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RESEARCH STATEMENT

Major directions of our past research

Relationship of past work, and our current studies to broader themes regarding development and learning.

 

OVERVIEW OF RECENT FINDINGS

Click here for a discussion of design issues when studying groups of individuals

Why study Cowbirds?

 

Two views of cowbirds from inside our aviaries showing the perspective of a human observer from two observation points             

 

WHY STUDY ANIMALS IN GROUPS?

 

 

 

 

WHY STUDY ANIMALS IN GROUPS? 

We believe that studying ecological relevant groups of individuals is fundamental to understanding social development. The interaction of behavior of different classes of individuals produces non-additive and non-intuitive outcomes. Furthermore, studying the acquisition of social information requires that we do not impose the social interactions upon subjects, but instead allow the subjects to choose the stimulation most important to them- something that cannot occur in confined lab settings. We have found the following effects that differ or do not exist in the confines of traditional lab settings:

  1. Modifiability of female song preferences can occur in groups in aviaries, but not in the pairs or triads in sound attenuating chambers. Females show obvious visual signals in aviaries to one another suggesting that their preferences are transmitted socially.
  2. Female social proximity to juvenile males in chambers serves to increase potency of male song. Female social proximity to juvenile males in aviaries serves to stimulate male-male competition and in turn reduce male potency.
  3. Group processes influence information acquisition. Groups in aviaries adjacent to one another show little cross-group interaction, no song sharing, and can even differ in reproductive stimulation, egg production, song potency and mating success.
  4. Countersinging by males stimulates female egg production. Countersinging by males requires groups of males to sing together and groups of females to be stimulated by them (and to stimulate them).
  5. During fall, winter and spring, individual birds self-select different social networks within a larger social group.  These social networks appear to correlate with reproductive success.

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  Male cowbird: A “bird’s-eye” view of a male cowbird on a cold morning in January.

 

Male cowbirds produce between 2 to 7 song types

A male singing an undirected song .

 

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Song

 

An example of a high quality recording of a typical cowbird song type

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Click here to see and hear the song played at 1/2 speed

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Click here to see and hear the song played at 1/4 speed

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Click here to see and hear the song played at 1/8 speed

Time-frequency spectrograms made using Igor Pro and BSound software written by Brian Nelson.

BSound is available at http://homepage.mac.com/bsnelson/Igor/BSound.html

 

The song types are used in several contexts. First, males broadcast undirected song. Second, males sing to other males, often in singing contests where two males exchange several song types with one another. Third, males sing to females as part of courtship. Male song elicits a variety of reactions in females. The most common reaction is to ignore the male, but song also can elicit approach or solicitation of copulation. Shown below is another reaction to song, a female moving her wing in a display called a wing stroke. The wing stroke occurs as the song is sung. Males and females orient to females who are wing stroking. Note the female’s head movement as she watches another female’s wing stroke. We believe that females’ interactions with one another with respect to song is a mechanism by which female preferences for song are formed.

During the breeding season, May and June, females can respond to a song with copulatory postures, see below. The female arches her back and raises and lowers her tail. If a male is present, he will mount her and copulate. But females also show this display in the absence of actual males, responding to playbacks of song. We use her responses to playback songs as a bioassay of song effectiveness, or potency. We do not add hormones to the females: the females respond to playbacks of song over the course of at least six weeks. The key to their responding is that there are no males present, depriving the females of song stimulation. Using this technique, we have found that females, with male experience show preferences for local over distant song. Females without experience appear to have to learn their preferences by interacting with males and by observing other females’ reactions. 

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Breeding season response to song playback

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Female sensitivity to male song is not limited to the breeding season. Although female cowbirds do not sing, they contribute to the learning of song by males throughout the year. Males pay attention to wing movements of females when they sing to them. These movements, called wing strokes, occur while the male’s one second song is in progress. Males can modify the content of their song prior to the breeding season in response to female reactions. Vocalizations eliciting wing strokes in early spring tend to develop into very effective courtship signals.

 

 

 

 

Like the sequence above, this recording was made in early March while the male’s song was variable from rendition to rendition. Prior to this sequence, this juvenile male had sung several hundred songs during the previous two hours. None of these songs had elicited any obvious reaction from the female.  In the first frame, the male sings an undirected song and the female wing strokes with her right wing while the song is being sung. He immediately jumps toward the female and tries to observe the wing stroke in frames 2 & 3. After the male has approached, the female then starts to stretch her right wing as can be seen in frames 3 and 4. The male continues to move closer to the female in frames 4, 5, attempting to observe the female wing action. By this time, the female has had enough of the male and in frame 6 she reminds him to keep his distance.