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Winter survival strategies of diving birds

Aquatic environments in the temperate, boreal and arctic climate zones are highly seasonal in terms of biological productivity. Many poikilothermic (whose internal temperature varies considerably ) aquatic organisms survive the winter, when food availability is low, by reducing their activity levels and/or performing vertical migrations to deep cold waters where energy consumption is low. This causes potential problems for homoeothermic (maintaing a stable internal body temperature regardless of external influence ) predators, which require constant access to nutritious prey to survive. Diving birds are particularly vulnerable to periods of low prey availability, as they are relatively small and unable to store significant amount of fat (due to buoyancy problems).

Among diving birds, many species resolve this by migrating to warmer waters, where prey items are more active and thus more accessible. However, piscivorous birds generally rely on high prey densities in order to forage efficiently, and areas with such high prey densities are restricted in less productive subtropical and particularly tropical waters. This probably explains why few migratory diving birds in the northern hemisphere winter south of the temperate zone. It has thus remained a bit of a mystery how the large numbers of seabirds and other aquatic birds breeding at high latitudes manage to access sufficient prey during the winter season and thus maintain their body condition, both in pelagic and coastal marine environments and in freshwater habitats.

With recent advances in technology, it is now possible to gain unprecedented insight into the survival strategies of these specialist foragers.

Great cormorant
Great Cormorant. Photo Tim Evanson

In this study I will examine day-to-day movement behaviour and energy used to catch prey by recording bird’s movements and diving patterns and thereafter link this information to environmental variability. I will use two different model species, one pelagic seabird (Brünnich’s guillemot) adapted to cold ocean environments and one (Great Cormorant) associated with temperate coastal and freshwater habitats.

 

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Centre for Animal Movement Research
Evolutionary Ecology, Department of Biology
Ecology building S-223 62 Lund Sweden