Male and female reproductive strategies and multiple paternity in the polygynandrous Alpine Accentor Prunella collaris

Abstract

Five breeding groups of the Alpine Accentor were studied in a Swiss alpine region. The studied groups showed a polygynandrous mating system and each group was formed of 1–4 females and 3–5 males. The females had exclusive territories, while the males cooperated in defending their group territory. Among the males of one group, a linear dominance relationship was usually well established among the alpha, beta and subordinate male S 1. Both frequent copulation and mate guarding strategies were applied. Females advertised their fertility, solicited most of the copulations and mated multiple times with several males. With approximately 350 matings during the short fertile period of 10 days, the Alpine Accentor is one of the bird species with the highest copulation frequency. Intensity of mate guarding and copulation frequency were highest starting 1 day before egg-laying and throughout the egg-laying period. The alpha male guarded a fertile female closely during the ovulation period, while the beta and other subordinate males (S 1, S 2 and S 3) were restricted in their access to fertile females by the alpha male’s mate guarding ability. In most cases, they did not guard mates and solely performed the frequent copulation strategy. Accordingly, higher ranking males got more solicitations from females, maintained a higher copulation frequency, but also refused a greater portion of all mating offers. Sperm competition was intense with 81.8 % of the broods having multiple paternity. The share of matings during the ovulation period best reflected the achieved share of paternity. Alpha, beta and S 1 sired most of the young, while S 2, S 3 and extra-group males were seldom fathers of offspring. At one nest, up to 4 males helped to feed the young, however, usually at a low rate and the overall male help (28 %) was smaller than the female contribution (72 %). In this polygynandrous mating system, females of the studied population lacked full male help but might have benefited from the greater genetic variation of their young, while males have a large individual variance in their lifetime reproductive success with higher ranking males raising their fitness to above average.