Introduction:

Understanding the origins and maintenance of animal social behavior remains a central issue of behavioral ecology. In particular, attention has focused on the presence of dominance hierarchies within groups as a means for structuring social interactions. In addition to generally asking why such social relationships evolve, we may also examine both the cues used by individuals to assess the dominance status of others and the specific costs and benefits of being dominant over others. In this exercise, we will observe individually marked Dark eyed Juncos, Black-capped Chickadees, and Song Sparrows in the field and record various aspects of interactions between individuals in an attempt to identify characteristics that are correlated with dominance. Our studies will concentrate on the relative importance of sex, size, plumage brightness, and age. Because this is an observational study, we will be unable to establish which of the characteristics that correlate with dominance actually confer dominance. Ideally, we would follow up such a study with experimental studies that quantify each variable’s role in conveying dominance.

Study Organism and Methods

Dark-eyed Juncos typically visit the Lewis and Clark campus between November to April. They spend most of their time foraging in small flocks of open membership (birds are free to leave or join the flock, without obvious territorial interactions). Dark-eyed Juncos have two basic plumage types. Immature birds (birds in their first winter) have light brown poorly contrasting crowns while adults have dark black crowns. In each age class, males are typically a bit larger and show more contrasting plumage than females, although sexual dimorphism is slight.

Color banded birds regularly visit the feeding area outside of Yellow Lab. These birds are the subject of ongoing behavioral studies and some of the birds you may see were banded more than a year ago. Although more than 50 birds have been banded at this site, currently it is uncommon to see more than about 10 banded birds at the feeding area at any one time.

Individually recognizable color combinations allow us to compare behavioral observations with data on size, age, and plumage color that were collected at the time of capture. Recaptured birds thus provide data on growth. We identify individuals by recording the band combinations in a specific sequence (i.e top left, bottom left, top right, bottom right). Some birds may have only one or two bands. Your instructor will give examples of how to record band combinations.

We will gather data on the dominance status of individual birds by observing birds in a feeding area and recording the outcome of social interactions ("displacements") between pairs of birds. A displacement occurs when one bird (the winner of an interaction) occupies the spot formerly occupied by another individual (the loser). Displacements occur quickly and there is usually no fighting between birds (Why might this be so?). The class will split up into pairs with one person recording data while the other observes. Members of a pairs should switch activities frequently.

When recording the outcome of interactions, try to record both age (immature or adult -- based on crown-color for juncos), sex (for finches) and band combinations for all birds. Things often happen too quickly to record everything, so some band combinations will have to be listed as "?". Birds without color bands should be recorded as "U" (unbanded). It is likely that some interactions will not be intraspecific but will instead be between juncos and other species such as chickadees, finches, or possibly sparrows.

Two common types of behavioral observations are "event" and "focal animal" sampling. In event sampling, all interactions within a group are recorded as they occur. This maximizes the number of interactions observed, but provides little quantitative data on how a particular individual behaves, especially on how often an animal does a particular behavior. In focal animal sampling, observations are focussed on a particular individual and all interactions involving that individual during a given amount of time are recorded. This sampling technique provides detailed data on an individual (e.g. the number of wins or losses per minute), but may not produce data on as many interactions as event sampling. We will conduct both types of sampling in the field, but will primarily focus on the data from event sampling for the analysis and write-up.

Click here for a detailed description of these methods.

 Lab Write-up

The data gathered by pairs of observers will be pooled into a larger data set. These will be added to the data on morphological characteristics of each banded bird, including several measures of size (wing length, bill length, and leg length, and, for some, weight). With data on interactions between individual birds and on the morphological characteristics of these birds, we should be able to establish the relative importance of size, age, plumage coloration and species in determining social dominance in wintering flocks. We will go over this part of the assignment later in the semester.