Saturday, August 20, 2011

Henslow's Sparrow

On 19 August 2011, Erika and I strolled through the Afton State Park interpretive prairie loop.  Dragonflies were our main goal. Aware that Henslow's Sparrows were a possibility, I stopped short when I heard a distinctive, single, hiccup-like "tsi-lick" from within the grass. (In this link, used with permission of Thayer Birding Software, the song is repeated a bit more rapidly than what we heard.) Using the Sibley App on my smart phone, Erika and I quickly confirmed that this was a singing Henslow's Sparrow. The location of the call and the bird were difficult to ascertain. In the photo above, the sparrow is in the dead center of its preferred prairie habitat.
To our surprise and delight, the Henslow's Sparrow flew up and continued to sing from to the top of a nearby goldenrod. Visually this sparrow proved far more difficult to identify than was its song. The olive-green characteristic of this species in the spring was reduced to a patch on its nape and a very faint wash across the head. The underparts were also only very faintly buffy. Although the bird showed a few flank streaks, the breast was faintly, if at all, streaked. This relatively lack of color and streaking may be the result of the bird's being in a very worn late summer plumage.
On the other hand, the double "mustache" stripes are quite visible (specially in the photograph just above). These field marks are actually a subauricular line and lateral throat-stripe. Furthermore, the bill is large and conical and the top of the head profile is relatively flat. The rusty wing coverts and tertial feathers are also characteristic of a Henslow's Sparrow. The spots on the head are also good field marks.
Recently Henslow's Sparrow populations have declined at rates approaching 10% a year. This decline is the steepest of any North American grassland bird (Herkert et al. 2002). The main reason for this decline has been their shrinking grassland habitat.  Local population increases have been associated with the Conservation Reserve Program and with efforts at prairie restoration such as at Afton State Park. But these conservation efforts are probably not sufficient to buck this species' downward population trend.

1 comment:

  1. I was just thinking I need to get to Afton to look for some Henslows. Every time I am at Afton I have my preschooler with me and that isn't especially conducive to finding sulky sparrows.

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