Last update: : Wednesday 15 February 2017, by
Par : Manfred Enstipp, IPHC-DEPE
Date : jeudi 2 mars 2017 de 16h à 17h30
Lieu : IPHC, Amphithéâtre Grünewald, bâtiment 25
Little is known about the early life at sea of marine top predators, like king penguins (Aptenodytes patagonicus). Their juveniles leave the colony for the first time when 1 year old and disperse at sea for an extended period (1-3 years), interrupted only by annual moult shifts, after which they recruit into the breeding population. This initial dispersal phase at sea is likely the most critical phase in their life. Apart from finding favourable foraging sites, birds have to develop effective prey search patterns as well as physiological capacities (breath-holding, thermoregulation) that enable them to capture sufficient prey, often at great depth, to meet their energetic needs. We implanted a small datalogger, recording pressure and temperature, into the subcutaneous flank tissue of 30 juvenile birds before their first departure to sea, to study the development of their foraging behaviour and thermoregulatory control over a period of 2.5 years. We found that dive capacity was sufficiently developed at first departure to enable birds to conduct dives deeper than 50 m within 2 days of leaving the colony, while within 4 days, dives exceeded 100 m. Clearly, after fasting during moult, birds have to capture food rapidly (typically at a depth exceeding 50 m) to restore their subcutaneous fat. Dive capacity increased over time, so that max dive depth and max dive duration was greater during the second year at sea, exceeding 300 m and 9 min, respectively. During a foraging bout, peripheral temperature declined rapidly and was only fully restored after diving activity ceased and birds rested for extended periods at the surface. During the first 6 months at sea, this drop in peripheral temperature during diving increased in amplitude, so that during the first month, peripheral temperature declined on average from 39.1°C to 28.7°C, while after 6 months it decreased to 18.7°C (lowest: 9.6°C). Thereafter, the peripheral temperature drop stabilized. These changes in peripheral temperature were unrelated to changes in the birds’ dive effort and reoccurred the following year after their moult fast. We suggest that rather than indicating a physiological maturation process, these seasonal temperature changes mainly reflect changes in thermal insulation. As birds forage successfully, they increase their amount of subcutaneous fat. During diving, this enables birds to build a strong thermal gradient between the core and periphery that preserves core heat and reduces thermoregulatory costs. Based on our recordings of behaviour and temperature, we constructed a heat loss model, which showed that heat loss of birds was high at the beginning of their trip and declined to half, after 6 months. This suggests that juvenile king penguins face a strong energetic challenge during their first months at sea.