Nothing in nature ever stays the same. This is a fact that seems to be easily overlooked by the average wildlife watcher or hunter. We tend to look back at the “good old days” and remember how great things were and lament of how things are now. This innate human behavior manifests itself in unrealistic expectations in regards to wildlife populations. We want peak numbers of wildlife all the time. All the good and none of the bad.
Nature is dynamic and is in a constant state of flux. It’s a good thing and more it importantly it is how nature works. Think of it as the ebb and flow of life. As one part of nature contracts or reduces there is always something else to expand and increase. Take the recent invasion of owls into some of our northern states. A change in the population of prey species (presumably the Red-backed Vole) has lead to a major movement of Great Gray Owls out of their normal range into areas where they have never been seen before. Due to the shortage of food and the rigors of winter some of the owls will die. A reduced number of owls relieve the hunting pressure on the voles allowing the remaining voles to quickly repopulate. Eventually the owls will return home to start the cycle all over again. That is how nature works.
On the other hand there are some species that have increased or decreased without such a clear reason. The Red-bellied Woodpecker is a good example of a species that has really expanded. Twenty years ago this bird was not very common. Now it inhabits most backyards throughout the eastern half of America. Why that is, is hard to say.
On the other side of the coin, the Red-headed Woodpecker (a very similar species) has declined dramatically in all regions. In fact in many parts of the country the red-head has completely disappeared—a term called extirpated. Areas where I use to see and photograph red-heads haven’t had a woodpecker in many years. Again, why this is, isn’t clear. You might be tempted to say it’s a loss of habitat, but how does that explain the ever increasing Red-bellied Woodpecker that lives in similar habitat.
The reasons for a bird’s sudden decrease or increase are not a simple one. I don’t believe you can point to just one reason for the decline of a given species. We people are always looking for something or someone to blame. Rarely in nature does anything happen due to just ONE reason. Usually it’s a combination of many factors and when a certain unseen threshold is reached the trigger is tripped.
One species of bird that has a well documented decline over the past 20 years is the Evening Grosbeak (Coccothraustes vespertinus). This bird use to be a common winter-time visitor to feeders throughout much of America. Now feeders that use to host hundreds of these birds now may see only a handful every couple of years or so. The decline of this finch has been well documented in the National Audubon Society’s 100-year-old Christmas Bird Count (CBC) results. See http://www.birdsource.org/Features/Evegro/index.html for more information.
Here is a synopsis of the report on the decline of the Evening Grosbeak:
The Evening Grosbeak nests in remote regions but spend the winter in areas that are more accessible. Since much of the breeding range of the Evening Grosbeak is inaccessible, winter surveys like the CBC provide the best indicator of the health of the species. Evening Grosbeak numbers were stable or increased until 1980 when their numbers began to decline significantly. The decline of Evening Grosbeak numbers between 1980 and 1998 was significant which indicates that there is less than one chance in one thousand that the decline in Evening Grosbeak numbers was due to random fluctuations in abundance. Also the rate of decline has increased between 1990 and 1998. Some states or province exhibited the most significant declines in Evening Grosbeak between 1980 and 1998. What is clear is that the Northeast and Great Lakes region show the steepest declines in Evening Grosbeak numbers.
The cause of the decline in Evening Grosbeak numbers is unknown, but there are several possibilities. The most obvious is that Evening Grosbeaks may simply not be moving as far south during the winter due to the hemispheric trend in warmer winter temperatures. The declines might also be related to food availability. Hardwood tree seeds, a favorite natural source of food of Evening Grosbeaks, may be less common due to broad-scale changes in forestry practices in Canada. Finally, one thing is for sure, the decline of the Evening Grosbeak is something that many people have noticed simply by watching the birds in their backyards. Until next time…