1. Fig. 1. Map of southern Sweden and adjacent islands showing the location of 12 sampling places and Falsterbo Bird Observatory.
Map of southern Sweden and adjacent islands showing the location of 12 sampling places and Falsterbo Bird Observatory. The map reaches north to latitude 61°N, whereas the coniferous forest tits P. ater (P.a.), P. cristatus (P.c.) and P. montanus (P.m.) coexist on the Swedish mainland up to about 63°N. Measurements of P. ater in SW Sweden are used as reference values. Black bars show by how many percent P. ater at each of the 11 other places differs from P. ater in SW Sweden. Each bar represents an average difference as calculated across three measurements. The left bar (W) shows the average of the percentage difference from the SW Swedish birds in (wing area)0.5, wing span and hand-wing length. The middle bar (L) shows the average percentage difference across tibiotarsus, tarsus ‘short’ and foot. And the right bar (B) shows the average percentage difference across bill length, width and height. As indicated at the graphs, P. ater coexists with P. montanus and P. cristatus on the Swedish mainland and the Finnish island of Åland. And P. ater is the same size in these places. The larger competitors P. cristatus and P. montanus are absent from the islands Gotska Sandön, Gotland, Bornholm, Sjælland, Anholt and Læsø. And an evolutionary increase of the body size of P. ater has taken place on all six islands. P. ater coexists with P. cristatus on the Danish penisnsula Jylland and with P. montanus on the island of Öland. The size of P. ater has increased also in these places, but not as much as where both P. cristatus and P. montanus are absent. The inset at top left shows how much P. montanus and P. cristatus from SW and SE Sweden differs from the reference values for P. ater in SW Sweden.
R. Åke Norberg, and Ulla M. Lindhe Norberg Biology Open 2015;bio
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