Cold birds under pressure; can thermal substitution ease heat loss in diving penguins?

FLAVIO QUINTANA; JAVIER CIANCIO; RORY P. WILSON; JUAN EMILIO SALA

MARINE BIOLOGY

SPRINGER

Lugar: Berlin; Año: 2016 vol. 163 p. 1 - 15

0025-3162

Thermoregulation could represent a significant fraction of the total energy budget ofendotherms under unfavorable environmental conditions. This cost affects severaltraits of the ecology of an organism such as its behaviour, distribution, or life history.Heat produced by muscle contraction during activity can be used to pay for heat loss orthermoregulation in many species (known as "thermal substitution"). This study seeksto unite the effects of temperature, depth, and activity on the energetic costs ofendotherm divers using the Magellanic Penguin as model species and to evaluate ifpenguins may benefit from thermal substitution. This species operates under highlyvariable temperature and depth conditions along its breeding range and provides anideal natural experiment. A developed thermodynamic model describing foragingactivity predicted that the major element affecting heat loss was depth, exacerbated bytemperature. Birds living in colder waters are predicted to be able to minimize costs byexecuting shallower dives and benefit from thermal substitution by swimming faster,particularly during deeper dives. The model was evaluated in two contrastingscenarios: (i) when birds swim near the surface commuting to the foraging areas and(ii) when birds dive to depth to forage. Activity data from tags on free-living penguinsindicated two of these predictions were apparent; penguins generally travelled fasterwhile commuting at the surface in colder waters while birds from warmer watercolonies dived deeper while foraging. Contrary to predictions, however, penguinsswam slower at deeper depths during both descent and ascent phases of foragingdives. These results suggest that penguins may benefit from thermal substitution byswimming faster when birds perform shallow dives commuting to and back fromforaging areas but they provide no evidence of behavioral response (via swimmingfaster) for thermoregulation when diving to depth to forage. Reasons for this arediscussed and include the relevance of prey abundance in 3-d space and maximizing dive duration by conserving oxygen reserves. The way the bird operates will haveprofound consequences for the energy needed and therefore necessary energyacquisition rates. Expansion of our findings to other diving endotherms might helpexplain both global activity patterns and energy flow in ecosystems