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Seasonal Variation in Group Size of Monk Parakeets

Yukie Wong

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Abstract

Monk parakeets (Myiopsitta monachus) are a species of parrots that arrived in the United

States from Argentina in the 1960s. They are gregarious parrots that cooperate when traveling

and building nests. These parakeets can now be found in the Brooklyn area of New York. In this

study, the group sizes of monk parakeets were observed in the months of March to August

(spring to summer) to test the variation of group sizes with seasonal time. The frequency of the

group size of monk parakeets will change with season because in its mating season, parakeets

will often be found in groups of two, but during its time of fledge, parakeets can be found in

singles and in pairs. Observations were made around the Brooklyn College campus to find a

pattern in frequency of group sizes over time that shows its seasonal variation. In March, the

mean group size was 2.6, ranging from a large standard deviation from group sizes of 1.5 to 3.7.

The mean group size correlates with the mating season because during the mating season, there

are often group sizes of two. During the summer, fledglings generally begin to fly on their own.

Figure 6 shows that there were often single birds in July, correlating with the time of the season

to fledge. In August, the mean group size was 2.0. The mean group size increased and there were

often pairs of parakeets than single parakeets as shown in July. It can be concluded that monk

parakeet group size does vary with the time of year and possibly the phase of mating cycle.

Introduction

Monk parakeets (Myiopsitta monachus) originated in Argentina and its surrounding

countries. There are at least nine species of parrots that have settled and established breeding

populations. The most abundant species is the monk parakeet that was first sighted in 1967 in

New York (Van Bael, Pruett-Jones, 1996). In the 1960s, the monk parakeets were brought to the

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United States via the pet trade and were released into the wild, allowing the expansion of these

parakeets into urban areas in cities (Spryer, Bucher, 1988). In 1971, the identity of two fledglings

was confirmed by John Bull of the department of ornithology of the American Museum of

Natural History in New York (Devlin, 1971). These birds resemble a parrot in its color and size,

but it is called a parakeet because it has a long, tapered tail rather than the blunt tail characteristic

of parrots (Devlin, 1970). In 1972, there were concerns that monk parakeets may have became

nuisance birds by driving away songbirds in New York (Devlin, 1972). These parakeets were not

only able to survive harsh winters, but were able to reproduce successfully. Because of this, the

United States Wild Fish and Wildlife Service began programs to control and remove the

widespread population of monk parakeets (Van Bael, Pruett-Jones, 1996). Unlike other species

of parakeets, monk parakeets promote their success as an invasive species by constructing nests

using twigs instead of nesting in holes. Their nests consist of chambers and are occupied by a

pair or group of parakeets (Eberhard, 1998). They form colonies to help each other build nests

for close social interactions. As sociable as the parakeets are, they have distinct calls. Also, the

monk parakeet’s diet consists of fruits, seeds, and buds (South, 2000).

Monk parakeets have a lower breeding success than other species of parrots due to its

larger clutch size (Navarro, Martella, 1992). They hatch eggs in the spring in the manner of all

northern birds, but normally in South America, parakeet births occur in the Southern

Hemisphere’s spring, which is our autumn (Devlin, 1971). Breeding only occurs in nests within

colonies or chambers with compound nests housing other parakeets. During the breeding season,

the male is responsible for all the nest construction and maintenance, and feeds the female during

incubation periods. Pairs have been reported to be socially monogamous but the duration of the

pair bonds is unknown (Eberhard, 1998). Parrot sociality is widely assumed to revolve around a

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pair bond, with breeding pairs functioning as a “fundamental social unit.” (Bradbury, 2003).

Breeding usually involves a male and female pair, but sometimes includes a trio. In a trio, it may

be a female and two males, or two males and a female. Within the trio, there is an auxiliary

parakeet to support the other two primary male and female breeders. Groups of parakeets that

repeatedly split into separate groups and merge again are characterized by a social structure

called fission-fusion (Hobson, 2014). When the nestling is born, it fledges approximately 40 days

after hatching and remains with its parents for about three months (Martin, Bucher, 1993).

When the nestling is grown, it often assists their parents by carrying food back to the nest.

