VAN IRSEL J, DE GRAAF L & MATSON K (2023) Fish as food for Common Blackbirds Turdus merula nestlings. LIMOSA 96 (3): 137-141.

On May 20th in 2022 we observed that a breeding pair of the Common Blackbird fed Three-spined Sticklebacks Gasterosteus aculeatus to their 5-days-old chicks twice. In 2016 an online video showed another Blackbird feeding its 9-day-old chicks with Sticklebacks in the Netherlands. To understand whether catching fish (and possibly feeding fish to nestlings) is perhaps more common among passerines, we sent out a nationwide call to report observations of fishing passerines and searched the scientific literature and online media for reports of this phenomenon. We received nine observations of fishing Common Blackbirds, and five observations of fishing by three other non-corvid passerine bird species. This suggests that capturing and feeding fish seems a rare but widespread behaviour among passerines. Blackbirds normally rely on earthworms and caterpillars to feed their chicks, however, 2022 was one of the driest years in the Netherlands. Drought and heat may have resulted in lower availability of earthworms and caterpillars, while chances of finding fish in shallow or dried-up streams would be relatively high. As a result, some Blackbirds may have substituted the low availability of earthworms and caterpillars with fish to feed their nestlings. Fish has a lower calorific value in gram dry mass than earthworms and caterpillars, but it has a higher content of lipids and consists of 10% less water compared to earthworms. Fish feeding may thus be profitable when other food sources become scarce, such as during severe droughts. However, more observations are needed to understand whether fish feeding is a novel behaviour driven by the more frequent occurrence of droughts or a common behaviour among passerines breeding near water.

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