We are creeping up on the exciting part of spring when stuff starts migrating north to breed. The excitement of finding species, newly arrived, can sometimes lead to misidentification. Every season somebody, somewhere identifies something too early for the expectations of those with more experience. Purple Finches are called Swainson’s Thrushes. Orange-crowned Warblers in their bright breeding duds are called Yellow Warblers. Western Wood Pewee or Common Nighthawk turn out to be starlings.
The study of seasonal patterns in nature is called phenology and it is fairly well studied in birds. Birds in migration can be remarkably predictable. Those of us with lots of years behind us have a pretty good grasp of regional expectations.
But we don’t know everything…
If one doesn’t go looking for a bird until it’s expected, there is a chance early arrivals might be missed. And there are remarkable differences in arrival times and species densities between coastal, inland valley and Columbia basin locations. When I first started looking at Rufous Hummingbird phenologies 20 years ago, I was surprised to find as much resistance to the idea of east/west variation in timing as I did. Now days a simple check of the graphs on eBird show these differences quite cleanly.
Some of the imprecision in our understanding of these finer scale differences in timing are an artifact of observer distribution. The Willamette Valley has a higher density of observers, so the precision with which we can make claims about arrival times is greater. These differences also have the potential for creating biases. If a records reviewer hails from the valley, he or she may be evaluating records from other places based on experiences and expectations from the wrong part of the region.
For example, if we look at Cassin’s Vireo occurrences in Oregon. This species is invariably noted earlier in the Willamette Valley than elsewhere.
Cassin’s Vireo is rare in Clatsop County, but when it is noted, there is an obvious lag. Cassin’s Vireo detections in Clatsop County are probably an artifact of spill-over birds at the peak of migration. One would not get a particularly good picture of the leading edge of Cassin’s Vireo migration from Clatsop County data and folks from the Valley would be quick to correct me if I tried to claim valley Cassin’s Vireos were early based on experiences on my home turf.
This brings us to Hermit Warbler. I reported Hermit Warbler from Coxcomb Hill twice this week. I reported them to eBird where they are listed as rare. The reviewer asked me for details on the first report. I expect to start finding Hermit Warblers at Coxcomb Hill and Shively Park here in Astoria beginning in mid-April. It didn’t occur to me that others might think this was early, and was a bit surprised when the reviewer said the bird I saw was too early and asked for details. Then again, I am probably the only person looking for Hermit Warblers in Clatsop County in the second week in April. They nest 5 blocks from my house. They are the most common forest warbler in the county during the breeding season. My experience level with Hermit Warblers is almost certainly different than that of the eBird reviewer. HE WAS NOT WRONG TO ASK.
I went out the next day and easily found another singing bird too far up in the treetops to photograph, but my camera can record sounds.
If you don’t own a copy of Stephenson and Whittle’s Warbler Guide (2013) that sonogram probably won’t mean much to you, but this guide is full of, among other things, comparative sonograms of every warbler in North America. I know Hermit Warblers when I hear them, but producing a recording and a sonogram now means you (and the eBird reviewer) don’t have to take my word for it. We have a really good reference on the book shelf.
If we look at the eBird abundance graph for Hermit Warblers, it turns out that Hermit Warblers are much more abundant along the North Coast and appear to arrive at least a week earlier than they do in the Willamette Valley based on current data.
One might even argue that Valley detections are (perhaps) an artifact of spillover during peak spring movements through the Coast and Cascade Ranges in the same way that Cassin’s Vireo detections in Clatsop County represent spillover as birds move through more vireo friendly habitat in the Valley. That argument is, at this point, entirely hypothetical. The only way to get a proper answer is to collect real data. So, if you think you’ve seen or heard a bird too early for the experts, take a picture, record a song, collect some evidence.
My experience in the field means something, but so does the experience of other people in other parts of the State many of whom have taken on the irksome task of reviewing data. At the end of the day, reality still hangs on the quality of the data we provide not our credentials or our age in birder-years.