European shag provisioning foraging dives

Foraging dives in birds and mammals involve complex physiological and behavioural adaptations to cope with the breaks in normal respiration. Optimal dive strategies should maximise the proportion of time spent under water actively foraging versus the time spent on the surface. Oxygen loading and carbon-dioxide dumping carried out on the surface could involve recovery from the consequences of the last dive and/or preparation in anticipation of the next dive depth and duration. However, few studies have properly explored the causal pattern of effects within such dive cycles, which is crucial prior to any assessment of optimal dive strategies. Using Time Depth Recorders and Global Positioning System loggers, we recorded over 42,000 dives by 39 pairs of male and female European shags (Phalacrocorax aristotelis). Dives either involved a straight descent and ascent, presumably reflecting an unsuccessful search for prey, or a descent followed by horizontal movement followed by an ascent, presu...