Food Provisioning and Body Mass of Nestling Meadow Pipits and Cuckoos

Abstract

Common Cuckoos Cuculus canorus are obligate brood parasites, laying eggs in nests of other species. Cuckoo nestlings are often thought to be insatiable, compared to host broods. However, in Reed Warblers Acrocephalus scirpaceus and a few other species, cuckoo nestlings are fed at most only as frequently as a host brood. To add to the small body of knowledge on feeding frequencies and body mass development of Cuckoo nestlings, I studied Cuckoos using another host, the Meadow Pipit Anthus pratensis, in the Dutch dunes (2019–2021). By filming feeding parents (hosts) I determined the provisioning frequency for broods of Pipits and for nestling Cuckoos. I found that nestling Cuckoos receive on average fewer feeds per hour than broods of Meadow Pipits. Furthermore, overall Cuckoos received as many feeds during their 22-day nestling period as a brood of Pipits during their 13 days in the nest. At 13 days of age (day 1 is the day of hatching), the single Cuckoo was as heavy as a brood of four Meadow Pipits. At 22 days, the maximum weights of the nestling Cuckoos were greater than the Meadow Pipit broods and varied between 91 and 105 g. Thus, although Cuckoos are being fed less frequently, young Cuckoos are heavier at fledging than a whole brood of Pipits. This could be because Cuckoos are fed larger prey. Alternatively, Cuckoos may require less food because their thermoregulatory costs could be smaller: they have almost black skin which absorbs solar radiation efficiently, do not have to compete with siblings in the nest and, once older and feathered, have a smaller surface-to-volume ratio than a Pipit brood of four nestlings.