Thursday, November 20, 2014

Frosty morning; Ageing Catharus Thrushes

We banded 16 new birds and had 16 recaptures of 9 different species today.  Many of the nets were covered with frost after the below freezing temperatures overnight which made opening them a little difficult.  I had defrost parts of the net with warmth from my hands and breath to get them from sticking together.

Frosty covered Mist Net (net # 4)

Thrushes in the genus Catharus can be aged by looking for molt limits within the greater coverts.  Sometimes the molt limit is not that obvious as either none of the greater coverts have been replaced or maybe just the inner 1 or 2 closest to the body.  Unreplaced greater coverts will usually have distinct "tear-drop" shaped buffy tips such as the hatch-year Hermit Thrush on the right in the photo below.  As you can see, this bird did not replace any of the greater coverts during its first prebasic molt as all of the greater coverts have that buffy tear-drop pattern.  The Hermit Thrush on the left is an adult because it is lacking the tear drops on the tip of the greater coverts.  A few greater coverts do have buffy corners which can be misleading but these are not juvenile greater coverts.

Close-up showing the buffy tear-drop pattern on the tips of the greater coverts of hatch-year Hermit Thrush.  

1 Ruby-crowned Kinglet
2 Hermit Thrush
2 Gray Catbird
10 Yellow-rumped Warbler (Myrtle)
1 Song Sparrow

1 Tufted Titmouse
5 Gray Catbird
4 Yellow-rumped Warbler (Mytle)
1 Prairie Warbler
1 Song Sparrow
3 Swamp Sparrow
1 White-throated Sparrow

# of New Birds:  16
# of Recaptures:  16
# of Species:  9
Effort:  131.1 net-hours
Capture Rate:  24.4 birds/100 net-hours
# of Nets:  23

Aaron Given
Mattie VandenBoom
Libby Natola
Matt Zak
William Oakley