Abstract
BackgroundBirds may allocate a significant part of time to comfort behavior (e.g., preening, stretching, shaking, etc.) in order to eliminate parasites, maintain plumage integrity, and possibly reduce muscular ankylosis. Understanding the adaptive value of comfort behavior would benefit from knowledge on the energy costs animals are willing to pay to maintain it, particularly under situations of energy constraints, e.g., during fasting. We determined time and energy devoted to comfort activities in freely breeding king penguins (Aptenodytes patagonicus), seabirds known to fast for up to one month during incubation shifts ashore.Methodology/Principal FindingsA time budget was estimated from focal and scan sampling field observations and the energy cost of comfort activities was calculated from the associated increase in heart rate (HR) during comfort episodes, using previously determined equations relating HR to energy expenditure. We show that incubating birds spent 22% of their daily time budget in comfort behavior (with no differences between day and night) mainly devoted to preening (73%) and head/body shaking (16%). During comfort behavior, energy expenditure averaged 1.24 times resting metabolic rate (RMR) and the corresponding energy cost (i.e., energy expended in excess to RMR) was 58 kJ/hr. Energy expenditure varied greatly among various types of comfort behavior, ranging from 1.03 (yawning) to 1.78 (stretching) times RMR. Comfort behavior contributed 8.8–9.3% to total daily energy expenditure and 69.4–73.5% to energy expended daily for activity. About half of this energy was expended caring for plumage.Conclusion/SignificanceThis study is the first to estimate the contribution of comfort behavior to overall energy budget in a free-living animal. It shows that although breeding on a tight energy budget, king penguins devote a substantial amount of time and energy to comfort behavior. Such findings underline the importance of comfort behavior for the fitness of colonial seabirds.
Highlights
Maintenance behaviors serve a variety of purposes and are widespread throughout the animal kingdom
When considering data obtained from the five videoed birds of which comfort behavior was examined during consecutive periods of 15 min spread over 24 hrs, we found no apparent day/night pattern regarding the proportion of time spent in global comfort behavior (GEE; Wald = 0.07, P = 0.80, n = 480 focal observations)
From the slope of this equation (0.28) and from equation 1a relating EE to heart rate (HR), we calculated that for a 1% increase in the time spent into comfort behavior (i.e. a 0.6 sec per min increase) the associated HR increase was equivalent to a 10.2 J increase in EE (36.4 * 0.28)
Summary
Maintenance behaviors (i.e. allo- and autogrooming, allo- and autopreening, bathing, scratching, stretching, etc.) serve a variety of purposes and are widespread throughout the animal kingdom (e.g. in mammals [1,2,3], in birds [4,5,6], in fish [7], in crustaceans [8], and in insects [9,10]). Comfort behavior is usually referred to as a set of activities concerned with the care of the integument and the maintenance of a functional body structure, i.e. by increasing proprioceptive sensitivity and circulation in the muscles for instance [4,5,11]. Several studies have previously shown that birds spend a substantial amount of time in comfort behavior. Captive birds may devote a greater amount of time to comfort behavior, as food is usually provided ad libitum in a safe environment, and the amount of time spent foraging or in vigilance may be decreased. Birds may allocate a significant part of time to comfort behavior (e.g., preening, stretching, shaking, etc.) in order to eliminate parasites, maintain plumage integrity, and possibly reduce muscular ankylosis. We determined time and energy devoted to comfort activities in freely breeding king penguins (Aptenodytes patagonicus), seabirds known to fast for up to one month during incubation shifts ashore
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