James W. Popp

Risk and Effectiveness in the Use of Agonistic Displays By American Goldfinches

In aggressive contests over access to feeders, American goldfinches (Carduelis tristis) appeared to be using displays based on their risk and effectiveness. Display types varied in both their effectiveness and the risk of their use. The effectiveness of using a display was positively related to the risk of using that display. When the value of the resource under dispute was increased individuals used more of the riskier yet more effective displays. Associated with the increased use of the riskier displays was a greater number of encounters ending in fights. Individuals also used each display type with different frequency depending on the relative dominance status of their opponent. Bluffing may have been kept at low levels among the goldfinches by the ease of detecting bluffing, due to individual recognition, and by the costs of being detected.

Comparative analysis of acoustic structure of passerine and woodpecker nestling calls

ABSTRACT We examined the acoustic structure of the calls of 71 species of nestling passerines (both suboscines and oscines) and 4 species of nestling woodpeckers. Calls varied greatly in general acoustic structure, frequency (pitch) and duration. Some phylogenetic trends occurred, e.g. calls of woodpeckers and suboscines tended to be simpler than those of most oscines. Body size was significantly correlated with both maximum and minimum frequency. Age-related changes occurred in some species but not others. The results suggest some phylogenetic and developmental constraints on call structure, but do not rule out the possibility that selection acts directly on nestling calls. However, the hypothesis that cavity-nesters would have more easily localizable calls than open-nesters because of lowered predation risk was not supported by our study, which showed no significant differences in any frequency or temporal measures of acoustic structure between cavity-nesters and open-nesters.

Long-term persistence of a culturally transmitted vocalization of the black-capped chickadee

Abstract The gargle vocalization of the black-capped chickadee, Parus atricapillus, was recorded at the same site over a 19-year period. This vocalization consists of an array of different note types that are combined to generate various call types. Each male has a large repertoire used in agonistic encounters, and many variants are shared with other members of the population. The vocalization was analysed at several different levels: note types and various lengths of note-type sequences including the whole call. Remarkable stability was shown for all levels, and the main changes observed were minor ones of relative frequency of occurrence. Reasons for stability may include persistence of note types in linkage groups that could be trasmitted as units (memes) and other rules governing ordering of note types in the call (syntax). Also, natural selection may impose some constraints on the process of cultural transmission. We compare our findings with those of the few available long-term studies of bird song. Chickadee gargles are transmitted very precisely compared to other vocalizations that have been previously studied.

The predictability and patterns of vigilant behaviour

While foraging, many animals alternate between feeding and scanning. Spectral analysis of continuous series of scan durations S and inter-scan intervals I for American Goldfinches Carduelis tristis, feeding either on small or large seeds, and choughs Pyrrhocorax pyrrhocorax showed that there were nonrandom fluctuations in the magnitude of S and I is all the examined series. Both the I and S showed cyclical oscillations between short and long events. Within individuals the sequential and temporal patterns in the I and S series were similar. However, the temporal patterns were more affected by variations in food-handling time than were the sequential ones. The predictability of the I and S series and the similarity, within individuals, of their sequential and temporal patterns seem general processes resistant to variations in behavioural constraints, and the temporal patterns in the I and S series fit to the method of handling food.

Effects of experience on agonistic behavior among American goldfinches

I investigated the effect of a winning or losing experience on the outcome of an individuals next aggressive encounter among captive American Goldfinches (Carduelis tristis ). Aggressive encounters occurring over access to a feeder were videotaped during the winter of 1985-1986. Both dominants and subordinates were more likely to win their next encounter after a win than after a loss. Individuals were more likely to initiate their next encounter and use higher risk displays after a win than after a loss.