Upload
merry-johnston
View
216
Download
2
Tags:
Embed Size (px)
Citation preview
Song & Communication• Song
– Only males sing – functions include mate attraction, territory defense
– Both sexes give calls – functions include mate-to-mate communication, flock cohesion, parent-offspring communication, predator mobbing
Songs versus Calls
Songs Calls
Given by males (usually) Given by both sexesFunctions: mate attraction, Variety of functions territorial defenseLong and complex Short and simpleUnder hormonal control NotUsually restricted to Given year-round breeding season
Song & Communication
• Song– Only males sing – functions include mate
attraction, territory defense– Both sexes give calls – functions include mate-
to-mate communication, flock cohesion, parent-offspring communication, predator mobbing
– An important part of bird surveys and birding is song identification
– Breeding Bird Survey
Song Learning
There is a diversity of degrees of avian song learning, ranging from no evidence of learning at all (innate, or under genetic control) to learning new songs or parts of songs throughout life.
Song learning (learned vs innate behavior):
• Some birds exhibit no evidence of song learning (brood parasites, doves)
• Others exhibit limited learning from the bird they are most closely associated with, usually the father (WCSP, INBU)
• Others are capable of learning songs of other birds but normally do not do so in nature (e.g., NA warblers)
Hooded Warbler
White-crowned Sparrow
IndigoBunting
Song & CommunicationSong learning (learned vs
innate behavior)• Others learn throughout life and
regularly mimic songs of other birds (e.g., mockingbirds, lyrebird) – why?
• Others learn throughout life from their mate (duetting –strengthens pair bond) – many wrens, antshrikes, etc.
Song learning in the White-crowned Sparrow
Characterized by critical periods, memory templates and eventual irreversibility of song patterns
• First critical period coincides when adult males are singing and young are about to fledge (10-20 days old).
• During this time a memory template is formed (i.e., young birds remember what they are supposed to sound like).
• Second critical period corresponds to a time when they are beginning to practice singing (~150 days).
• They must be able to hear themselves sing to make use of their auditory template, attempting to match their song to it.
• Eventually they are able to match their song to the template, and by ~200 days the song is crystallized (unchanged forever after).
• Non-auditory memory is involved too,
matching internal sensory information
about muscle and air movements used
to produce particular notes.
Territory and Home Range
Territory – any fixed area defended continuously for some period of time.
Home range – an area used by an animal in the course of its normal daily activities.
Considered roughly the same thing for birds.
Territories are usually established for the purpose of defending a limited resource. Also, for breeding territories, a nest and mate are usually contained within the territory, and will be vigorously defended.
The result is that the population size is regulated and resources are not over-consumed.
Types of Territories
Most songbirds (and their allies; e.g. cuckoos, hummingbirds, etc.), woodpeckers, raptors, and kingfishers, have an all-purpose territory, in which they find all their food, build a nest and raise young.
Many waterbirds, especially colonial nesters, defend a small area around the nest, but will tolerate other individuals near them when they feed away from the colony, and often form flocks. Even in flocks, though, each bird will defend a small area around itself.
Other oddities exist. Oropendola nests
Territory-size Regulation in Black-shouldered Kites (Elanus caeruleus)*
• BSKI occupy coastal grassland in northern California, where they feed almost entirely on Microtus californicus.
• M. californicus exhibit a 12-month population cycle, in which their density fluctuates from only a few to about 1000/ha.
• Other raptors, including BSKI, migrated there in fall, left in spring
• Dunk (1991) measured BSKI territory
sizes year-round• Found that territory size was related to
both food and # of competitors –
proximate versus ultimate factors.
* Now known as White-tailed Kite
Key players in the Arcata grassland ecosystem
Keystone prey item – California vole (Microtus californicus)
Kite’s exact position could be measured when they perched or
hovered
Even wading birds ate voles
Intraspecific encounters were often violent
And so were interspecific encounters
The inverse relationship between food abundance and territory size in known as the Food Value Theory (Stenger 1958).
Does it hold for the majority of species that obtain food in a 3-dimensional area?• Yes: Marshall and Cooper showed
that Red-eyed Vireos’ territory volume was inversely related to caterpillar density.• Also holds for fish.
Does it hold for migratory species, which must assess a territory’s future food value when they arrive in the spring?• Yes: Ovenbirds have been shown to use structural cues (litter depth) to assess habitat and adjust territories.• Also holds for REVI, whose
territories were inversely related to foliage density.• Known as Structural Cues
Hypothesis
From Marshall and Cooper (2004). Ecology.
Opportunistic flocks formed for food acquisition still have individuals that defend territories – Ant-following birds