Great tit males that are fed start singing later in the morning. This changes their territorial behavior - which could have implications for their reproductive success. Although about half the population feeds free-living birds in winter, the effects on their behavior have hardly been studied.
When the days start to get longer again from Christmas onwards, the first great tits start to sing, and only the males, as is usual for native songbird species. Spring and the breeding season are still far away, but the animals are already practicing their song, with which they defend their territory against other males. Numerous great tit territories are located in our cities and gardens, and in many of these territories there is a feeder or tit dumplings are hung up.
How feeding affects bird behavior, however, is poorly understood - yet bird feeding is probably the activity that brings most people around the world into conscious contact with wildlife. It is known that blue tits that are fed in winter lay eggs earlier in the breeding season and have more offspring than their non-fed counterparts. Increasingly, however, bird feeding is not limited to the winter, but is practiced into the spring or even throughout the year.
Do females become unfaithful?
Researchers have now investigated how great tit males react when bird food is offered in their territories until the beginning of April, shortly before the start of egg laying. To do this, they hung up feeders in 28 great tit territories. In half of these territories, the silos were filled with food for two weeks and titmouse dumplings were also hung up; the other half of the territories served as a control without titmouse dumplings and with empty feeders. Before the start of feeding, at the end of the two weeks of feeding and again two weeks later, the song of the males was recorded with directional microphones, one hour before and one hour after sunrise.
The result of the study: males that were fed in their territory started singing on average 20 minutes later in the morning than their non-fed colleagues. This effect was still noticeable two weeks after the end of feeding. The reason for this delayed onset of singing is still unclear; possibly other birds and male rivals attracted to the territory by feeding distract the territory-owning male from singing.
This may be pleasant for the feeding garden and balcony owners, because they are awakened by singing great tits only 20 minutes later. However, previous studies have shown that birdsong before sunrise plays a special biological role. In some bird species, such as the nightingale, morning song is particularly important for territorial defense. In the case of the great tit, it is suspected that the early morning song also serves to keep one’s own female from straying. It is possible, therefore, that fed males, precisely because they start singing later in the morning, are less successful in defending their own female, have more "cuckoo young" in the nest, and thus have lower reproductive success.
Winter feeding makes sense
Should birds now be fed at all in winter, and if so, for how long? According to Valentin Amrhein, who led the study, winter feeding is very valuable from an educational point of view: "There are probably many people who - just like me - have already observed the winter guests on the balcony as children and have thus come to bird watching and nature conservation. But you have to be aware that by feeding you also influence the behavior of the animals. Based on our results, I advise to stop feeding at the end of March at the latest, so that the animals can pursue their breeding business undisturbed in April."
The Swiss Ornithological Institute Sempach and the Swiss Society for the Protection of Birds (SVS) recommend moderate feeding, especially during permafrost and closed snow cover. Only the most common breeding and visiting birds, such as great tits and blue tits, benefit from winter feeding. In order to promote rarer and endangered species, one should above all be concerned about the preservation of diverse and healthy habitats.
