Thursday, August 30, 2012

Solving a Warbler Mystery

Well,after a long layoff, I'm finally back. Over the last several months I've spent some time out of town working and doing things just not associated with birding. It was always my plan after the big year to take some time off and focus on non-birding related activities but now that fall migration is in full swing, I'm back. 

I was prompted to write this article by a birding friend of mine who sent me several photos of a 'mystery' warbler. Mostly the bird was a mystery because the photos were quite blurry,but this is often the case with fall warblers, especially the more furtive species. So, my purpose for writing this is twofold. Firstly, I'll seek to identify the mystery warbler and in doing so I'll provide reasoning to support my conclusion. Along the way, I'll also try to shed some light on fall warbler identification in general and outline a basic approach for tackling such problematic birds.

 So lets get right to it. Below you will see several photos, none of which are clear and none of which show the entire bird. In order to even begin to identify this bird we need to put the pieces of the puzzle together. I'm not sure the identification would have been possible if any one of these photos were missing,since all of them provide vital clues. Lets look at each photo separately and work towards an identification, ruling some species out along the way.
At first look this photo might useless,since its just a blur. While it doesn't show any plumage detail it does give us some critical information about the birds general shape,posture and color.The bird appears to be greenish above, rich yellow below and having a grey head. Its a profile view and no wing bars are visible, but the photo is so blurry that I'm not sure they would show up, so this is at most circumstantial. I think the large yellow spot on the rump is an out of focus leaf or some type of reflection,since it intersects the wing and just doesn't look quite right.Here are the key features to take from this photo

- green above
-yellow below
- greyish head
- upright posture
 -probably lacking wing bars

 Using this list we can already rule out most species and create a list of possible species including;
1) Mourning Warbler
2) Connecticut Warbler
3) Macgilivary's Warbler
4) Nashville Warbler
5) Orange-crowned Warbler
6) Magnolia Warbler

 So let's keep these possibilities in mind as we move to the next 3 photos.




This photo adds some more pieces to the puzzle.In this photo we can clearly see the bird does indeed have a olive/grey hood. It also appears to have a broken eye ring, with a darkish line through the eye. The photo is still pretty blurry so again this feature is only useful in combination with other characters. We can also see what looks like an odd yellowish spot between the eye and the bill. This is quite strange doesn't really seem to mesh with any of the possibilities we outlined above!Also, worth noting is the yellow undertail coverts and a thickish looking all green undertail,lacking tail spots.Also, the bill appears somewhat thick (as warblers go),but this can be misleading in a blurry photo,but it sure doesn't look needle thin.

 Once again the bird is standing quite upright and to me at least the legs appear as though they are pale.Leg color is a critical detail and useful in the separation of some very similar species

.So,to recap we know that the mystery bird is; - green above -yellow below - greyish head - upright posture -probably lacking wing bars - has a broken eye ring with what appears to be a dark eye line - seems to have an odd yellowish spot in the lores or supra loral area - yellow undertail coverts - green undertail feathers-lacking tail spots


When I first saw this photo it confused me. The bird seems to have a pale supercilium and a dark eye line. This didn't fit with the species I had in mind at the time,until I gave it some thought.The yellow throat was a key piece of information though. In fact, after seeing the first two photos, this photo that initially confused me pretty much clinched the identification. So, to the above list we can add what looks like a pale supercilium and a yellow throat.



Again at first look this photo might seem useless. Actually it took me a second to even realize what I was looking at when I saw this photo initially. Then after a couple of seconds the birds head revealed itself and if you look hard enough you can see the broken eye ring,at least on the bottom of the eye.That's pretty much all I took from this photo.

Now that we've gathered all our evidence and created a list of possible suspects its time to start narrowing things down a bit. To aid this process we'll make use of some background information as well. I'll break down the list one by one until we arrive at the identification.

 1)Connecticut Warbler- There are three records for Newfoundland, all in late September. This bird is rarely seen in the east before mid to late September, this is a big strike against this bird.If that wasn't enough the lack of a thick,bold eye ring and the presence of a bright yellow throat rule this species out.

 2) Macgillivary's Warbler- Western Species that is extremely rare in the east. When it does appear it generally does so in late fall. There aren't any records for Newfoundland. While this makes this species unlikely it isn't enough to rule it out. However,I'd expect even an immature Magillivary's to show a much more defined split eye ring and should not show a yellow throat. The adults of course have a dark grey,backish throat and the immatures have a whitish throat, but never yellow.

3) Nashville Warbler- a very uncommon breeder in Newfoundland, but a few do turn up every fall. The greyish head, green above yellow below with yellow throat do match this species, so maybe that's it! Not so quick. Nashville Warblers have a VERY bold eyering,they also have black legs and a very fine, pointed bill.They also,never show any kind of dark eye line. So you can check that off too.

 4) Orange-crowned Warbler- This bird could superficially resemble an OCWA. The greyish head, with split eye ring, dark eye line actually are very good OCWA characters, however that's where the resemblence ends. Orange-crowned Warblers are late migrants and the few that do turn up in Newfoundland every year do so usually in October or later, maybe early as late September. Again its not impossible that one could turn up here in August, but this bird is just too bright below for an OCWA. Also the posture doesn't look quite right and the apparent pale legs are also wrong for this species...moving on.

 5) Magnolia Warbler- A common breeder and routine in late summer/fall in eastern Newfoundland,so a good start. However,its just clear that this bird is not a Magnolia Warbler. We have to look no further than the under side of this birds tail to give us all the information we need. Magnolia Warblers have white under tail coverts and a unique black and white pattern on the under side of their tail feathers. This bird clearly has yellow under tail coverts and green under side of the tail feathers.So after all of this deducing, we are left with a single possibility, Mourning Warbler.So lets consider that.

 Mourning Warbler is a common breeder in parts of Newfoundland and a patchy breeder in the east. They are seen with some regularity in the alder beds on of eastern Newfoundland in late summer and the first half of September. As well, all of the characters list above fit we will with this species. It is green above, yellow below and lacks wing bars. It has yellow under tail coverts and green underside to its tail feathers,lacking tail spots. It spends much time walking and often has an upright posture,it has pale pink legs and as other members of the genus Opornis, it has quite a thick bill for a warbler.As well, immatures of this species do show a moderate,split eye ring, with a dark eye line. There is also often a yellowish line running above the lore,in immatures,which is somewhat reminiscent of Kentucky Warbler. In a couple of the photos above there is a yellowish area in front of the eye and I think its explained by this feature, but looks larger because the photo is blurred. Look at the web photo below for an example of what I'm referring to. This is not a character that you see talked about in field guides, but is clearly present.



As you can see there is much to consider when making these identifications and while it took quite some time to present this reasoning here,the exact same method is employed, to make split second identifications in the field. The more you practice the quicker you get at making such evaluations on the spot.

If you would like to get some insight into using this type of reasoning to identify fall warblers, I'll be holding a fall warbler identification workshop on either Sept 8th or 9th. It will be 3-4 hours and will include my usual power point slide show. I'll be breaking down all the look alike and confusion species. Space is limited and the registration fee is $50. If you interested contact me at dave.browneATgmail.com to reserve your spot.

1 comment:

  1. This was posted hastily and there are undoubtedly grammatical and spelling errors. I'll get around to proof reading later, so please forgive me ;)

    ReplyDelete