Many small birds scout for food in the morning but only return to eat it in late afternoon to maximise their chances of evading predators in the day without starving to death overnight, Oxford University research has found. Birds have to store body fat to avoid starving during the cold winter nights, but this can make them slower and less manoeuvrable so that they are more likely to be caught by predators. So there is a trade-off, where birds need to remain lean enough in order to "outrun" their predators, or at least the next slowest bird, during the day but also store enough fat to survive each night.
New tracking technologies were used to investigate how birds balance the competing risks of predation and starvation.....results show that these birds display very different patterns of food discovery in the morning and afternoon – very few new food sources were found during the afternoon, whereas nearly every new food source put out during the morning was quickly discovered. It supports the idea of an "early bird" strategy of scouting for food early on so that they can return to feast a couple of hours before dusk in preparation for a long winter's night.
Winter is a tough time for small garden birds as not only is there less natural food available but their predators, such as the sparrowhawk, are keen to stock up their own fat reserves and so are hunting every day. The short days and long cold nights mean that small birds can lose around 10% of their body weight over a single night so that individuals failing to pile on the grams on even one day can starve and won't be around to pass on their genes the next summer.
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