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Data from: Hidden survival heterogeneity of three common eider populations in response to climate fluctuations
Guéry, Loreleï; Descamps, Sébastien; Pradel, Roger; Hanssen, Sveinn Are; Erikstad, Kjell Einar; Gabrielsen, Geir W.; Gilchrist, H. Grant; Bêty, Joël — 2018-01-18 (1) Understanding how individuals and populations respond to fluctuations in climatic conditions is critical to explain and anticipate changes in ecological systems. Most such studies focus on climate impacts on single populations without considering inter- and intra-population heterogeneity. However, comparing geographically dispersed populations limits the risk of faulty generalizations and helps to improve ecological and demographic models. (2) We aimed to determine whether differences in migration tactics among and within populations would induce inter- or intra-population heterogeneity in survival in relation to winter climate fluctuations. Our study species was the Common eider (Somateria mollissima), a marine duck with a circumpolar distribution, which is strongly affected by climatic conditions during several phases of its annual cycle. (3) Capture-mark-recapture (CMR) data were collected in two arctic (northern Canada and Svalbard) and one subarctic (northern Norway) population over a period of 18, 15 and 29 years, respectively. These three populations have different migration tactics and experience different winter climatic conditions. Using multi-event and mixture modelling, we assessed the association between adult female eider survival and winter conditions as measured by the North Atlantic Oscillation index. (4) We found that winter weather conditions affected survival of female eiders from each of these three populations. However, different mechanisms seemed to be involved. Survival of the two migrating arctic populations was impacted directly by changes in the NAO, whereas the subarctic resident population was affected by the NAO with time lags of two to three years. Moreover, we found evidence for intra-population heterogeneity in the survival response to the winter NAO in the Canadian eider population, where individuals migrate to distinct wintering areas. (5) Our results illustrate how individuals and populations of the same species can vary in their responses to climate variation. We suspect that the found variation in survival response of birds to winter conditions is partly explained by differences in migration tactic. Detecting and accounting for inter- and intra-population heterogeneity will improve our predictions concerning the response of wildlife to global changes.
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Data from: Annual movement patterns of endangered ivory gulls: the importance of sea ice
Spencer, Nora C.; Gilchrist, H. Grant; Mallory, Mark L. — 2015-11-21 The ivory gull (Pagophila eburnea) is an endangered seabird that spends its entire year in the Arctic environment. In the past three decades, threats from various sources have contributed to a >70% decline in Canada. To assess the annual habitat needs of this species, we attached satellite transmitters to 12 ivory gulls on Seymour Island, Nunavut in 2010, which provided up to four breeding seasons of tracking data. Analysis of migratory behaviour revealed considerable individual variation of post-breeding migratory route selection. Ivory gulls traveled a median of 74 days during post-breeding migration, but only 18 days during pre-breeding migration. In contrast to predictions, ivory gulls did not use the Greenland coast during migratory periods. Ivory gulls overwintered near the ice edge in Davis Strait, but also used the Labrador Sea in late February and March. We suggest that the timing of formation and recession and extent of sea ice plays a large role in ivory gull distribution and migratory timing. https://creativecommons.org/publicdomain/zero/1.0/
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Data and code from: Opposite, but insufficient, phenological responses to climate in two circumpolar seabirds: relative roles of phenotypic plasticity and selection
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Whelan, Shannon; Hatch, Scott A.; Gaston, Anthony J.; Gilchrist, H. Grant; Elliott, Kyle H. — 2022-04-12 <p><span lang="EN-US">The magnitude of climate change has been greatest in the Arctic, accelerating climate-induced shifts in phenology, but wildlife responses vary. Variation may be due to the relative importance of phenotypic plasticity or phenotypic selection.</span></p> <p><span lang="EN-US">Here, we examine and contrast the environmental drivers of plasticity in breeding phenology of two circumpolar seabirds at their receding summer range limit using unique datasets of marked individuals </span><span lang="EN-US">covering </span><span lang="EN-US">25 and 30</span><span lang="EN-US"> years</span><span lang="EN-US">. Based on prior knowledge of the local ecosystems, we predicted that climate would generate opposing patterns of plasticity in the two populations.