hannar i skandinaviska populationer av svarthakad buskskvätta Saxicola rubicola

IN WESTERN EUROPE , the European Stonechat Saxicola rubicola , occurs in two subspecies; rubicola , with a large distribution in Europe, and hibernans , mainly distributed on the British Isles. A small population of presumed hibernans birds breed in Norway. However, difficulties in distinguishing hibernans from rubicola at an individual level has led to speculation regarding the origin of the Norwegian birds. There are no clear genetic differences between the subspecies and their plumage appearance can be considered to overlap within parts of the range. To investigate this, I studied the plumage variation among males during the breeding season in the Scandinavian populations of European Stonechats in Sweden, Norway and Denmark. The study is based on photos of 404 males during the period March–May. The presence or absence of six typical hibernans characteristics were registered for each individual. The results show that males with both hibernans and rubicola characteristics occur during the spring in the Scandinavian populations. There was a clear over-representation of males with hibernans characteristics in Norway as compared to Sweden, and to a lower degree also to Denmark. If the expansion of rubicola progresses in Scandinavia, one could expect a larger proportion of rubicola -like males in the Norwegian population.

Norska fåglar är i likhet med brittiska i stor utsträckning stannfåglar, till skillnad från svarthakade buskskvättor i Sverige och Danmark, där praktiskt taget alla flyttar. Stannfåglar producerar generellt fler kullar under en säsong än flyttande populationer (Cramp 1988, Størkersen 1994, Urquhart 2002 (Cramp 1988, Urquhart 2002, Opaev 2018. The origin and taxonomic status of Norwegian birds have been a matter of speculation for some time. According to Shirihai & Svensson (2018), they consist of rubicola, but that information has later been revised to hibernans (M. Ullman, L. Svensson, in litt.). Urquhart (2002), on the other hand, believes that they are hibernans that have dispersed from the Orkney and Shetland Islands to the southwestern coastal areas of Norway during the 1970s. The main reason to the uncertainties regarding the Norwegian population is the difficulties in distinguishing the subspecies on an individual level.
So far, molecular studies have not shown any genetic differences between hibernans and rubicola (Wink et al. 2002, Illera et al. 2008, Zink et al. 2009, van Doren et al. 2017). In addition, the plumage appearance of the two subspecies are considered to overlap within certain parts of the range, with a continuous transition towards darker birds in west and northwest. However, when larger number of birds have been examined, it has been possible to see morphological differences in an average sense (Urquhart 2002, Clements 2015, Opaev 2018. Norwegian males have a remarkable similarity to Scottish hibernans, which are in general darker than rubicola. One finding that possibly supports the claim that the Norwegian population originates from the British Isles was made on the 26th of March 2016, when a colour-ringed female was photographed and observed close to Søgne, Vest-Agder in southern Norway. This individual turned out to be ringed as nestling in Norfolk in southwestern England on the 7 June 2015 (Secker 2016).
During spring, males with typical hibernans characteristics appear with relatively wide, dark red-brown tips and fringes on crown and upperparts. Breast and flanks are dark red-brown. The white neck patch is relatively narrow with red-brown fillings. The dark redbrown fringes are replaced by a light buff/grey-brown English Summary tone for males with rubicola characteristics. Usually, the underparts and flanks appear as a limited buff-orange colour tone on a white bottom. Both subspecies are darker and more contrasting in fresh autumn plumage, compared to spring when the birds have a more worn plumage (Urquhart 2002, Shirihai & Svensson 2018.
The ambiguities regarding the origin of the Norwegian breeding birds prompted me to investigate the plumage variation in males during breeding season in the Swedish, Norwegian and Danish populations. In addition to reflect the geographical spread of the plumage variation, the purpose was to provide the current status of hibernans and rubicola in these particular areas.
The material is based on photos of 404 different males, relatively evenly distributed over the breeding season March-May (see Table 1). During this time of the spring, the males seem to be more easily classified since wear makes the differences appear clearer. By limiting the time scope to this period, it was possible to avoid a too large variation of the wear between the different individuals. In the material there were males with hibernans characteristics in both March and May and the same holds true for individuals with rubicola characteristics. The material consisted of 240 Swedish, 89 Danish and 75 Norwegian birds that have mainly been observed within the last ten years. The photos were obtained from four different websites; Swedish www.artportalen.se, Norwegian www.artsobservasjoner.no as well as the Danish www.dofbasen.dk and www.netfugl.dk. Females were disregarded since the difference in plumage is subtler and thereby difficult to classify.
The study included all photos up to March 2019 that were of sufficiently good quality to make a judgment. In most cases, several photos were available, showing the individual from different angles. One drawback with this method, however, is that the samples are not random, but dependent on spontaneous reports submitted to the different databases. If this has biased the results is difficult to judge. In any case, the purpose of the study is to give a preliminary overview, based on the existing photo material, and possibly provide a foundation for future studies.
I chose to base the classification on six typical hibernans characteristics that are possible to apply to the photo material. These characteristics have been described in the literature by other authors (cf. Figure 1, Cramp 1988, Urquhart 2002, Shirihai & Svensson 2018. The considered hibernans characteristics are the following: 1) Anterior flank (feathers below the grater coverts) is dark red-brown. 2) Rear flank (feathers above the leg near the wing) is dark red-brown. 3) Crown has relatively wide dark red-brown tips and fringes. 4) Upperpart have relatively wide dark red-brown tips and fringes. 5) Neck patch is relatively narrow. 6) Neck patch has red-brown fillings in the white.
The presence of these six characteristics were registered for each individual. All classifications were carried out by the author in a manner as consistent and comparable as possible.
The proportion of recorded hibernans characteristics varied substantially between the investigated populations. In Sweden, 89 % of the males completely lacked hibernans characteristics, 7 % had one to five, and 4 % displayed all six characteristics. In Norway the distribution was opposite, with 69 % of the males displaying all hibernans characteristics, 15 % one to five and 16 % lacking the characteristics. Interesting, in Denmark the distribution was somewhere in between Sweden and Norway, with 46 % of the males completely lacking the characteristics, 32 % showing one to five and 22 % showing all six ( Figure 2). Figure 3 shows that the presence of the six different hibernans characteristics occurred in equal ratio in the three countries.
Since there is a certain spread within each respective range in Sweden and Denmark, it is not possible to conclude any geographical pattern of the hibernans findings that fulfil all six criteria. The material studied indicate that males showing rubicola characteristics (i.e. absence of the six hibernans characteristics) in Norway are mainly found in the southern and southeastern parts of the country (Figure 4).
The taxonomy of the European Stonechat has been discussed for a long time (e.g. Hellström et al. 2011, Hellström et al. 2014. Several of the subspecies are relatively well examined in parts of their range, while the situation among others, e.g. hibernans, is more unclear (e.g. Illera 2008). Its existence in certain areas, e.g. Portugal, has been questioned (e.g. Siddle 2006). Some claim that it is a transition of different morphologies with darker birds in west and northwest rather than subspecies in Western Europe. Despite morphological overlap and a lack of genetic differences, others claim that there are in fact two different subspecies (e.g. Urquhart 2002, Illera et al. 2008.
This study shows that both hibernans-and rubicolalike males are present in the Scandinavian populations during the breeding time in spring. The differences in plumage are clear, with an over-representation of males with hibernans characteristics in Norway as compared to Sweden. The same, although not to the same degree, can be said regarding comparisons between Norway Ornis Svecica (ISSN 2003(ISSN -2633 is an open access, peer-reviewed scientific journal published in English and Swedish by BirdLife Sweden. It covers all aspects of ornithology, and welcomes contributions from scientists as well as non-professional ornithologists. Accepted articles are published at no charge to the authors. Read papers or make a submission at os.birdlife.se.
Ornis Svecica (ISSN 2003(ISSN -2633 är en fritt tillgänglig granskad vetenskaplig tidskrift som ges ut på svenska och engelska av BirdLife Sverige. Den täcker ornitologins alla områden och välkomnar bidrag från såväl forskare som icke-professionella ornitologer. Accepterade uppsatser publiceras utan kostnad för författarna. Läs uppsatser eller skicka in ditt bidrag på os.birdlife.se. and Denmark. The relatively large proportions of such males in the Danish population could possibly be explained by the geographical location closer to Norway and Great Britain. Males with hibernans characteristics are very rare in Sweden during the breeding season. The presence of rubicola-like males in southern and southeastern Norway could be due to the Danish and Swedish populations spreading north. As the expansion of rubicola progresses, one could expect a larger proportion of rubicola-like males in the Norwegian population. More research, e.g. targeted and controlled ringing activities, is however necessary to obtain a more accurate picture of the current status of hibernans and rubicola in Scandinavia.