Do you use eBird? Do you routinely bird in South Central Wisconsin? If you answered yes to both of these questions then please keep reading!
The Wisconsin eBird Team has been hard at work with a massive revision of all the filters for the state. I recently finished the South Filter (Columbia, Dane, Green, Iowa, Jefferson, Lafayette, Richland, Rock, Sauk, Walworth, and Waukesha Counties). Most species in this region are less likely to be flagged after the revision, but for a handful of species the filter was tightened.
What is likely to be flagged and require documentation? The short answer is anything rare plus a few species that are routinely vexing when it comes to identification.
So what does “rare” mean? Rare can mean a species that rarely ventures into the state—think Vermillion Flycatcher. Rare can also mean out of season—for example an early-April Hooded Warbler or a Baltimore Oriole in December. Rare can also mean, extremely high concentrations of a common species at a single location—a recent observation of 4000 Ruddy Ducks on Lake Koshkonong comes to mind.
In some cases you may report a relatively common species and be surprised that you are asked to provide documentation. If you dig a bit further (check out the eBird Bar Charts for the South Filter Region, or the WSO Arrival and Departure Dates) you are likely to discover you’ve observed a bird that is nearly record late or record early.
Early this fall Red Crossbill required documentation on the South Filter. Until this year, it was rarely observed in Southern Wisconsin away from Lake Michigan. As the wave of Red Crossbills continued the eBird team decided to relax the filter for this species. So, while I claimed earlier that the South Filter is “finished” this is not entirely accurate. Due to the idiosyncrasies of each year’s migration or irruptions the filters will require occasional tweaks.
So… for what species was the filter tightened?
1) Trumpeter vs. Tundra Swan—the filters are not exceptionally tight on this species pair, but this is a tough id when the birds are distant and silent. When you observe distant swans and you keep going back and forth on the id consider using Trumpeter/Tundra Swan.
2) Greater Scaup—often a tough identification. This bird is rare but regular in the South Filter Region. Field guide range maps show both Lesser and Greater Scaup migrating through the interior of the state, which is accurate, but Lessers outnumber Greaters by an overwhelming margin away from the Great Lakes. In the past the filter on this species was lax. Many checklists were submitted with Greater Scaup, but no Lesser Scaup. Was this the intention of the observer? An accidental click of the mouse? A misidentification? Due to the difficulty of answering these questions without any documentation, we will be asking for more comments on all Greater Scaup observations in the South Filter Region.
3) Sharp-shinned Hawk—the South Filter Region is south of the primary breeding range for this species. Reports of this species hunting in late June-July around backyard bird feeders are much more likely attributed to small, male Cooper’s Hawks.
4) Godwits in Late May—Both Godwits have occurred after May 15th in the South Filter Region, but Hudsonian Godwit is overwhelmingly more likely to occur past this date. Birders in the South Filter Region are more likely to find Marbled Godwits between April 15th and May 1st than May 15th and June 1st. An analysis of the Marbled Godwit eBird map for May and June, shows only two distinct observations after May 15th (Note: There are a number of observations at Harvey Road in ’08, but these were likely the same group of birds that lingered for an extended period of time). Observations of “Hudwits” after May 15th are far more numerous. I think female plumaged Hudsonian Godwit vs. Marbled Godwit is an underappreciated id challenge—perhaps more challenging for those that use the Sibley Guide (on p. 177 the breeding plumaged female Hudsonian is depicted at about ¼ the size of the breeding plumaged male—making this plumage option easy to overlook).
5) Common Terns (in any month except May)—During May in the early to late 1960’s William Hilsenhoff was routinely reporting 15-40 Common Terns in Dane and Columbia Counties. Sadly this species has experienced a significant population decline (it was listed as a state endangered species in 1979). Now, inland birders are lucky to see this species at all. Finding 10 or more Common Terns in the South Filter Region has only occurred once in the eBird data set since the late 60’s.
During May, Common Terns continue to be rare but regular in the South Filter Region. Outside of May, there is, at best, one Common Tern observation every 5 years. Due to their rarity and potential for confusion with Forster’s Tern, all Common Terns observed outside of May will require documentation in the South Filter Region.
Forster’s Terns are the “common” sterna tern in our region and observers reporting Common Terns should carefully note field marks which rule out Forster’s. See the ID article on this here.
In May and late Sept−October area birders should also be on the watch for Arctic Tern, which is likely to be found associating with groups of Common Terns near larger bodies of water. At this time there are no Arctic Tern records for the South Filter Region in the eBird database.
Alder, Yellow-bellied and Olive-sided Flycatchers are late migrants with peak migration occurring near the end of May.
Notice the lack of a fall “peak” for Alder Flycatcher. Does this truly reflect their migratory pattern or does this reflect the difficulty associated with identifying this species in fall? The new filter will require better documentation of fall empids—helping us answer these questions.
Rarely are these late-migrating flycatchers observed in early May. April records are virtually nonexistent.
Finally, Olive-sided Flycatchers are typically solitary during migration, so claims of 3 or more different individuals at one location are unusual and will require documentation.
7) Cerulean Warbler & Louisiana Waterthrush in August through September—Based on the eBIrd data, the bulk of the population for both of these warbler species departs Wisconsin before August 1st. Thus records from late July through September, which did not require documentation in the past will now be flagged. Descriptions of Louisiana Waterthrush should rule out the sister species—Northern Waterthrush.
8) Nelson’s and Le Conte’s Sparrows—In the South Filter Region these two species are typically found from late September through early November. Spring records are very rare. Nelson’s is typically observed from late September through the first week of October, while Le Conte’s is more likely in October-early November. Due to the similar plumage and skulking nature of these two species this can be a difficult identification. Juveniles are often observed in fall, which adds to the difficulty associated with identifying these ammodramus species. When you observe a LeConte’s or Nelson’s Sparrow please briefly explain how you ruled out the sister species.
9) Rusty and Brewer’s Blackbirds—Again, a species pair which poses an identification challenge. Rusty Blackbird, while declining, is the more common species in every season except summer. Brewer’s Blackbirds are, at best, uncommon during migration and rare summer residents nesting on large prairies/grasslands (e.g. Zeloski Marsh in Jefferson Co.). Rusty Blackbirds are more likely to attempt to over-winter—a handful of January records compared to none for Brewer’s. Rusty’s also are more likely to be observed in November through December.
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Text by Aaron Stutz