title: An Analysis of Flock Organization in Black-Capped Chickadees
Creators: name: Mosher, John Ivan
Publisher: name: Utah State University
Year: 1972

description: An analysis was made of individual behavior and flock organization among 33 color-banded Black-capped Chickadees (Parus atricapillus) on a woodland tract in wester New York State, from December 1967 to June 1970. Also, three of these flocks were confined at various periods for an average aviary tenure of 26 days. From these observations I concluded that the hierarchy and interindividual relationship of a flock remain as observed in the field; testosterone propionate causes an increase in injected subordinate bird's activity; but did not effect a change in its rank.
From the observations in the aviary, it was found that subtle differences in male and female bibs and caps facilitated sexing of the chickadees. All 9 resident flocks of adults usually consisted of 4 birds (9 of 11 flocks) and had a 1:1 sex ratio, whereas first-year and itinerant flocks were more likely to have an uneven sex ratio, indicating that these flocks were not made up entirely of pairs. All flock members observed through the breeding season mated with other members of their flock Nest sites were heavily concentrated in a section of dead trees near the border of the coniferous sector. Six nest boxes placed in the coniferous woods were not used, though fifty percent of the breeding territories on the study area included coniferous woods, and the birds with the longest tenure in the area used the coniferous woods as part of their winter flocking range and breeding territories.
Establishment of feeders affected patterns of flock size and behavior. Also the alpha male's mate took precedence over other flock members at a restricted food source. From other observations of alpha males, it was noted that in one instance in three winters one resident flock disbanded, with its alpha male taking a beta position in its new association, and the beta male becoming the alpha of another flock. Also, it was discovered that the removal of the alpha male from flocks of free-living and confined chickadees for a two day period did not result in disorganization of the flock.
All resident flocks and 2 flocks of first-year birds exhibited a linear hierarchy. Further observation of first-year flocks confirmed that there was no special relationship or pair bond among the male and female members; however, both males and females were present in these flocks and mated with flock members. These flocks of first-year birds also seemed to function as a reservoir for replacing lost members of resident flocks, the formation of which was deferred by the adults until the young dispersed. The independent young formed large bands and ranged widely.
From observations in the aviary it was found that there was no change in hierarchy from that observed for the flock in the wild. Also in the aviary, the subordinate male bird received three injections of testosterone propionate. No apparent elevation in his social posit.ion was observe. However, a statistically significant (P = 0.01) increase in activity among members of one of the flocks was recorded. Finally, caching of surplus food was observed both in the wild and in captivity.
Contrast in social relationships of adult and first-year birds prior to onset of breeding is more pronounced than heretofore recognized. First-year birds apparently are not paired, and tend to travel more widely in flocks that may be larger than those of resident flocks.
Learning appears to be the most important response in the organization of the resident flocks.