Swedish Breeding Populations of Honey Buzzards
The information below is mainly taken from the web pages of the Raptor Group studying Honey Buzzards in Dalsland . Contact Ilmo Södergren <ilmo.s@telia.com> for further information.
In 2000-2001 earlier pages from this group reported the following:
The breeding population was estimated as 5,000-6,000 pairs for the whole of Sweden in 1989 (Extension - Sweden).
In the seven years 1993-99 there was a strong negative trend with population down about 3-4% per annum and now under 5,000 pairs. Over a longer time span the population is apparently down one-third since 1986 (Population - Trends). In Dalsland, Sweden, the breeding population has fallen from 120-140 pairs in 1990 to a maximum of 100 pairs in 2000 (Density and Population - Trends).
The numbers of juveniles ringed has declined in the 1990s in Sweden from c40 in 1990 to just under 20 each year from 1997-99. In Dalsland 95 juveniles and three adults were ringed from 1992-98 (Moulting and Ringing).
In very recent work in Dalsland on 16 nest-plots, a number of active nests were found and monitored in 1999 and 2000. In the first year no young were fledged from five nests, in the second an average of 0.33 young was ringed per nest from nine nests. The comment for 2000 is: "Another year with very low reproduction level. But this year (as opposed to 1999) some breeding succeeded .... the results from the two latest years may be caused by not only food shortages but probably even that birds from our controlled plots have alternative plots/nests outside our control?"(Further Investig. HB 2000).
The current versions of the web pages for Honey Buzzards in Dalsland (December 2007) have information on distribution of sites by mapping, reproductive success from 1992-2007 and (described below) satellite tracking of three birds to west Africa from 1997-8.
The downward trend continued until 2007 when six pairs raised just one young. But overall there seems to be some bottoming out of the decline in recent years and to give some hope 2008 was better with 9 young from 8 pairs. The density of pairs was however quoted as declining from a maximum of 7 pairs per 100 sq km in 1992-94 to a maximum of 3 pairs per 100 sq km in 2006-08.
Falsterbo Trends: The numbers of Honey Buzzards at Falsterbo in autumn 2000 appears to be low at 3,591, compared to the long-term average of 5,024 from 1986-1999. Numbers in 1997 were 4,198, in 1998 3,790 and in 1999 5,522 (Fågelobsar i Skåne, http://www.skof.se/obs/index.html , click on Obsar 1998, then the week number, then Rovfågelsträcket. Note: this route not available in 2001, check archives).
Satellite Tracking: The migration of three juveniles in autumn was followed by satellite tracking in 1997 and 1998. Two juveniles crossed in the Falsterbo area and flew over western Germany, Luxembourg, central France, eastern Pyrenees, eastern Spain, Gibraltar, Tangier and then almost due south to Sierra Leone and Ghana respectively. Another left Sweden to the south-east, arriving in Poland, then moving south to Czechoslovakia, south-east Germany, Austria and north-east Italy. It then moved south-west along the Mediterranean coast to Gibraltar, crossed to Tangier and flew south to the Ivory Coast.
A juvenile present in Dalsland from 7th-10th September was on the Czech border by 15th. Other juveniles started in Dalsland on 28th-30th August and 7th-8th September (Telemetry Studies/ Satellite Receiving).
Discussion: after recent declines the Swedish population of Honey Buzzards is under 5,000 pairs with a strong negative trend. Productivity is very low, due at least partly to food shortages. In 2000 the productivity for the sample in Dalsland is a maximum of 0.33 young/ active nest based on numbers ringed. Not all those ringed will fledge and exit the country on autumn passage. The upper bound at 5,000 pairs and 0.33 young/ active nest is 1,650 juveniles; the lower bound at 4,000 pairs and perhaps 0.2 young/ active nest is only 800 juveniles. The relationship between pairs in the population and active nests needs to be clarified. At Falsterbo a total of 931 birds were noted in September 2000 (293 1st-9th, 638 10th-30th). Most of these were probably juveniles so there seems to be an approximate agreement between the numbers actually recorded at Falsterbo and estimates of the number of juveniles fledged. The total autumn count at Falsterbo was very low at 3,591 perhaps reflecting the declining population level and poor productivity.
On the information available, it seems surprising that such an unprecedented and massive movement in Britain should originate from a population that is suffering a decline and poor productivity. Information from other Swedish study areas of breeding Honey Buzzards would be very useful in providing larger sample sizes and a broader perspective.
Migration routes through Europe appear to be quite diverse but are strongly south through Africa.
See also Further Information on Swedish Breeding Populations for a status review by Martin Tjernberg (2006). This confirms the negative trends in Honey Buzzard populations at the current time.
