Saturday, October 26, 2013

The Fine Points of Aging Gray Catbirds

It was another cold morning at KIBS with a starting temperature of 46 degrees F.  We had a fairly slow morning with 53 new birds banded and 22 birds recaptured.  Yellow-rumped Warblers seem to be taking their place at KIBS as most numerous birds around with 27 of them banded.  With catbirds tapering off we decided today would be a good opportunity to photograph characteristics used in aging catbirds before they’re gone.
During the fall, there are several helpful characteristics that banders can look for when determining the age of Gray Catbirds.  Eye color can be very useful during the fall.  Young catbirds will have milky grey to light brown iris in which it is relatively easy to distinguish the pupil from the iris.  Adult catbirds will have dark reddish brown iris and it is hard to distinguish the pupil from the iris.  

HY Gray Catbird
AHY Gray Catbird
The mouth color lining can also be helpful in determining the age of catbirds.  As nestling, catbirds have a bright yellow mouth that they use to demand food from their parents.  They will retain the yellow mouth lining for most of the fall.  As they grow older, the mouth lining will become much darker and appear blackish.

HY Gray Catbird

AHY Gray Catbird
The best way to determine age in catbirds, as with most birds, is by looking for molt limits within the wing.  Hatch year catbirds will usually have a molt limit within the greater coverts because they have a partial prebasic molt.  A molt limit is created by the retention of juvenile feathers contrasting with newer and fresher adult feathers.  The juvenile feathers are usually shorter and have rusty tipping.  Adult catbirds will lack molt limits because they go through a complete prebasic molt after the breeding season. Adults wings will be completely uniform in wear and all the feathers will have a pearly gray coloration.  The best thing about molt limits is that they can be used anytime of the year. 

HY Gray Catbird with a typical molt limit

Another HY that went through a more extensive molt replacing all of its greater coverts

AHY Gray Catbird 


1 White-eyed Vireo
1 House Wren
2 Ruby-crowned Kinglet
1 Hermit Thrush
9 Gray Catbird
1 Northern Mockingbird
27 Yellow-rumped Warbler (Myrtle)
1 Palm Warbler (Western)
1 American Redstart
2 Common Yellowthroat
1 Painted Bunting
2 Song Sparrow
4 Swamp Sparrow

3 House Wren
13 Gray Catbird
1 Black-and-White Warbler
1 Common Yellowthroat
3 Painted Bunting
1 Northern Cardinal

# of Birds Banded:  53
# of Recaptures:  22
# of Species:  15
Effort:  96.4 net-hours
Capture Rate:  77.8 birds/100 net-hours
# of Nets:  19                     

1 comment:

  1. Very interesting! I would love to hear more about how you all age the birds you catch.