Data for: Causes and consequences of variation in diet composition of nestling Canada jays

Diet quality during development can impact growth, physiology, behaviour,
and survival. The Canada jay is a resident boreal passerine that caches a
wide variety of perishable food items in late summer and autumn for its
over-winter survival and late-winter reproduction. A previous experiment
found evidence that food supplementation of Canada jay pairs during the
nestling period had a positive effect on the condition of their nestlings.
However, given that foods cached by adults vary widely in nutritional
content, the composition of nestling diets could also have an important
influence on offspring development. In a population of Canada jays in
Algonquin Provincial Park, Ontario, Canada, we investigated the influence
of environmental conditions before and during the breeding season on
nestling diet composition and the consequences of nestling diet
composition on the body condition of nestlings and on their subsequent
survival. Using stable-carbon (δ13C) and
-nitrogen (δ15N) isotopes, we estimated the proportion
of three food groups (vertebrates+human food, invertebrates and plants) in
feathers from almost 200 nestlings. Nestling diet in March and April was
influenced by environmental conditions 5 – 6 months prior to hatching,
with warmer and more variable autumn temperatures associated with a
greater proportion of vertebrate flesh and human food in the diet.
However, the proportion of vertebrates and human food in the diet had no
influence on nestling body condition or whether an individual was observed
the following fall. Our results, in conjunction with previous work on
Canada jays, suggest that the quantity of food available to a nestling
during development may be more important than diet composition.