Taiwan yuhinas: Unrelated joint-nesters cooperate in unfavorable environments
Journal
Cooperative Breeding in Vertebrates: Studies of Ecology, Evolution, and Behavior
Pages
237-256
ISBN
9781107338357; 9781107043435
Date Issued
2016
Author(s)
Abstract
IntroductionThe cooperative breeding behavior of Taiwan yuhinas (Yuhina brunneiceps) - an endemic to Taiwan - was first described by Yamashina (1938) more than 70 years ago. He observed 4-8 birds attending the same nest and, based on the different color patterns of the eggs, inferred that there were 2-3 females laying eggs communally. However, there is no subsequent detailed study on Taiwan yuhinas until we started our pilot work in 1995. Taiwan yuhinas are elevational migrants and are widely distributed at elevations ranging from 800-2,800 m during breeding season and at somewhat lower elevations in the winter. They primarily inhabit natural forests but also breed in fragmented and disturbed habitats. Yuhinas are open-cup nests and they build their nests in concealed places as diverse as small ferns near the ground, fruit trees, dense epiphytes, underneath concrete roofs, and various trees. It is the most abundant breeding bird species in the mountainous areas of Taiwan (Koh and Lee 2005). Taiwan yuhinas are joint-nesting plural breeders (Brown 1978; Vehrencamp and Quinn 2004) in which several monogamous pairs defend a group territory and females lay eggs in joint nests. They are very different from cooperative breeders that form groups with kin, usually through offspring staying in the natal groups, but in some cases also cobreeding with relatives (Vehrencamp and Quinn 2004). In such kin-based cooperative breeders helpers and cobreeders are typically making the “best of a bad job” and are remaining in their natal group in order to gain a small indirect fitness benefit that is essentially better than nothing at all. By examining the fitness of joint nesting and the ecological drivers of cooperation in Taiwan yuhinas, we sought to explore direct fitness benefits of cooperation and the selective pressures favoring cooperation in a system where indirect fitness benefits and natal philopatry were not part of the equation. This led to investigation of insider-outsider conflict, a framework we believe is necessary for understanding group membership in cooperative breeders, but that can also be extended to explore determinants of group size and group composition in a broader spectrum of cooperative breeding systems (Giraldeau and Caraco 1993; Higashi and Yamamura 1993). The yuhina study is thus an example of how studying an unusual species allows us to test existing hypotheses while also expanding the theoretical approaches and understandings.
Type
book part