</span></p> <p><span lang="EN-US">Laying phenology of kittiwakes in the Gulf of Alaska was associated with a large-scale climate oscillation (Pacific Decadal Oscillation) while the Arctic-breeding murres adjusted </span><span lang="EN-US">laying to sea-ice conditions. Kittiwakes laid earlier after experiencing colder climate about two years prior and laying dates did not advance over the study, but murres laid earlier when warmer climate led to earlier spring sea-ice break-up, and murre laying dates advanced by one week since 1990. Selection favoured earlier laying in both species.</span></p> <p><span lang="EN-US">Both populations adjusted breeding phenology to environmental variation, but we anticipate opposing effects on phenology with continued climate change. Ice-constrained species can likely adapt to some extent because plasticity can provide the necessary shift to this physical barrier, although individuals were only able to adjust by ~one week while ice conditions advanced by over a month</span><span lang="EN-US">. </span><span lang="EN-US">In more temperate regions</span><span lang="EN-US">,</span><span lang="EN-US"> where phenology is driven by bottom-up effects, plasticity and selection counteract one another leading to limited adaptability. We provide insights into the likely adjustments by Arctic marine animals to an increasingly warmer and ice-less summer.</span></p>
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Data from: Feather corticosterone reveals effect of moulting conditions in the autumn on subsequent reproductive output and survival in an Arctic migratory bird
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Harms, N. Jane; Legagneux, Pierre; Gilchrist, H. Grant; Bêty, Joël; Love, Oliver P.; Forbes, Mark R.; Bortolotti, Gary R.; Soos, Catherine — 2014-12-04 For birds, unpredictable environments during the energetically stressful times of moulting and breeding are expected to have negative fitness effects. Detecting those effects however, might be difficult if individuals modulate their physiology and/or behaviours in ways to minimize short-term fitness costs. Corticosterone in feathers (CORTf) is thought to provide information on total baseline and stress-induced CORT levels at moulting and is an integrated measure of hypothalamic–pituitary–adrenal activity during the time feathers are grown. We predicted that CORTf levels in northern common eider females would relate to subsequent body condition, reproductive success and survival, in a population of eiders nesting in the eastern Canadian Arctic during a capricious period marked by annual avian cholera outbreaks. We collected CORTf data from feathers grown during previous moult in autumn and data on phenology of subsequent reproduction and survival for 242 eider females over 5 years. Using path analyses, we detected a direct relationship between CORTf and arrival date and body condition the following year. CORTf also had negative indirect relationships with both eider reproductive success and survival of eiders during an avian cholera outbreak. This indirect effect was dramatic with a reduction of approximately 30% in subsequent survival of eiders during an avian cholera outbreak when mean CORTf increased by 1 standard deviation. This study highlights the importance of events or processes occurring during moult on subsequent expression of life-history traits and relation to individual fitness, and shows that information from non-destructive sampling of individuals can track carry-over effects across seasons.
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Data from: No assortative mating based on size in black guillemots breeding in the Canadian Arctic
Berzins, Lisha L.; Gilchrist, H. Grant; Burness, Gary — 2015-05-27 The Black Guillemot (Cepphus grylle) is a monomorphic, socially monogamous member of the Alcidae. Although aspects of their breeding and foraging ecology have been extensively studied, less is known about possible sex-based differences in morphology, nor whether Black Guillemots mate assortatively based on body size. Using molecular techniques, we identified the sex of 26 male and 21 female Black Guillemots captured in the Canadian Arctic, and measured six external body measurements: outer tarsus length, wing length, culmen length, bill depth, head plus bill length and body mass to test for sexual size dimorphism (SSD) and assortative mating. Overall, males were 1.7% and 8% larger than females in outer tarsus length and bill depth, respectively. Within breeding pairs, bill depth was the most dimorphic trait. Despite these morphological differences no evidence of assortative mating based upon body size was found. Thus, mate choice for body size does not appear to be an underlying mechanism of SSD in bill depth in Black Guillemots.
