Distributional patterns of a marine bird and its prey: habitat selection based on prey and conspecific behaviour

We examined the predator-prey interaction between an apex seabird predator, the common murre Uria aalge, and capelin Mallotus villosus, the primary forage fish in the Northwest Atlantic. Sampling of parental deliveries to murre chicks was carried out during the breeding sea- son on Funk Island, located off northeast Newfoundland, Canada. Concurrent vessel surveys were conducted throughout the murre's diving and foraging range around the colony to charac- terize the prey field. Results indicated that in years when capelin was abundant in the size range consumed by murres (suitable capelin), murres delivered large and small fish in similar propor- tions, whereas they delivered more large fish when suitable capelin abundance was low. Consid- ering the relative abundances of small and large suitable capelin, these observations suggest neg- ative prey switching by the predator. Using foraging theory, we derived a model which estimates the probability of delivering a specific prey type (large or small capelin or other prey) to the chick based on prey availabilities. This quantitative model was capable of reproducing the general pat- terns in the observations. It also allowed estimating the shape of the common murre's multispecies functional response (MSFR) which indicated that this would conform to the definition of prey switching, and could then be classified as a Type 3. From an applied perspective, our results support the use of predator diets as indicators of their food base, but also highlight the need for understanding the shape of the predator's MSFR for quantitative development of these types of applications.

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 258:253-261 (2003) - doi:10.3354/meps258253 Signals from seabirds indicate changing biology of capelin stocks Gail K. Davoren*, William A. Montevecchi Biopsychology Programme, Departments of Biology and Psychology, Memorial University, St. John's, Newfoundland A1B 3X9, Canada *Email: z73gkd@ mun.ca ABSTRACT: Key forage species lie at the core of complex marine food webs, providing essential linkages among trophic levels. We examined the interactions of an important forage and commercial fish, capelin Mallotus villosus, and its primary avian predator, the common murre Uria aalge, in the NW Atlantic. Murres are capelin specialists and robust samplers of capelin biology. During the 1990s, the coldest surface-water event in the past 50 to 100 yr occurred in the NW Atlantic (1991), and the eastern Canadian ground-fishery was closed (1992). Concordantly, the biology and behaviour of capelin has undergone very substantial changes. We examined parental food deliveries and production at the world¹s largest common murre colony on Funk Island off the northeast coast of Newfoundland throughout the 1990s. Murres delayed breeding and delivered smaller and lower quality capelin to their chicks. These changes, corroborated with independent fisheries data, resulted in poor condition of murre chicks, indicating significant effects of changing capelin demographics at higher trophic levels. The diets of the murre chicks indicate that the composition of the capelin population has shifted from high size diversity to mainly smaller capelin. We hypothesize that this change resulted from the elimination of the larger-sized and earlier-spawning genotype and that the NW Atlantic capelin population is exhibiting signs of reduced reproductive potential that likely reflects lower spawning biomass. KEY WORDS: Predator-prey interaction · Bio-indicator · Ecosystem dynamics · Common murre · Uria aalge · Capelin · Mallotus villosus Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 258. Online publication date: August 29, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

We examine the provisioning constraints of a pursuit‐diving seabird in a cold ocean regime by comparing the behaviour of common murres Uria aalge rearing chicks at two colonies in the Northwest Atlantic during 1998‐2000. Funk Island is the largest (340,000–400,000 breeding pairs) and most offshore (60 km) colony of common murres in eastern Canada. Seventy‐five percent of the Northwest Atlantic population of common murres breeds on this island. Great Island is one island within the Witless Bay Ecological Reserve, which is the second largest breeding aggregation (100 000 breeding pairs) and is located near‐shore (2 km). The primary forage fish species in Newfoundland waters is capelin Mallotus villosus, which spawns on or near coastal beaches during summer. Therefore, the two study colonies differ in their distance to food resources and colony size. It is within this natural context that we compare: (1) prey types and frequency of delivery (amount of prey), (2) parental time budgets, and (3) the mass and condition (mass/wing length) of fledglings at both colonies. Similarly sized female capelin (100–150 mm) were delivered to chicks at both colonies. Foraging time per day per parent, a proxy of foraging effort, was similar at both colonies (Great Island: 5.1 h; Funk Island: 5.5 h), as was the percentage of time spent with mates (Great Island: 12.3%; Funk Island: 10.9%). Foraging trips, however, were longer at Funk Island (4.1 h) than at Great Island (2.9 h). This resulted in lower feeding rates of chicks (0.17 feeds per h) and poorer condition of fledglings (2.9 g/mm) at Funk Island compared to those at Great Island (0.22 feeds per h; 3.9 g/mm). We hypothesize that provisioning efforts are constrained at Funk Island by (1) distant food resources and increased competitor density, resulting in longer foraging trip durations and (2) the time spent paired with mates at the colony, which may reflect a minimum time required to maintain breeding sites due to higher breeding densities at Funk Island compared to Great Island. Demographic consequences of this poor fledgling condition at Funk Island are unknown, but fledglings may sufficiently accelerate growth at sea due to their closer proximity to an important nursery area. If fledgling survival is compromised, however, the lower potential for growth at Funk Island will impact the entire Northwest Atlantic population of common murres.

