Foraging effort in relation to the constraints of reproduction in free‐ranging albatrosses

Abstract

Summary1. Theoretical models predict that animals will vary their effort to maximize different currencies such as time and energy when the constraints of reproduction change during breeding, but this has been poorly studied in free-ranging animals. 2. Foraging effort (energy per unit time) was examined by comparing mass changes, foraging costs and activity-specific behaviours of Wandering Albatrosses ( Diomedea exulans Linnaeus) during the incubation and chick-brooding stages. In 1998, 38 albatrosses (20 during incubation and 18 during brooding) were injected with doubly labelled water and equipped with satellite transmitters and activity data loggers. 3. During incubation, albatrosses travelled 3·7 times farther and were at sea 3·2 times longer, yet foraging costs were significantly lower than trips made during brooding (incubation 4·52 ± 0·50 SD W kg − 1 vs brooding 4·98 ± 0·55 SD W kg). 4. The rate of daily mass gain decreased significantly with time at sea during incubation whereas the rate of daily mass gain increased significantly with time at sea during brooding. 5. Foraging effort was higher during brooding, suggesting that birds were minimizing time at sea to maximize the rate of food delivery to chicks. In contrast, foraging effort was lower during incubation, suggesting that birds were maximizing time at sea and minimizing the energy costs of foraging. 6. Foraging costs were also different between sexes. However, this was related to body size differences and not to differences in foraging effort as suggested in previous studies.

A new algorithm for the identification of dives reveals the foraging ecology of a shallow-diving seabird using accelerometer data

“…Surprisingly, we did not find differences in dive frequency between incubation and late chick-rearing, even though several studies suggested an increase of parents foraging effort during chick-rearing (Shaffer et al 2003;Navarro et al 2007). Nevertheless, these studies considered chick-rearing as a single phase covering possible differences in birds' foraging activity over it.…”

“…Later, parents reduced their mean trip length during chick-rearing phase. During this period, the energetic demands of the parents increase (Shaffer et al 2003;Navarro et al 2007), since they must feed both their chick and themselves. Our observations showed that Scopoli's shearwater foraging ecology changed also within the chickrearing period.…”

“…Some differences in the foraging strategy between incubation and chick-rearing have been described in shearwaters (Shaffer et al 2003;Navarro et al 2007). However, differences in birds' foraging activity within the chick-rearing period have been poorly investigated.…”

Foraging distance affects reproductive success in Magellanic penguins

“…Foraging locations at sea, particularly distance to food, influence offspring feeding frequency (Pinaud et al 2005), reproductive success (Inchausti et al 2003), and adult energy balance (Shaffer et al 2003). How central-place foragers use the ocean affects not only their breeding parameters, but also their conservation, because of increasing conflicts between human activities and wildlife (Boersma 2008).…”

“…For central-place foragers, distance to foraging areas is often related to trip duration and the frequency of offspring feeding (Shaffer et al 2003, Boersma et al 2007). Many seabirds and pinnipeds feed at particular oceanographic features (Hunt et al 1999, Boersma et al in press), and flying or swimming from breeding sites to the foraging areas make up a large percentage of the trip duration.…”