Date: 11/7/18 5:18 am From: Matt Bartels <mattxyz...> Subject: [Tweeters] Follow up on summer [not] Alder Flycatcher in Skagit County - WBRC deliberations
Hi Tweeters -
I’ve heard from some folks asking for more detail about one of our recent decisions from the Fall 2018 Washington Bird Records Committee <http://wos.org/records/votingsummary/fall-2018/>. Here’s a little follow up. For those not interested in getting into the weeds, better to skip this message!
The committee voted not to accept the Skagit County bird reported as an Alder Flycatcher originally. This bird was present from 24 June - 11 July and widely discussed on Tweeters & eBird at the time.
After some recordings were made, the some committee members began to have doubts about the id. We then reached out to some experts to gain insight into the identity of this bird. Their comments came back with comments that pointed to a potential hybrid Alder/Willow Flycatcher, [“Traill’s Flycatcher” in past eras] rather than a full Alder. In some ways, a hybrid is even more rare than a ‘pure’ Alder. They just aren’t documented very often.
For easy reference, here are comments from Arch McCallum, noted expert on the Traill’s Flycatcher complex and Tayler Brooks, of Cornell Labs:
… The three sounds on the Pullen cut are not typical of any standard vocalization of either Alder or Willow,
or for that matter, White-throated, known to me.
These sounds are aberrant, and the bird could be, probably is, a hybrid. Hybrids are great, because they help us figure out homologies. Which of the three Willow song-types are homologous with Alder's "Feebeeo?" I don't as yet have any ideas for how this sample helps us answer that question, partly because it's Alder-like.
The two-note songs most resemble Feebeeo. The first note rises too high and the second note ends too soon, but they are more like Feebeeo than any other vocalization in either repertoire.
On every cut the bird sang either the two-note song, or occasionally the one-note song. The lack of variety is the second point in favor of Alder.
A third point would be the presence of a frequently used Pip call, although Willows occasionally use this sound.
A fourth point would be the frequent use of the Double-Peak call, which Alders use a lot and Willows seldom use. I hope someone will get out there with professional recording equipment and get some long cuts. Even if it is a hybrid, Cornell should be happy to have good material from a hybrid.
So, he has Alder genes, he's just not a "good" Alder, and therefore probably not a "pure" Alder.
When you listen to the anonymous eBirder's recording (ML106786991), do you hear WIFLs calling in the background as well? Looking at the calls at 10 and 19 seconds in particular, these calls are a closer match for some of WIFL's 'pip' calls than ALFL. WIFL pips are longer, but span a similar range of frequencies, so on the spectrogram they look like a shallower upside down V shape. ALFLs pips are shorter, so look more sharply peaked. There are in fact a few more sharply peaked 'pip' calls in this same recording, but can we be sure all the 'pip' calls in this person's recording are all coming from the same bird?
In your recording (ML106806261), the oddness continues showing a few more intermediate characteristics between what is typical for ALFL/WIFL to my eyes. I think the specific vocalization in this recording is the ALFL "zweeoo" call, #6 in the McCallum's reference site I sent earlier. As you can see for ALFL, the call begins with deep modulation before becoming clear in the second half of the call, creating an overslurred effect. The second call in this clip is the weird one, seeming as if the call nearly becomes disyllabic midway through. Instead of being a cleanly arching overslur, there's a kink at the top of the overslur. WIFL's version of the 'zweeoo' call (#5 in McCallum's reference) is disyllabic. With other putative hybrid tyrannids I've seen recordings of, a recurring theme in extended recordings of these birds is that they give a mixture of calls that sound pretty typical of one of their parents, combined with some calls that show intermediate characteristics the two parent species. That might be going on there, but that's hard to tell.
Overall, there was enough consistent doubt about the identity of this bird to prevent acceptance as a solid Alder Flycatcher. As one of the people who listened to this bird and thought I was hearing Alder too, it was a great learning experience to hear from these experts and gain better insight into the difficulty this species id entails.
Sorry for everyone removing a species from their lists, and I hope this has been a little informative.