Explore the vast range of titles available.

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; N = 14 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 divingper 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.

Bird migration is commonly defined as a seasonal movement between breeding and non-breeding grounds. It generally involves relatively straight and directed large-scale movements, with a latitudinal change, and specific daily activity patterns comprising less or no foraging and more traveling time. Our main objective was to describe how this general definition applies to seabirds. We investigated migration characteristics of six pelagic seabird species (northern fulmar, common guillemot, Brünnich’s guillemot, little auk, Atlantic puffin, black-legged kittiwake). We used an extensive geolocator positional and activity dataset from 29 colonies in the North-East Atlantic and across several years (2008-2019). We used a novel method to identify active migration periods based on segmentation of time series of track characteristics (latitude, longitude, net-squared displacement). Additionally, we used the wet/dry data of geolocators to infer bird activity. We found that the six species had, on average, three to four migration periods and two to three distinct stationary areas during the non-breeding season. On average, seabirds spent the winter at lower latitudes than their breeding colonies and followed specific migration routes rather than non-directionally dispersing from their colonies. Differences in daily activity patterns were small between migratory and stationary periods, suggesting that all species continued to forage and rest while migrating, engaging in a “fly-and-forage” migratory strategy. We thereby demonstrate the importance of habitats visited during seabird migrations as those that are not just flown over, but which may be important for re-fuelling.

Seabirds within the Alcini subfamily have a unique breeding strategy, with their offspring leaving the colony flightless, at only a quarter of adult body size, accompanied by the father and fledge (become independent) out at sea. In this study we test several hypotheses about this elusive second part of the breeding season, termed swimming migration, for common guillemots Uria aalge and Brünnich's guillemots Uria lomvia by tracking 34 chicks (of which 17 transmitted data) equipped with satellite linked Argos PTTs (Platform Transmitter Terminals) at Bjørnøya, a major colony in the European Arctic. All chicks, presumably accompanied by their fathers, swam actively towards species‐specific autumn staging areas, rather than passively drifted away from the colony with a swim speed generally twice that observed of surrounding surface currents. They swam fastest during the first two days after departure. This coincides with the only time they actively crossed a current and the time needed to leave the area of prey depletion around the colony. They otherwise took advantage of available currents, while still swimming actively during the remainder of their migration towards species‐specific autumn staging areas. These staging areas corresponded to areas used by breeding adults during their moulting period (as confirmed by complementary light‐level logger tracking of adults), rather than being specific nursery areas. Migration duration correlated with distance resulting in species‐specific migration periods that were only a fraction of previously reported fledging periods out at sea, indicating that not only the swimming migration, but also known adult autumn staging regions constitute in effect breeding areas. This work has important implications for our understanding of population dynamics within the Alcini subfamily and the management of these species under multiple threats, while providing the foundation to investigate swimming migrations across their distributional range.

Spatial patterns of breeding seabirds are influenced by the distribution of resources in relation to the colony and the density of conspecifics from the same or adjacent colonies. We conducted an inter-colony comparison of foraging space use and behavior, diet, and reproductive success of common murres Uria aalge breeding at a large offshore and a small inshore colony on the northeastern coast of Newfoundland (Canada) during 2016–2018 under varying prey (capelin Mallotus villosus) biomass. Murres from the large offshore colony foraged over a greater area, with greater individual foraging distances, indicative of higher commuting costs compared to the smaller inshore colony. Although this pattern might reflect prey depletion near the offshore colony due to higher conspecific densities, it likely also reflects the greater distance to predictable, high-abundance prey aggregations. This is supported by high spatial overlap of foraging areas from both colonies near coastal, annually persistent capelin spawning sites. Adult diet was similar be tween colonies during incubation, but diverged during chick-rearing, with offshore murres consuming a higher proportion of alternative prey, while inshore murres consumed more capelin. These differences did not affect fledging success, although hatching success was lower in the larger colony, suggesting that divergent factors (e.g. predation, nest attendance) influence colony-specific population dynamics. Overall, our findings suggest that abundant local prey is key in shaping spatial patterns of breeding common murres in northeastern Newfoundland and results in apparently minimal intraspecific competition. As anthropogenic pressures on resource availability heighten, insight into factors influencing intraspecific foraging niche dynamics will be critical to inform management.

