Foraging and food provisioning strategies of Northern Fulmars and Manx Shearwaters

Northern fulmars and Manx shearwaters are pelagic seabirds of the Order Procellariiformes, a group that is characterised by extreme life-history traits. Many of these traits have been associated with the unpredictability of marine food sources. However, fulmars and Manx shearwaters feed their chicks at relatively frequent intervals compared with other procellariiforms, and the life-history implications of this strategy are poorly understood. In this thesis I examined food provisioning and chick growth strategies in fulmars and Manx shearwaters, and discussed these strategies in the context of life history - environment interactions. 1 tested the efficacy of a periodic weighing method for assessing food provisioning, and found that this gave a very similar estimate of the frequency and size of feeds compared to periodic weighing combined with data on parental attendance, determined by radio tracking. However, periodic weighing was much less effective at distinguishing meals from one or two parents. In Manx shearwaters, chick growth was highly correlated with food provisioning rate, and both variables showed significant annual variation. Both individual and environmental effects contributed to this variation, and in particular, peak mass showed highly significant repeatability coefficients. Fulmars showed significant variation in breeding success, diet and chick growth between two years, but chicks were apparently heavier in a very poor year. This was caused by differential mortality of chicks in poor condition. In Manx shearwaters, male parents visited the nest more frequently and made a greater contribution to food provisioning than females, a strategy that has seldom been reported in sexually monomorphic seabirds. I used a cross-fostering experiment to examine the parent-chick interactions responsible for the mass recession period prior to fledging in Manx shearwaters. Both parents and chicks had an active role in controlling food intake, and the results indicated that mass recession was not caused by parental desertion as previously thought.