Tuesday, August 26, 2014
A Last Outing? - 24 Aug 2014
Caleb Putnam provided a very nice reasoning for hedging against calling these birds anything other than Plegadis ibis: I accidentally implied in my description that the lack of red/pink tones in the eye, facial skin, and legs, eliminated White-faced Ibis (WFIB), but want to clarify that this is false and my description was poorly worded. What I should have said was that my ID as GLIB was based first and foremost on the presence of two bluish stripes on the facial skin of all three birds, in the classic adult GLIB pattern (I can find no evidence that WFIB ever shows this, and much evidence that HY GLIB often [but not always] does), and secondarily on the lack of pink/red in the bird's eye, facial skin, and legs. The latter field mark doesn’t eliminate the possibility of a WFIB or hybrid, but it is necessary to establish this before calling any hatching-year bird a GLIB. In other words, if a HY ibis shows red in the eye or facial skin, GLIB is out, and if it lacks it, the discussion continues, but it is not yet clinched as GLIB. The bird must then match the classic face pattern of adult GLIB before one can call it. As for the sticky issue of hybrid Glossy X White-faced Ibises, which are rare but well known, including from this location: the literature on identifying these birds as HYs is scanty, as few (no?) known-identity birds have been tracked from the nest to adulthood. HY WFIB show at most one, non-blue upper facial skin stripe, often pink, and no lower stripe, so pure WFIB are eliminated. It is probably not possible to state with 100% certainty that hybridization can be eliminated, but the lack of any intermediate traits supports the stance for pure GLIB. If these birds showed very diffuse lower stripes, or lacked them completely, I’d be inclined to identify them as *Plegadis* ibises. Instead, the features we have are consistent with the literature for HY GLIB, so I don't see any need to invoke the hybrid possibility. If future studies show that pure WFIB or WFIB X GLIB can show the classic adult GLIB face pattern, I would revoke my ID. Finally, I want to implore others to study these birds, and the literature, and to make their own conclusions (in other words: don’t just eBird these based on someone else’s opinion). I was really glad to see many careful descriptions, a lot of ID hedging, and several eBird checklists with these birds listed as GLIB/WFIB. But regardless of which category you use (Glossy, White-faced, Glossy/White-faced, or Glossy X White-faced), these are all Michigan review species. So, I encourage everyone to submit a written description and/or photos of these birds to the MBRC – don’t assume that others will, as that’s usually not the case! Photographs, especially under the conditions at Mouillee, often don't cut it, and I know from experience that voting members often rely heavily, or even solely, on written descriptions to evaluate certain key field marks. In this case, there appear to be good photos surfacing, but so far apparently only for one or two of the three birds. Anyway, here’s a link to a template for the MBRC’s rare bird report form:
Should this be my last outing before the end of August, I'll just say that Pt. Mouillee SGA has provided some wonderful memories this year! We'll see you again when the weather gets cold...