Lecture 16 Ornithology, Territory and Flocking

Social Behavior

What are the types of territory?

1. all purpose territory

2. mating and nesting, feed elsewhere

3. nesting, plus small area around feeding

4. mating, the lek territory

5. winter territory, feeding only

6. roosting

Example of all purpose territory bird

American Robin, CA Towhee, song sparrows

Example mating and nesting territory bird

a lot in marsh habitats

Northern harriers, red-winged black birds, marsh wrens

Example nesting plus small area around nest for mating

many colonial birds

gulls, terns, Common Murre

Example mating territory = the lek territory

often most colorful species

hummingbirds, birds of paradise, Greater Sage Grouse

Example winter territory, only for feeding

Northern Mockingbirds, Hermit thrushes

Example roosting territory

red winged blackbird, American crows, European starling

What is a group territory? How does it involve a dominance hierarchy?

When more than one of a species occupies the same space, in different areas different ones have dominance but all defend the overall territory.

Example of a species with group territories

Stellar’s Jay

What is the economic defensibility model?

Territory behavior should be favored when the costs of defensive behavior are outweighed by the benefits of primary access to resources

When is defense of territory favored?

1. resources are relatively predictable in space and time

2. resources are not overly scarce

3. resources are not overly abundant

What is an example of the economic defensibility model?

Sanderlings defend winter beach territories when prey concentrations are intermediate

What are the benefits of territory defense?

1. access to food, cover and other resources

2. increased opportunity for mating

Example of territory defense benefits

Dickcissels on territory with denser vegetation have greater mating success

What factors affect territory size?

territory sizes of birds directly increase in proportion with their body size and energy requirements

for a given body size, predators require larger territory size than herbivores

How is social rank asserted in flocks?

Showing “badges” of dominance vs a plain appearance, and agonistic behavior

What is agonistic behavior?

Competitive encounters between rivals result in a complex mix of aggression and escape actions. When birds fight, they avoid direct contact and risk of injury by using threat and appeasement displays

Example of threat display

Stellar’s Jays elevate creasts to different degrees to show threat

What is a flock?

any group of two or more birds whose formation depends on positive responses to individual members of their own species or other species

What is the difference between a flock and an agreggation?

An aggregation is a group of individuals gathered together by an external resource, a flock involves members to positively associate with one another regardless of external conditions

What are the costs and benefits of flocking?

Costs:

association with more dominant individuals, competition for resources, exposure to disease

Benefits:

more food due to assistance in locating food and assistance catching food

less danger from predators due to increased vigilance and predator confusion

What are the costs and benefits of colonial nesting?

Costs:

association with mor dominant individuals, competition for resources, exposure to disease

Benefits:

less danger from predators due to increased vigilance and predator confusion

more food due to assistance locating and assistance catching

Example of feeding in flocks

Harris Hawks hunt in teams.

They assemble and split into smaller groups, move in a coordinated leapfrog pattern, and then converge on a rabbit to kill it with successive relay strikes.

All members eat the kill.

What are mixed species flocks?

contain the nuclear species, followers and opportunistic species that feed/nest /roost together

What is an example of a mixed species flock?

Oscillated, bicolored and spotted antbirds space themselves around ant swarms.

What are the trade offs that determine optimal group size in flocks?

1. feeding

2. fighting

3. scanning for predators

time allocated to these changes in presence of a predator and changes optimal flock size

Example of species that has communal roosts

Crows

What are the benefits of communal roosts, what are the costs

Benefits: Decreased predation, synchronized nesting

Costs: increased disease and greater competition

Under what conditions does colonial nesting evolve?

1. shortage of individual nesting sites

2. abundant or unpredictable food that is distant from safe nesting sites