Wespendieven Pernis apivorus figurerend in gesprekken met Ray Teixeira

The late Dutch ornithologist Ray Teixeira (1940-2019) was a critical observer who was constantly validating his own and other birdwatcher’s records. This note brings back memories about two particular conversations with him, and the associated field observations. One is reflecting on two records of Honey-buzzards in August 1982, in the vicinity of a nest in a Birch that Ray had found in 1977. On 6 August, around 11.00 h, a male Honey-buzzard was disturbed in the act of taking two Woodpigeons Columba palumbus chicks from a nest 12 m high in a Quercus rubra along a dirt road in Het Hurkske, province of Noord Brabant. The Honey-buzzard was probably startled when the observer rapidly cycled past right below. The bird flew away with one chick tucked under its tail, the other chick fell to the ground. The latter chick, 8-9 days old, was covered with scratches, slightly bleeding but still alive. The second observation was made on 16 August, 15.00 h, when two dark brown Honey-buzzard fledglings (50-55 days old) were seen to inspect cow dung in a grassland, walking from one dung pile to the next without obvious pecking. This record was interpreted as inquisitive behaviour of an exploring juvenile. Upon inspection of the cowpats only some tiny Diptera larvae were found. The second conversation dates from 2009 and deals with the methodology of mapping Honey-buzzards, and particularly with the possibilities to validate the interpretations from field observations against observed behaviour from birds with known breeding status and equipped with a GPS-sender. Ray stressed the importance of systematic validation of treetop-based interpretations of behaviour, notably where these concerned failed and/or non-breeding birds and sex-specific differences in behaviour. Combining field observations with GPS-tracking was eventually not effectuated within two Dutch tracking projects with Honey-buzzards (2008-10 by Van Manen et al. 2011, and 2013-15 by Van Diermen et al. 2016). This was partly caused by lack of time, but also by the technically and biologically complicated studies in which GPS-data were not instantly available and the birds roamed widely in search of food. In field biology, particular individuals typically do not show up on demand. The tree-topping raptorphile therefore has to work with positive clues on nesting (food transportation) and lacks any clues when no such nest-indicating behaviour is observed. As a sideline the capture of a male trapped at its neighbours’ nest is mentioned, when using a live Eagle Owl Bubo bubo as decoy to capture the local breeding bird (in order to equip the bird with a GPS-sender). Both males were near-indistinguishable from one another, unless closely scrutinised. The first male captured and tagged at the nest did not show up later-on. Only after a second male was capturd on camera at the nest, whilst feeding a chick, the truth dawned that the first male captured was not the male belonging to the nest. It had been a visitor that, as it turned out, had no chicks of its own (anymore?), and later in the same year built a summer nest (which was occupied by the same male the following year).