Monk parakeets demonstrate different social behaviors that may be affected by season.

Behaviors such as allofeeding, in which a parakeet passes food to another, and courtship dance.

These parakeets build courtship by doing a dance together that consists of two major

components: spinning in place and moving side to side. These behaviors were seen in the

observations that were made.

The research was designed to study the change in frequency of group sizes with season

and the variation of the number of group sizes with season. The frequency of the group size of

monk parakeets will change with seasonal time because there will be correlation with the number

of parakeets in a group during the mating cycle. The number of parakeets in a group will

decrease after mating season, when it is time for the parakeet to fledge on its own because

fledglings generally travel alone.

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B

A C

Image A shows a group of four parakeets on nest 27N. Image B shows a group of two parakeets

allofeeding (the passing of food from one to another). Image C shows two parakeets in a

chamber of the nest.

Methods

This study of monk parakeets was conducted on the nativized population in Brooklyn,

specifically that around Brooklyn College campus. Five nests near the campus were the focus.

These nests had multiple chambers often with entrances facing in different directions (e.g. North

and South). The observations were made to measure the group size of the parakeets over time.

The definition of a group in this study is when the parakeets are within two parakeet-body sizes

next to each other (See Figure 1). Each nest direction will be observed over two five minute

intervals. The time, date, number of groups present, and group numbers (e.g. Group 1, Group 2)

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need to be recorded during the ten minute observation. The number of parakeets in different

group numbers may change as a parakeet flies off from one group to another or away from all of

the groups. When the parakeets have all left a group, then that group will be abandoned and

marked with an X. After the X is marked, and a new group is formed, that group will be labeled

with a different number. When the ten minute observation is completed, continue until all views

of each nest are observed (See Figure 3).

A group size of one or more that changes to a group size of zero is marked on the data

sheet but removed when analyzed graphically. The results were analyzed by error bars that show

the 95% confidence intervals. These error bars were used to identify the group sizes of monk

parakeets as seasons alter. If the most frequent group size observed consists of two parakeets

during spring, it can be inferred that the mating season consists of group sizes of two. When

mating season is over, the juveniles begin to fledge and travel alone, showing a decrease in the

mean group size. If the mean group sizes in each month do not all correlate with the seasons, the

group sizes do vary with the time of the year.

Figure 1

Figure 1 shows the definition of a group. The

definition of a group is when the parakeets are within

two parakeet body sizes next to each other.

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Figure 2

A B C

E

D

Figure 2 shows the five nests, three in which there are two directions (North and South). All the nests are

circled and labeled with letters A, B, C, D, or E with the first letter of the direction next to it (e.g. chamber

AN: the letter A is used to identify the chamber, and the letter N is the North direction).

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Results and Analysis

Figure 3

Figure 3 shows a sample observation table that was used to record the data of group sizes. The

X’s represent an abandoned group (a group in which the parakeets have moved over the distance

of two parakeet-body sizes away from each other).

Nest Date Time # of groups

1 2 3 4 5 6 7

4N 7/30/14 17:32 0 0 0 0 0 0 0 0

4N 7/30/14 17:35 0 0 0 0 0 0 0 0

27S 7/30/14 16:18 1 1 0 0 0 0 0 0

27S 7/30/14 16:18 2 1 1 0 0 0 0 0

27S 7/30/14 16:18 3 1 1 2 0 0 0 0

27S 7/30/14 16:18 4 1 1 2 1 0 0 0

27S 7/30/14 16:18 4 1 2 2 1 0 0 0

27S 7/30/14 16:18 5 1 2 2 1 1 0 0

27S 7/30/14 16:23 6 1 2 2 1 1 2 0

27S 7/30/14 16:23 3 1 3 2 X X X 0

27S 7/30/14 16:23 2 X 4 2 X X X 0

131N 7/30/14 17:00 2 1 1 0 0 0 0 0

131N 7/30/14 17:05 1 X X 1 0 0 0 0

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Figure 4

GROUP

6.05.04.03.02.01.0

400

300

200

100

0

Std. Dev = .75

Mean = 1.5

N = 650.00

Figure 4 shows the frequency of different group sizes (between 1 bird and a maximum observed

group size of 6) parakeets observed in the Brooklyn College parakeet population. The most

frequent group size was the group size of 1 and the rarest group size was of 6 (on one occasion).

