Social organization, demography and genetic mating system of a Tibetan cooperative breeder

Abstract

Knowledge of cooperative breeding in birds from longitudinal studies is available only for a small proportion of species. This paper reports data from a 12‐year study on the Tibetan Ground Tit Pseudopodoces humilis. On average, 27.2% (range: 13.0–36.1%) of monogamous pairs in each year contained one (85.4%) or more (14.6%) male helpers, 83.7% of which were yearlings staying on natal territories. Most helpers (89.6%) helped once and then bred independently. Adults had male‐biased sex ratios, low annual survival rates (averaging 0.50) and shorter longevities (averaging 1.8 years) compared with low‐altitude avian cooperative breeders, suggesting that mate shortage promotes helping behaviour in this species. Incest occurred rarely (2.1% of pairs), probably because kin recognition occurs through year‐around living in family groups. There was a low level (3.1% of broods) of extra‐pair parentage, which could facilitate the maintenance of cooperative breeding.

Egg investment in response to helper presence in cooperatively breeding Tibetan ground tits

“…Female apostlebirds Struthidea cinerea and chestnut‐crowned babblers Pomatostomus reficeps also increase clutch size with helper assistance, but whether they adjust egg size is not known (Woxvold and Magrath 2005, Russell and Lummaa , Liebl et al ). Finally, female Iberian magpie Cyanopica cooki do not adjust their clutch size but produce larger eggs in response to helper presence (Valencia et al ). Similar to what was found in the acorn woodpecker Melanerpes formicivorus , both egg size and clutch size were not associated with helper presence in female ground tits (Koenig et al ).…”

“…In some studies, a load‐lightening strategy has been shown in response to helper presence (Russell et al , Canestrari et al , Santos and Macedo ). In contrast, other studies have shown that females may increase their investment in eggs when they are assisted by helpers (Woxvold and Magrath 2005, Russell and Lummaa , Liebl et al , Lejeune et al , Valencia et al ) or show no response (Koenig et al ). Although a change in egg investment in relation to helper presence is expected to affect survival and reproductive success, few studies have investigated this (Russell et al ).…”

“…Helping is kin-directed; in 83.3% of cases, helpers assist breeding pairs of which at least one member is the helper's parent (Tang et al 2017). Helpers, which are always males, join the breeding pairs before egg laying and subsequently assist with nest building, nestling provisioning and territory defence (Ke and Lu 2009, Li et al 2015, Tang et al 2017). Females lay one egg each day until the clutch is completed (average clutch size = 6 eggs, range: 4-9; Tang et al 2017).…”

“…In many avian cooperatively breeding species, helpers may assist the dominant breeding pair during reproduction, for example through their help with nest building, incubation, predator deterrence and provisioning (Stacey and Koenig , Koenig and Dickinson , 2016, Komdeur et al ). The presence of helpers may induce different investment strategies for breeders.…”

Hamilton's inclusive fitness maintains heritable altruism polymorphism through rb = c

“…Here we test the prediction using a 12-y dataset of individual relationship and lifetime reproductive success from a population of the Tibetan ground tit Pseudopodoces humilis (16). As in most avian cooperative breeders, helping in this species is kin-directed.…”