Daily energy expenditure in precocial shorebird chicks: smaller species perform at higher levels

Abstract

We measured daily energy expenditure (DEE) during the development periods of precocial chicks of five species of Arctic shorebirds spanning a broad range in size, in order to investigate the relationships between DEE, body size, and growth rate. We also quantified the effect of weather conditions on the energy expenditure of chicks to establish the impact of cold arctic weather on their time and energy budgets. We used the doubly labeled water method to measure DEE at ambient temperatures in an outside enclosure on the subarctic tundra at Churchill, Manitoba, Canada. Growth rate was highest in the smallest species, and in general decreased with adult size, as shown by the decrease in growth rate constant and later inflection point with increasing adult body mass. DEE ranged from 14 kJ day -1 in young chicks of the smaller species to 365 kJ day -1 in older chicks of the larger species. From hatching onward, DEE of shorebirds was high compared to DEE of chicks of altricial species, reflecting the high costs of locomotion and thermoregulation, and mass-specific DEE increased rapidly to adult levels. Chicks of smaller species metabolized more energy per unit mass and functioned at higher multiples of resting metabolic rate than chicks of larger species. As chicks of smaller species also had higher growth rates, and thus simultaneously invested in growth and mature function, it seems that shorebird chicks can adjust total metabolizable energy as well as its relative allocation between investment in growth and mature function. DEE was similar to cold-induced peak metabolic rates achieved by shivering thermogenesis. Because chicks were motionless during laboratory metabolism measurements, the relatively high level of DEE compared to these metabolic rates suggests that locomotion produces similar amounts of heat as shivering. Ambient temperature did not affect DEE in outdoor pens, although higher wind speed resulted in slightly increased energy expenditure. Heat produced by locomotion is possibly sufficient to sustain thermoregulation under local environments. Furthermore, when ambient temperatures are low, chicks spend more time brooding and less time foraging, which presumably counters the tendency to increase thermogenesis in response to cold.

Arctic-nesting birds find physiological relief in the face of trophic constraints

“…Of course, a comprehensive understanding of these bioenergetics trade-offs will require more detailed knowledge of metabolic energy expenditure and how this expenditure changes with the environment26. Though data exist on energy expenditure of arctic-nesting shorebirds and their chicks, effects of ambient temperature on energetics of free living chicks have not been well studied to date2728. Given the suite of other potential climate related pressures on arctic-nesting shorebirds (habitat loss due to increased shrub cover and decreases in permafrost, increased predation risk etc 24…”

Physiological, Morphological and Behavioural Responses of Self-Feeding Precocial Chicks Copying with Contrasting Levels of Water Salinity during Development

“…We performed RMR measurements during the nocturnal period (resting period of the fledglings’ circadian cycle) and in post-absortive state (fledglings were placed in outdoor cages without food for about 3 h but with water ad libitum − salinity according to treatment). Fledglings were individually placed in metabolic chambers (15 L) in darkness and housed in a temperature-controlled cabinet at a constant temperature (27°C; within the thermoneutral zone of precocial shorebird chicks [27]). The metabolic chambers received atmospheric air at a rate of 1,000 ml·min –1 from calibrated mass flow controllers (MFS-5; Sable Systems, Las Vegas, NV, USA).…”

Foraging ecology and time budgets of non-breeding shorebirds in coastal Cuba

“…plovers, yellowlegs, Calidris sandpipers) would exhibit similar foraging techniques and time budgets (Barbosa & Moreno 1999). As larger species generally have lower mass-specific metabolic rates (Krijgsveld et al 2012) and may forage more efficiently on a wider range of prey sizes (Radloff & Du Toit 2004), we also predicted that both the proportion of time spent foraging and foraging rates would be negatively related to body mass (Fasola & Biddau 1997). We predicted that foraging birds of all species would have larger intraspecific and interspecific distances than non-foraging birds, as a tactic to reduce competition for food resources.…”