Monday, March 18, 2013

March 17, 2013: Erv's Field Notes #54

Canada Geese in flight over north lake on a sunny February day at near sundown. 2/23/13 (Kevin Kane)

In previous field notes and on Kevin’s blogs, Wolf and I have mentioned several different names for geese observed at Ada Hayden Heritage Park. These include Canada Goose, Cackling Goose, White-fronted Goose, Ross Goose and Snow Goose (blue and white phase).

Here I will just talk about the various forms of Canada Geese. Let’s start with the definition of a species. Taxonomists (people who name species) first used morphological characters to describe and name a species. One of the most famous taxonomists was the Swedish naturalist, Carl Linneaus (1707-1778), who spent his entire life describing and naming preserved plants and animals brought to him by explorers of the new world. Linneaus devised a binomial system of nomenclature, that is, each species was given two Latin names, the genus and species. This system is still in use today. Closely related species were given the same genus name. Later, a trinomial system came into use for closely related species, to designate what zoologists called the subspecies and botanists called a variety.

In the mid-20th Century, biologists agreed that morphological characters were no longer sufficient to fully describe a species. For example, sometimes males and females of the same species were so different morphologically that they were named as separate species. The great ornithologist, Ernst Myer, devised a biological definition of a species that has been widely adopted. This definition states that a species is a population of individuals that interbreed, or that can potentially interbreed with each other, but cannot interbreed with other populations. Many populations show geographical variation in their morphology and biologists use the subspecies designation to identify them. Not surprisingly, biologists often disagree in these designations leading to confusion in the naming systems. This is very evident in the world of Canada Geese. This species has a great amount of geographical variation across its range in North America and many subspecies have been named to designate the many subpopulations. One long-time student of Canada Geese claimed that he could recognize 135 subspecies. However, in 1991, at an International Symposium on the Canada Goose held in Milwaukee, Wisconsin, Gerald Shields, presented a thorough analysis of the phylogeny of North American Canada Geese based on mitochondrial DNR. He showed that Canada Geese can be divided into two major groups which last shared a common ancestor about one million years ago. One group, which is primarily continental in its breeding distribution, is composed of all large bodied subspecies consisting of seven subspecies. The second group, which breeds in coastal Alaska and Arctic Canada includes four small-bodied subspecies. More recently, it has been shown that several subpopulations of the smaller Canada geese can be considered as a full species. Thus, under the rules of nomenclature, the name for the Cackling Goose had precedence, so the Richardson’s Canada Goose now is called the Cackling Goose, Branta hutchensii.

This is a long-winded preamble to explaining what we observe at Hayden Park. The most numerous of the geese wintering in Ames is the Giant Canada, Branta canadensis maxima. The Giant Canada is a non-migratory subspecies breeding mostly in Midwestern states although it has been introduced into southern states as far south as Florida. A small number of a slightly smaller goose, Branta canadensis interior, is present. The Interior Canada is difficult to distinguish from the Giant Canada in the field. This subspecies breeds along the western shore of Hudson Bay in Canada and winters from Iowa south to Louisiana. A few dozen Cackling Geese have been using the park this winter. This species breeds in the arctic regions of northern Canada and most of this population winters in northern Missouri at Swan Lake National Wildlife Refuge. The Cackling Goose is not much bigger than a Mallard duck and has a very short bill. Otherwise it looks like all of the other geese in the flock. So, the next time you are out at the park, take along a good pair of binoculars or a spotting scope and see if you can pick out these three kinds of geese that all look like alike at first glance. I’ll say more about the other three species of geese in a later note.

Erv Klaas

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