Variation in Growth Drives the Duration of Parental Care: A Test of Ydenberg’s Model

Abstract

The duration of parental care in animals varies widely, from none to lifelong. Such variation is typically thought to represent a trade-off between growth and safety. Seabirds show wide variation in the age at which offspring leave the nest, making them ideal to test the idea that a trade-off between high energy gain at sea and high safety at the nest drives variation in departure age (Ydenberg's model). To directly test the model assumptions, we attached time-depth recorders to murre parents (fathers [which do all parental care at sea] and mothers; [Formula: see text] of each). Except for the initial mortality experienced by chicks departing from the colony, the mortality rate at sea was similar to the mortality rate at the colony. However, energy gained by the chick per day was ∼2.1 times as high at sea compared with at the colony because the father spent more time foraging, since he no longer needed to spend time commuting to and from the colony. Compared with the mother, the father spent ∼2.6 times as much time diving per day and dived in lower-quality foraging patches. We provide a simple model for optimal departure date based on only (1) the difference in growth rate at sea relative to the colony and (2) the assumption that transition mortality from one life-history stage to the other is size dependent. Apparently, large variation in the duration of parental care can arise simply as a result of variation in energy gain without any trade-off with safety.

A critical evaluation of the index of patch quality

“…A third issue arises from the fact that diving parameters, and in particular the time allocation from which the IPQ is derived, may be influenced by other factors, so that the IPQ may not only reflect local prey conditions, but how the diver uses those prey conditions. This is supported by findings showing differences in IPQ between male and female common guillemots Uria aalge during the male-only parental care period, but no difference outside that period [25,26]. Here, differences in IPQ may reflect the fact that the males are under different pressures from females because of chickrearing duties.…”

“…[ 26 ] ln( x ) ∈[−1, −0.2] chick-rearing n/a (IPQ of females > IPQ of males) Elliott et al . [ 25 ] Razorbill Alca torda ln( x ) ∈ [0.12, 0.16] incubation and chick-rearing IPQ independent of the frequency of dives in bout but decreased with dive-pause ratio of dive bouts (p.e. : −0.04 ± 0.01, ΔAIC = −10) IPQ increases with distance from the colony (p.e.…”

Spatial variation in vital rates and population growth of thick-billed murres in the Atlantic Arctic

“…Thickbilled murres are long-lived, and pairs produce a maximum of 1 chick annually, which leaves the colony when less than half grown accompanied by the male parent (Gaston & Jones 1998). Males provide postfledging parental care for several weeks (Elliott et al 2017). Many murre populations in the Atlantic Arctic are declining rapidly, particularly those in Svalbard, Iceland and a large part of Greenland, which mainly overwinter off southwest Greenland and around Iceland (Frederiksen et al 2016).…”

Individual migration strategy fidelity but no habitat specialization in two congeneric seabirds

“…This constrains their movements and hence their capacity to demonstrate IMSF. Additionally, reproductively successful males are accompanying a flightless chick as it departs the colony, which further limits their movement (Elliott et al., 2017; Harris & Wanless, 1990). Thus, it is not surprising that some populations exhibit IMSF only for females during autumn as these are not constrained by a dependent and flightless chick and have the possibility to move large distances after breeding and prior to moulting.…”