e q u e n t v i s it s ). A

l a g p e r i o d m a y b e i n v o l v e d in l e a r n i n g t o g e n e r a l i ze

t h e r e c e i p t o f r e w a r d s f r o m a l l s i m i l a r f l o w e r s

r a t h e r t h a n f r o m s p e c if i c f l o w e r s. W i t h e x p e r i e n c e ,

j u v e n i le s m a y a s s o c i a te m e m o r y a n d a v o i d a n c e o f

p r e v i o u s l y v i s i t e d f l o w e r s w i t h i n c r e a s e d e n e r g y

i n t a k e p e r f o r a g i n g e ff o rt . T h u s b a n a n a q u i t s m a y

i m p r o v e t h e i r f o ra g i n g a b i l i t y b y l e a r n i n g t o u s e

t h e i r m e m o r y a n d b y g e n e r a li z i n g t o f l o w e rs w i th

c h a r a c t e r i s t i c s s i m i l a r to t h o s e f r o m w h i c h t h e y

r e c e i v e d e a r l i e r r e w a r d s .

W h i l e t h e a g e d i f fe r e n c e s i n f o r a g i n g b y b a n a n a -

q u i t s m a y b e a t t r i b u t e d p r i m a r i l y to e x p e r i en c e

( p r a c t i c e ), w e a r e u n a b l e t o e x c l u d e c o m p l e t e l y t h e

p o s s i b i l i ty o f a g e n e r a l i m p r o v e m e n t i n s p a t i a l

p e r c e p t i o n o r n e u r o m u s c u l a r c o o r d i n a t i o n a s s o -

c i a t e d w i th m a t u r a t i o n . F o r i n s t an c e , th e p e c k i n gb y y o u n g c h i c k s a t g r a i n i n v o l v e s p e c k i n g , s e i zi n g

a n d s w a l l o w i n g , a l l o f w h i c h i m p r o v e w i t h a g e

( B r e e d 1 91 1). H o w e v e r , e x p e r i m e n t a l s t u d i e s i n d i -

c a t e t h a t t h e i m p r o v e m e n t t h a t a c c o m p a n i e s p ra c -

t i c e i n t h e d e v e l o p i n g c h i c k m a y r e s u l t f r o m

i n c r e a s e d p o s t u r a l s t a b i l i t y a s w e ll as l e a r n i n g

( C r u z e 1 93 5) . H e n c e t h e d e v e l o p m e n t o f m o t o r o r

p e r c e p t u a l a b i l i t i e s c o u l d i n f lu e n c e t h e f o r a g i n g

a b i l i t i e s o f j u v e n i l e b i r d s , b u t u n f o r t u n a t e l y t h i s

a s p e c t o f o n t o g e n y r e m a i n s u n k n o w n .

T h e h i g h f r e q u e n c y o f f l o w e r r e v i s i t a t i o n b y

j u v e n i l e b a n a n a q u i t s c o u l d b e a n i m p o r t a n t f a c t o r

i n t h e i r s e l e c ti o n o f f o o d i t e m s . F o r e x a m p l e , t h e i r

f o r a g i n g i n e f f ic i e n cy m i g h t c a u s e t h e m t o a v o i d

d e n s e f l o w e r p a t c h e s a n d s e l ec t m o r e w i d e l y d i s -

p e r s e d f l o w e rs . O r , a s f o u n d i n E u r o p e a n s t a r l i n g s

( S te ve ns 1985 ) , j uve n i l e s m a y se l e c t f ood i t e m s

r e qu i r ing l e s s f o r a g in g sk i l l , suc h a s f r u i t . I n f a c t , a t

t h e e n d o f t h e b r e e d i n g s e a so n , ju v e n i l e b a n a n a -

q u i t s t e n d t o c o n g r e g a t e a r o u n d f r u it i n g tr e es ,

w h e r e a s a d u l t s f e e d o n n e c t a r a n d i n s e c t s w h i c h

p o s s i b l y r e q u ir e m o r e f o r a g i n g s k i l l ( W u n d e r l e ,

u n p u b l i s h e d d a t a ) . F u r t h e r m o r e , p e r i o d i cd r o u g h t s a r e k n o w n t o r e d u c e s o m e b a n a n a q u i t

7/28/2019 8802483-mainyhj


W u n d e r l e & L od ge ." F l o r a l p a t c h u s e b y b a n a n a q u i t s 53

p o p u l a t i o n s ( F a a b o r g e t a l . 19 84 ) a n d m a y d i s p r o -

p o r t i o n a t e l y a f f e ct j u v e n i l e s w h i c h h a v e i n e f f i ci e n t

f o r a g i n g s k i l l s .

A C K N O W L E D G M E N T S

W e w i s h t o a c k n o w l e d g e t h e f i n e a s s i s t a n c e p r o -

v i d e d b y t h e f o l l o w i n g s t u d e n t s : A n n e t t e B o n i l l a ,

F e r n a n d o C a l i m a n o , Z o r a i d a C o t t o , C a r l o s C r u z,

J os 6 F e r n a n d e z , E d g a r R o d r i g u e z a n d M a r i a

S a n t a . A s s i s t a n c e i n c a r i n g f o r t h e b i r d s w a s

p r o v id e d b y M i c h a el M e l a m p y , C h a r l o t te T a y l o r ,

R o b e r t R o s s a n d J o s 6 V e l a z q u e z . T h e b i o l o g y

d e p a r t m e n t d i r e c t o r a t U . P . R . , C a y e y , D r J o s 6

V e l a z q u e z , p r o v i d e d v a l u a b l e a s s i s t a n c e a n d e n -

c o u r a g e m e n t d u r i n g t h e r e s ea r c h . V a l u a b l e a s s is t -

a n c e w i t h t h e s t a t i s t i c a l a n a l y s i s w a s p r o v i d e d b y

S a r a h N u s s e r , J o r g 6 P r r e z -C o f f i e a n d M i c h a e l

W i l l ig . T h e m a n u s c r i p t b e n e f i t e d f r o m t h e c r i t i c a l

c o m m e n t s o f R a n d a l l B r e it w i s ch , M i l b r e y L e i g h -

t o n , T i m o t h y C . M o e r m o n d a n d M i c h a e l W i l l i g .

F i n a n c i a l s u p p o r t w a s p r o v i d e d b y N a t i o n a l

S c ie n c e F o u n d a t i o n g r a n t B N S 8 4 -0 5 65 5 .

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(Rece ived 10 N ovember 1986; r ev i s ed 2 M ar ch 1987;M S . n u m b e r : A 4 8 9 4 )

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