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Behaviour and breeding biology of the cooperatively breeding Grey‐backed Fiscal Shrike Lanius excubitorius in Kenya
Author(s) -
ZACK STEVE
Publication year - 1986
Publication title -
ibis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.933
H-Index - 80
eISSN - 1474-919X
pISSN - 0019-1019
DOI - 10.1111/j.1474-919x.1986.tb02670.x
Subject(s) - breeding pair , fledge , cooperative breeding , shrike , biology , population , seasonal breeder , dominance (genetics) , reproductive success , ecology , demography , zoology , predation , habitat , biochemistry , sociology , gene
Grey‐backed Fiscal Shrikes Lanius excubitorius were studied over a 2j year period near Lake Naivasha, Kenya. Grey‐backs are cooperative breeders, with group sizes ranging from two to II. Only one pair breeds per group, with all other group members aiding in the rearing of young. The study population ranged from 64 to 79 individuals that occurred in from 13 to 16 groups. Non‐breeding helpers made up to 66% of the population, with male helpers being more numerous overall than females. The annual survival rate was 65%, with no differences detected between the survival of males and females, or of breeders and helpers. Only male helpers were observed to acquire breeding status within the natal territory. Some female helpers acquired breeding positions in territories adjacent to their natal territories. Group territorial displays occurred throughout the year but were most pronounced prior to breeding during rainy periods. Reproductive success was very low, with only 14.5% of the recorded breeding attempts leading to fledged young. Large groups (four or more birds) had greater reproductive success than small groups, but many factors other than, or in addition to, group size may have influenced this pattern. The breeding male contributed the most food to the incubating female and to the nestlings. Male helpers and the breeding female contributed more to nestlings than did female helpers. Observations on the post‐fledging period indicate that socialization and establishment of dominance may be of importance in group‐living species living in a restricted ecological and social setting.