We’ve all seen them — ugly ducks that defy identification.

They have mallard heads with blotchy white bodies, or yellow legs instead of orange, or a wild duck head with a domestic duck’s body.  They look odd because they’re hybrids, a phenomenon that occurs easily in Aves because birds have retained a high level of genetic compatibility.

Hybrids confuse ornithologists.  Brewster’s and Lawrence’s warblers were classified as unique species until they discovered that both are hybrids of blue-winged and golden-winged warblers.  Dr. Frank Langdon fell into the hybrid trap with his Cincinnati warbler, revealed 100 years later to be a Kentucky and blue-winged hybrid.  The AOU famously lumped Bullock’s and Baltimore orioles into the “northern oriole” in 1983, thinking that their hybridization meant they were the same species.  Not!  Fifteen years later the orioles were split back into Bullock’s and Baltimore. (Whew!)

Hybrid birds aren’t always sterile but when they are it happens to the females.  Sterile females lay eggs that never hatch because their genetic blend causes their embryos to die during development.  In the early days of peregrine falcon reintroduction, management agencies removed sterile hybrid peregrines so the male could find a fertile mate and increase the species.  This happened at Cleveland’s Terminal Tower in 1993 (Zenith moved into that opening) and in Harrisburg, PA in 1998.

Male hybrids are fertile but they often fail to find a mate because their plumage, voices and courtship displays are “off” enough that they don’t attract any females.

Did this hybrid mallard in Germany have a mate?  I wonder if the ladies think he’s ugly.

(credits: photo by Andreas Trepte, www.photo-natur.de via Wikimedia Commons.  Click on the caption to see the original. Today’s Tenth Page is inspired by page 590 of Ornithology by Frank B. Gill.)