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Happening NOW: Palm Warbler Fest in Colorado

By Dean Shoup

Something is going on with Palm Warblers in Colorado this fall of 2018. The species is a regular visitor to Colorado in the fall, with scattered reports every year. But 2018 has been a crazy banner year for the species. The nearest year in recent times with a similar irruption was 2012, but nothing close to what is happening right now in the state.

After doing a bit of data mining in eBird, I have found that this regional occurrence is restricted to Colorado and not happening in the nearby regions of Wyoming, western Nebraska, western Kansas, the Oklahoma panhandle, or New Mexico. Perhaps a little history of the species based on eBird data would shed a little light on what has occurred leading up to this influx of Palm Warblers in the fall. Going back in time, 2017 had only six reports of the species in Colorado with hardly any in the aforementioned other regions. In 2016, there were ca. 12 reports, mostly in the Front Range region of Colorado, with the nearest cluster of multiple sightings being in the Kansas City, Missouri, area, at the edge of its typical range on fall migration. With the exception of one report in western Nebraska, the nearby regions did not report the species at all in 2016. In 2015, the state only had a total of three reports for the season with two being in the Front Range and one on the eastern plains.

This Palm Warbler (Western) Setophaga palmarum palmarum seen here 24 November in Jefferson at South Platte Park-South Platte Reservoir was one of many birds in the area this season. It has been seen by many for over a week at this local hot spot. Photograph by Glenn Walbek.

Out of the five neighboring regions, only one report came in that year—from Wyoming. In 2014, Colorado had only two reports of Palm Warbler for the entire season. Neighboring states reported zero in Wyoming, two in western Nebraska, one in central Kansas, zero in the Oklahoma panhandle, and two in the state of New Mexico. A broader look at the region for all years shows that Wyoming has had a total of six reports with one coming from 2018. The panhandle region of Nebraska has had five with one in 2018. The southwestern corner of Kansas has had only three reports from 1993 to 2017. The panhandle of Oklahoma has had just one report coming from 2017. Over the years, from 1996 to 2018, New Mexico has reported the species from six different locations. One particular hot spot in New Mexico has been Melrose Woods in Roosevelt County. From 1996 to 2018 there have been 15 reports at this location, with two being from 2018. To recap, the recent totals for 2018 in nearby regions: We have had one in Wyoming, one in the Nebraska panhandle, zero in w. Kansas, zero in the Oklahoma panhandle, and two in New Mexico.

Now back to Colorado. Going back over the past ten years, as well as all years combined, the fall of 2012 jumped out as the last and maybe only other banner year for the species. This was determined by mining eBird data using the bar charts feature and utilizing the frequency charts. Although frequency charts can be somewhat misleading on their own, when combined with other data, including totals from all checklists, they can put things into perspective better. For example, in 2012, Palm Warbler was reported on 2.9% of all checklists submitted from August–November, with a total of 19 birds coming from 21 reports. In 2018, we had a lower percentage of 1.8% from all checklists, but the totals have been 37+ birds from a staggering number of locations–at least 34 in the state. (The imprecision is due to a bit of ambiguity in how eBirders report locations.) In any event, this phenomenon is without recent precedent.

While most reports are of the expected palmarum (“Western”) subspecies, 2018 brought at least two reports of the rarer hypochrysea (Yellow or Eastern subspecies). San Miguel County in the mountainous southwestern region of the state, which rarely reports any type of eastern warbler, had two reports this fall—one from the ski town of Telluride, and one from remote Miramonte Reservoir. The mountain town of Buena Vista in Chaffee County got in on the fun with two birds seen at a local coffee shop. At this point, it really feels like Palm Warbler is being found everywhere in Colorado this fall, not just the typical Front Range and e. plains locales. Also interesting is that there have been reports with multiple birds in various locations.

At left is a screenshot of eBird Palm Warbler sightings for all years in Colorado taken on 30 November 2018; focusing on the Front Range, where most sightings typically occur in the state. Some of the blue pins as well as all of the red are from 2018.

As the reports started coming in, starting with one from Colorado Springs, they seemed typical. With six reports being received by the end of September, it seemed like a more-or-less normal year. Beginning in October we began to see an increase, with reports from 16 different locations. By November, Palm Warblers seemed to be falling out of the sky everywhere. Birders started wondering what was going on with so many reports seeming to flow in from everywhere, and with multiple birds at some locations. Typical high counts were only of two birds at any one location, but this happened multiple times throughout the state, not typical for any year.

By the end of November, Colorado had piled up well over 30 different reports of Palm Warbler, and the trend continues.  As I am writing this report, I took a quick look at the rare bird alert for the day to find that yet another Palm Warbler (Western) has been reported in the Denver suburb of Littleton in Arapahoe County here on December 1st, as well as a report of two from Pueblo County. Maybe this trend will continue through the winter months? At this time I am not sure why this is happening this particular year. 2012 was also a good year; perhaps there were similar conditions that were also occurring that year? Palm Warbler typically winters with some regularity on the West Coast.  Are the wildfires in CA pushing the species further east? There are similarities in the data from 2012 compared to 2018. In 2012, there were a series of 7,950 wildfires across the state burning a total of 869,599 acres, including the massive Rush Fire, which was the third largest wildfire for the state in modern times.

For 2018, the wildfire season has been the most destructive on record, with a similar number of 7,579 fires, but burning a larger total of 1,667,855 acres. This may or may not be the reason for the influx of Palm Warbler as CA experiences many wildfires every year. Could it be the timing of the fires during fall migration that causes the shift?  It is hard to know for sure the answer. The species does seem to like the Front Range on an annual basis, but the numbers in 2018 have eclipsed all previous records and have included some County firsts.  It will be interesting to see in the years to come if this is a trend that will continue, or are we having a one off, banner year of Palm Warbler in Colorado?

In talking with birders who have been active in the state for 30 years or more, Palm Warbler had been a bird that you found after many years of birding; it wasn’t a given species for the state.  It took lots of time in the field and effort to find, especially in the pre eBird era. Even in the age of eBird reporting, Palm Warbler is not a given find for avid listers. If Palm Warbler was a bird you needed for the state, this was the year to find or chase one.  Let the Palm Warbler Fest continue!

Corrigendum: The text has been changed in two places for clarity regarding the number of birds and locations reported via eBird. Thanks to Andy Bankert for his careful read and for catching the sections that were unclear. (Dec. 7, 2018)

  • Dean Shoup is a North American Birds regional reviewer for Colorado-Wyoming.
Happening NOW is an ongoing series of posts highlighting bird population phenomena of broad interest to birders and field ornithologists across the continent. Full analysis will appear in print in the ABA’s North American Birds journal. To learn more or to subscribe, please go online: http://publications.aba.org/north-american-birds/
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