Tuesday, May 31, 2011

An over-the-wing headscratcher

"Head scratching is so essential to birds that even one-legged individuals will attempt it." This according to the Birder's Handbook, which also says that it's purpose (in addition to spreading oil around) may be to remove molted feathers, discourage ecoparasites, or even to relieve pressure in the ear! It also says that some birds scratch by stretching their foot over the wing (such as this tree swallow photographed in Warren Co., NJ this weekend), and some scratch with their foot under the wing. It might be more typical to scratch over the wing, as they mention that 31 out of 38 wood warblers examined scratch this way, while only 7 prefer underwing scratching. Why, I don't know.

Monday, May 23, 2011

Dove on a wire

I feel like this symbolizes something, but I'm not sure what...

(taken a few days ago in Ocean County, NJ)

Wednesday, May 11, 2011

Casualties of migration

Found this American redstart yesterday in a Massachusetts parking lot. No trees in site. Since there are no signs of injury (although what is that thing in it's cloacal region?!) I'm guessing it landed exhausted after a night of migration and just keeled over from lack of food? But it could have just fallen off of somebody's grill. 

In a previous May, I found an ovenbird dead outside of a convenience store in an urban area. These two observations lead me to conclude that migration is: 1) difficult and 2) messy, with a certain percentage just dropping dead along the way...a percentage that is certainly higher (and rising) in this age of parking lots and convenience stores.

Monday, May 9, 2011

Night swallows

Early this morning, around 4:15, long before the first hint of light dawned on my New Jersey backyard, I heard...tree swallows.

And they appeared to be flying around, foraging! I remember hearing barn swallows flying and calling in pitch darkness several years back too. I wonder what is going on? (A quick google search yields no answers.) 

Feeding on moths? Early / late migration? I'm pretty sure they are mainly diurnal migrants. Who knows? Golondrinas de la noche.

A foot-trembling woodcock?

I had one of those encounters today where you meet a bird and then think "why aren't you running away from me?" (And luckily had a camera with me.) This nice woodcock allowed me to park my car right next to her while she went about her business. This business was actually the interesting part: instead of probing over and over to look for worms, she appeared to be feeling with her feet! In a rocking-back-and-forward motion, she would put a foot down twice before putting her weight on it and advancing one step to do the same with the other foot. 

Other shorebirds, especially Charadrius plovers, but also solitary sandpipers and others, use a "foot trembling" foraging technique that apparently helps scare inverts up to the surface. To quote one paper on foot-trembling in the semi-plover (Cestari 2009): 

  • Tapping or trembling movements involve the use of one leg at time during foraging in order to expose or incite movement in cryptic invertebrates of intertidal zones and grasslands (Sparks 1961, Piersma 1996). The advantage of this technique lies in the transfer of vibrations from the foot through the substrate to the prey (Tarburton 1989). This kind of movement may also startle insects on the surface, facilitating the capture of prey by visual-foraging birds (Piersma 1996, USFWS 1996).
This sounds a lot like what I observed, and woodcock are "shorebirds" after all. (What a bad name for this group of birds.) ... But wait, after checking the Birds of North America account, I discover that alas I'm not the first one to observe this rocking, foot-feeling walk, although it does still seem to have some mystery associated with it. From the BNA account (Keppie and Whiting 1994):
  • While feeding on lawns, birds seen to rock their body forward-backward without moving the head, as they slowly walk about, placing weight heavily upon lead foot. Does rocking motion and heavy foot generate vibration that causes shallow earthworms to move, a response then heard by woodcock (Marshall 1982b) or detected by its bill in contact with soil? Fascinating anecdotal reports in early literature suggest this may be so (Pettingill 1936).
Maybe so. I should have watched longer instead of getting greedy for photos!

Tuesday, May 3, 2011


A sparrow-hawk? No, a beetle-hawk.
Two pellets (a.k.a. puke) freshly coughed up by American kestrels (they were still moist...note the ant). Also part of a dismembered iridescent beetle (a scarab?). All were found beneath favored kestrel feeding posts in an Ocean County (NJ) grassland. Almost all the kestrel pellets I've found so far this April have pieces of beetle shells in them. I think there are lots crawling out of the soft sandy soil -  maybe as hibernating adults, or maybe freshly-metamorphosed from wriggling, dung-fattened grubs. Some they are definitely catching on the ground, but I wonder if some of the aerial insect hawking I see them doing (way high up) is after these big and tasty slow-flying beasts. The pellets are about 1 inch long, for scale.