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In order to forage and to provision offspring effectively, seabirds negotiate a complex of behavioural, energetic, environmental and social constraints. In first tests of GPS loggers with seabirds in North America, we investigated the foraging tactics of free-ranging northern gannets (Sula bassana) at a large and a medium-sized colony that differed in oceanography, coastal position and prey fields. Gannets at Low Arctic colony (Funk Island) 50 km off the northeast coast of Newfoundland, Canada provisioned chicks almost entirely with small forage fish (capelin Mallotus villosus, 89%), while at boreal colony (Bonaventure Island) 3 km from shore in the Gulf of St. Lawrence, Quebec, Canada, large pelagic fish dominated parental prey loads (Atlantic mackerel Scomber scombrus 50%, Atlantic herring Clupea harengus 33%). Mean foraging range and the total distance travelled per foraging trip were significantly greater at the larger inshore colony (Bonaventure) than at the smaller offshore colony (Funk Island; 138 and 452 km vs. 64 and 196 km, respectively). Gannets from Funk Island consistently travelled inshore to forage on reproductive capelin shoals near the coast, whereas foraging flights of birds from Bonaventure were much more variable in direction and destination. Birds from the Low Arctic colony foraged in colder sea surface water than did birds from the boreal colony, and dive characteristics differed between colonies, which is concordent with the difference in prey base. Differences between the colonies reflect oceanographic and colony-size influences on prey fields that shape individual foraging tactics and in turn generate higher level colony-specific foraging “strategies”.

We examined the behavioural interactions of a mobile marine predator, the common murre Uria aalge, and its prey in a cold ocean regime in the context of shifting foraging constraints of the predator during various periods of the year. To do this, we explored the scale-dependent distribution patterns of murres in relation to their prey under 2 mobility regimes: (1) during the pre-breeding period when murres can fly and (2) during the post-breeding or moulting period when murres are flightless and are accompanied by flightless juveniles. In addition, we documented for the first time the relative contributions of different prey types in the diets of murres during moult using stable isotopic analysis. Flightless adult and juvenile murres were concentrated on a meso-scale (>100 km) in an area (nursery area) where significantly greater amounts of non-capelin, mainly crustaceans, were located in closely spaced aggregations. Accordingly, flightless murres had variable proportions of fish (capelin Mallotus villosus) and crustaceans in their diet, whereas breeding murres exclusively ate capelin. At fine- and coarse-scales (0.1 to 100 km), murres that could fly during pre-breeding tracked prey at smaller spatial scales (3 to 4 km) than flightless murres (6 to 9 km). We hypothesize that varying mobility regimes and energetic demands (activity levels) of murres during these 2 periods resulted in divergent perceptions of the foraging environment and subsequently in varying tracking scales of prey. This has important implications for the scale of study during different periods of the annual cycle of a predator, when varying constraints and trophic levels may interact to produce diverse behavioural responses to prey distribution and densities.

Shifting prey availability can lead to altered species interactions, indicated by variation in the dietary niche breadth and position of species within an assemblage. On the Newfoundland coast, annual inshore spawning migration of the dominant forage fish, CapelinMallotus villosus, provides an excellent opportunity to investigate the influence of varying prey availability on dietary niche breadth and position among species. During June–August 2017, we investigated species‐ and assemblage‐level dietary responses to shifting Capelin availability of three Capelin‐eating, sympatrically breeding auk species, the Atlantic PuffinFratercula arctica, RazorbillAlca tordaand Common MurreUria aalge. The diet of Leach's Storm PetrelsOceanodroma leucorhoa, which breed alongside the three auk species but are not known to rely on Capelin, was also examined to determine dietary shifts throughout breeding that were unrelated to Capelin availability. We quantified stable isotope ratios (δ15N, δ13C) in seabird blood components (plasma, cellular component) collected both before and after spawning Capelin arrived in the study area and compared isotopic niche breadth within a Bayesian framework. At the species level, auk trophic position increased and isotopic niche breadth narrowed after Capelin arrived, suggesting a more Capelin‐based diet. Simultaneously, trophic diversity of the auk assemblage, reflecting the extent of spacing among niches of species, decreased after spawning Capelin arrived inshore. Contrastingly, increased trophic position but broader isotopic niche breadth during higher relative to lower Capelin availability for Leach's Storm Petrel confirm that this species is probably not affected by the inshore arrival of Capelin, but instead that isotopic changes may be more related to a shift in breeding stage to chick‐rearing. Overall, our findings reiterate the importance of Capelin as a prey resource for breeding auks in coastal Newfoundland, but that the degree of reliance on Capelin varies among species, possibly allowing coexistence of these ecologically similar species. The findings highlight potential changing species interactions, such as increased competition, under declines in Capelin biomass.

