Limited heat tolerance in a cold-adapted seabird: implications of a warming Arctic.

The Arctic is warming at approximately twice the global rate, with well-documented indirect effects on wildlife. However, few studies have examined the direct effects of warming temperatures on Arctic wildlife, leaving the importance of heat stress unclear. Here, we assessed the direct effects of increasing air temperatures on the physiology of thick-billed murres (Uria lomvia), an Arctic seabird with reported mortalities due to heat stress while nesting on sun-exposed cliffs. We used flow-through respirometry to measure the response of body temperature, resting metabolic rate, evaporative water loss and evaporative cooling efficiency (the ratio of evaporative heat loss to metabolic heat production) in murres while experimentally increasing air temperature. Murres had limited heat tolerance, exhibiting: (1) a low maximum body temperature (43.3°C); (2) a moderate increase in resting metabolic rate relative that within their thermoneutral zone (1.57 times); (3) a small increase in evaporative water loss rate relative that within their thermoneutral zone (1.26 times); and (4) a low maximum evaporative cooling efficiency (0.33). Moreover, evaporative cooling efficiency decreased with increasing air temperature, suggesting murres were producing heat at a faster rate than they were dissipating it. Larger murres also had a higher rate of increase in resting metabolic rate and a lower rate of increase in evaporative water loss than smaller murres; therefore, evaporative cooling efficiency declined with increasing body mass. As a cold-adapted bird, murres' limited heat tolerance likely explains their mortality on warm days. Direct effects of overheating on Arctic wildlife may be an important but under-reported impact of climate change.

Earlier colony arrival but no trend in hatching timing in two congeneric seabirds (Uria spp.) across the North Atlantic.

A global analysis recently showed that seabird breeding phenology (as the timing of egg-laying and hatching) does not, on average, respond to temperature changes or advance with time (Keogan et al. 2018 Nat. Clim. Change8, 313-318). This group, the most threatened of all birds, is therefore prone to spatio-temporal mismatches with their food resources. Yet, other aspects of the breeding phenology may also have a marked influence on breeding success, such as the arrival date of adults at the breeding site following winter migration. Here, we used a large tracking dataset of two congeneric seabirds breeding in 14 colonies across 18° latitudes, to show that arrival date at the colony was highly variable between colonies and species (ranging 80 days) and advanced 1.4 days/year while timing of egg-laying remained unchanged, resulting in an increasing pre-laying duration between 2009 and 2018. Thus, we demonstrate that potentially not all components of seabird breeding phenology are insensitive to changing environmental conditions.

Balancing personal maintenance with parental investment in a chick-rearing seabird: physiological indicators change with foraging conditions.

Seabird parents use a conservative breeding strategy that favours long-term survival over intensive parental investment, particularly under harsh conditions. Here, we examine whether variation in several physiological indicators reflects the balance between parental investment and survival in common murres (Uria aalge) under a wide range of foraging conditions. Blood samples were taken from adults during mid-chick rearing from 2007 to 2014 and analysed for corticosterone (CORT, stress hormone), beta-hydroxybutyrate (BUTY, lipid metabolism reflecting ongoing mass loss), and haematocrit (reflecting blood oxygen capacity). These measures, plus body mass, were related to three levels of food availability (good, intermediate, and poor years) for capelin, the main forage fish for murres in this colony. Adult body mass and chick-feeding rates were higher in good years than in poor years and heavier murres were more likely to fledge a chick than lighter birds. Contrary to prediction, BUTY levels were higher in good years than in intermediate and poor years. Murres lose body mass just after their chicks hatch and these results for BUTY suggest that mass loss may be delayed in good years. CORT levels were higher in intermediate years than in good or poor years. Higher CORT levels in intermediate years may reflect the necessity of increasing foraging effort, whereas extra effort is not needed in good years and it is unlikely to increase foraging success in poor years. Haematocrit levels were higher in poor years than in good years, a difference that may reflect either their poorer condition or increased diving requirements when food is less available. Our long-term data set provided insight into how decisions about resource allocation under different foraging conditions are relating to physiological indicators, a relationship that is relevant to understanding how seabirds may respond to changes in marine ecosystems as ocean temperatures continue to rise.

Effects of Added Lipids on Digestibility and Nitrogen Balance in Oiled Common Murres ( Uria aalge ) and Western Grebes ( Aechmophorus occidentalis ) Fed Four Formulations of a Critical Care Diet.

Nutritional support is a primary therapy administered to oiled animals during responses to oil spills, but data informing nutritional decision-making during events are limited. In this study, 44 common murres ( Uria aalge ) and 6 Western grebes ( Aechmophorus occidentalis ), naturally oiled by oceanic seeps off the coast of Ventura and Santa Barbara Counties, CA, USA, were assigned to 1 of 4 groups fed diets with varying levels (6.8% [no added oil], 11%, and 20%) and types (salmon, corn) of oil added to a partially purified basal diet. Birds used in the study ranged from extremely emaciated to thin body condition (62%-80% wild bird mean body mass). Acid-insoluble ash was used as an indigestible dietary marker to quantify nitrogen retention, apparent nitrogen digestibility, nitrogen-corrected apparent metabolizable energy, energy digestibility, fat retention, fat digestibility, and estimated fat excretion. Fat excretion is important in these species because once birds have been cleaned they are at risk of plumage recontamination from excreted fat during care. Lower fat diets resulted in lower fat excretion but higher nitrogen retention, higher apparent nitrogen digestibility, and higher apparent metabolizable energy. Decreases in nitrogen retention were significantly related to increases in fat excretion. Regardless of diet, energy digestibility significantly declined with declines in body mass, suggesting severity of emaciation reduced a birds' ability to extract energy from food. Energy digestibility was highest in the 11% (low) salmon oil diet; hence, this diet had the highest effective energy content despite a lower gross kcal/kg diet. Diets fed during oil spills historically have had high fat concentrations to provide maximum caloric support. Results of this study suggest that lower fat diets may be more efficacious for nutritionally depleted seabirds. This study provides valuable data to guide clinical decision making regarding nutritional support during oil spills and other mass stranding events.