Sunday, July 10, 2011

Balancing Habitats by Removing Invasive Species

By observing the cycles in Central Texas, we see the cause and effect of climate, the patterns in plant life,  and, unfortunately, we also see the results of the invasive species.  An "invasive species" is legally defined as a species that is non-native to the ecosystem and whose introduction causes or is likely to cause economic or environmental harm.  Being stewards of the land puts the responsibility on us to manage wildlife, balance habitats, and restore eco-systems.  As we mentioned in the last few posts, in most cases, the best choice to balance an environment is to bring in more variety; however, with invasive species, the unfortunate answer is to remove existing invasive species.

Brown-headed cowbird
Unlike indigenous species, the other wildlife will not balance the numbers of invasive species.  Feral hogs and imported red fire ants are two examples; since introduced to the US, they have no natural predators.  Without human intervention, their populations will continue to grow causing degradation to the environment.  Cowbirds are another example of an animal that upsets the natural balance. 

While cowbirds have always migrated through the south and central Texas areas, they did not live here and breed here until after the decline of the roaming herds.  These birds were named "cowbirds" when ranchers noticed them following the cattle drives.  It is commonly believed that these birds followed the wild bison across much of the US.  Because these birds were nomadic, they would breed all over the country and lay eggs in other birds nests. 

They still do this; the difference being that they never leave the area. These birds do not sit on their own eggs nor do they feed their young. Females breed consistently for 12-14 days, laying an egg each day in a different nest.  In some cases, they will push other eggs out of the nest.  This behavior is considered parasitic because of the burden it puts on the nesting adults who take care of the baby cowbird.  Since the end of the roaming herds, these birds live year-round in areas with cattle, such as Texas and Montana. 

To see what these notorious bad birds look like, see this video of a bronze-headed cowbird in our backyard:

In Texas, the brown-headed cowbird and its urban cousin, the bronze-headed cowbird, have become quite a problem because the cowbirds eggs hatch earlier than other songbird breeds.  The baby cowbird is also larger than other birds and they are able to bully the other birds and take the majority of the food.  Cowbirds are one of reasons for the declining numbers of songbirds.

Wikipedia has some excellent information about the Brown-headed cowbird.

The solution to this problem is to eradicate the overpopulation of cowbirds.  Since they are considered an "invasive species" by the state of Texas, cowbirds can be eradicated by trapping or shooting.  However, there are some problems with catching and removing birds. 
  1. Trapping or shooting other birds is illegal. 
  2. Shooting requires a level of accuracy and is prohibited in urban areas. 
  3. To trap any bird requires certification by the state of Texas. 

If interested in getting certified to trap invasive bird species or to assist with trapping and banding, contact Texas Parks and Wildlife Department for a contact in your area. Training and certification is usually conducted in the winter months and trapping is usually done in the spring.

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