Bird Word: Irruption

• Irruption: when large numbers of a particular species move to an area where they are not commonly found in large numbers, often in response to drought, rainfall or other environmental changes. In Australia, some species of hawks and kites can irrupt into areas experiencing mouse plagues or locusts. Water birds irrupt into areas experiencing sudden flooding.

An irruption of birds can be a spectacular event. This is something that happens quite regularly in Australia, often as a result of our wildly fluctuating environmental conditions.

Mouse Plague

I can remember back to about 1990 when there was a serious mouse plague in the wheat growing areas east of home. Millions of mice infested sheds and barns on the local farms. During this time we went on a camping holiday to Hattah-Kulkyne National Park.We drove through this area and it was impossible not to run over hundreds of mice as we drove along. In fact, there were so many dead mice on the road, they caused corrugations. It was a rough ride.

Letter-winged Kites:

While we were travelling along we kept looking out for Letter-winged Kites. This species is usually confined to areas much further north. Because of the mice plagues they had moved south in significant numbers and were seen in the area we drove through. This Kite is a rather hard species to find normally. I was excited at the prospect of seeing at least one. I still haven’t seen one. [sigh]

Black-tailed Native-hens:

On other occasions I have seen large numbers of other species. I remember seeing literally thousands of Black-tailed Native-hens on the road south of home on our way to Meningie. Normally we might see two or three. At other times Australian Pelicans have been known to breed up in huge numbers, especially after flooding in some areas.

Lake Eyre in flood:

As I write this in mid-March (2007) Lake Eyre in far north South Australia is filling with flood waters from heavy rain in parts of Queensland. This lake is usually a dry salt lake. Over coming months, many species of water birds will breed in massive numbers in response to this water. In a year or two, as the lake dries out, there may well be an irruption of some of these species as they move in large numbers to other parts of the country.