During reproduction, seabirds need to balance the demands of self‐ and offspring‐provisioning within the constraints imposed by central place foraging. To assess behavioral adjustments and tolerances to these constraints, we studied the feeding tactics and reproductive success of common murres (also known as common guillemots) Uria aalge, at their largest and most offshore colony (Funk Island) where parents travel long distances to deliver a single capelin Mallotus villosus to their chicks. We assessed changes in the distance murres traveled from the colony, their proximate foraging locations and prey size choice during two successive years in which capelin exhibited an order of magnitude decrease in density and a shift from aggregated (2004) to dispersed (2005) distributions. When capelin availability was low (2005), parental murres increased their maximum foraging distances by 35% (60 to 81 km) and delivered significantly larger capelin to chicks, as predicted by central place foraging theory. Murres preferred large (>140 mm) relative to small capelin (100–140 mm) in both years, but unexpectedly this preference increased as the relative density of large capelin decreased. We conclude that single prey‐loading murres target larger capelin during long foraging trips as parents are ‘forced’ to select the best prey for their offspring. Low fledgling masses suggest also that increased foraging time when capelin is scarce may come at a cost to the chicks (i.e. fewer meals per day). Murres at this colony may be functioning near physiological limits above which further or sustained adjustments in foraging effort could compromise the life‐time reproductive success of this long‐lived seabird.

Forest ungulates impact ecosystems in a number of ways. Most studies have focused on consumptive effects that may cascade to other components of the ecosystem, and tend to be motivated by harvest management or the mitigation of undesired effects on vegetation. In this study, we demonstrate that white-tailed deer (Odocoileus virginianus), a common forest ungulate in eastern North America, may directly increase availability and heterogeneity of nitrogen due to excretion of nitrogenous wastes. We conducted fecal pellet counts in 39 winter cover habitat patches, ranging in area from 0.04 to 59.6 ha, each spring for eight consecutive years. Pellet counts were used to develop allometric models of annual deer-associated nitrogen inputs at both whole-stand and fine (<10 m2) spatial scales. Deer-associated nitrogen estimates were in the range of 1–4 kg[N] ha−1 in persistently used patches when estimated at the stand scale. Fine-scale estimates in areas of consistent aggregation were equivalent to up to 20 kg[N] ha−1. These areas, such as bedding sites and trails, experienced greater N inputs compared to the surrounding forest matrix. Annual deer use and associated nitrogen inputs were highly variable over space, and spatial patterns in use were consistent over time at both stand and fine spatial scales. Deer-associated nitrogen likely represents a cross-boundary nitrogen flux into patches of conifer cover because deer accumulate nutrients in other habitat types during the warm season, and lose body mass during winter. Nitrogen hotspots and heterogeneity derived from the nitrogenous wastes of forest ungulates may be a generally overlooked phenomenon in forest ecology, with impacts varying according to ecological context.

Understanding factors that influence population connectivity and the spatial distribution of genetic variation is a major goal in molecular ecology. Improvements in the availability of high-resolution geographic data have made it increasingly possible to quantify the effects of landscape features on dispersal and genetic structure. However, most studies examining such landscape effects have been conducted at very fine (e.g. landscape genetics) or broad (e.g. phylogeography) spatial scales. Thus, the extent to which processes operating at fine spatial scales are linked to patterns at larger scales remains unclear. Here, we test whether factors impacting wood frog dispersal at fine spatial scales are correlated with genetic structure at regional scales. Using recently developed methods borrowed from electrical circuit theory, we generated landscape resistance matrices among wood frog populations in eastern North America based on slope, a wetness index, land cover and absolute barriers to wood frog dispersal. We then determined whether these matrices are correlated with genetic structure based on six microsatellite markers and whether such correlations outperform a landscape-free model of isolation by resistance. We observed significant genetic structure at regional spatial scales. However, topography and landscape variables associated with the intervening habitat between sites provide little explanation for patterns of genetic structure. Instead, absolute dispersal barriers appear to be the best predictor of regional genetic structure in this species. Our results suggest that landscape variables that influence dispersal, microhabitat selection and population structure at fine spatial scales do not necessarily explain patterns of genetic structure at broader scales.

