J. Mark Hipfner

Infectious disease, shifting climates, and opportunistic predators: cumulative factors potentially impacting wild salmon declines

Emerging diseases are impacting animals under high‐density culture, yet few studies assess their importance to wild populations. Microparasites selected for enhanced virulence in culture settings should be less successful maintaining infectivity in wild populations, as once the host dies, there are limited opportunities to infect new individuals. Instead, moderately virulent microparasites persisting for long periods across multiple environments are of greatest concern. Evolved resistance to endemic microparasites may reduce susceptibilities, but as barriers to microparasite distributions are weakened, and environments become more stressful, unexposed populations may be impacted and pathogenicity enhanced. We provide an overview of the evolutionary and ecological impacts of infectious diseases in wild salmon and suggest ways in which modern technologies can elucidate the microparasites of greatest potential import. We present four case studies that resolve microparasite impacts on adult salmon migration success, impact of river warming on microparasite replication, and infection status on susceptibility to predation. Future health of wild salmon must be considered in a holistic context that includes the cumulative or synergistic impacts of multiple stressors. These approaches will identify populations at greatest risk, critically needed to manage and potentially ameliorate the shifts in current or future trajectories of wild populations.

Are yolk androgens adjusted to environmental conditions? A test in two seabirds that lay single-egg clutches

It is widely believed that female birds strategically allocate androgens to yolk in the manner that best equips offspring for feeding conditions during their development. Because most avian studies have focused on multi-egg clutch species, and interpreted results within the framework of sibling competition, we still know little about how yolk androgens might be allocated in direct response to environmental conditions. Most oceanic birds are long-lived and lay single-egg clutches, and their breeding success is tightly linked to highly variable marine production. That combination: a variable breeding environment, long lives, and single-egg clutches, makes oceanic birds good subjects to test hypotheses about yolk androgen allocation strategies. We measured concentrations of two yolk androgens, androstenedione (A4) and testosterone (T), in the single-egg clutches laid by early-laying Cassins (Ptychoramphus aleuticus) and rhinoceros (Cerorhinca monocerata) auklets at Triangle Island, British Columbia, Canada, in 2002-2004. Environmental conditions including sea-surface temperatures and the timing and intensity of marine primary production varied over the 3 years, and in response, both the timing and success of seabird breeding varied. As in other avian species, concentrations of A4 and T varied markedly among individual eggs in both species (by factors of 3-8), yet contrary to expectation, little of the variation could be attributed to year effects. The high interindividual variation and the lack of interannual variation suggest a non-adaptive explanation for yolk androgen deposition relative to environmental conditions in these species.

Leucocyte profiles of Arctic marine birds: correlates of migration and breeding phenology

We examined white blood cell profiles of marine birds breeding in the Arctic, as an index of stress. Within species, birds that had to migrate farther had higher heterophil:lymphocyte ratios during incubation (i.e., residual stress) than those that migrated short distances. These reference values will be important as global warming and anthropogenic activities change the Arctic marine landscape.

Seasonal variation in the foraging ecology of a zooplanktivorous seabird assessed with stable isotope analysis

Abstract We used δ15N and δ13C analyses on blood drawn from zooplanktivorous Cassins auklet (Ptychoramphus aleuticus Pallas, 1811) on Triangle Island, British Columbia, over four years to address two questions: (1) do these seabirds systematically alter their trophic level and foraging habitat from one breeding stage to the next; and (2) do auklets select prey at the same trophic level and from the same foraging habitat to self-feed and provision offspring? Adult trophic level (inferred from δ15N values) tended to be higher prior to egg-laying than during incubation, perhaps reflecting an abundant zooplankton biomass in early spring. Season-long declines in δ13C values suggested that the auklets foraged on the continental shelf early in the season, but thereafter increasingly used habitats seaward of the continental shelf-break to obtain Neocalanus cristatus copepodites. Similarity in the δ15N and δ13C values of provisioning adults and nestlings suggested that adults consumed the same prey from those oceanic habitats to both self-feed and to provision offspring at the nest, a behaviour that may save time and energy. The results of this study show the dynamic nature of seabird foraging ecology and the utility of stable isotope analysis for assessing seasonal variation in the foraging ecology of oceanic species.

Introduced mammals, vegetation changes and seabird conservation on the Scott Islands, British Columbia, Canada

Summary The Scott Islands, British Columbia, Canada, support the largest aggregation of breeding seabirds intheeasternPacificOceansouthofAlaska.However,largeseabirdpopulationswereeradicatedby American Mink Neovison vison and Raccoons Procyon lotor introduced to Lanz and Cox islands in the 1930s, while the ecological consequences of the introduction of European Rabbits Oryctolagus cuniculus to Triangle Island in the 1920s are unknown. We have seen dramatic changes in the vegetation on Triangle Island in recent decades, chiefly a decrease in Tufted Hairgrass Deschampsia cespitosa cover and a concomitant increase in Salmonberry Rubus spectabilis cover. We carried out vegetation surveys at Triangle Island (1989 and 2004) and its nearest neighbour, rabbit-free Sartine Island (1987 and 2006), to test the hypothesis that rabbits have caused these changes. We found, however, that similar changes have occurred at Sartine Island as at Triangle Island over the same time period. Because these two islands support the bulk of the world’s breeding population of Cassin’s Auklet Ptychoramphus aleuticus, a small seabird that selects grass-covered habitat but avoids tall Salmonberry for nesting, the vegetation changes raise serious concerns for a species that has experienced dramatic population declines in recent years. Restoration of seabird nesting habitat by removing American Mink and Raccoons from Lanz and Cox islands will be vital for long-term seabird conservation in the Scott Islands.

Evolution of embryonic developmental period in the marine bird families Alcidae and Spheniscidae: roles for nutrition and predation?

BackgroundNutrition and predation have been considered two primary agents of selection important in the evolution of avian life history traits. The relative importance of these natural selective forces in the evolution of avian embryonic developmental period (EDP) remain poorly resolved, perhaps in part because research has tended to focus on a single, high taxonomic-level group of birds: Order Passeriformes. The marine bird families Alcidae (auks) and Spheniscidae (penguins) exhibit marked variation in EDP, as well as behavioural and ecological traits ultimately linked to EDP. Therefore, auks and penguins provide a unique opportunity to assess the natural selective basis of variation in a key life-history trait at a low taxonomic-level. We used phylogenetic comparative methods to investigate the relative importance of behavioural and ecological factors related to nutrition and predation in the evolution of avian EDP.ResultsThree behavioural and ecological variables related to nutrition and predation risk (i.e., clutch size, activity pattern, and nesting habits) were significant predictors of residual variation in auk and penguin EDP based on models predicting EDP from egg mass. Species with larger clutch sizes, diurnal activity patterns, and open nests had significantly shorter EDPs. Further, EDP was found to be longer among birds which forage in distant offshore waters, relative to those that foraged in near shore waters, in line with our predictions, but not significantly so.ConclusionCurrent debate has emphasized predation as the primary agent of selection driving avian life history diversification. Our results suggest that both nutrition and predation have been important selective forces in the evolution of auk and penguin EDP, and highlight the importance of considering these questions at lower taxonomic scales. We suggest that further comparative studies on lower taxonomic-level groups will continue to constructively inform the debate on evolutionary determinants of avian EDP, as well as other life history parameters.