Feature Article June 26,2003
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FecundityBy Jean GriffinFecundity - is the number of young birds that are raised to fledgling age (when they leave the nest) by a pair of adults each year.
A couple of reports of nests being disturbed by another species made me wonder about the effect of nest predation on the success of a species. Not surprisingly, there is still much unknown about predators, and nesting success, but nest predation is a large and very important factor.
One report was about a Merlin attacking a Baltimore Oriole nest. The Merlin is, of course, a raptor or hawk, and like all raptors it is a predator or carnivore - whichever you wish to call it. Its diet consists primarily of small birds (I have seen it take a Mourning Dove) which it catches in fast, low, horizontal flight. But this report indicates that it will attempt to take nestlings from a nest.
The second report that interested me was of a Black-capped Chickadee's nest being disturbed by a Brown Thrasher. The nest hole was larger than needed for the chickadee, and was large enough for the thrasher. Brown Thrasher diet includes insects, invertebrates, small birds and animals, fruit, berries and nuts. Was this an attempt to include a chickadee nestling in its diet? Nest predation is one of the most significant reasons for a failure to successfully fledge young, and is influenced by forest fragmentation, the creation of forest edges, changes in forest cover, and changes in predator assemblages and behavior. Predation plays a large part in the success of ground-nesting birds, and while predation on nests in trees and shrubbery is often by other larger predatory birds (though mice, coons and tree-climbing animals also predate nests), on the ground much of the predation is by animals like skunks, cats (yes, your pampered pet as well as feral cats), and other carnivores.
Nest parasitism by the Brown-headed Cowbird is another major factor in nest failure for those species which have not learned to recognize the presence of a cowbird egg and either eject the egg, or abandon the nest. What should one do when you see a nest being predated? I would suggest - nothing. For one thing the predator now knows where the nest is, and even if driven away will probably return later. And while we may feel sympathy for the nestling, particularly if it is the offspring of a favourite bird, we should also realize that the death of one bird means life for the predator or its offspring. It is part of nature's cycle. Human activity has caused many changes in nature - habitat loss or alteration, introduction of non-native species, killing of native species, introduction of pesticides, etc. etc.
Now perhaps we need to learn to leave nature alone and allow each species to develop its own strategy for survival. We should leave nests alone - if one if found, avoid returning to it or disturbing the grasses or leaves that protect it; and we need to protect habitat, particularly wetlands which are a vital part of our environment. Observations - Diann Lawton enjoyed seeing a mother American Woodcock and her young near Armstrong Road, and watched a Ruffed Grouse lead her little balls of fluff across the road. Helm, in Oconto, saw his first ever Luna - a large, beautiful moth. Call Jean Griffin at 268-2518 with your reports.
Editors note: After reading Jeans article on Hummingbird Moths last week, we were curious about them and looked on the internet. Alas, we outsmarted ourselves, and published a photo of a Striped Morning Sphinx, not a Hummingbird Moth. Well, at least theyre of the same family.
