This picture is taken at the bird observatory area. Photo: Jan Erik Røer
The Blackcap is a migratory bird from which our populations migrate to the Mediterranean in winter.There are a number of different populations of Blackcaps in Europe, with different migration routes.
Parts of the Central European population have changed its wintering area over the last hundred years. Many birds now migrate to the UK in winter, where they survive on berries and food from the feeders. This is something also visible along the south and west of Norway. This movements affect Lista from the end of September, through October and all the way into November. This has been proven through ring recoveries in the autumn, observing that birds caught at the bird station have shorter wings in late autumn. In spring, there is little indication that Lista is affected by this move from Great Britain to the Continent.
During the first autumn season, there was use of playback for this species during the ringing. The material from the autumn of 1990 is therefore not included in the presentation.
The total number of monitored Blackcaps has shown a fluctuating but consistently steady increase throughout the period.
There are many indications that the Blackcap can take advantage of the fact that spring starts earlier, so that it does not move so far. It can also have several clutches, having a longer breeding season.
The phenology of all observed Blackcaps has a marked peak in the first third of May in spring. The spring migration is more concentrated than the autumn migration which starts at the end of July. The figure shows a peak in early October, which indicates that the migration of Central European Blackcaps dominates numerically in the autumn.
As the spring catch probably only consists of Scandinavian breeding birds (mainly Norwegian), our spring material indicates that the population has had a formidable increase.
The standardized ringing in the autumn does not show the same clear trend as in the spring. This is probably due to the fact that several populations are involved and that the fluctuation in the Central European population that overwinters in the north is greater and partly affects the trend we see in the spring in the northern breeding populations.
There is a marked trend in the material where the median date after 2005 is around the shift of month April-May, while in the period before this there were significantly more years that had a median date closer to 10 May. It thus looks as if the Blackcap may have adapted to the climate and may arrive earlier in the spring than it did before.
The autumn migration has varied greatly since 1990. As mentioned above, this probably means that there are two different populations involved. Mediandato will depend on whether it is most of the early-migrating Scandinavian (large) Blackcaps or the smaller central-European birds which migrate late.
The figure partly shows that the small Blackcaps dominated in the nineties, when there were many mild winters in Northern Europe, while the trend thereafter is that the large early migrating Blackcaps have become significantly more numerous, so that the median date several times after 2007 is shifted to the end of August, when the northern breeding populations have their main feature.