Sociality in spiders has evolved independently multiple times, resulting in convergently evolved cooperative breeding and prey capture. In all social spiders, prey is captured by only a subset of group members and then shared with other, non-attacking group members. However, spiders' propensity to attack prey may differ among species due to species-specific trade-offs between risks, costs and benefits of prey capture involvement. We explored whether engagement in prey attack differs among three social Stegodyphus species, using orthopteran prey, and found substantial differences. Stegodyphus mimosarum Pavesi, 1883 had a low prey acceptance rate, was slow to attack prey, and engaged very few spiders in prey attack. In S. sarasinorum Karsch, 1892, prey acceptance was high, independently of prey size, but more spiders attacked when prey was small. While medium-sized prey had higher acceptance rate in S. dumicola Pocock, 1898, indicating a preference, the number of attackers was not affected by prey size. Our results suggest that the three species may have different cooperative prey capture strategies. In S. mimosarum and S. dumicola, whose geographical ranges overlap, these strategies may represent niche specialization, depending on whether their respective cautious and choosy approaches extend to other prey types than orthopterans, while S. sarasinorum may have a more opportunistic approach. We discuss factors that can affect social spiders' foraging strategy, such as prey availability, predation pressure, and efficiency of the communal web to ensnare prey. Future studies are required to investigate to which extent species-specific cooperative foraging strategies are shaped by ontogeny, group size, and plastic responses to environmental factors.

Foraging strategies employed by American white pelicans were studied at a riverine site in Manitoba, Canada, during the breeding season in 1985 and 1986. Six strategies were identified during both diurnal and nocturnal foraging periods. Sit-and-wait was the least common strategy (four instances). Mobile individuals were common but had low rates of bill dipping and prey capture, as did relatively rare and uncoordinated aggregations. A degree of flock coordination occurred in following flocks, characterized by foragers following one after the other, with occasional synchronization of bill dipping among flock members. The largest number of pelicans foraged within more or less circular groups called nuclei. Synchronous bill dipping and apparent herding of prey towards shore were common within nuclei. The most highly coordinated strategy, semicircles, involved small numbers of foragers (2 to 30 birds) that maintained their positions relative to one another, usually in a semicircle but sometimes moving to a closed circular pattern. The greatest degree of synchronized bill dipping occurred in semicircles. Small inter-bird distances and synchronized bill dipping in nuclei and semicircles may enhance their effectiveness in driving or herding clumped fish prey. Foraging strategies could be arranged along a continuum based on degree of coordination, ranging from mobile individuals, then uncoordinated aggregations, through increasing degrees of coordination in following, nuclei, and semicircles. Along this continuum, prey size and capture rats were greatest for the more highly coordinated strategies, while less coordinated strategies appeared to be involved primarily in searching. Switching among strategies fit along the same continuum, with a tendency to switch from less to more coordinated strategies when prey were located and to return to less coordinated search when capture rates declined. Video analysis of captures within large nuclei and observations of positional shifts among foragers in nuclei and following flocks indicated that all individuals within a coordinated group potentially benefited from the presence of others, supporting the view that coordinated foraging strategies in this species are examples of true cooperative foraging. The range of strategies, and interplay among them, appear to provide the American white pelican with a highly effective group foraging system for harvesting mobile, clumped fish prey.

Of 247 harp seal (Phoca groenlandica) stomachs collected between December 1988 and October 1990 from western Hudson Strait (autumn), the northern Gulf of St. Lawrence (December), the St. Lawrence estuary (winter and April), and the Magdalen Islands (March), 140 (57%) contained food. The Magdalen Islands sample contained significantly more empty stomachs (62%, n = 164) than those from all other locations. Both the unreconstructed mass of stomach contents and the proportion of fish and invertebrate prey within individual stomachs varied significantly with location and season. Harp seals obtained from the northern Gulf of St. Lawrence during their southward migration fed less intensively, and on a wider variety of both invertebrate and fish prey, notably Parathemisto libellula, Pandalus sp., sand lance (Ammodytes sp.), and Atlantic cod (Gadus morhua). Feeding was more intensive and specialized in Hudson Strait and the St. Lawrence estuary where capelin (Mallotus villosus) dominated in the diet. Capelin contributed 89 and 98% of gross energy in samples from Hudson Strait (1990) and the estuary (April). The number of capelin per stomach consumed by seals from the St. Lawrence estuary in April was high (169.4 ± 58.9, mean ± SD, n = 9). The mean estimated lengths of capelin and cod consumed were 132 and 140 mm.