Why have Canadian Geese stopped migrating

Why have Canadian Geese stopped migrating – Boston Science | Examiner.com.

A good rule of thumb, if you live near a place where Geese breed, is to never count the goslings. It gets too depressing.

In the past few weeks, the honking flying V’s of Canadian Geese have nearly ceased. Almost all of the geese that are headed south to avoid the harsh New England winter this year have already flown the coop, so to speak. However, many have instead chosen to remain behind and are seeking greener pastures not in the warm southern latitudes like their fellows, but around lakes and fields across the northeast.

Historically, Canadian Geese (Branta canadensis) migrate south from the location of their hatching (throughout the northeastern United States and much of Canada) to their wintering habitats in the southern United States in the fall of each year. The migration allows them to avoid the harshest weather during the winter and competition from other bird species during the summer.

However, in living memory, this has changed. Canadian Geese are becoming residential – or “non-migratory” – in areas across the United States, including the northeast. The question of course, is why?

As it would happen, there are a number of potential reasons for this change. Some have been explored by the scientific community more than others, but most of them seem, even those that haven’t been investigated as thoroughly, all seem plausible. Among the possible reasons for this shift from migratory to residential are: A lack of serious predatory threats, an increase in available food during the winter, and the release – many years ago – of captive goose flocks. In all likelihood, it is a combination of these causes – rather than one over the others – that has allowed Canadian Geese to become so widely residential.

To begin, Geese are most vulnerable to predation while they are incubating and raising their chicks. During this time the adult geese shed their flight feathers, effectively grounding them for the duration of incubation. The Geese are vulnerable during this period. However, residential populations are in less danger, due to reduced predatory pressure. The widespread destruction of habitat in the northeastern United States capable of supporting predators like foxes, bears, wolves, and eagles has reduced the pressure on residential populations of Geese that would otherwise be consumed.

The second large change that has allowed Canadian Geese to become residential is also related to changes in the northeastern ecological landscape. The same changes that made the northeast less habitable for predators like wolves or foxes made it a much easier place for browsers like geese to find food. Geese are almost entirely herbivorous, primarily eating grass, and so the spread of suburbs across the Northeast (along with the simultaneous loss of forest habitat) has dramatically increased the amount of food available for them. As a general rule in ecology, any set of circumstances which reduce predators while also increasing the amount of food available to a population will allow that population to flourish and grow. Geese are no exception to this rule, at least one study says that the number of Canadian Geese in the northeastern United States has tripled in the last twenty years.

These two trends go a long way towards explaining why established residential populations of Geese would do so well. However, they don’t manage to explain how the trend began. One theory that makes sense, though it’s unlikely to be the final word in the discussion, is that the release of geese raised in captivity into the wild gave rise to a population that had never been taught as juveniles “how” to migrate (the behavior is learned, not innate). Because of recent changes in the ecology of the northeastern United States, those geese that were unable to join their fellows in the southern United States survived to reproduce. The wild born offspring of the captive raised geese were never “taught” how to migrate either, continuing the cycle.

Canadian Geese are native to North America. However, never before have they been residential. In the United States the changes wrought by their continued presence are minor. Other countries however, are not so lucky. In Australia  and New Zealand for example, they are currently considered invasive. With the rapid growth the American Residential Canadian Geese populations have been experiencing, it could be possible that – at some point in the future – they become more than the annoyance they are currently. Luckily, research is already ongoing on ways to cull out of control goose populations, should the need arise.

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Posted on December 1, 2010, in Related Reading and tagged , , , , . Bookmark the permalink. Leave a comment.

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