Freeberg et al. (2006)

Question 1

Aim

Answer 1

• to see if group size affects the diversity and proportional frequency of a chick-a-dee call
• social organisation of chickadee species changes from female to male pairs defending territory during breeding season
• in larger groups, may need to have a vocalisation of easy distinguishability

Question 2

Prediction

Answer 2

“One was based on the diversity and proportional frequency of different note types in calls, and the other was based on the diversity and proportional frequency of different pairs of consecutive note types in calls. I tested whether group size affected these com- plexity measures in chick-a-dee calls in both a field study and an experimental aviary study.”

• social complexity is a predictor of vocal complexity
• aviary group would increase linearly with group size in VL because less predators

Question 3

Method

Answer 3

FIELD STUDY

• 3 sites, 400m away
• recordings at feeding stations
• 2 months (8am-3pm
• 19 sites f small groups (1-2) and 11 sites of large groups (3+)
• interrater reliability was 88.1%

AVIARY STUDY

• 3 groups, each containing 2 different group sizes in 2 outdoor aviaries
• small and large group
• captured from same flock
• sexes were balanced to mimic a natural flock

Question 4

Results

Answer 4

FIELD STUDY

• 4152 chickadee calls were recorded
• larger group calls were more complex compered to calls made from smaller groups
• complexity was defined as amount of info available

AVIARY STUDY

• 1322 calls recorded and analysed
• specific group sizes of 4+ had greater complexity
• birds in larger groups had fewer D notes, and more other notes, so increased the proportionate frequency

The present work indicates that one basic component of chickadee social com- plexity, group size, affects the complexity of the chick-a-dee call. Birds in larger groups in field and laboratory settings used chick-a-dee calls with greater diversity of note types and note
combinations, and thus were theoretically capable of transmit- ting a greater number of messages to receivers.

The fact that the changes in call complexity in the aviary study occurred over the course of weeks indicates that call complexity in this species can be a facultative and fairly rapid response to the social context.

Question 5

Strengths

Answer 5

• aviary condition had dif groups from same area, so birds started with same level of communication

Question 6

Limitations

Answer 6

• inter-rater reliability not 100%
• only one species of bird so cannot generalise
• doesn’t explain why there is more uncertainty
• sexes may be unclear
• field study may have missed some birds
• confounding variables of birds kept in captivity

Question 7

Follow-up studies

Answer 7

• vary length of aviary testing to see when social complexity changes
• look at time course
• look at long term social dynamics and communication
• other species of bird
• more varied singing = more mating?

Question 8

Honest signalling

Answer 8

• experimental support that social complexity may enhance vocal complexity for communication in animal species
• flock cohesion