Provisioning tactics of great tits (Parus major) in response to long-term brood size manipulations differ across years

Parents provisioning their offspring can adopt different tactics to meet increases in offspring demand. In this study, we experimentally manipulated brood demand in free living great tits (Parus major) via brood size manipulations and compared the tactics adopted by parents in 2 successive years (2010 and 2011) with very different ecological conditions. In 2011, temperatures were warmer, there were fewer days with precipitation, and caterpillars (the preferred prey of great tits) made up a significantly larger proportion of the diet. In this “good” year, parents responded to experimental increases in brood demand by decreasing mean inter-visit intervals (IVIs) and reducing prey selectivity, which produced equal average long-term delivery of food to nestlings across the brood size treatments. In 2010, there was no evidence for effects of brood size manipulations on mean IVIs or prey selectivity. Consequently, nestlings from enlarged broods experienced significantly lower long-term averag...