The dive performance of immature king penguins following their annual molt suggests physiological constraints

Abstract

Like all birds, penguins undergo periodic molt, during which they replace old feathers. However, unlike other birds, penguins replace their entire plumage within a short period while fasting ashore. During molt, king penguins (Aptenodytes patagonicus) lose half of their initial body mass, most importantly their insulating subcutaneous fat and half of their pectoral muscle mass. The latter might challenge their capacity to generate and sustain a sufficient mechanical power output to swim to distant food sources and propel themselves to great depth for successful prey capture. To investigate the effects of the annual molt fast on their dive/foraging performance, we studied various dive/ foraging parameters and peripheral temperature patterns in immature king penguins across two molt cycles, after birds had spent their first and second year at sea, using implanted data-loggers. We found that the dive/foraging performance of immature king penguins was significantly reduced during post-molt foraging trips. Dive and bottom duration for a given depth were shorter during post-molt and post-dive surface interval duration was longer, reducing overall dive efficiency and underwater foraging time. We attribute this decline to the severe physiological changes that birds undergo during their annual molt. Peripheral temperature patterns differed greatly between pre-and post-molt trips, indicating the loss of the insulating subcutaneous fat layer during molt. Peripheral perfusion, as inferred from peripheral temperature, was restricted to short periods at night during pre-molt but occurred throughout extended periods during post-molt, reflecting the need to rapidly deposit an insulating fat layer during the latter period.

Biologging of emperor penguins – attachment techniques and associated deployment performance

“…g . hydrostatic pressure, water conductivity and temperature, environmental luminosity) on a multi-year scale 102,116 , the leg-band technique appears as a high potential alternative.…”

Thermoregulatory Strategies of Diving Air-Breathing Marine Vertebrates: A Review

“…They attributed a decline in the weekly average subcutaneous temperatures to increased insulation associated with a thicker fat layer accumulated over their year-long foraging trip during their dispersal phase. In contrast to pre-molt trips, periods of normothermic temperatures were longer and even occurred during some shallow dives during post-molt trips, underscoring the physiological need to restore their insulation layer after fasting for the duration of the molt on land (Enstipp et al, 2019). This example highlights the importance of considering how seasonal changes and varying energetic challenges across different life stages might influence thermoregulatory strategies.…”

“…As molting reduces the animal's insulation and requires perfusion of the skin that also increases heat loss, several species have found ways to reduce the physiological burden of molting. Many amphibious species return to land to molt (Worthy et al, 1992;Boily, 1995;Enstipp et al, 2019;Walcott et al, 2020), while others molt gradually and sometimes migrate to warmer waters (Boily, 1995;Pitman et al, 2019). FIGURE 6 | Ex vivo blubber conductivity vs. mass-specific blubber thickness demonstrates the variability between species occupying different thermal habitat ranges in balancing the trade-offs between quality and quantity of blubber.…”

The early life of king penguins: ontogeny of dive capacity and foraging behaviour in an expert diver

“…King penguins (Aptenodytes patagonicus Miller) are the second largest penguin species and, in the avian world, their dive performance is surpassed only by the larger emperor penguins (Pütz et al, 1998;Pütz and Cherel, 2005;Wienecke et al, 2007). Recently, studies have investigated behavioural and physiological aspects of king penguins during their early life at sea (Orgeret et al, 2016(Orgeret et al, , 2019Enstipp et al, 2017Enstipp et al, , 2019. These birds spend the first year of their life at their natal colony and, upon completion of their first moult into waterproof plumage, enter the sea during the austral spring.…”

“…These birds spend the first year of their life at their natal colony and, upon completion of their first moult into waterproof plumage, enter the sea during the austral spring. During the following 1-3 years, they roam over a large oceanic area (Orgeret et al, 2016(Orgeret et al, , 2019, only returning to land for their annual moult (Enstipp et al, 2019). Unfortunately, no information concerning their physiological status at the time of fledging is available (e.g.…”