UC Davis

Sexual conflict occurs when males and females do not maximize reproductive success in the same way. Conversely, when the fitness prospects of each sex are aligned, there is greater advantage to cooperate and to coordinate. This situation, where breeding partners share a higher proportion of their lifetime reproductive output, is most likely to be realized when pairs remain together for multiple breeding attempts. As a group, seabirds are notable for the number of species that maintain long-term pair bonds and display biparental care across a protracted breeding period. Consequently, in this group behavioral cooperation and coordination is expected to be critical. Behavioral coordination between breeding partners may also improve with the experience of the pair, further incentivizing the maintenance of long-term pair bonds. The scope for coordination, however, is likely to be constrained by various intrinsic extrinsic factors, which may differ between species. This dissertation is an examination of the causes and consequences of behavioral coordination between breeding partners in three allopatric seabird species with contrasting foraging strategies. Specifically, I studied the Cassin’s auklet (Ptychoramphus aleuticus), the Leach’s storm-petrel (Oceanodroma leucorhoa), and the Manx shearwater (Puffinus puffinus). While all of these species share many similar life-history traits, they display markedly different foraging routines, ranging from consistent day-long trips in Cassin’s auklets, to multi-day trips of variable duration in Leach’s storm-petrels, to trips with a bidmodal duration, ranging from one day to more than 10 days in Manx shearwaters. The distinct foraging routines displayed by each species are expected to create different possibilities and incentives for coordination. Additionally, coordination may be influenced by a variety of intrinsic factors, such as individual age and pair experience, or extrinsic factors, such as environmental conditions. By monitoring parental care across the breeding period and combining these behavioral observations with demographic data, this dissertation aims to extend our understanding of behavioral coordination during parental care in seabirds. In Chapter 1, I evaluate the causes of sex-specific parental care in a monomorphic seabird, the Leach’s storm-petrel. While there are many reported cases of sex-specific parental care in monomorphic species, the drivers of this behavior are not well-understood. I examine several of the hypotheses that have been proposed to account for sex-specific provisioning rates in monomorphic species by combining extended observations on provisioning rates and chick growth from a large number of pairs (n = 74). I found the strongest support for energetic constraints limiting the female contribution to chick provisioning. These findings are important for understanding how investment in parental care fluctuates throughout the breeding season. In Chapter 2, I assess the functional benefits of a unique form of coordinated provisioning displayed by Manx shearwaters and whether the degree of coordination changes with pair-bond duration. Previous work demonstrated that during chick rearing, individuals will alternate between short and long foraging trips and that partners coordinate the timing of long trips. In this chapter, I show that this coordination benefits chick provisioning and growth. I also examine whether the degree of coordination is related to pair bond duration, but find no evidence for increased coordination in more experienced pairs. In Chapter 3, I examine the ‘mate familiarity effect’ in Cassin’s auklets using a long-term dataset on breeding success in known-age individuals. I find evidence for both direct and indirect benefits of pair experience on hatching success, suggesting that beyond laying earlier in the year, more experienced pairs also differ in breeding competence. Moreover, this effect was strongest during environmentally poor years. To evaluate behavioral differences between pairs, I monitored nest attendance during three breeding seasons. I find no differences in the rate of egg neglect between new and experienced pairs, suggesting that coordination during incubation does not drive differences in hatching success in this species.