THE VEILED BLACKCAP - GENETIC-BASIS, RECE NT OBSERVATIONS, AND HISTORICAL ASPECTS OF THIS MELANISTIC FORM OF THE BLACKCAP SYLVIA-ATRICAPILLA

In 1829, a melanistic form of the Blackcap (B) was reported in Madeira ; it was later shown to also occur on the Azores and Canary Islands. G erman bird lovers called it ''Schleiergrasmucke'', and we propose as a n English name: the ''Veiled Blackcap'' (VB). On Madeira and the Azore s, they were regularly observed in low frequencies of about 2 % of the B populations, on the Canaries a small closed population disappeared. The genesis of the rare VB has been a matter of endless debates. This form was thought to be caused by nutritional or climatic factors, to be inherited as a single-factor recessive, or to represent a special r ace. From 1987 to 1994 we were able to observe 5-6 VBs on Madeira, to trap there 4 males and 2 females, to hand-raise 50 Bs from the island and to breed the birds in our aviaries. From the pairings B x B, VB x VB, B x VB, F-1 x F-1 and back-crosses with VB we obtained a total of 65 offspring. The results show that morph development in Madeiran Blac kcaps is genetically controlled and consistent. with a single-locus, t wo-allele autosomal dimorphism resulting in B and VB. The sex ratio of VBs in our study was 1:1, indicating that the reported scarcity of me lanistic females is due to observational bias. All trapped VBs and mos t of their offspring were released on Madeira after the breeding exper iments. We also report on many details of the VB, present the first ph otographs of living individuals of this form, refer to its unique tame ness as a possible heterozygous advantage in maintaining plumage polym orphism and discuss general aspects of melanism in birds.