A female Montagu’s Harrier (Circus pygargus) from southern Brandenburg – just 60 km south of Berlin – was found a few days ago as a breeding bird on the nest in Plzensky Kraj about 10 km west of Plzen. The Montagu’s Harrier was ringed 2021 when it was a nestling together with its 3 nest siblings. The distance from the nest near Zeuden, near Treuenbrietzen in Brandenburg, to the breeding site in the Czech Republic is approx. 260 km.
Questions concerning dispersion, the occurrence of individuals of a species in space, plays a major role, especially after fledging. Dispersion is an important part of bird ecology, plays a key role in many ecological and evolutionary processes, and has important conservation implications. However, for many bird species, especially raptors, there is still a lack of detailed knowledge about dispersion. A Spanish project reviewed and collected information from five tagging programs for young Montagu’s Harriers in different Spanish regions to allow an assessment of the philopatry, breeding site fidelity, and contrastingly the dispersion of Montagu’s Harriers in Spain. It was found that only 7% of all marked Montagu’s Harriers could be observed as breeders in the following years. The percentage of philopatric (i.e. breeding within 10 km from birthplace) males and females was less than 5%. There were no sex differences in percentage of philopatric birds or dispersal distances.
The low breeding site fidelity observed indicates a high dispersal ability of this species in both sexes and therefore a high level of genetic mixing between populations.
The female, which has now been caught in the Czech Republic, is therefore a good example of a standard distribution strategy that does not consist of loyalty to the breeding site. This enables birds that follow this strategy to adapt to changing living conditions and to (re)colonize areas that were previously unsuitable.
In general, in birds, the dispersing sex is usually female, while males are more philopatric. This is also common in other raptor species. Males are known to select breeding grounds in many species of birds of prey. In this sense, returning to a familiar spot can be beneficial for males as they can secure a good, at least well-known, breeding ground. The Montagu’s Harrier is a bird of prey with breeding areas in Europe and Asia and wintering areas mainly in Africa.
Male Montagu’s Harriers usually arrive at the breeding grounds first and select the nest site. They are also what provide the female with food for most of the breeding season. The female, which has now been caught in the Czech Republic, may have simply “stuck” in the Czech Republic on the retreat to the breeding areas, as she liked both the breeding site and the male.
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