Thursday, 25 August 2011
THE HONEY BUZZARD IN EXTREMADURA (2009-2010)
Honey Buzzard (Pernis apivorus). Left: adult female with a honeycomb in its claws(Joel Brueziere, taken from Fat Birder). Right: adult male (Stephen Daly, taken from IberiaNature). Adults are distinguished by their yellow iris and tail with dark bars only at the base. Males have grey heads and lack the female's "tiger stripe" pattern running across the secondaries. The plumage of this species is very variable, ranging from very dark to very light forms through various reddish and brownish hues.
In 2009-2010 SEO/BirdLife brokered a national count of nine diurnal woodland raptors (Palomino and Valls, 2011). One of the species that came into this trawl was the Honey Buzzard (Pernis apivorus) [click for general survey aspects and methodology]. According to this survey Extremadura's population comes out as an estimated 43 territories (range 29-58), 36 in the province of Cáceres and 8 in the province of Badajoz. This represents only 2.3% of Spain's total population (1850 territories), way below the figures for Galicia (710), Castilla y León (510) and Asturias (280). The mean regional density was 0.10 territories per 100 km2, a long way below the national mean (0.37); the figure was much higher in Cáceres (0.18) than in Badajoz (0.04). As expected the highest densities were recorded in Atlantic Spain; the four Galician and Asturian provinces are the only ones clocking up a mean of 2 territories per 100 km2.
The Honey Buzzard has a local range in Extremadura, with at least 5 population clusters. The main one is in the Cáceres part of the Gredos mountain chain (La Vera and the valleys of Jerte and Ambroz), then stretching westwards to Tierras de Granadilla and Valle del Alagón. The second biggest nucleus occupies the Sierra de Gata and the third Villuercas. In Badajoz there are 2 small clusters, recently discovered, one in Cíjara and the other in Tentudía. In general, Honey Buzzards choose patchwork deciduous woodland and farming habitat in areas with rainy springs. Most of Extremadura's population nests in oakwoods (Quercus pyrenaica), although in marginal areas there are also territories occupied in Cork-Oak woods and pinewoods (Cíjara).
Predictive map of the Honey Buzzard's range in Spain (Pernis apivorus), taken from Palomino and Valls (2011). Notes: (1) The highest likelihood of a Honey Buzzard sighting in the whole country is in the Cáceres part of the Gredos mountain chain. (2) The five sites with proven nesting in Extremadura are marked in red. (3) The sectors marked in grey outside these areas have no known Honey Buzzard sightings in the breeding period. (4) The Tentudía site does not feature on the map.
The lookout counts showed Honey Buzzards to be especially common in the valleys of the Jerte and Ambroz rivers , where the likelihood of sightings is the highest in the whole of Spain. Densities sometimes build up to 9 territories per 100 km2. The vehicle transects were far less successful. In Extremadura as a whole an average of only 4 Honey Buzzards were seen every 1000 km, albeit with local sightings of 3 birds per 100 km in Jerte valley. Lastly, the Honey Buzzard population trend in Extremadura is unknown, although the trend is considered to be "possibly upwards" for Spain as a whole.
So much for the results thrown up by the SEO/BirdLife survey, carried out by volunteers and drawn from complex statistical calculations, all subject to a certain error. The survey authors themselves point out that the results are lower than previous estimates (in the cases of Madrid, Catalunya and Cantabria) and should be considered as minimum figures. The same goes for Extremadura, with previous estimates of 75 pairs. The actual population might well exceed 43 territories, for in Jerte valley alone the fieldwork showed up 25 possible territories plus 12 more in adjacent areas (J. Prieta, own figures). Such doubts are inevitable when dealing with a species so poorly studied in Spain as the Honey Buzzard, a highly idiosyncratic raptor because of its diet (bees and wasps) and its short stay among us (only from May to August). The sampling period was therefore very short and the sample itself was small (detected in Extremadura in only 10 of the ten-k grids with lookout points). Other aspects of the Honey Buzzard's behaviour makes them difficult to quantify: they pair off very quickly and their wing-clapping display flight period is also very brief; the significant non-breeding population (50-85%) is very visible sometimes with sizeable flocks; territories overlap; they range over large hunting areas (7-10 km from the nest) and they rarely betray their presence with any calls (Bijlsma, unpublished). Lastly, they are sometimes hard to tell apart from Buzzards (Buteo buteo), especially when a long way off.
The fieldwork was coordinated and carried out by SEO volunteers and personnel of the Environment Board (Dirección General del Medio Natural) of the Regional council of Extremadura (Junta de Extremadura).
- Palomino, D., and Valls, J. 2011. Las rapaces forestales en España. Población reproductora en 2009-2010 y método de censo. SEO/BirdLife. Madrid. [download in PDF format]
- Bijlsma, R. B. Inédito. Abejero Pernis apivorus. Propuesta de método de censo. Informe inédito para SEO/BirdLife.