WikiFindings

Managing fat to survive the night explains why birds sing at dawn

Background

Like people non-human animals have daily routines. Perhaps the most well-known phenomenon of this is the dawn chorus, where most bird species sing in the early morning especially in Spring. Previous explanations for the dawn chorus include reasons that singing is best at that time because sounds travels better or that is when females are listening. Singing is costly in terms of energy and birds have to spend much of their day finding food to stay alive, so singing and foraging are competing demands on their time. This study used a model in which birds must decide between foraging and singing over the day and can store fat to keep themselves alive when singing and during the night.

Findings

The daily routine of birds is strongly influenced by how they need to make sure they survive the night by having enough fat in their body at dusk. They can mostly forage in the evening if they haven’t managed to build up fat during the day. If the temperature at night varies then birds need different amounts of fat to survive the night. To make sure they survive for a long time birds need to be prepared for the worst, so have as much fat as it takes to survive the coldest night. This means that most mornings they will have fat remaining. Since they have chance all day to build up fat again, they can afford to allow their fat to drop further in the morning whilst having a long period of intensive singing.

Implications

The model shows that the explanation for the dawn chorus does not require complex explanations based on the behaviour of females nor environmental changes over the day that affect sound transmission or foraging success. All that is necessary is that birds can’t forage at night and the overnight temperature varies. This hypothesis is supported by observations that birds sing more if given extra food, and sing less after colder nights.