Geolocators provide information on the year-round movements of birds. The effect of the year-round deployment of such devices has, however, largely been examined via measures that are relatively insensitive to small changes in nutritional condition, such as return body mass, return rate and reproductive success. To address this issue, we equipped 34 common murresUria aalgeand 35 thick-billed murresU. lomviaat 6 colonies in the eastern Canadian Arctic and sub-Arctic with geolocators for 1 yr and measured baseline corticosterone levels (4 colonies) and body mass (6 colonies) upon device retrieval. Across all colonies, birds equipped with geolocators averaged higher levels of corticosterone and lower body mass than controls, although there were substantial differences among colonies. Despite effects of the devices on corticosterone and body mass, survival (90%) in equipped birds was no different than in control birds at the one colony where long-term resighting data were available, and chick feeding rates were also similar between equipped and unequipped birds. We suggest that even very small devices can cause chronic stress when applied over long periods, at least for a diving bird with a very high wing loading, but effects on birds in the present study were not sufficiently pronounced to influence adult survival or chick provisioning rates.

Partitioning of resources by competing species of seabirds may increase during periods of food shortages and elevated energy demands. Here, we examined whether food resource partitioning (differential use of foraging habitat or the consumption of different prey species) between common murres (COMU, Uria aalge) and thick‐billed murres (TBMU, U. lomvia) breeding on the same colony in the Bering Sea increases with a predictable increase in energy demands between the incubation and chick‐rearing stages of reproduction. We assessed the seasonal dynamics of food availability via corticosterone (CORT) levels and examined adult diet (via stable isotope analysis of nitrogen and carbon, SI) and chick diets (based on nest observations). We compared chick provisioning patterns and examined the characteristics of parental foraging habitat via deployment of bird‐borne temperature‐depth recorders. We found that CORT levels remained low and similar between the species and reproductive stages, reflecting relatively stable and favorable foraging conditions for both murre species during the study period. Comparisons of SI between murres and their potential prey indicated that diets were similar between the species during incubation and diverged during chick‐rearing. Chick‐rearing common and thick‐billed murres also used different foraging habitats, as reflected in travel distances to foraging areas and sea surface temperature distributions of their foraging dives. TBMUs performed shorter foraging trips, deeper dives and delivered squid to their chicks, while COMUs foraged farther from the colony, performed shallower dives, and delivered fish species to their chicks. These results suggest that food resource partitioning between murre species increased during chick‐rearing under favorable foraging conditions. Whether the dietary segregation reflected species‐specific differences in adults' foraging efficiency, differences in chicks' dietary requirements, or was a way of reducing competition remains unknown. Regardless of the causal mechanism(s), food resource partitioning might ameliorate interspecific competition between sympatrically breeding birds during periods of increased energy demands.

Competition for high‐quality breeding sites in colonial species is often intense, such that individuals may invest considerable time in site occupancy even outside the breeding season. The site defense hypothesis predicts that high‐quality sites will be occupied earlier and more frequently, consequently those sites will benefit from earlier and more successful breeding. However, few studies relate non‐breeding season occupancy to subsequent breeding performance limiting our understanding of the potential life‐history benefits of this behavior. Here, we test how site occupancy in the non‐breeding season related to site quality, breeding timing, and breeding success in a population of common guillemots Uria aalge, an abundant and well‐studied colonially breeding seabird. Using time‐lapse photography, we recorded occupancy at breeding sites from October to March over three consecutive non‐breeding seasons. We then monitored the successive breeding timing (lay date) and breeding success at each site. On average, sites were first occupied on the 27th October ± 11.7 days (mean ± SD), subsequently occupied on 46 ± 18% of survey days and for 55 ± 15% of the time when at least one site was occupied. Higher‐quality sites, sites with higher average historic breeding success, were occupied earlier, more frequently and for longer daily durations thereafter. Laying was earlier at sites that were occupied more frequently and sites occupied earlier were more successful, supporting the site defense hypothesis. A path analysis showed that the return date had a greater or equal effect on breeding success as lay date. Pair level occupancy had no effect on breeding timing or success. The clear effect of non‐breeding occupancy of breeding sites on breeding timing and success highlights the benefits of this behavior on demography in this population and the importance of access to breeding sites outside the breeding season in systems where competition for high‐quality sites is intense. The relationship between occupancy of breeding sites in the non‐breeding season and subsequent breeding success is not well‐understood despite having likely impacts on population fitness. We used time‐lapse photography to record occupancy throughout the non‐breeding period, October–March, in a population of common guillemots to investigate how site occupancy related to site quality, timing of breeding, and breeding success. High‐quality sites were occupied earlier and more often with positive consequences for breeding timing and success and highlighting the benefits of this behavior on demography in this population and the importance of access to breeding sites outside of the breeding season in systems where competition for high‐quality sites is intense.

