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Cavity nesters

April 8, 2012
Kevin Williams - Grundy County Conservation Director , Reinbeck Courier

"What an incredible spring. What a crazy spring. Can you believe this weather?" Those phrases and many others have been repeated around Iowa countless times in countless conversations these past few weeks.

It is still March as I write this and there are leaves on many species of trees, flowers on shrubs like wild plum, and nesting activity in Canada Geese, Wooducks, and many other birds.

Nick and Cole came back to the shop the other day with the report of a pair of wooduck drakes and a hen perched out at Blackhawk Creek Wildlife area. The nest-boxes for these ducks have all been cleaned of last year's nests. These include not only past wooduck nests but a few squirrel nests show up in some, as well. Fresh wood chips are added to the boxes with the goal that these beautiful members of the waterfowl community will grace our county parks with their presence.

Spread out across Grundy County on the various parks and wildlife areas are fifty wooduck nest-boxes along creeks and at wetland edges. Forty-two percent of those boxes had nesting activity from 2011 and one hundred percent of those nests were successful in hatching young. The nest-boxes are effective.

But these nest-boxes are substitutes for natural cavities that occur in mature trees. When we think of forests and woodlands, we commonly focus on living trees. But the death and decay of these trees is an integral part of the forest ecosystem. As trees grow older, they increasingly become susceptible to damage from disease, insects, strong winds, lightning and floods. Damaged areas on trees provide entry points for fungi, which colonize the heartwood and eventually consume it, producing hollow trees. And, of course, woodpeckers do their share of "home construction" when pursuing the insects within the trees.

Any tree in developed areas of our parks is monitored and trimmed of broken or dead branches and dead trees are removed before decay makes them a hazard. But those trees in the undeveloped "wildlife areas" are left standing to provide those cavity homes.

Many, many species of wildlife utilize cavities for nesting or denning. I began putting together a mental list of birds that utilize cavities. I quickly came up with a list of twenty-six bird species that need these hollow cavities for nesting and security.

In the nest-boxes for bluebirds and wooducks that you'll find in our county areas, we make real effort to place those in specific environments that will make them as attractive to the birds as possible. Grassy areas close to natural taller perching trees are attractive to bluebirds. It is what they need. Wooduck box openings are placed opposite of the western hot afternoon sun, and near or over water. These and many more considerations are taken into account when the birds are choosing their home that is "just right."

Some species of animals will choose an opening that they must squeeze into. This helps prevent larger predators from gaining access and some of these homeowners will even make improvements. The great-crested flycatcher often hangs a snake skin in the cavity entrance. The skin works like a scarecrow, frightening away other cavity nesters. It's a home security system of sorts.

And besides birds, many mammals such as squirrels, opossums and raccoons den in hollow trees. Other mammals, including bats, striped skunks, mink, gray foxes also den in tree cavities.

So you can see how important these natural homes are and why they should be protected. Those of you who cut and burn wood, please make an effort to leave some of those den trees. Biologists recommend leaving or establishing a minimum of seven hollow trees per forest acre. These trees should be marked and saved when harvesting timber. And if no suitable trees exist, girdle or wound selected individuals to create snags or hollows in future years.



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