Monday, December 31, 2007

What are the odds?

Part 1:

On 6 December 2007 at about 8PM, in the midst of an intense winter storm, a resident of Lilllooet, BC heard a thump on their front door. Thinking the dog wanted to come in, they opened the door to find a strange bird lying on the front porch. It later died despite their best efforts, and it turns out to be a Cook's Petrel (although similar species still need to be ruled out)! This is the first for BC and for Canada.

Lillooet is west of Kamloops, in southern interior BC. It is over 100 miles to the nearest salt water, and at least 250 miles to the nearest open ocean where a Cook's Petrel would be "comfortable". How many were blown into BC and simply perished in bogs and lakes? Maybe only one, but what are the odds that the only one happened to crash into the front door of a house? And on top of that a house where the residents would take enough interest to report it?

Part 2:

In early December 2007 it was reported on the OregonBirds listserv that a Jacksnipe had been shot by a hunter in November - a first record for Oregon and only the 6th for North America of this secretive and cryptic species. But then it was discovered that the same hunter shot a Jacksnipe in the same area of coastal Oregon in late October 2004 , making this the 7th for North America.

How many other Jacksnipes have been shot and never reported? How many are wintering along the Pacific coast of North America? Maybe none. But what are the odds that one snipe-hunter, in a single patch of coastal Oregon, could personally find about one-third of all the North American records of this species?

Part 3:

On 23 December 2007 I went on one of my infrequent birding trips to Cape Ann, Massachusetts with my son and two friends. I was aware of recent Slaty-backed Gulls in Illinois and Pennsylvania, so my expectations were up, but it was still a shock to see a Slaty-backed Gull in Gloucester Harbor - the first ever for Massachusetts. I even thought that "the" bird an hour later had a very different looking bill color, and the next day Rick Heil was able to confirm that there were indeed two Slaty-backed Gulls in Gloucester. Most amazing, just an hour or so after I saw the first one in Gloucester, Wayne Petersen and Dave Larsen found another individual on Cape Cod (they thought they had a first state record, only to find that theirs was the second ... or third, by a matter of minutes - Ouch!).

How many other Slaty-backed Gulls are scattered around the eastern US? Maybe only these few. But what are the odds that the very-thoroughly-birded state of Massachusetts would suddenly have three records? Interestingly, at Gloucester and Cape Cod, the Slaty-backeds coincided with an unprecedented invasion of hundreds of Bohemian Waxwings. It seems bizarre to even suggest that movements of these species are related, but could it be just a coincidence?


And now we enter a new year filled with possibilities....

Thursday, December 6, 2007

Calendars and columns

I was in Washington DC recently and signed some calendars at my cousin's flower shop in Mount Airy, Maryland. So if you've been thinking about getting a calendar and you'd like one that I've signed, you can order them here.

And my new Birder's World column about identifying songbirds by flocking habits is now available online here.

Perspective on a mystery bird

Our perspective and the assumptions and decisions that are triggered by that point-of-view, strongly influence how we perceive the world around us. In short, what we see often depends on how we look at it.

This classic drawing looks like a frog sitting on the edge of a pond...

but rotate it ninety degrees and it turns into a horse's head!

This horse/frog drawing comes from a generic internet source and I assume it is public domain.
If not please let me know, and if anyone knows the artist or original source I'd like to give credit.

We can all remember times when we've experienced this kind of perceptual flip-flop in real life, insisting one thing is correct only to realize in a flash that our underlying assumptions - and our conclusions - were wrong. It certainly comes up a lot in bird identification. A flash of what "could only be" a male Yellow-headed Blackbird resolves into a Common Grackle holding a corn chip; or a carefully-studied Western Sandpiper turns into a Dunlin when it walks next to a much smaller Least.

Clear photographic examples of this are rare, but one such example is this mysterious photo of an apparently black-faced bird taken in late September 2007 by an automatic Wingscapes birdcam and discussed on the Birdcouple blog, with most viewers suggesting either a Carolina Chickadee or a Common Redstart (a Eurasian species not previously recorded in North America).

Photo by Warren and Lisa Strobel. Used by permission.

We probably all look at this picture and assume, quite reasonably, that the bird is holding it's head in a normal position looking to the left and slightly down. And in the image below I've zoomed in and taken the liberty of adding the outline of an eye in about the right position to fit this assumption. In this case the pattern of black face, pale crown, pinkish-buff underside, etc. is a pretty good match for Common Redstart. There are lots of details that are not quite right, some of which have been mentioned in comments with the original blog post. Many experienced birders will notice the details, or simply note that the location is very unlikely for Common Redstart, and will step back to look for another explanation. (If you think the eye looks like it isn't in quite the right place, I can assure you that I moved it around in photoshop and this was the best placement I could find. The eye just doesn't fit this way, which is another clue that the black pattern and head shape is not right for Redstart.)

Below, again, I've taken the liberty of adding a dark spot, this time to show where I think the eye actually is (and a helpful arrow to point it out). I think the head is rotated ninety degrees and the bird is looking up at the sky with one eye, so we're seeing the black throat, and the white band on the upper edge of the head is the "cheek". With the eye in this position the bird's head plumage is a perfect match for Carolina Chickadee. Other details also fit and give no reason to question the ID, and the species is common in the area where the photo was taken.

So I agree completely with the few respondents who have already suggested that this bird is a Carolina Chickadee with its head turned. This particular identification pitfall might never come up in field observations, when we would be able to see the bird move and quickly correct our error, but lots of similar things do happen under field conditions. This story demonstrates that there are nearly infinite possibilities for misidentification, and shows how one misleading glimpse can trigger assumptions that set us firmly onto the wrong path.

