Storskarv

Mälarens häckande storskarvar, representerade av underarten Phalacrocorax carbo sinensis (”mellanskarv”), inventerades under perioden 20-30 april 2014. Detta var en upprepning av de inventeringar som utfördes årligen 2004-2011. Sammanlagt inräknades 2 210 aktiva bon på 14 lokaler vilket ligger på ungefär samma nivå som de närmast föregående åren.

Fågelskären

Mälarens fågelskär inventerades heltäckande för tionde året i följd, det vill säga årligen 2005-2014. Med fågelskär menas öar som hyser kolonihäckande måsar eller tärnor, såväl tidigare kända som nyupptäckta. Använd metod var räkning av individer som bedöms som bofasta på lokalen. Inventeringen gäller i första hand måsar och tärnor, samt andfåglar och vadare.Inventeringen utfördes under perioden 20 maj – 2 juni och omfattade totalt 350 holmar och skär som uppfyller nyssnämnda definition. På 15 lokaler landstegs också i syfte att dels kalibrera metoden, dels dokumentera förekomst av sjuka och döda fåglar. Sedan 2009 dokumenteras också fisktärnans reproduktion. Tretton personer deltog i fältarbetet.

Sammanlagt inräknades 6 320 fågelindivider av 32 arter (exkl. storskarv och gråhäger) som bedömdes häcka på fågelskären. De tio talrikaste arterna var fisktärna (1 579), gråtrut (1 488),skrattmås (1 198),fiskmås (866),vigg (279),gräsand (234),silltrut (114),kanadagås (91),vitkindad gås (75) och strandskata (54).

Ingen sjuk fågel dokumenterades i år, men fyra (4) döda adulta gråtrutar noterades på en lokal.

Flertalet av de arter som övervakas genom detta inventeringsprogram tenderar att minska i antal. Det gäller särskilt vigg, småskrake, skrattmås, fiskmås, gråtrut och havstrut. Däremot tycks bestånden av några andra arter ligga rätt stabilt över tid eller uppvisar tendenser till ökning; vitkindad gås, storskarv, strandskata, silltrut, fisktärna.

These surveys of waterbirds in Lake Mälaren in south-eastern Sweden were initiated by the Lake Mälaren Management Association, together with four County Administrative Boards in the region. These surveys are important components of an environmental monitoring programme to follow up the numbers of certain bird species. Birds are considered to be good indicators of environmental conditions. The overall aim is consequently to monitor environmental conditions, indicated by the number of birds. This report deals with the results from the survey of Great Cormorant and birds on islets respectively in 2014.

Great Cormorant

The breeding population of the Great Cormorant (the subspecies Phalacrocorax carbo sinensis) was surveyed from 20^th to 30^th April 2014. This was the ninth time that a comprehensive survey was carried out (the previous surveys were carried out annually 2004-2011) since the species colonized Lake Mälaren in 1994. As usual active nests were counted, by surveying the islands on foot. The survey included a check of known or possible nest sites and a search for new colonies. The conditions for this year’s census were in terms of temperature and break-up of ice earlier than average.

Altogether 14 colonies were found, with a total of 2,210 active nests. This is a decrease (–2) in the number of colonies compared with last year 2013, but an increase (+12 %) in the number of breeding pairs compared with 2011. Eight sites had more than 100 nests; the largest colony had 499 nests and the smallest 9 nests.

There were no significant signs of disturbance this year, neither by humans or White-tailed Sea-eagles Haliaeetus albicilla.

The population seems to have stabilized at around 2,000+ pairs annually.

Islets with gulls and terns

We carried out a comprehensive survey of small islands (islets) with breeding gulls or terns for the ninth year in a row. The census unit is defined as an island with at least three (3) adults of gulls and/or terns. We counted individuals judged as breeding at the site. The survey concentrated on gulls and terns, but we also surveyed wildfowl and waders. We also visited 15 sites in order to fine tune the method and also to survey sick and dead birds, and since 2009 also to measure the reproduction in the Common Tern. This gives us also the opportunity to estimate the number of breeding pairs of certain species. The survey was carried out from 20^th May to 2^nd June 2014 and covered a total of 350 islets. Thirteen people participated.

Altogether 6,320 individuals of 32 species (Great Cormorant and Grey Heron excluded) were counted. The ten most numerous species were the Common Tern, Sterna hirundo (1,579); the Herring Gull, Larus argentatus (1,488); the Common Black-headed Gull, Larus ridibundus (1,198); the Mew Gull, Larus canus (866); the Tufted Duck, Aythya fuligula (279); the Mallard, Anas platyrhynchos (234); the Lesser Black-backed Gull, Larus f. fuscus (114); the Canada Goose, Branta canadensis (91); the Barnacle Goose Branta leucopsis (75); the Eurasian Oystercatcher Haematopus ostralegus (54). A summary of the results is found in appendices 1-3.

No sick birds were found this year but four dead adult Herring Gulls were found at one site.

Most of the species covered by this survey show tendencies to decline in Lake Mälaren, in particular Tufted Duck, Red-breasted Merganser, Common Black-headed Gull, Mew Gull, Herring Gull and Greater Black-backed Gull. However, populations of some other species seem stable during the period 2005-2014 or in some cases even increasing; Barnacle Goose, Great Cormorant, Eurasian Oystercatcher, Lesser Black-backed Gull, Common Tern.