Abstract
This dissertation deals with the direct and indirect effects of food availability in different phases of
breeding in a small insectivorous bird, the Blue Tit (Parus caeruleus). Previous studies have
emphasised the dual nature of food influencing reproductive decisions in
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birds. On the one
hand, food constitutes energy and nutritional resource for the individual. This thesis has focused
on the effects of food as a resource in two highly demanding phases: (1) the period of egg laying
and (2) the period of brood rearing. On the other hand, food in the laying phase could also
function as a cue predicting the best time for rearing the brood. This hypothesis was tested by
means of a series of additional feeding experiments in which extra food was offered to the
parents throughout the nestling period. Female Blue Tits experiencing additional food during the
nestling period laid relatively later the next year than unfed females, controlled for between-year
changes in the environment. As a result, those females mis-timed reproduction and raised the
brood far from the caterpillar peak the next year. This suggests that food levels experienced
during breeding are involved in fine-tuning the timing of breeding the next year.
The additional feeding experiments provided the opportunity to investigate the provisioning rules
of parents that experience different degrees of food availability. The parents that had access to
extra food delivered similar amount of food as control, unfed parents, but with a different
combination of feeding frequency and size of prey. They fed the chicks less frequently, but with
larger prey items. This suggests that the change in the state of the parents (which spent less time
self-feeding because of the food addition) and of the nestlings (because the parents delivered
some extra food to them) produced a significant change in the parents' provisioning rules. The
availability of more time caused the food-supplemented parents to get access to larger prey,
presumably through an increase in selectivity. This is because larger prey could be obtained only
by making longer foraging excursions.
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