Harmful algal blooms (HABs) are dense concentrations of phytoplankton that can have deleterious effects on marine life. We documented two of the largest marine bird mortality events ever definitively ascribed to a single HAB, the cause of which was death resulting from plumage fouling by surfactant-like proteins produced by the dinoflagellate Akashiwo sanguinea. The two mortality events were observed along the coast of Washington State in September and October 2009, collectively representing an estimated deposition of 10 500 carcasses, of which the majority were surf scoters, white-winged scoters and common murres. Each mortality event was coincident in space and time with observed bloom landfall, with each event preceded by a similar chain of environmental conditions. Prior to each event, the presence of A. sanguinea and upwelling-favourable conditions likely led to bloom proliferation. In both cases, this period was followed by conditions that transported the senescent bloom into the nearshore environment, whereupon subsequent wave action lysed A. sanguinea cells, creating foam that contained surfactant-like compounds. This sequence of conditions, exacerbated by the presence of aggregations of marine birds in wing moult, appear to be the necessary requirements for marine bird mortality of this scale due to foam-induced plumage fouling. This mechanism of HAB-induced mortality may become more prevalent in the California Current System given the apparent increasing occurrence of HABs and the broad environmental tolerances exhibited by A. sanguinea.

Diving behaviour of seabirds has been studied using data logging devices, but little is known about underwater predator–prey interactions during dives. We used stationary video cameras to investigate how the underwater foraging behaviour of common murres Uria aalge was influenced by the density and behaviour of their main prey fish, capelin Mallotus villosus, at spawning sites on the northeast Newfoundland coast during July, 2009−2012. From ~720 h of video, we analyzed 99 events where capelin and murres were observed together, ranging from 1−20 s, and 952 events where murres were observed alone, ranging from 1−14 s. Although 91% of all video footage of capelin was in high density schools, 69% of active foraging behaviour of murres (i.e. attempted contacts, approaches) was exhibited on individual capelin, compared to 24% on low density shoals and 7% on high density schools. Similarly, more murres were observed turning, a proxy of area-restricted search behaviour, when solitary and low density capelin shoals persisted for longer durations relative to when schools persisted for longer. When murres made contact with capelin (n = 16), ~70% (n = 11) were deemed successful (i.e. resulted in ingestion or ascent with fish in bill). Unsuccessful contacts resulted from fish escaping during beak manipulations to orient the fish head-first. Capelin were 7−11 times more likely to accelerate when murres displayed active versus passive (i.e. search, travel) foraging behaviours and 5−6 times more likely to accelerate in response to murre presence when in schools relative to low density shoals or solitary individuals. Overall, these results suggest that murres may increase their foraging success within areas of high prey density by preferentially searching for and targeting solitary fish that are less responsive to predators.

Sympatric nesting seabird species are often found to differ in one or more aspects of their foraging ecology. This is usually interpreted as resource partitioning, potentially due to current or past competition, but other explanations have been proposed. Three closely related species of alcids breeding together in subarctic southwest Greenland differed in several aspects of their foraging ecology during chick rearing. Thick-billed Murres (Uria lomvia) and Common Murres (U. aalge) did not differ in their diving behavior but both species differed markedly with Razorbills (Alca torda). Thick-billed Murres foraged mainly close to the colony, whereas Common Murres and Razorbills also made foraging trips to the mainland coast. Common Murres made significantly more bouts (series of dives) per trip than Thick-billed Murres, but significantly fewer dives per bout than Razorbills. Median dive depth of Thick-billed and Common murres was twice that of Razorbills. Thick-billed Murres nested on open ledges and spent most of their non-foraging time on the ledge attending the chick. Common Murres and Razorbills nested under boulders and in crevices and often left their chicks alone (particularly at night) and rested on the water. One interpretation of this pattern is that the risk of predation from Glaucous Gulls (Larus hyperboreus) was much higher on open ledges, and that Thick-billed Murres therefore had to guard their chicks at all times.