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Whelan, Shannon; Hatch, Scott A.; Benowitz-Fredericks, Z. Morgan; Parenteau, Charline; Chastel, Olivier; Elliott, Kyle — 2020-11-13 <p class="CxSpFirst">Current food supply is a major driver of timing of breeding in income-breeding animals, likely because increased net energy balance directly increases reproductive hormones and advances breeding. In capital breeders, increased net energy balance increases energy reserves, which eventually leads to improved reproductive readiness and earlier breeding. To test the hypothesis that phenology of income-breeding birds is independent of energy reserves, we conducted an experiment on food-supplemented (“fed”) and control female black-legged kittiwakes (<em>Rissa tridactyla</em>). We temporarily increased energy costs (via weight handicap) in a 2 × 2 design (fed/unfed; handicapped/unhandicapped) during the pre-laying period and observed movement via GPS-accelerometry. We measured body mass, baseline hormones (corticosterone; luteinising hormone) before and after handicap manipulation, and conducted a gonadotropin-releasing hormone challenge. Females from all treatment groups foraged in similar areas, implying that individuals could adjust time spent foraging, but had low flexibility to adjust foraging distance. Consistent with the idea that income breeders do not accumulate reserves in response to increased food supply, fed birds remained within an energy ceiling by reducing time foraging instead of increasing energy reserves. Moreover, body mass remained constant until the onset of follicle development 20 days prior to laying regardless of feeding or handicap, implying that females were using a ‘lean and fit’ approach to body mass rather than accumulating lipid reserves for breeding. Increased food supply advanced endocrine and laying phenology and altered interactions between the hypothalamic-pituitary-adrenal axis and the hypothalamic-pituitary-gonadal axis, but higher energy costs (handicap) had little effect. Consistent with our hypothesis, increased food supply (but not net energy balance) advanced endocrine and laying phenology in income-breeding birds without any impact on energy reserves.</p>

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>

Elliott, Kyle H.; Ricklefs, Robert E.; Gaston, Anthony J.; Hatch, Scott A.; Speakman, John R.; Davoren, Gail K. — 2013-05-22 Flight is a key adaptive trait. Despite its advantages, flight has been lost in several groups of birds, notably among seabirds, where flightlessness has evolved independently in at least five lineages. One hypothesis for the loss of flight among seabirds is that animals moving between different media face tradeoffs between maximizing function in one medium relative to the other. In particular, biomechanical models of energy costs during flying and diving suggest that a wing designed for optimal diving performance should lead to enormous energy costs when flying in air. Costs of flying and diving have been measured in free-living animals that use their wings to fly or to propel their dives, but not both. Animals that both fly and dive might approach the functional boundary between flight and nonflight. We show that flight costs for thick-billed murres (Uria lomvia), which are wing-propelled divers, and pelagic cormorants (Phalacrocorax pelagicus) (foot-propelled divers), are the highest recorded for vertebrates. Dive costs are high for cormorants and low for murres, but the latter are still higher than for flightless wing-propelled diving birds (penguins). For murres, flight costs were higher than predicted from biomechanical modeling, and the oxygen consumption rate during dives decreased with depth at a faster rate than estimated biomechanical costs. These results strongly support the hypothesis that function constrains form in diving birds, and that optimizing wing shape and form for wing-propelled diving leads to such high flight costs that flying ceases to be an option in larger wing-propelled diving seabirds, including penguins.