The ecological consequences of solitary breeding in a species with bi-parental care

摘要

A higher rate of nestling development reduces their exposure time to predators, which is advantageous but simultaneously it involves an increased parental investment in incubation, brooding and feeding, which may be difficult to obtain by a single parent. An interesting question is whether, and to what degree, a single parent in a typical bi-parental species is able to compensate the lack of its mate's contribution in species with fast developing nestlings. Our study species is the Blackcap Sylvia atricapilla, a small passerine that experiences high levels of nest predation and rapid development of nestlings. We test the hypotheses that (i) single parents are not able to fully compensate for the lack of mate in rearing a brood and (ii) parents pay cost for breeding alone by increasing the time that the offspring is exposed to predators in the nest. We also inquire in potential trade-off between brooding and feeding and its consequences for nestling growth in nests reared by single parents. Our results show that single parents were able to compensate for the lack of the mate in terms of feeding rate, but this was at the cost of time spent brooding. Nestlings in uni-parental nests grew more slowly and lagged about two days behind their bi-parental counterparts, which may extend nestling exposure time to a predator by about 20%. In an environment with high nest predation risk, this is expected to strongly affect offspring survival. Slower growth of single-parent nestlings might have resulted from deficiency in brooding of poikilothermic offspring observed in our study, which reveals the important role of both mates in shortening the nestling period. It also demonstrates that although single parents are capable of full mate compensation in one activity, it is by the cost of other parental investments, finally leading to impairment in offspring development.