Birds may hybridize more frequently in captivity than in the wild because natural isolating mechanisms can fail under captive conditions (Sibley 1994). Until recently the only documented hybrid between the American Avocet (Recurvirostra americana) and the Black-necked Stilt (Himantopus mexicanus) was a bird hatched in May 1971 from a known mixed pair held in captivity at the San Francisco Zoo (Principe 1977). We report here three similar apparent hybrids in the wild.
In all cases, the presumed hybrid resembled an American Avocet but showed a dark stripe up the back of the neck, a straighter bill, a dark smudge on the face, and intermediate leg coloration. Also the white patch normally visible on the folded wing of an American Avocet was reduced so that only a narrow strip of white feathers was visible. All three wild hybrids had a fairly straight bill, slightly shorter than that of an American Avocet, with a slight upturn at the tip. In addition, all three birds appeared to have tibias longer than those of a typical American Avocet. This combination of intermediate characters and the similarity of all three wild birds to the known captive hybrid support the hypothesis of hybrid origin rather than coincidental odd mutations. The shorter bill of the captive bird may have been a sex difference. The captive bird was thought to be a male, and males of these species have shorter, straighter bills than do females.