May 27, 2002 Prologue:

In Eugene S. Morton's and Russell Greenberg's excellent article, "The Outlook for Migratory Songbirds:'Future Shock' for Birders" (Spring 1989, Vol. 43, No. 1), the authors state that "people who have birded during spring migration in the same area(s) for two or three decades or more, have valuable insight into the migrant songbird issue." They express concern why records and recollections of such observers are not documented more often by professional scientists.

I have studied birds in the field, mostly in Ohio, but frequently on the East Coast, for a period of 50 years. During that time, I have accumulated volumes of personal checklists with which I have tabulated the actual or estimated numbers of every species recorded on any given day. These records number in the thousands and include specific localities, temperatures, wind direction and other weather-related information.

Are migratory songbirds (especially those which winter in neotropical areas) declining in numbers? My response is that in many cases this is undoubtedly true. This is a generalized impression and is not based on any statistical data evaluation.

Although I am nonplussed as to whether destruction of habitat on the wintering grounds of many of these bird species is a factor in their decline, it surely must be a contributing cause.

As we are all well aware, there are also many other reasons for bird mortality resulting in permanent or short-term decline in numbers of a given species. Frequently these agencies are at work in our own northern hemisphere.

Aside from natural causes, such as adverse weather conditions, disease, and predators, a partial list would have to include expanding metropoliton areas, changing farming practices and other losses of habitat including commercial lumbering and the draining of wetlands, the use of toxic chemicals, obstructions such as tall buildings, towers, and plate glass windows, fast moving vehicles, unlawful shooting, uncontrolled pets, and on and on. South of our borders all of the above reasons for bird mortality would also be evidential, but exacerbated by huge human population increases and the rather common practise of taking birds for food, ornamental feathers, and the cage bird trade. The mist net, which was such a boon to bird banders, is standard gear in obtaining birds for such practices.

There certainly can be little doubt that the destruction of forests throughout Central and South America is also having an adverse affect on migratory birds that winter in those regions. However, it is almost impossible to prove such a theory because of the huge land masses and the widespread distribution of the birds involved.

Perhaps a good way is to carefully monitor the numbers of these birds each spring in designated areas as they migrate through the United States and southern Canada. Since many migrants seem to follow the same route with individuals even showing up in exactly the same locations, this method of censusing could be invaluable in determining variations in population. At this critical juncture in our environmental history, such a census might be of greater importance than the annual Christmas Bird Counts.

During the past few years, there has been a noticeable diminishment in the numbers of migratory neotropical species as they migrate through Ohio. I have found it useful in considering this decline in the following manner.

During migration I visualize the populations of the various species under discussion as they are depicted by bar-graphs in many bird guides. From
my own observations, here is what is happening. There is a contraction of the line that indicates the earliest and the latest individuals at the beginning and end of the migratory period. In other words, the duration of migration for many species is shorter. Even more alarming, the times of maximum concentration during migration seem to be much more abbreviated than formerly.

I have also been in the enviable position of having taken a breeding bird survey during the past 18 years in the Clear Creek Valley, Hocking County, Ohio. This beautiful seven-and-a-half-mile-long area, hemmed in by hills and outcroppings of sandstone is mostly protected and the only discernible effects on bird populations are the result of natural plant progression. An average of 89 breeding species occur each year and 113 species have been recorded since the count was initiated in 1971.

Of the nesting songbirds, approximately 45 species are neotropical in their winter distribution. Some species such as the indigo bunting (Posserino cyonea) with an average of 38+ pairs nesting per year and the Acadian flycatcher (Empidonax virescens) with an average of 42+ pairs nesting per year exhibit a re-markable degree of stability, in spite of some fluctuations.

Other neotropicals, especially warblers, show greater numerical disparities from year to year and many of these species seem to have five- or six-year-cycles of greatest abundance. During the past four or five years, however, some of these species have failed to cycle back to maximum numbers or, if a cycle is evident, the numbers achieved were less than expected. A number of other species have continued a downward slide without abatement and without any evidence that such population decreases could be attributed to local conditions.

Overall population peaks of breeding warblers in the valley declined from 249 pairs in 1977 to 205 pairs in 1988. Cyclic periods of minimum numbers dropped to 165 pairs in 1978, then crashed to 140 pairs in 1985. All of the figures cited are approximate and are based mostly on singing territorial males and do not take into account unmated birds.

To sum up. From my own observations of over 50 years, there. definitely seems to be a decline in the number of migratory species that winter in the neotropics. This diminishment has accelerated during the past five years. From my own experience, the multitude of nocturnal migrants that could be heard as they flew across nighttime skies has been reduced to a fraction of their former numbers. Previously wonderful spring birding locations have been painfully disappointing during the past few years. When there is a good day, even at hot spots like Crane Creek State Park on Lake Erie, the numbers of individuals of most species are lower than at any time in my memory.

 

- Tom Thomson Columbus, Ohio

 

Author of Birding in Ohio, Indiana University Press, Bloomington, Indiana, 1983.

Author of A Checklist of Ohio Birds, published by the Columbus Audubon Society.

Author of The Breeding Birds of the Clear Greek Valley, Hocking County, Ohio, in preparation.

Former nature writer for The Columbus Citizen-Journal.

Past president of the Columbus Audubon Society.

Past president of the Wheaton Club.

Former trustee of the Ohio Historical Society.

 

 

Oct. 22, 2000 Post Script: After the most lackluster fall migration in my memory, I can only conclude that the patterns of migrating
birds are fragmenting with many areas receiving few if any individuals. Some areas, especially along Lake Erie, still have
a few good days, but many less than in former years. Elsewhere, it is very depressing. The area along the Scioto River south of Columbus used to be
a wonderful place to find many migrating neotropical species in the fall. This year, not a single warbler was seen during August and September.
Another observer saw a handful of migrants on one day. A few Yellow-rumps were the only warblers seen in October. There were also
no thrushes or vireos. This habitat remains the same, little if anything has changed - except for the lack of birds. This is sorrowful news -
and I dislike being the messenger.