Wednesday, September 23, 2015

Rails at Ellis Creek - Virginia and Sora

Alerted in a post on NorthBayBirds (YahooGroups site), Patti and I went to the Ellis Creek Water Treatment ponds in Petaluma on September 12, 2015. Access there is off Cypress Drive, just a bit south of PRBO Conservation Science headquarters.

The northernmost pond (C) is currently being drained, mostly to control the bullfrog population. Hundreds of birds are attracted to wealth of prey, as the fish are concentrated in shallow puddles and the invertebrate rich mud is exposed like a giant buffet table. Hundreds of Dowitchers gathered, along with a host of herons, egrets, Wilson's Snipes and dabbling ducks. Best to go early (8-9am). Highlights for us were jaw-dropping frame-filling sights of Sora's (more than 10) and Virginia Rails at the northeast corner of the pond along the shoreline vegetation.

The Virginia Rail ( Rallus limicola) looks like a small version of a Ridgway's Rail (split from the Clapper Rail of the east and gulf coast). The dull leg color of this one may indicate a young rail transitioning to basic adult plumage. Note the downcurved bill, absence of white streaks on the back, minimal color in the bill, and soft gray face.


Another view shows how the fine tips of the bill are perfect for grasping tiny prey from the surface of the mud. Note the limited black and white barring on the flank patch over the legs, more sharply defined than the barred patch on a Ridgway's rail:


The Sora, Porzana carolina, is in a different rail genus. They have been breeding for years at Ellis Creek and the Las Gallinas ponds. The yellow bill, white edges on the back feathers and more extensive black and white barring on the flanks make for a certain identification. This is an adult in basic plumage. In winter the bill will be brighter yellow, and the black mask will be become larger.


​Another view shows how rails often cock their short tails upward. The 8.75" Sora is just a bit smaller than the 9.5" Virginia Rail. Both species prefer fresh water marshes. 

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