Sex-specific responses to GnRH challenge, but not food supply, in kittiwakes: Evidence for the "sensitivity to information" hypothesis.

Seasonal timing of breeding is usually considered to be triggered by endogenous responses linked to predictive cues (e.g., photoperiod) and supplementary cues that vary annually (e.g., food supply), but social cues are also important. Females may be more sensitive to supplementary cues because of their greater role in reproductive timing decisions, while males may only require predictive cues. We tested this hypothesis by food-supplementing female and male colonial seabirds (black-legged kittiwakes, Rissa tridactyla) during the pre-breeding season. We measured colony attendance via GPS devices, quantified pituitary and gonadal responses to gonadotropin releasing hormone (GnRH) challenge, and observed subsequent laying phenology. Food supplementation advanced laying phenology and increased colony attendance. While female pituitary responses to GnRH were consistent across the pre-breeding season, males showed a peak in pituitary sensitivity at approximately the same time that most females were initiating follicle development. The late peak in male pituitary response to GnRH questions a common assumption that males primarily rely on predictive cues (e.g., photoperiod) while females also rely on supplementary cues (e.g., food availability). Instead, male kittiwakes may integrate synchronising cues from their social environment to adjust their reproductive timing to coincide with female timing.

The effects of food supply on reproductive hormones and timing of reproduction in an income-breeding seabird.

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 (Rissa tridactyla). 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.

Foot web pentosidine does not covary strongly with age in four species of wild seabirds.

Age is an important parameter for a variety of ecological applications, including population viability analyses, contaminants monitoring and targeting of individuals for conservation. While many organisms can be aged by annual rings, dentition and other techniques (i.e., fish otoliths, clam growth rings, mammal tooth wear), there are no minimally invasive biomarkers for accurately aging birds in the wild. For the past century, banding has been the only way to identify a bird of known age, which requires continuous effort on a large scale with possibly low return rates. Recent studies have identified pentosidine as a potential biomarker of chronological aging in several bird species. To test this idea in four species of long-lived seabirds, we collected skin biopsies from the foot webs of previously banded, known-age seabirds: black-legged kittiwakes (Rissa tridactyla; 0-19 y old), Atlantic puffins (Fratercula arctica; 5-26 y old), razorbills (Alca torda; 0-15 d old) and thick-billed murres (Uria lomvia; 0-35 y old). Foot web samples were specifically chosen because this was the least invasive site for substantial skin biopsy. Samples were analysed with high performance liquid chromatography to quantify pentosidine levels. Collagen levels were estimated through hydroxyproline assays to normalize pentosidine content across individuals. Kittiwakes displayed a weak correlation (r2 = 0.20) between age and pentosidine/collagen. Puffins (adults only, r2 = 0.02), razorbills (chicks only, r2 = 0.08), and murres (adults, r2 = 0.04) did not show any associations with age. We concluded that pentosidine content in the foot web does not appear to be a reliable method for aging seabirds in the wild. An absence of change in pentosidine in the foot web with age is further evidence that long-lived seabirds may maintain physiological performance into old age.

Reprint of: Trouble on takeoff: Crude oil on feathers reduces escape performance of shorebirds.

The ability to takeoff quickly and accelerate away from predators is crucial to bird survival. Crude oil can disrupt the fine structure and function of feathers, and here we tested for the first time how small amounts of oil on the trailing edges of the wings and tail of Western sandpipers (Calidris mauri) affected takeoff flight performance. In oiled birds, the distance travelled during the first 0.4s after takeoff was reduced by 29%, and takeoff angle was decreased by 10° compared to unoiled birds. Three-axis accelerometry indicated that oiled sandpipers produced less mechanical power output per wingbeat during the initial phase of flight. Slower and lower takeoff would make oiled birds more likely to be targeted and captured by predators, reducing survival and facilitating the exposure of predators to oil. Whereas the direct mortality of heavily-oiled birds is often obvious and can be quantified, our results show that there are significant sub-lethal effects of small amounts crude oil on feathers, which must be considered in natural resource injury assessments for birds.

Trouble on takeoff: Crude oil on feathers reduces escape performance of shorebirds.

The ability to takeoff quickly and accelerate away from predators is crucial to bird survival. Crude oil can disrupt the fine structure and function of feathers, and here we tested for the first time how small amounts of oil on the trailing edges of the wings and tail of Western sandpipers (Calidris mauri) affected takeoff flight performance. In oiled birds, the distance travelled during the first 0.4s after takeoff was reduced by 29%, and takeoff angle was decreased by 10° compared to unoiled birds. Three-axis accelerometry indicated that oiled sandpipers produced less mechanical power output per wingbeat during the initial phase of flight. Slower and lower takeoff would make oiled birds more likely to be targeted and captured by predators, reducing survival and facilitating the exposure of predators to oil. Whereas the direct mortality of heavily-oiled birds is often obvious and can be quantified, our results show that there are significant sub-lethal effects of small amounts crude oil on feathers, which must be considered in natural resource injury assessments for birds.