Seasonal Variation in Parental Care Drives Sex-Specific Foraging by a Monomorphic Seabird

Abstract

Evidence of sex-specific foraging in monomorphic seabirds is increasing though the underlying mechanisms remain poorly understood. We investigate differential parental care as a mechanism for sex-specific foraging in monomorphic Common Murres (Uria aalge), where the male parent alone provisions the chick after colony departure. Using a combination of geolocation-immersion loggers and stable isotopes, we assess two hypotheses: the reproductive role specialization hypothesis and the energetic constraint hypothesis. We compare the foraging behavior of females (n = 15) and males (n = 9) during bi-parental at the colony, post-fledging male-only parental care and winter when parental care is absent. As predicted by the reproductive role specialization hypothesis, we found evidence of sex-specific foraging during post-fledging only, the stage with the greatest divergence in parental care roles. Single-parenting males spent almost twice as much time diving per day and foraged at lower quality prey patches relative to independent females. This implies a potential energetic constraint for males during the estimated 62.8 ± 8.9 days of offspring dependence at sea. Contrary to the predictions of the energetic constraint hypothesis, we found no evidence of sex-specific foraging during biparental care, suggesting that male parents did not forage for their own benefit before colony departure in anticipation of post-fledging energy constraints. We hypothesize that unpredictable prey conditions at Newfoundland colonies in recent years may limit male parental ability to allocate additional time and energy to self-feeding during biparental care, without compromising chick survival. Our findings support differential parental care as a mechanism for sex-specific foraging in monomorphic murres, and highlight the need to consider ecological context in the interpretation of sex-specific foraging behavior.

Taking the Bite Out of Winter: Common Murres (Uria aalge) Push Their Dive Limits to Surmount Energy Constraints

“…This study was carried out in strict accordance with ethical guidelines outlined by the Canadian Council on Animal Care, and approved by Memorial University of Newfoundland's Institutional Animal Care Committee (Permit Numbers: 10-01-WM, 11-01-WM, 12-01-WM, 13-01-WM Burke et al (2015).…”

“…Based on the approach of Frederiksen et al (2016), we ran latitudinal adjustments on our data, the details of which are explained in Supplementary Material (S2). Further processing followed the methods outlined by Burke et al (2015) involving a two position smoothing, and exclusion of data points representing improbable daily movements (i.e., >500 km/day; Hedd et al, 2011;McFarlane-Tranquilla et al, 2013). The total number of retained, post-processing winter positions represented 67% (n = 1034 days) of the original 1,544 raw positions (n = 17 individuals).…”

“…This behavior can lead to spurious identification of flights, resulting in over-estimation of the total daily time spent flying. We programmed our loggers to eliminate dry records associated with leg-tucking behavior (detailed in Burke et al, 2015), which was successful for 8 individuals only (possibly due to inaccurate temperature reading for some loggers). We restrict our activity-budget analysis to these eight birds for which we are certain that dry periods during the day represent flight time and not some combination of flight and leg-tucking time.…”

“…Explanation of sampling rates, dive and bout processing procedures are provided in detail in Burke et al (2015). Postdive intervals >1800 s (30 min) representing 6.7% of all dives by number (n = 83,703) were excluded from analysis of interbout rest time since pauses >30 min were conservatively deemed to be related to inter-foraging activity (i.e., flying or resting on surface).…”

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

“…Murres and razorbills are unique among birds in their intermediate departure strategy (although some pigeons depart the nest at ∼60% of adult body size; Crome 1975;Robertson 1988). Miniature electronic recorders (such as time-depth recorders and geolocators) have recently been attached to murres, ascertaining their dive behavior and at-sea location (Croll et al 1992;Benvenuti et al 2002;Gaston et al 2011;MacFarlane-Tranquilla et al 2013) and the behavior of males and females after they leave the colony (Linnebjerg et al 2013;Burke et al 2015;Harris et al 2015). Both males and females are flightless (presumably moulting) for 2-3 months after leaving the colony Burke et al 2015).…”