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Data from: Higher rates of pre‐breeding condition gain positively impacts clutch size: a mechanistic test of the condition‐dependent individual optimization model
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Hennin, Holly L.; Dey, Cody J.; Bety, Joel; Gilchrist, H. Grant; Legagneux, Pierre; Williams, Tony D.; Love, Oliver P. — 2019-05-02 1. A combination of timing of and body condition (i.e., mass) at arrival on the breeding grounds interact to influence the optimal combination of the timing of reproduction and clutch size in migratory species. This relationship has been formalized by Rowe et al. in a condition-dependent individual optimization model (American Naturalist, 1994, 143, 689-722), which has been empirically tested and validated in avian species with a capital-based breeding strategy. 2. This model makes a key, but currently untested prediction; that variation in the rate of body condition gain will shift the optimal combination of laying date and clutch size. This prediction is essential because it implies that individuals can compensate for the challenges associated with late timing of arrival or poor body condition at arrival on the breeding grounds through adjustment of their life history investment decisions, in an attempt to maximize fitness. 3. Using an 11-year data set in arctic-nesting common eiders (Somateria mollissima), quantification of fattening rates using plasma triglycerides (an energetic metabolite), and a path analysis approach, we test this prediction of this optimization model; controlling for arrival date and body condition, females that fatten more quickly will adjust the optimal combination of lay date and clutch size, in favour of a larger clutch size. 4. As predicted, females fattening at higher rates initiated clutches earlier and produced larger clutch sizes, indicating that fattening rate is an important factor in addition to arrival date and body condition in predicting individual variation in reproductive investment. However, there was no direct effect of fattening rate on clutch size (i.e., birds laying on the same date had similar clutch sizes, independent of their fattening rate). Instead, fattening rate indirectly affected clutch size via earlier lay dates, thus not supporting the original predictions of the optimization model. 5. Our results demonstrate that variation in the rate of condition gain allows individuals to shift flexibly along the seasonal decline in clutch size to presumably optimize the combination of laying date and clutch size.
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Data from: Unpredictable perturbation reduces breeding propensity regardless of pre-laying reproductive readiness in a partial capital breeder
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Legagneux, Pierre; Hennin, Holly L.; Gilchrist, H. Grant; Williams, Tony D.; Love, Oliver P.; Bêty, Joël — 2016-06-06 Theoretically, individuals of migratory species should optimize reproductive investment based on a combination of timing of and body condition at arrival on the breeding grounds. A minimum threshold body mass is required to initiate reproduction, and the timing of reaching this threshold is critical because of the trade-off between delaying breeding to gain in condition against the declining value of offspring with later reproductive timing. Long-lived species have the flexibility within their life history to skip reproduction in a given year if they are unable to achieve this theoretical mass threshold. Although the decision to breed or not is an important parameter influencing population dynamics, the mechanisms underlying this decision are poorly understood. Here, we mimicked an unpredictable environmental perturbation that induced a reduction in body mass of Arctic pre-breeding (before the laying period) female common eiders (Somateria mollissima; a long-lived migratory seaduck) while controlling for individual variation in the pre-laying physiological reproductive readiness via vitellogenin (VTG) - a yolk-targeted lipoprotein. Our aim was to causally determine the interaction between body condition and pre-laying reproductive readiness (VTG) on breeding propensity by experimentally reducing body mass in treatment females. We first demonstrated that arrival body condition was a key driver of breeding propensity. Secondly, we found treatment and VTG levels interacted to influence breeding propensity, indicating that our experimental manipulation, mimicking an unpredictable food shortage, reduced breeding propensity, regardless of the degree of pre-laying physiological reproductive readiness (i.e., timing of ovarian follicles recruitment). Our experiment demonstrates that momentary environmental perturbations during the pre-breeding period can strongly affect the decision to breed, a key parameter driving population dynamics.

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(Author: Gilchrist, H. Grant)

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