In birds, timing of arrival in a breeding area influences who ends up breeding and who does not. This aspect of behaviour, well-known in migratory birds, has now been studied for the first time in a non-migratory species, the blue tit. Researchers at the Max Planck Institute for Ornithology in Germany found that arrival time in the breeding area was an individual-specific and fitness-relevant trait for this resident bird species, as early-arriving individuals were more likely to breed in that year. The study suggests that it might be worthwhile to consider migration on different scales, not only as movements over thousands of kilometres to wintering grounds, but also more generally as movements between breeding and non-breeding sites.
For migratory birds, early arrival in spring in the breeding area increases the likelihood of getting a mate and/or a high-quality territory, and therefore increases breeding success. However, early-arriving birds may face harsher environmental conditions that might offset the benefits, as they lead to a higher mortality risk. For non-migratory or year-round resident species, the timing of arrival in the breeding area and its effect on reproductive success has not been considered previously, perhaps because it is assumed that most individuals stay in the local area also during the non-breeding season.
The blue tit is a partial migrant in the northern part of its range but is considered to be non-migratory in the rest of Europe. In a study site in Southern Germany, researchers from the Max Planck Institute for Ornithology installed a self-designed, custom-built automated monitoring system that registered all visiting blue tits throughout the year. Individuals could be “followed” because they carried a “Passive Integrated Transponder” (PIT-tag). The PIT tag is a tiny tag with an individual code that is activated externally by a scanning device present in 16 feeders and all 277 nest boxes in the study area. With this setup, the researchers could record the date, time, and identity of every PIT-tagged blue tit visit and thus estimate the arrival date of all adult individuals in the study site. MORE
Header image: Blue tit arriving at a “smart nest box” with food for the chicks. Credit: © Julius Kramer.