• Energy Research

Energy management models provide theories and predictions for how animals manage their energy budgets within their energetic constraints, in terms of their resting metabolic rate (RMR) and daily energy expenditure (DEE). Thus, uncovering what associations exist between DEE and RMR is key to testing these models. Accordingly, there is considerable interest in the relationship between DEE and RMR at both inter- and intraspecific levels. Interpretation of the evidence for particular energy management models is enhanced by also considering the energy spent specifically on costly activities (activity energy expenditure [AEE] = DEE - RMR). However, to date there have been few intraspecific studies investigating such patterns. Our aim was to determine whether there is a generality of intraspecific relationships among RMR, DEE, and AEE using long-term data sets for bird and mammal species. For mammals, we use minimum heart rate (fH), mean fH, and activity fH as qualitative proxies for RMR, DEE, and AEE, respectively. For the birds, we take advantage of calibration equations to convert fH into rate of oxygen consumption in order to provide quantitative proxies for RMR, DEE, and AEE. For all 11 species, the DEE proxy was significantly positively correlated with the RMR proxy. There was also evidence of a significant positive correlation between AEE and RMR in all four mammal species but only in some of the bird species. Our results indicate there is no universal rule for birds and mammals governing the relationships among RMR, AEE, and DEE. Furthermore, they suggest that birds tend to have a different strategy for managing their energy budgets from those of mammals and that there are also differences in strategy between bird species. Future work in laboratory settings or highly controlled field settings can tease out the environmental and physiological processes contributing to variation in energy management strategies exhibited by different species.

Parasites have profound fitness effects on their hosts, yet these are often sub-lethal, making them difficult to understand and quantify. A principal sub-lethal mechanism that reduces fitness is parasite-induced increase in energetic costs of specific behaviours, potentially resulting in changes to time and energy budgets. However, quantifying the influence of parasites on these costs has not been undertaken in free-living animals. We used accelerometers to estimate energy expenditure on flying, diving and resting, in relation to a natural gradient of endo-parasite loads in a wild population of European shagsPhalacrocorax aristotelis. We found that flight costs were 10% higher in adult females with higher parasite loads and these individuals spent 44% less time flying than females with lower parasite loads. There was no evidence for an effect of parasite load on daily energy expenditure, suggesting the existence of an energy ceiling, with the increase in cost of flight compensated for by a reduction in flight duration. These behaviour specific costs of parasitism will have knock-on effects on reproductive success, if constraints on foraging behaviour detrimentally affect provisioning of young. The findings emphasize the importance of natural parasite loads in shaping the ecology and life-history of their hosts, which can have significant population level consequences.

Abstract Animals are expected to be judicious in the use of the energy they gain due to the costs and limits associated with its intake. The management of energy expenditure (EE) exhibited by animals has previously been considered in terms of three patterns: the constrained, independent and performance patterns of energy management. These patterns can be interpreted by regressing daily EE against maintenance EE measured over extended periods. From the multiple studies on this topic, there is equivocal evidence about the existence of universal patterns in certain aspects of energy management. The implicit assumption that animals exhibit specifically one of three discrete energy management patterns, and without variation, seems simplistic. We suggest that animals can exhibit gradations of different energy management patterns and that the exact pattern will fluctuate as their environmental context changes. To investigate these ideas, and for possible large‐scale patterns in energy management, we analysed long‐term heart rate data—a strong proxy for EE—across and within individuals in 16 species of birds, mammals and fish. Our analyses of 292 individuals representing 46,539 observation‐days suggest that vertebrates typically exhibit predominantly the independent or performance energy patterns at the across‐individual level, and that the pattern does not associate with taxonomic group. Within individuals, however, animals generally exhibit some degree of energy constraint. Together, these findings indicate that across diverse species, some individuals supply more energy to all aspects of their life than do others, however all individuals must trade‐off deployment of their available energy between competing functions. This demonstrates that within‐individual analyses are essential for the interpretation of energy management patterns. We also found that species do not necessarily exhibit a fixed energy management pattern but rather temporal variation in their energy management over the year. Animals’ energy management exhibited stronger energy constraint during periods of higher EE, which typically coincided with clear and key life cycle events such as reproduction, suggesting an adaptive plasticity to respond to fluctuating energy demands. A plain language summary is available for this article.

The archetypal foraging behaviour of tropical seabirds is generally accepted to differ from that of their temperate and polar breeding counterparts, with the former exhibiting less predictable foraging behaviour associated with the less predictable prey of the tropical marine environment. Similarly, temperate and polar species have predictable, annual breeding seasons, enabling them to profit during periods of the year when prey availability is highest, while tropical seabird species exhibit considerable variability in their breeding strategies. Until now, the reasons for such variation in breeding strategies between tropical seabirds are yet to be investigated. We hypothesise that while some tropical species breed asynchronously in response to unpredictable fluctuations in prey availability, others adopt a seasonal breeding strategy for the same reasons that temperate and polar species do. Consequently, the predictability of seabird foraging behaviour in the tropics may be related to breeding strategy, with populations that breed seasonally exhibiting more predictable foraging behaviour than those that breed aseasonally. To test these predictions, we used GPS tracking to examine the foraging behaviour of two closely related tropical seabird species that colonise the same island yet exhibit markedly different breeding strategies: the asynchronously breeding brown booby Sula leucogaster and the seasonal breeding masked booby Sula dactylatra. We obtained tracks for 251 birds over five years. We found that brown boobies forage less predictably than masked boobies, indicated by larger core foraging areas, lower levels of foraging area overlap between individuals and exhibit more variability between breeding periods. Our results challenge the view that the foraging behaviour of tropical seabirds is always less predictable than that of seabirds breeding in temperate and polar regions and highlight the considerable variability in the breeding and foraging strategies adopted by tropical seabirds which demand further exploration.

Arctic seas have warmed and sea ice has retreated. This has resulted in range contraction and population declines in some species, but it could potentially be a boon for others. Great Cormorants Phalacrocorax carbo have a partially wettable plumage and seem poorly suited to foraging in Arctic waters. We show that rates of population change of Cormorant colonies around Disko Bay, Greenland, are positively correlated with sea surface temperature, suggesting that they may benefit from a warming Arctic. However, although Cormorant populations may increase in response to Arctic warming, the extent of expansion of their winter range may ultimately be limited by other factors, such as sensory constraints on foraging behaviour during long Arctic nights.

Seabirds are facing a growing number of threats in both terrestrial and marine habitats, and many populations have experienced dramatic changes over past decades. Years of seabird research have improved our understanding of seabird populations and provided a broader understanding of marine ecological processes. In an effort to encourage future research and guide seabird conservation science, seabird researchers from 9 nations identified the 20 highest priority research questions and organized these into 6 general categories: (1) population dynamics, (2) spatial ecology, (3) tropho-dynamics, (4) fisheries interactions, (5) response to global change, and (6) management of anthropogenic impacts (focusing on invasive species, contaminants and protected areas). For each category, we provide an assessment of the current approaches, challenges and future directions. While this is not an exhaustive list of all research needed to address the myriad conservation challenges seabirds face, the results of this effort represent an important synthesis of current expert opinion across sub-disciplines within seabird ecology. As this synthesis highlights, research, in conjunction with direct management, education, and community engagement, can play an important role in facilitating the conservation and management of seabird populations and of the ocean ecosystems on which they and we depend.