Tuesday, October 2, 2012

Tuesday's Results

We banded 14 new birds and had 13 recaptures of 14 different species this morning.  We had to close down the nets a little early due to strong winds.  Birds can get seriously entangled and even injured when stuck in a net that is being blown around by the wind.  Bird safety is our #1 priority, so when the wind reaches a certain point and the nets are deemed too dangerous to operate, we close them.


A couple days ago I talked about how to age Swainson's Thrushes by looking at molt limits in the greater coverts.  Today, we captured another Swainson's Thrush and as I was looking at the wing to age it my finger happened to move the 3 alula feathers revealing something that I had learned (but forgotten about) at an Advanced Bird Banding Workshop that I attended at the Powdermill Avian Research Center in Pennsylvania.  At the workshop, I learned that if there are buffy spots on the coverts underneath the alulas, the bird is most likely a hatch-year (juvenile).  This characteristic should always be used in combination with other criteria such as the presence of a molt limit.   

Swainson's Thrush (hatch-year, sex unknown)

American Redstarts exhibit a molt strategy called delayed plumage maturation (DPM).  DPM is when a male bird retains female-like plumage characteristics until its second prebasic molt.  In other words, males in their first year of life will resemble females until after next summer when it molts all of it feathers and get its gaudy male plumage.  There are some subtle differences though that allow us to sex hatch-year American Redstarts.  First, males will have bright orange (or salmon-colored) sides that contrast with the underwing coverts.  Females will have yellowish sides that do not contrast in color with the underwing coverts.  Additionally, males will usually have dark gray or black upper tail coverts while females will have lighter gray upper tail coverts.  The last criteria that can be used to sex hatch-year American Redstarts is the amount of yellow on the 3rd retrix (tail feather).  Males will have a large patch of yellow while females will have a small patch or sometimes no yellow on r3.

American Redstart (hatch-year, male)

Note the contrast between the bright orange sides and
the lighter yellow underwing coverts.
American Redstart (hatch-year, female)

Note the lack of contrast of the yellow on the
sides and the yellow on the underwing coverts. 

American Redstart (hatch-year, male)

Note the black upper tail coverts.

American Redstart (hatch-year, female)

Note the gray upper tail coverts.

















1 Swainson's Thrush

2 Gray Catbird

1 Northern Mockingbird

2 Yellow Warbler

1 Cape May Warbler

1 Black-throated Blue Warbler

2 American Redstart

1 Common Yellowthroat

1 Eastern Towhee

1 Summer Tanager

1 House Finch



2 House Wren

6 Gray Catbird

1 Brown Thrasher

1 Black-throated Blue Warbler

2 Common Yellowthroat

1 Northern Cardinal



# of Birds Banded:  14

# of Recaptures:  13

# of Species:  14

Effort:  68.2 net-hours

Capture Rate:  39.6 birds/100 net-hours

# of Nets:  17

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