Hybrid Goose at Garden Hill

Nature Notes for April 1, 2011

Among about 2000 Canada Geese on Garden Hill pond was one that looked different. At first glance it seemed to be a Greater White-fronted Goose. It had the pink bill and white around the base of the bill.

However, on closer inspection, it lacked a white line on its side and there were faint white patches on the cheeks in the place where a Canada Goose is white. The consensus of those who saw this bird was that it was a hybrid between a Canada Goose and a Greater White-fronted Goose.

Studying this bird was a challenge last Sunday. Just finding it amongst the many Canadas was like playing a moving “Where’s Waldo”. Many of the geese were sleeping, so had their heads under their wings, obscuring the important field marks. Many had their backs to observers and observers were facing into a howling wind. But is was seen well enough by a couple of observers to confirm its identity.

The Sibley Guide to Birds states that these hybrids are “seen occasionally.” These two species are not even in the same genus and I couldn’t find references which inwww.allaboutbirds.org/.../Northern_Pintail/dicated whether the hybrids would be able to reproduce.

Perhaps because waterfowl are big birds, hybrids are seen relatively frequently. During this past winter, two hybrid ducks were reported from Presqu’ile, one a Hooded Merganser crossed with Common Goldeneye, the other a Mallard crossed with Northern Pintail.

A more common hybrid occurs between Mallards and American Black Ducks. In the early 1970s, birders along the eastern seaboard started to notice American Black Ducks which showed a white wing marking characteristic of a Mallard.

These two species are in the same genus and they readily hybridize. Their offspring are fertile. In time, the Mallard genes may swamp American Black Duck genes and American Black Ducks may disappear as a species. In the twenty years between the two Ontario Breeding Bird Atlases, the number of confirmed breeding records for American Black Duck had reduced quite noticeably.

Among landbirds, hybridization between Blue-winged and Golden-winged Warblers is well-known. Prior to European settlement, the breeding range of the two species did not overlap. With clearing of the eastern forests and subsequent regrowth of shrubby fields, the Blue-winged Warbler started to move north. Where their range met that of the Golden-winged Warbler, the two did interbreed.

These two species are also closely related and in the same genus. The favoured habitats of these two are also very similar.

The offspring of these pairings are distinctively marked and were once thought to be separate species – Brewster’s and Lawrence’s Warblers. These names are now used to indicate particular forms of the hybrids.

Blue-winged Warblers are more aggressive than Golden-winged and over time, tend to displace Golden-wings. The Golden-winged Warbler is now considered an officially designated “threatened” species.

These are just a few examples of the several bird species which are known to hybridize.

Determination of species is a tricky thing. DNA analysis of birds is changing long-held ideas about the relation of one species to another. It has also found that some species which look very similar are actually different species. This all makes things very challenging for the field observer.