Nestling diet variation in an insular Mediterranean population of blue tits Parus caeruleus: effects of years, territories and individuals

Abstract

Mediterranean evergreen forests of Corsica are characterized by relatively high species diversity of arthropods with low population densities. Food is never superabundant for Corsican blue tits Parus caeruleus. This study focused on the composition of the food of blue tit nestlings and especially on two main components, caterpillars and spiders. The nestling diet was studied for two years using 8-mm cameras that automatically took photographs of adult birds with food. The diet was composed of c. 50% caterpillars and c. 30% spiders. There were between-year and between-individual differences in these proportions. In both years of the study the proportion of caterpillars declined during the course of the breeding season. Individual and time effects on prey sizes were also observed. Pairs and individuals were fairly constant in the proportions of prey over the feeding period. Different food items were not brought in runs. These findings suggest that strong food limitation exists on Corsica, which can considerably influence life-history traits of the blue tit.

Habitat and Annual Variation in Arthropod Abundance Affects Blue TitCyanistes caeruleusReproduction

“…It has been shown in many studies that the abundance of caterpillars does influence tit laying time and breeding success (Perrins 1965, van Balen 1973. In general, the abundance of caterpillars in our study habitats is high in comparison with many other areas (Bańbura et al 1994, Thomas et al 2001, Bańbura et al 2004. Blondel et al (2006) suggested that the abundance of caterpillars has a direct effect on Corsican Blue Tit reproduction up to the threshold value of 0.5 g/m 2 /day of frassfall.…”

“…As a consequence, the period when nestlings need the greatest amounts of food is on average synchronised with the seasonal dynamics of caterpillars. Profitability of caterpillars as food for tits depends not only on their numbers but also on their individual body sizes (Blondel et al 1991, Bańbura et al 1994. Because the development of tree leaves and the growth of caterpillars are temperature-dependent processes (Perrins 1991, Nager & van Noordwijk 1995, the optimal time for tits to feed nestlings is about three weeks after the bud-burst, but the date may change even a couple of weeks between years , Murakami 2002.…”

Effects ofProtocalliphoraParasites on Nestling Food Composition in Corsican Blue TitsParus caeruleus: Consequences for Nestling Performance

“…In 1996, the peak value of the frassfall, ca. 97 mg/m²/day, was three or even more times lower than the peak value in 1992 and some other years (Bańbura et al 1994, Simon 2003, Simon et al 2004.…”

“…The reason for considering the above prey taxa in this study is that caterpillars are the preferred prey, while spiders and grasshoppers are the main alternative prey in the study area with only a small proportion of other arthropods such as Coleoptera, Diptera, Dermatoptera, and Hemiptera (Blondel et al 1991, Bańbura et al 1994, 1999. Caterpillar and spider items of prey were classified to three ordinal categories of body size by comparison with the beak and head size of adult birds: 1 = small (length < 1cm for caterpillars, and abdomen diameter < 0.2 cm for spiders), 2 = middle (length 1-2 cm, and diameter 0.2-0.6 cm, respectively), 3 = large (length > 2 cm for caterpillars and diameter > 0.6 cm for spiders).…”

“…The abundance of caterpillars was monitored by measuring their frass dropping from the canopy trees in four 0.25 m 2 collectors at each of five stations randomly distributed throughout the study area (Blondel et al 1991, Bańbura et al 1994.…”