Female offspring desertion and male-only care increase with natural and experimental increase in food abundance

Abstract

In species with biparental care, one parent may escape the costs of parental care by deserting and leaving the partner to care for the offspring alone. A number of theoretical papers have suggested a link between uniparental offspring desertion and ecological factors, but empirical evidence is scarce. We investigated the relationship between uniparental desertion and food abundance in a natural population of Tengmalm's owl Aegolius funereus, both by means of a 5-year observational study and a 1-year experimental study. Parents and offspring were fitted with radio-transmitters in order to reveal the parental care strategy (i.e. care or desert) of individual parents, and to keep track of the broods post-fledging. We found that 70 per cent of the females from non-experimental nests deserted, while their partner continued to care for their joint offspring alone. Desertion rate was positively related to natural prey population densities and body reserves of the male partner. In response to food supplementation, a larger proportion of the females deserted, and females deserted the offspring at an earlier age. Offspring survival during the post-fledging period tended to be lower in deserted than in non-deserted broods. We argue that the most important benefit of deserting may be remating (sequential polyandry).

Effect of male provisioning on the parental behavior of female Boreal Owls Aegolius funereus

“…Similarly, Eldegard and Sonerud (2009) reported a brood where the male deserted and the female deserted shortly thereafter. One of our females, however, although widowed when the oldest chick was 21 days old, managed to fledge one chick.…”

“…Our findings indicate that the stage of the nesting phase can influence whether or not a Boreal Owl female provides single-parent care. Because successful offspring desertion by female Boreal Owls (in the late nesting phase) and male-only care are positively related to food abundance (Eldegard and Sonerud 2009;Zárybnická 2009a;Korpimäki et al 2011), the responses of female owls to low male food provisioning may vary in different environments and particularly under fluctuating food conditions. Similarly, female Eurasian Kestrels Falco tinnunculus and Northern Goshawks Accipiter gentilis adjust hunting efforts and nest attendance to the abundance of their main prey (Tolonen and Korpimäki 1994;Dewey and Kennedy 2001;Riegert et al 2007).…”

“…The male, however, almost always arrives at the nest with prey (Korpimäki 1981;Zárybnická 2009a, b;Zárybnická et al 2009). After the brooding period, females may either help males in providing food for the young or desert them (Eldegard and Sonerud 2009;Zárybnická 2009a;Korpimäki et al 2011). When a female deserts, its mate compensates for the absent female's contribution and continues to care for the nestlings (Korpimäki 1981;Zárybnická 2009a;Eldegard and Sonerud 2012) and fledglings until they become independent (6 to 7 weeks after fledging, Eldegard and Sonerud 2012).…”

“…While the female incubates eggs and broods young for 3 to 4 weeks after hatching (i.e., the brooding period, Korpimäki 1981;Zárybnická 2009a), the male provides nearly all of the food for the female and young (Korpimäki 1981;Eldegard and Sonerud 2009;Zárybnická 2009a). During this time, the female typically leaves the nest for a few minutes each night in order to defecate, regurgitate the remains of food, or for preening, and usually returns to the nest without prey (Korpimäki 1981;Zárybnická 2009a).…”

“…Using a relatively recently developed methodological approach (e.g., Reif and Tornberg 2006;Nuka et al 2011) of continuous nest recording with a camera system, we obtained data on the feeding rate of males and time spent away from the nest and the provisioning rate by females. We tested the following hypotheses: (1) females whose mates provide sufficient food for their family brood more intensively than females exposed to insufficient male provisioning, (2) females whose mates fail in food provisioning stop brooding, and their nesting attempts fail, and (3) because the female is dependent on provisioning by the male at time of brooding (Korpimäki 1981;Eldegard and Sonerud 2009;Zárybnická 2009a), we expect that the body mass of females in nests with insufficient food provisioning by males are lower than that of the females in nests with a high male feeding rate.…”