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Archive for the ‘Invasive Species’ Category

Mute Swans (Cygnus olor) are a species that is growing more and more numerous, and this is a problem.

Mute Swans are the “classic” swan from stories and art. They are large and showy and beautiful and these traits are exactly why they have been introduced to North America. Birds were brought from Europe in the 1800s and released in parks, gardens, etc. as ornamental additions (New York was the original release area). These birds have since reproduced and spread across the continent as far north as New Hampshire, as far south as Florida, and as far as west as California.

Adult male Mute Swan (Cygnus olor). Source: USFWS digital library.

They are becoming problematic for several reasons. One is that they are quite aggressive, and will chase and bite humans if that human trespasses on the swan’s territory. Another is that they consume quite a bit of food. They are big birds reaching up to 25 to 30 pounds, and that means they eat about eight pounds of aquatic vegetation every day. That is food which is then not available to native birds, and it disrupts habitat for native birds, mammals, fish, and other species. And a third reason is that the swans are directly aggressive to other species of bird driving them off nests, breaking eggs, and killing the chicks of other species, and so displacing those other species from areas where they would otherwise live. With habitats becoming ever smaller and more fragmented, this can mean the native species can be left with no where to go.

These problems have all contributed to Mute Swans being added to California’s restricted species list in 2008. This listing means the birds cannot be imported, transported, or possessed in the state without a permit. This has not completely prevented the swans from beginning to become established in California. Small populations can be found in Petaluma and the Suisun Marsh. I suggest that removing this species while the population is still small is the best course of action. There is every reason to suspect that the population will grow, and as it does so, the problems listed above will become more and more apparent. However, control will become more and more difficult.

One interesting thing about Mute Swans in North America is that they do not migrate very much. There are certainly some, relatively short, seasonal movements that occur in some parts of the continent, but not much. Certainly nothing compared to the long migrations that Mute Swans in Europe engage in. The evolution of this behavior in a novel environment illustrates how different geographic regions can cause a species to adapt and change. This behavioral evolution could then lead to the evolution of a new species, if it persists and becomes dramatic enough.

So, what can you do to help native birds and habitats, and prevent Mute Swans from taking over? If you spot a Mute Swan in California, contact the California Department of Fish and Wildlife – Invasive Species Program by sending an email to: invasives@wildlife.ca.gov or calling 886-440-9530. Together, we can act as citizen scientists to gather data that tracks where these birds are and how they move around. This data will help us all make the best and most informed decisions we can about this species.

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The management of wild horses and burros is a topic that I have felt strongly about for a long time. I can sympathize with those who see the horse as a symbol of the American West, of independence, and of strength and beauty. However, that sympathy does not last very long or go very far.

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A group of wild horses in Nevada.

The wild horse and the wild burro in North America are invasive species. Plain and simple. As such, it is my opinion that those invasive populations should be controlled so as not to negatively impact native species or the overall health of the ecosystem.

The Wildlife Society has recently produced a short documentary called “Horse Rich & Dirt Poor” that lays out some of the issues surrounding horse management in the USA.

One of the points that the film makes is that under current policies and procedures, everyone (native mammals, native birds, native fish, native plants, the land itself, and even the wild horses and burros) is loosing.

Give this 15 minute video a watch, and think about where we are. Where do you think we should go? How do you think we should get there?

 

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A study was published earlier this month in the journal Frontiers in Ecology and the Environment on the effects that invasive species have on other species around the globe. The study is by Tim M. Blackburn, Celine Bellard, and Anthony Ricciardi, and it can be found here.

The main thrust of the paper is that invasive species of plants and animals have been found to have a significant impact on the extinction of other plants and animals all around the world. Specifically, 25% of the plant species that have gone extinct in recent years have been the result, at least in part, of invasive species. Additionally, 33% of the animal species that have gone extinct in recent years have been the result, at least in part, of invasive species.

These numbers are pretty compelling components to the story of just how damaging invasive species can be. It is part of the reason I find working on invasive species control in California to be rewarding.

I am currently working on the control of Arundo (which is a large invasive reed), water primrose (an invasive aquatic plant), Phragmites (which is another invasive reed that is a bit smaller than Arundo), and Nutria (which is a 20 pound semi-aquatic rodent). Each of these species pose unique threats to the native species of California and to many other aspects of the ecosystem as well.

Hopefully, protocols can be developed to stop invasive species before they contribute even more extinctions!

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