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Sex specific survival in the southern anteater-chat Mymecocichla 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]

Survival is a key factor behind life-history variation both between and within species. It is also a major influence on sociality in species which delay dispersal and live in family groups. Knowledge of differential survival rates between males and females and juveniles and adults give insights into the costs and benefits of different behavioural and life-history strategies. Here we investigate patterns of survival in a population of the southern anteater-chat (Myrmecocichla formicivora), a facultative cooperatively breeding passerine of southern Africa. Using data from a 9-year mark-capture-recapture study, we examined juvenile and adult sex related variation in survival, and the role of environmental variables (rainfall, temperature) for survival patterns in the population. Annual adult survival probability (mean ± SE) was 0.71 ± 0.03 for males and 0.60 ± 0.04 for females. Juvenile survival was lower for each sex, with juvenile female survival (0.36 ± 0.04) being 35% lower than juvenile male survival (0.55 ± 0.04). Using these estimates we calculated the mean life span (MLS) in years for male southern anteater-chat to be 4.0 ± 0.7, considerably higher than for females at 2.0 ± 0.4. These figures closely matched the population-age structure of the study area, and could explain the high male biased sex skew of adult birds in this population. Higher annual mean temperature was associated with higher survival, whereas higher annual rainfall was associated with lower survival for both sex and age classes. Female survival, particularly female juvenile survival, may be reduced due to prompt dispersal and longer dispersal distances, and the additional costs of breeding early in life. Differential survival can promote male philopatry and this in turn could well encourage the cooperative breeding we see in the southern anteater-chat.

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-179072OAI: oai:DiVA.org:uu-179072DiVA: diva2:544039
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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