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Notes on the dowager: Rush Creek has the oldest reported Willow Flycatcher

July 29th, 2009 by tdomf_e48ef
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Date of sighting: 29 July

Endangered Willow Flycatcher at Rush Creek. Photo courtesy of Chris McCreedy.

The oldest known Willow Flycatcher is at Rush Creek. Photo courtesy of Chris McCreedy.

Attached are photographs of likely one of the founding females of the Rush Creek Willow Flycatcher population.  I found her nest in June of 2001, she was the second nesting female I found on Rush Creek that year.  Mark Pollock, working for Sacha Heath, banded her on July 29, 2001, and he aged her After Second-Year (meaning she was born before 2000).  That means she is at least 10 years old this summer.  The previous record reported to the USGS was 8 years and 11 months.  I suspect the Southern Sierra Research Station may have older birds, but they have not reported them to the Bird Banding Lab.

She has nested on Rush every season since.  She is the most successful female of the population, and has fledged chicks in 2001, 2002, 2003, 2004, 2005, and 2006.  Her longtime mate did not return in 2007, and she mated with a neighboring male, Phil (OK/S, or Orange-Black/Silver).  She was his second female, and due to lots of ruckus and not much room, she was a non-factor in 2007 and 2008, abandoning a parasitized nest and leaving by July 15 in 2007 and raising a Brown-headed Cowbird in 2008.

She is one of only 3 females I have followed that knows how to bury cowbird eggs.  In 2008, she buried one cowbird egg only to be parasitized by another.

This year, she has switched to a male I named Yossarian (his colors are Yellow-Orange/Silver), who himself has two mates.  Her first nest had three eggs and was unparasitized.  However, Brown-headed Cowbirds eventually located the nest and destroyed all contents around hatch day.  Her new nest only has two eggs.  Cowbirds did not find it, and this second nest hatched today or perhaps yesterday afternoon.

The Rush Creek population is down to seven adults in 2009, the fifth consecutive year of decline.  There were three males and four females.  The four females laid 12 eggs.  None of the nests were parasitized, but cowbirds located all 4 nests around each nest’s hatch day and destroyed all contents.  Each female re-nested, for a total of another 7 eggs (cowbirds were on one female’s second attempt and she abandoned the B-nest before laying).  Cowbirds located all of these nests (save the dowager in the photograph) and destroyed 4 more of the eggs (they left one in Yossarian’s second female’s B attempt, which she then abandoned).

Careless bird feeding kills endangered Willow Flycatchers on Rush Creek.

Careless bird feeding kills endangered Willow Flycatchers on Rush Creek. Photo courtesy of Chris McCreedy.

Due to cowbird activity, Rush is now down to 3 females (Yossarian’s 2nd female gave up and left), two with two eggs each and a female that has built a C attempt but has not yet laid eggs in it.  It is dreadfully late, if she lays eggs it will be by far the latest-ever nest on Rush Creek, with the negative trade-off of the female having to fight for her wintering territory should she fledge her chicks around the end of August, and of the chicks being raised late/dealing with more accipters on migration/arriving to wintering grounds last/ etc.

This season, I addled cowbird eggs for the first time.  This worked for Dusky Flycatchers – thus far 17 have fledged, and it would have only been 9 if I didn’t addle cowbird eggs.  But Willow Flycatchers are poor cowbird hosts and they simply abandoned all nests that the cowbirds discovered, rendering addling useless.

Brown-headed Cowbirds are not adapted to survive in desert habitats without subsidization from people. There are virtually no agricultural or grazing activities within the 25-kilometer Brown-headed Cowbird commuting range around Rush Creek – the cowbirds responsible for the Willow Flycatchers’ decline are fed by people in Lee Vining and Mono City, primarily at bird feeders. During a presentation to the Mono Basin Science Council, David Winkler brought up a good point to me – not only do people feeding birds support cowbirds, but it also means that the cowbirds have to spend virtually no time searching for food – enabling them to spend more time on the creeks.  As always, I urge those who visit these bird sightings pages to not feed birds during the spring and summer (April 1 – September 1), and to spread the word to your neighbors that may be feeding birds during the cowbird season.  I would be happy to provide anyone with more literature/reports if you have questions.


2 Responses to “Notes on the dowager: Rush Creek has the oldest reported Willow Flycatcher”

  1. avatar Terry Says:

    Chris –
    thank you for this informative report on the flycatchers. it would be a shame if they disappeared completely.

  2. avatar The Science Essayist » An Outfield of Flycatchers Says:

    […] nests and abandoning them to the care of unsuspecting adoptive parents. According to a number of observers, Willow Flycatchers that find cowbird eggs in their nests have been known to bury the unwanted […]