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Figure 5

1118568162113180N =

NEST

4N3N27S27N134S134N131S131N

GR

OU

P S

IZE

(9

5%

CI)

3.0

2.5

2.0

1.5

1.0

.5

Figure 5 shows the 95% confidence intervals of the mean group size in each nest. There is no

significance difference in nests 134N, 134S, 27N, 27S, and 4N because the mean group sizes that

were observed in the nests overlap and are within the same range. The nests of both directions

are within the same range and mean group size. In nest 3N, there was only one parakeet observed

throughout all observations.

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Figure 6

60298212365N =

MONTH

8.007.006.005.004.003.00

GR

OU

P S

IZE

(9

5%

CI)

4.0

3.5

3.0

2.5

2.0

1.5

1.0

Figure 6 shows the 95% confidence intervals of the mean group size observed in each month.

The error bars show the range of the group sizes two standard deviations from the mean group

size. In March, there is a wide range indicating a large spread of data and less precise results. In

June, there is no range because there were very few observations made in that month. There is no

range in June due to the small number of observations done in that month. In July, there is a

narrow range, indicating the data points are more clustered around the mean group size than in

the other months observed creating a more precise range. There is a 95% confidence that the true

mean lies within the range shown. There is no significant difference in the months of March,

April, May, June and August, but there is a significant difference in the July because the error

bars do not overlap with the other months.

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Conclusion and Discussion

The group size of monk parakeets does vary with season and the frequency (number of

occurrences) of the group size changes with seasonal time. The group sizes change with the

season of spring and summer. These variations of group sizes show a pattern, indicating the time

of mating, incubating, and fledging of the young parakeet. The duration of the mating season in

March can be supported by the data because of the frequent group sizes of two. As shown in

Figure 6, the group sizes ranged from 1.5 to 3.7, with a mean of 2.6. During the summer, in the

months of July and August, the group sizes vary from one to three parakeets indicating the

forming of a family and the fledging of a juvenile. The average mean of group sizes in July

decreased significantly to an average mean group size of about 1.3. However, in August, the

range of the group sizes increased. A possibility may be that the fledging has joined its parents in

flying to different areas (e.g. trees) to find new sticks for their nest, or to search for food.

An explanation for the frequent group size of 1 in July may be that during the summer,

the juvenile is fledging and beginning to fly on its own. These single parakeets may be adapting

to its urban environment and learning to find food for its family. However, it may be the

surrounding factors such as house construction that affect the group size of the parakeets. A

source of error is the number of observations made in each month, causing a discrepancy in the

graphs. For example, in Figures 5 and 6, the error bars show a wide or narrow range of the mean

group sizes in which a wide range shows a larger spread of data and less precise data. In Figure

6, the number of observations is shown on the x-axis. In July, there were a total of 298

observations and in August, there were 60 observations.

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This knowledge and information of the group sizes during different time of the year may

give an idea of an appropriate time to remove nests when necessary. The United Illuminating

utility company has made attempts to get these parakeets off power and lighting fixtures by

capturing these birds and turning them over to the United States Department of Agriculture, who

euthanized them (Silverman, 2009). They also spent over $60,000 on a campaign to remove the

nests, leading to an economic impact. Because the group sizes changes with season, it will be

predictable when there will be fewer groups of two or more during the months of July and

August in which local companies can safely remove nests without harm to the parakeets. Also,

they can save money from starting campaigns to remove nests due to complaints of harm to the

parakeets from neighbors. The group sizes of monk parakeets can be observed further to describe

the behavior of these parakeets. A future work on this project may be to continue observing the

nests for patterns and frequency of the group sizes throughout the year. There have also been

questions raised about the shift in mating season of these monk parakeets, in such that mating

season might also be occurring in autumn in the United States. This can lead to a future study in

how mating season in the United States compares to mating season in Argentina.

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