Saturday, December 8, 2007

Lesser Nighthawk identification revisited

No, I am not suggesting that the bird was misidentified or that the i.d. is in question even. Simply, I wanted to revisit the photos (with a couple new included) and add some commentary. Let's face it nighthawk identification is not straight forward.

(click on the photos to enlarge)

So, using a photo that Kevin Karlson took of the bird (above), I have pointed arrows to all of the prominent field marks used in identifying this bird. Michael O'Brien has also allowed use of a brief summary of filed marks he wrote up which entails a few more points than I described in my original post about the finding of the bird. For additional comparison, I have included two photos by Karl Lukens, of Common nighthawks taken this fall.

Below is the Karlson photo from above with arrows pointing out the major field marks which are discussed. Something I just noticed as I was looking this post over before posting; look at the common above and the lesser below. The length difference between the two birds is evident (to me) in the photos. The common having longer primaries gives the bird a much longer drawn out appearance. Somewhat analogous to the shape of a White-rumped or Baird's sandpiper in comparison to a Least sandpiper. The lesser is a much more "stubby" looking bird that is relatively compact. Note Michael's 7th i.d. note below.

Text in italics is from Michael O'Brien's identification summary(not all points are included);

Identification as Lesser based on the following points, in approximate order of importance:

outer end of white primary patch falling even with tip of longest tertial and with tip of p5 (usually well before tertial tips and in line with p4 in Common; "farther out" position of primary patch also indicated by extensive dark basal area of primaries exposed beyond secondaries; Commons/Antilleans show minimal dark basal area beyond secondaries

Compare the first Common nighthawk photo for a visual comparison of the white patch in reference to how far it extends beyond the tertials. In a common, it doesn't! Well, at least if the bird is roosting with it's wing in a typical position as exhibited in the photo above. If you look closely you can see a bit of the white patch on the bird in the first photo; the tertials extend well beyond.

2 - p10 distinctly shorter than p9 (equal or longer in Common)

This the photo (above) I posted with the original announcement of the nighthawk. To me at least, it is obvious that P10 is shorter than P9. But to further aid in seeing the distinction I have traced the outer edge of P10 & 9 on both wings. P10 is RED and P9 is YELLOW. One thing to consider is that Lesser nighthawk could about be completely ruled out if we assumed that this bird was still in molt. Lessers, as I have discovered in my own personal research, molt on the breeding grounds. While others (common and antillean) will molt on the wintering grounds. Given that this bird was found past typical migration timing adds to some confusion. But, since there really was no other evidence of molt in the bird and that the primaries are slightly worn (there would be a contrast between fresh inner primaries and worn outer primaries on a molting bird), I think that the shortened primaries being caused by molt can be ruled out.

3 - small buffy spots at base of primaries (lacking in Common/Antillean)

In the event you are not seeing the small buffy spots at the base of the primaries, the photo below has been modified to point the area out. Some photos you may see will not readily show the buffy spots as the bird did move a little and adjusted its position on the branch. When I arrived at the scene these were some of the first photos taken and the best for showing the spots in question. Note also how extensive the dark basal area of the primaries is (see ID point no. 1) and how large the white patch is on p10 (the bottom primary feather; see ID point no. 5).

For the following points refer to the previous photos.

- white restricted to outer four primaries (outer five in adult male Common/Antillean)

5 - white primary patch includes broad section on outer web of p10 (outer web black or with small white patch in most Common/Antillean)

6 - prominent buff-white spots on wing coverts and scapulars (rarely if ever so large and prominent on Common/Antillean)
7 - relatively compact shape with short, broad primaries and largish head (similar to Antillean but different from typical Common)"

Note the distinct "pointyness" to the common primaries compared to the lesser. The images are significantly cropped using photos from above.

So there you have it, Lesser Nighthawk identification in a nutshell. That was written tongue in cheek by the way. Hopefully this will help you learn as much about nighthawk identification as I have.

No comments: