Contrasting offspring dependence periods and diving development rates in two closely related marine mammal species

An annual cycle perspective on energetics and locomotion of migratory animals

Animal migrations, or long-distance movements, on land, through water or in the air, are considered energetically costly because of the investment in persistent locomotion typical for migration. Diverse strategies exist to manage these energetic costs. Yet migration is only one stage in an annual cycle and may not be the most energetically costly. To better understand how free-ranging animals adaptively organize energy expenditure and locomotion, an annual cycle perspective is needed. Bio-logging data are collected for a range of animal species and could facilitate a life cycle approach to study energy expenditure. We provide examples from several studies across different taxa, as well as a more in-depth exploration from our own recent research on time activity budgets based on field observations and bio-logging data to estimate daily energy expenditure in a migratory seabird throughout a year. Our research has shown that daily energy expenditure is highest (1.7× average daily energy expenditure) during the spring migration of long-distance migratory gulls, whereas short-distance migrants expend the most energy (1.4× average daily energy expenditure) during the breeding season. Based on the examples provided, we show how bio-energetic models create exciting opportunities to study daily energetics and behaviour of migratory animals, although limitations also still exist. Such studies can reveal when, where and why peaks and lulls in energy expenditure arise over the annual cycle of a migrant, if long-distance movements are indeed energetically expensive and how animals can adapt to fluctuating demands in their natural environment throughout the year.

From land to ocean: One month for southern elephant seal pups to acquire aquatic skills prior to their first departure to sea

Weaned southern elephant seals (SES) quickly transition from terrestrial to aquatic life after a 5- to 6-week post-weaning period. At sea, juveniles and adult elephant seals present extreme, continuous diving behaviour. Previous studies have highlighted the importance of the post-weaning period for weanlings to prepare for the physiological challenges of their future sea life. However, very little is known about how their body condition during this period may influence the development of their behaviour and brain activities. To characterise changes in the behavioural and brain activity of weanlings prior to ocean departure, we implemented a multi-logger approach combining measurements of movements (related to behaviour), pressure (related to diving), and brain electrical activity. As pups age, the amount of time allocated to resting decreases in favour of physical activity. Most resting (9.6 ± 1.2 h/day) takes place during daytime, with periods of slow-wave sleep representing 4.9 ± 0.9 h/day during the first 2 weeks. Furthermore, an increasing proportion of physical activity transitions from land to shore. Additionally, pups in poorer condition (lean group) are more active earlier than those in better condition (corpulent group). Finally, at weaning, clear circadian activity with two peaks at dawn and dusk is observed, and this pattern remains unchanged during the 4 weeks on land. This circadian pattern matches the one observed in adults at sea, with more prey catches at dawn and dusk, raising the question of whether it is endogenous or triggered by the mother during lactation.