Tuesday, December 4, 2007

Redpoll subspecies

If identifying Hoary Redpoll is not enough of a challenge for you, maybe you'd like to look for subspecies of Hoary and Common Redpolls?

First, check out this map from the Canadian Atlas of Bird Banding.

This shows selected western band recoveries of Common Redpolls, and the obvious suggestion is that some of the Common Redpolls being seen in the east right now might be coming from Alaska! Troy (1983) shows a map with a similar pattern, including a redpoll that traveled from New Hampshire to Barrow, Alaska, and another that traveled from Michigan to Siberia. Lots of redpolls also come to the eastern US from the north or northeast, but we should not assume that we are only seeing redpolls from the nearby subarctic regions.

Both species of redpoll are represented in Greenland and Baffin Island by larger and more distinctive subspecies. These "Greenland" Hoary Redpolls are large and very pale, while the "Greenland" Common Redpolls are large and dark. An excellent summary of status and identification is in Pittaway (1992). Greater Common Redpoll can appear in the eastern US in significant numbers some winters, outnumbering Hoary (Pittaway 1992, Wetherbee 1937). Hornemann's Hoary Redpoll is the rarest subspecies in the US, but has been recorded at least south to Maryland and west to Michigan.

Common Redpoll Carduelis flammea
Southern C. f. flammea
Greenland (Greater) C. f. rostrata

Greater is distinguished from Southern by:

  • larger size
  • darker color
  • larger bill with curved (bulging) culmen
  • said to have more upright posture and harsher calls
Hoary Redpoll Carduelis hornemanni

Southern C. h. exilipes
Greenland (Hornemann's) C. h. hornemanni

Hornemann's is distinguished from Southern by:
  • larger size
  • even paler color
Some photos and discussion of Greater Common Redpolls from Toronto already this winter are available here. And a detailed discussion with photos of specimens by the Maryland/District of Columbia Records Commmittee is here (beginning on page 16).

Other references:
Pittaway, R. 1992. Recognizable Forms: Redpolls. Ontario Birds 10(3): 108-114

Troy, D. M. 1983. Recaptures of Redpolls: Movements of an Irruptive species. J. Field Ornithol., 54: 146-151.

Saturday, December 1, 2007

Redpoll Identification

Some updates 4 and 6 December -
check out Jochen's comments and blog post here

With the predicted superflight of finches beginning to develop (1st ever Common Redpoll in New Mexico last week) more and more questions are coming up about finch identification.

Hoary Redpoll, although always less numerous than Common south of the Arctic, is probably more numerous than reports indicate. Identification is very difficult, requiring close and lengthy study, and observers are usually conservative on this ID, so lots of darker Hoarys are never even picked out, possible Hoarys are never confirmed, and lots of passing flocks are simply reported as Commons (1).

If you have a chance to study some redpolls and want to look for Hoary, here are some tips:
  1. The first step is simply to scan the group looking for a paler bird. But by just looking through a flock for paler color you will miss a lot of Hoary Redpolls. With practice you should begin to look for the specific types of paleness listed below - a "frosty" look to the upperparts or wings, a whiter breast, a pale rump, etc.
  2. Once you've found a pale redpoll, check the breast color - If it has pink on the breast it's a male (most 1st winter males have pink on the breast according to Pyle 1997), and identification of males is generally a little easier, but since males of both species tend to be paler than females, a male Common can often stand out as the palest bird in the flock. A male Hoary should look really pale. If there is no pink it's a female (or possibly an immature male), and identification will be more challenging, but since females of both species tend to be darker than the males, the fact that you've picked out a pale female from the flock is promising.
Then check details in no particular order, depending on what part of the bird you can see well, and try to make direct comparisons with birds of the same plumage type:
  • the scapulars should be paler with frosty whitish edges on Hoary
  • flank streaking should be sparse and narrow on Hoary
  • undertail coverts should be white or with only narrow streaks on Hoary (female Hoary often have narrow shaft streaks not as broad as on Commons, and male Common can have no streaks)
  • rump should be mostly white on Hoary, whiter on males (but male Commons can also have a noticeably pale rump)
  • the bill should look short and small, with fluffy nasal bristles covering the base of the upper mandible and making the forehead bulge a bit (but Commons also have tiny bills, you have to study some Commons at close range before you will feel confident using this feature)
  • The pale edges on the wing coverts and secondaries should be broader and whiter on Hoary (but this is variable in both species and, as with all of these clues, it's important to compare birds of the same sex) (2)
If most of these features line up with Hoary, I think it's safe to make the call. It's still subjective and really tough, so it's best to look at a lot of redpolls and get a sense of the variation before you start labeling them, but it looks like there may be plenty of redpolls to practice on this winter!

At this link you can see photos of a recent Hoary and accompanying Commons in Indiana by Peter Grube, showing the features well.

Good luck!

1) A reader suggests that many people are not as conservative as perhaps they should be, and simply slap the "Hoary" label on any noticeably pale redpoll. I agree, but I also think that many true Hoarys are overlooked, so it may actually be that many birds reported as Hoarys are not, but an equal or greater number of real Hoarys are overlooked!

2) Other features that have been mentioned and that might be worth watching for and testing (but many of these are very subjective and my impression currently is that these are less useful than the ones mentioned above):
  • a smaller and brighter red "poll" on the forehead of Hoary
  • less dark color on the throat and lores on Hoary: more restricted and not as dark (but appearance varies with angle of view)
  • Hoary overall larger and fluffier (but note subspecies differences in size)
  • neck appears thicker on Hoary
  • fluffy "leggings" on Hoary
  • A tendency for Hoary to raise tail when foraging on the ground
  • relatively longer tail
  • there may be subtle differences in calls, and this deserves more testing, but singling one calling bird out of a flock is usually impossible. The larger "Greenland" subspecies also may have different calls.