While working at the park back in 1980, I noticed a high number of Northern Parula Warblers,Setophaga americana, and Black-throated Green Warblers, Dendroica virens. They weren't just passing through, but apparently nesting. These two species are few to absent in many of the other forest types in the surrounding counties, at least in the numbers found here. I wondered what other species might be present, so I decided to make a count of all the warblers found at Ash Cave.
Surveys were conducted in 1980 and again in 1981 between 7:00 and 9:00am. The route included the picnic area, gorge trail, rim trail, and part of the Buckeye trail behind the falls. Birds were recorded by both sight and song. Soon after the project I moved out of state, and never did anything with the data.
Years later I returned to the area and asked Pat Quackenbush, naturalist for Old Man's Cave and surrounding parks, if he would like to participate in repeating the surveys. I wanted to see if the diversity had changed over the 25 years. We gathered data using the same methods as before. With both of us busy with other projects, we hem-hawed on what to do with the results. Before we knew it, another 5 years had passed. So in 2013, we did it again. Now we can compare over a 30 year period.
19 species of warblers were recorded over the five survey years. The most frequently encountered species include, Black-throated Green, Parula, Ovenbird, Louisiana Waterthrush, Yellow-throated, Black & White, Hooded, and Worm-eating.
Those that were occasional or uncommon were Pine, Yellow, Blue-winged, Blackburnian, Cerulean, Canada, Kentucky, Common Yellowthroat, Prothonotary, American Redstart, and Tennessee.
The three most common species were Black-throated Green, Parula, and Ovenbird,Seiurusaurocapillus. If we were to compare 1980-81 to 2005-06 & 2013, their numbers have declined by over 50%. The Cerulean Warbler, Dendroica cerulea, has gained a lot attention, showing the most rapid decline of all in North America. In 1980-81 there were 14 records. In 2005-06 we saw 2, and last year zero.
There were four birds in particular that showed the most drastic results. Yellow-throated Warbler,Dendroica dominica, and Kentucky Warbler, Oporornis formosus dropped by 93%. Worm-eating Warbler, Helmitheros vermivorus, by 90%, and Hooded Warbler, Wilsonia citrina, down by 85%. In S.E. Ohio, these are not rare warblers by any means, but at Ash Cave they are nearly non existent today.
Although I included a table at the end, the number of times we surveyed varied between the years, so comparing the total number of birds seen may be misleading. I think the best way to see the change is to average the number of birds per visit.
1980-81=16.7
2005-06=6.6
2013=4.7
Of the original 19 species from 1980-81, only 7 were recorded this past year.
So what's happening? Succession of the old fields on either side of the picnic areas have made the habitat unsuitable for species like Prairie, Blue-winged, Yellow Warbler, etc. The hardwoods in the canopy can survive for several hundred years, and the Hemlocks easily twice that. So the vegetation through most of the park, including the understory, has changed little over the years.
Why does the understory still have Ovenbirds and Waterthrushes, but not Worm-eating Warblers? If they forage throughout the woods, their behavior should not have been affected. Has there been too much soil compaction from off trail hiking? Perhaps visitation in the park has reached numbers that are uncomfortable for this species to nest on the ground here. The same could be asked of Hooded and Kentucky, which also prefer understory. Surveys often end up asking more questions than they answer.
Other causes include the deforestation of tropical sites these birds overwinter in. The increased number of windmills, cell phone towers, and building collisions take their toll during migration. The change in land use in our country. Increased Cowbird parasitism is another factor. Pesticides, destruction of wetlands and riparian zones, climate change, and cats! (Don't get me started on that one). The list goes on and on. It's probably not one cause, but a combination of factors.
Pat and I are considering writing this up for publication.
All warbler photographs courtesy of Michael Williams.
