Paul M. Regular

Fishing in the Dark: A Pursuit-Diving Seabird Modifies Foraging Behaviour in Response to Nocturnal Light Levels

Visual predators tend not to hunt during periods when efficiency is compromised by low light levels. Yet common murres, a species considered a diurnal visual predator, frequently dive at night. To study foraging of murres under different light conditions, we used a combination of archival tagging methods and astronomical models to assess relationships between diving behaviour and light availability. During diurnal and crepuscular periods, murres used a wide range of the water column (2–177 m), foraging across light intensities that spanned several orders of magnitude (103–10−10 Wm−2). Through these periods, they readily dived under conditions equivalent to ambient moonlight (∼10−4 Wm−2) but rarely under conditions equivalent to starlight (∼10−8 Wm−2). At night, murres readily foraged during both moonlit and starlit periods, and diving depth and efficiency increased with nocturnal light intensity, suggesting that night diving is at least partially visually guided. Whether visually guided foraging is possible during starlit periods is less clear. Given the dense prey landscape available, random-walk simulations suggest that murres could benefit from random prey encounters. We hypothesise that murres foraging through starlit periods rely either on close-range visual or possibly nonvisual cues to acquire randomly encountered prey. This research highlights the flexibility of breeding common murres and raises questions about the strategies and mechanisms birds use to find prey under very low light conditions.

Must marine predators always follow scaling laws? Memory guides the foraging decisions of a pursuit-diving seabird

Foraging animals are expected to adapt their movement patterns to their environment in a way thatmaximizes efficiency. The search strategies they rely on to achieve this is an enduring question inecology. Scale-free Levy and Brownian search strategies have received particular attention as bothstrategies are considered effective when prey are abundant and Levy search is thought to optimizesuccess when prey are patchy. Environmental context has been shown to explain Levy and Brownianmovement patterns for various marine predators, but potential effects of habitat structure and cognitiveskills are often overlooked. We used bird-borne global positioning sensors (GPS) and temperature depthrecorders (TDR) to assess flight paths and dive profiles of foraging parental common murres, Uria aalge.Movement patterns while flying and diving were best approximated by Brownian motion even thoughtheir primary prey, capelin, Mallotus villosus, are patchily distributed. Contrary to expectations, there wasvirtually no support for Levy flights. Further analyses revealed that murre foraging activities are notrandom, but are rather more deterministic. Murres repeatedly returned to previously visited sites (withinw2 km), indicating a role of memory, and they focused foraging activities using small-scale arearestricted search (ARS; <2 km radius). Such behaviour appears to induce movement patterns that reflectthe distribution of capelin. These findings highlight the efficacy of assessing deterministic searchbehaviour when interpreting the movement patterns of animals that may be informed about theirenvironment. 2013 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Why timing is everything: Energetic costs and reproductive consequences of resource mismatch for a chick‐rearing seabird

Timing reproduction to overlap with peak prey availability is vital to success for many species. This may be especially true for species that rely on one or a few prey species that exhibit strong seasonal peaks in abundance. Any mismatch must be mediated by parents that provision offspring through flexible behavioral changes within the bounds of their physiological tolerances. In Newfoundland, common murre Uria aalge breeding coincides with the inshore movement of capelin Mallotus villosus—their primary prey—such that peak prey availability overlaps with chick-rearing, the most energy demanding phase of breeding. We use colony-based observations and temperature-depth recorders to track the behavioral responses of murres to temporal match and mismatch with capelin availability. Activity budgets, daily energy expenditure (DEE) and chick-provisioning rates were constant across years when chick and capelin timing matched. However, when capelin were late, despite increasing diving effort and DEE, parents deliv...

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

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.

Large-Scale Changes in Abundance of Breeding Herring Gulls (Larus argentatus) and Great Black-Backed Gulls (Larus marinus) Relative to Reduced Fishing Activities in Southeastern Canada

Abstract. Large-scale relationships between changes in abundance of coastal breeding Herring (Larus argentatus) and Great Black-backed (L. marinus) gulls and commercial fisheries landings of bottom-dwelling groundfish spanning 28 years in four of Canadas east coast Provinces were investigated. Herring and Great Black-backed gull abundance data were compared between survey periods prior to (1986–1990) and following (2002–2006 and 2010–2014) the widespread reduction of groundfish fishing activities due to a moratorium that began in 1992. Regionwide declines in the number of breeding Herring and Great Black-backed gulls were observed between the 1986–1990 and 2002–2006 survey periods (Herring Gull: -3.7% per year; Great Black-backed Gull: -3.6% per year) and between the two periods following the moratorium (Herring Gull: -1.6% per year; Great Black-backed Gull: -4.1% per year). Total groundfish landings reported for the study area declined by 76% between the 1990–1992 and 2002–2006 fishing periods, and declined by an additional 25% between the two periods following the moratorium. A positive relationship was found between Province-wide groundfish landings and the number of breeding Great Black-backed Gulls corrected for coastline length. These results support the hypothesis that the moratorium reduced the availability of discards, which in turn played a role in the regions widespread decline of breeding Herring and Great Black-backed gull populations. In addition to continued declines in available discards, additional factors are likely influencing recent regional breeding population trends, including declines in available refuse and forage fish and increases in novel food sources such as expanding American mink (Neovison vison) farms.