Images

What Is A Keystone Species?

bruce85@mac.com Educational February 28, 2009

The Beaver is often called a “Keystone Species”, but what does this mean? If we want to be good advocates of our beavers we should all understand this concept. It was introduced in 1966 by R.T. Paine who studied the impact of removing one predator from an ecosystem. (In that case a starfish) Starfish take mussels from rocks and the space they create can then be used by other species.

Paine found that the original 15 species community was quickly reduced to only 8 species when the starfish was removed, prompting his analogy to the collapse of an archway if a “keystone” is taken out. (The keystone is the center piece which holds up both sides of the arch) Beavers have a similar role because their dams create habitat which are used by other wildlife. They raise the water table, create richer sediment, alter the vegetation, and spur bushy tree growth by “coppice cutting” trees. By protecting one keystone species, you actually make conditions better for an entire eco-system of other insects, fish, birds and animals. By the same token, in removing one keystone species, you threaten the viability of an entire habitat. Just another reason why our beavers are worth fighting for.

Spring In The Air

bruce85@mac.com pictures February 12, 2008

This mockingbird was spotted near the footbridge yesterday.

Photo: Cheryl Reynolds

Another Dam?

bruce85@mac.com Beaver News, Educational, pictures February 11, 2008

Heidi Perryman

Discerning beaver watchers have noticed something new in the water over the past few days. Another little dam. Kindly and protective souls have wondered if this should be kept secret from the city, immediately removed without their involvement, or maybe covered up with water lillies so that it doesn’t provoke a general response of panic. I photographed the new structure and sent the pictures around to our beavy of beaver experts, including Skip Lisle. The general response was that this was likely a “secondary dam” not a relocation of the first one. Secondary dams are usually down stream from the “main dam”, and form what Skip calls a kind of “terrace effect” for the pond.

They are are lower in height and primarly help by backing up water against the main dam for extra support. Here’s what authors Steve Boyle and Stephanie Owens say in their paper prepared for the CO forest service: North American Beaver: A Technical Conservation Assessment.

Beavers usually build one “home” dam to create a pond for the main lodge. Secondary dams may also be built depending on food availability, soil type, and terrain (Rutherford 1964). Sometimes these dams are built at different levels, resulting in a “lock” system to control water at each level. Secondary dams allow beaver to transport food and materials to the home pond over greater distances while minimizing travel over dry land (Rutherford 1964). Beavers often construct extensive canal systems in shallow ponds or wetlands to aid in the transport of cut wood (Novak 1987).

The beavers continue to use their lodge, and work on the main dam. Indications are very strong that this will be maintained and that the beavers effort in this secondary structure will be minimal. Remember that the influence of tide gets much stronger the farther downstream they go, so the beavers success will be mitigated by very strong forces. You can tell from the patterns of the rushes that they are using this area to feed and forage.

Secondary dams are a sign of beavers doing what they are supposed to, settling in and adapting to their life.

They are not a cause for alarm, and there is little point to their removal since the beavers will likely rebuild. Since their ultimate water height is controlled by the main dam they do not present a flooding danger and will probably never need a secondary flow device.

And, as one clever beaver supporter mentioned to me, they have again chosen an area with a bridge for optimal viewing. Pretty smart beavers.

Caged? Part Deaux

bruce85@mac.com Beavers February 11, 2008

A recent report of a “city truck with a huge cage in the back” at the dam site appear to have been erroneous. Gary Bogue has more…

Dispersers

bruce85@mac.com Beaver Behavior, Educational May 28, 2010

Heidi PerrymanI was at a not-beaver conference in LA this weekend and decided to take a closer look at this book on the airplane: The Beaver: Natural History of A Wetlands Engineer. It’s a rich and accessible read, and would easily make any willing participant a beaver expert in very short time. One of the parts that interested me the most was the information on youngsters leaving home to start out on their own.

The author, Dietland Müller-Schwarz, calls these kits “dispersers” and talked about their high-risk journey towards independence. They have to sleep under roots or in culverts on their way, and often meet the beaver of their dreams while their looking for a possible home. These beavers are also called “floaters” because they are essentially nomads searching for a residence. He noted that they are somewhat more likely to go downstream than up, (just because it’s less work than swimming against the current) but that “downstream-ers” tend to make a U-turn and come back up because conditions aren’t right more often than “upstream-ers” come back for the same reasons.

He said that dispersers can go any distance from 2-30 miles, but interestingly, it is the females that tend to disperse over the greatest distances, perhaps because they need a better food supply for their future breeding. It made me think that we should be taking a serious look at our creek, and identifying sites where a disperser is likely to settle, but also identify sites where we would *like* them to settle. Since no launch is expected before March 2009 we have time to make the potential sites more attractive, luring the kits where we want them, rather than dealing with any problems they might cause later.

At the Friends of Alhambra Creek Meeting the train tressel bridge was discussed as a possible good beaver site. Where else can you think of? As always you can email your thoughts to mtzbeavers@gmail.com.