User:Mpellegrom12/Irruptive Bird Species

Irruptive Bird Species



Description:
An irruption of bird species is a large and irregular migration of a very large amount of birds to a location where they are not often found. It is even possible for birds to fly hundreds of miles to change areas. While it is normal to find a northern species of bird feeding with southern species on occasion, an irruption is classified by the enormous number of birds participating in the migration.

Reasons for Irruptions
While there are many reasons for an irruption of bird species to occur, a lack of food source in the bird’s natural habitat is the main reason that birds are forced to change their geographical location. This often occurs during the winter season when seeds, flowers, and insects are hard to come by. Birds will return to their natural feeding ground when spring comes and their food source is once again in abundance. Other reasons for these migrations can be famine or over breeding. There is no one definition for the large migration or a consistent reasoning.

Biologists’ working definition:
These southward autumn invasions can be a result of failure of coniferous cone crops. Populations also can be larger after a year of abundant growth. This creates a pressure on scarce food resources and serves as an additional food impetus to migrate. Seed crop size and large population size can all be contributing factors to these large flocks of migration by these extensive groups of raptors.

Difficulty of defining “irruptive” and identifying particular species:
There are three questions which are continually without one answer concerning irruptive bird species. This makes it extremely difficult to define why the species migrate in these certain ratios during certain years and not others. These questions are: •	What causes the migrations? •	Are they really irregular events? •	Are they synchronized among populations within their species between their species?

Definitions of “irruptive bird species”:
The species shift to other regions following a cyclical pattern. Most of the irruptive birds come from the finch family. There are two main cycles for boreal species. There is a four year cycle among grassland and tundra rodents. Also, there is a ten year cycle among snowshoe hares. Movements outside these irruptive bird species’ normal range can constitute a need for their large migrations. Overall the cycles can range from two to ten years but are still not set in stone. Even those drastically different numbers of years can surprisingly be incorrect in random cases among species and their yearly changing habitats. The idea of several species migrating in one year can also be defined as a “super flight.”

Numbers of irruptive bird species:
Species Included:

Pine siskin

Bohemian waxwing

Evening grosbeak

Boreal chickadee

Purple finch

Common redpoll

Red crossbill

White-winged crossbill

Northern shrike

Red-breasted nuthatch

Hoary redpoll

Great grey owl

Snowy owl

Rough-legged hawk

Historical development of irruptive bird species as a concept:
This irruption can also be known as a population shift or Malthusian growth. The name “Malthusian” resulted from population studies and analyses by Thomas Malthus.

British scholar Thomas Malthus (1766-1834) contributed to studies concerning political economy and demography. According to Malthus, the threats of population increase will rule out never ending development creating culture similar to a Utopia. He believes that the control of population is forever better than the control in the world to create survival for humans.

Scientists have influenced every day people to do back yard bird counts throughout every winter. Considerations that people need to be careful about while counting are diseases. People need to watch for illnesses in the birds in their backyard and clean their birdfeeders. Also there are concerns about the kinds of feeders and seeds that they provide. In order to avoid territoriality and aggression people should supply extra feeders, different types of feeders, and different types of seeds so they can supply for the many different species that irrupt and avoid conflict as much as possible. This will make it easier to level the multiple changing factors that occur in such undefined reactions and migrations.

Carl Bock and Larry Lepthien constituted the Audubon Christmas counts that people should conduct in their own backyard. They create graphs yearly on the amount of bird species and how and why so many irrupt yearly or do not.

There are many examples in history of when these species have had large flights or different types of species take over and engage in a “super flight.” There was an irruptive series of species in the Northeast in 1997-1998 where red and white-winged crossbills, common redpolls, evening grosbeaks, and pine grosbeaks had a “super flight.”

An example of Common Redpolls is that their main prey is what is produced by birch and alder trees, catkins. Low production of catkins makes it so the Common Redpolls abandon these habitats and flee into places where there is more abundant prey. The super flight of Common Redpolls can be widespread and range far south to places like the Middle Atlantic States or central Kansas.