Food, reproductive success and multiple breeding in the Great Tit Parus major.

We studied the reproductive success of facultatively double brooded Great Tits Parus major in relation to (seasonal) variation in abundance of their main food supply: caterpillars in Oak Quercus robur. Data were collected in two mixed woods (Vlieland and Hoge Veluwe, from 1985-1996). The caterpillar food stock is characterised by a strong peak in the breeding season, and height and timing of this peak vary between years. In first broods, nestling survival, number of fledglings and fledging mass were highest at the time of the food peak and lower before and after this time. Clutch size, and success of the first clutch, were positively related to the caterpillar density on individual territories. On the annual level, multiple breeding (defined as the proportion of pairs starting a second clutch after fledging young from the first brood) occurred at increasing frequency as the tits bred earlier relative to the food peak, while there was no additional effect of absolute laying date. As has previously been shown, also within years multiple breeding decreased strongly with time. Early in the season, family-flocks foraged in Oak, and later switched to Pine Pinus nigra, and we hypothesise that multiple breeding is more frequent in early breeding pairs, because good feeding conditions for the family flock may reduce the effect of a second clutch on fitness of the first clutch.

Verboven N., Tinbergen J.M. & Verhulst S., ARDEA 89 (2): 387-406.