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Group-living in the southern anteater-chat Myrmecocichla formicivora.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Population and Conservation Biology.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Group-living sets the scene for complex social behaviours such as cooperative breeding, and exploring the factors that shape group-living is crucial in understanding these behaviours. Here we describe some aspects of the ecology of a population of the facultative cooperative breeding southern anteater-chat (Myrmecocichla formicivora), a group living bird species endemic to southern Africa. We used data from a four year study of individually marked birds, with pedigrees completed using microsatellite genotyping. Southern anteater-chats live in groups of 2-5 individuals - a breeding pair and up to three additional none-breeders. These auxiliary birds were either retained offspring or unrelated individuals, and all birds in a group assisted by feeding at the nest. Our population had a skewed sex ratio of approximately 58% males to 42% females, yet the sex ratio of fledglings was equal, suggesting sex-biased mortality. Helpers were predominantly retained male offspring; however 21% of helpers were unrelated to either of the breeding pair. Southern anteater-chats appear to be non-territorial, with an apparent lack of aggression both within and between groups. Our study confirms that the southern anteater-chat is a facultative cooperative breeder, with both pair breeders and groups with helpers capable of fledging youngsters. We provide evidence suggesting that the breeding system of the southern anteater-chat is based on prompt female dispersal, and male philopatry due to an apparent shortage of mates, potential benefits of the natal site and possible high costs of floating. It appears that ecological constraints promoting delayed dispersal are reinforced by benefits gained from remaining philopatric.

Keyword [en]
Southern anteater-chat, cooperative breeding, social evolution, behavioural ecology, delayed dispersal, family living, Africa
National Category
Evolutionary Biology
Research subject
Biology with specialization in Population Biology
Identifiers
URN: urn:nbn:se:uu:diva-179071OAI: oai:DiVA.org:uu-179071DiVA: diva2:544037
Available from: 2012-08-13 Created: 2012-08-07 Last updated: 2012-09-05
In thesis
1. Cooperative Breeding in the Southern Anteater-Chat: Sexual Disparity, Survival and Dispersal
Open this publication in new window or tab >>Cooperative Breeding in the Southern Anteater-Chat: Sexual Disparity, Survival and Dispersal
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Group-living sets the scene for complex social behaviours such as cooperative breeding, and exploring the factors that shape group-living is crucial in understanding these behaviours. This thesis explores the ecology of a population of the facultative cooperative breeding southern anteater-chat (Myrmecocichla formicivora), a group-living bird species endemic to southern Africa. It reveals a breeding system based around a breeding pair and up to three auxiliary males. Despite equal numbers of males and females produced as fledglings there was a surplus of adult males, which remained philopatric. Dispersal was strongly female biased. Females dispersed within their first year, they dispersed further than males, and they lost the benefits of the natal site. The sex skew in the population suggested that these factors drive differential mortality, with juvenile females having much lower annual survival than juvenile males. Adult survival was higher, with female survival only slightly lower than male survival. Dispersal distances suggested that males selected the breeding location, nearer to their natal site. There was no evidence of surplus non-breeding females. On the loss of a breeding female there was no replacement until new females entered the population, yet if a breeding male disappeared the female promptly re-paired with a male from another group. There was no indication of birds floating in the population, and if males were orphaned or widowed they joined other groups as unrelated helpers in preference to floating. There was no sign of inter-group or individual aggression among chats, and unrelated helpers were peacefully accepted into groups, suggesting mutual benefits. In fact all birds in a group helped raise offspring of the breeding pair, and groups with more helpers fledged more offspring, which implies that both direct and indirect fitness benefits can be gained through joining a group and helping. There was surprisingly little inheritance of breeding position by auxiliaries, and strikingly low levels of extra-pair paternity. This study suggests that the Southern anteater-chat group structure arises through male philopatry due to a shortage of breeding females, the benefits of remaining on the natal site and helping, and the potentially high costs of living alone.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 50 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 953
Keyword
Southern anteater-chat, Myrmecocichla formicivora, cooperative breeding, social evolution, behavioural ecology, delayed dispersal, family living, Africa
National Category
Evolutionary Biology Zoology
Research subject
Biology with specialization in Population Biology
Identifiers
urn:nbn:se:uu:diva-179070 (URN)978-91-554-8426-2 (ISBN)
Public defence
2012-09-25, Lindahlsalen, Evolutionary Biology Centre, Norbyvägen 14-18, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2012-09-04 Created: 2012-08-07 Last updated: 2013-01-22

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Barnaby, Jonathan

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