Monday, October 20, 2014

Indigo Bunting Molt and FOS White-throated Sparrow

Another productive day of banding with 128 new birds and 19 recaptures of 17 different species. The Gray Catbird migration has been impressive this fall.  We banded another 74 of them today giving us a total of 899 for the season so far and we will continue to catch new ones all the way through the end of November.  But the highlight of the day was our first White-throated Sparrow of the season!

We have been banding a bunch of Indigo Buntings lately so I thought it would be a good time to explain how we age and sex them.  Hatch-year Indigo Buntings (and Painted Buntings) have a somewhat complex molt strategy.  Their first prebasic molt starts almost immediately after they leave the nest.  This molt consists of most or all of the body feathers and some wing feathers including lesser and median coverts but not the greater coverts, primary coverts, secondaries, and primaries.  The resulting plumage is almost identical to the juvenal plumage and males and females look the same at this point.  Later in the fall or winter, they undergo an extra molt (presupplemental molt) in which they replace the body feathers again along with more wing feathers including the lesser coverts, median coverts, greater coverts.  In addition the outer 3-5 primaries and inner 3-4 secondaries are also replaced showing eccentric molt pattern.  The resulting plumage is usually a little brighter than the previous plumage, and males and females still look similar.  However, we should now be able to separate most males from females based on the amount of blue in the wing.

The photo below shows the wing of an hatch-year Indigo Bunting in its 1st basic plumage.  Note that no greater coverts, primary coverts, secondaries, and primaries have been replaced.  The unreplaced feathers are the same feathers that were grown in when the bird was in the nest.  Males and females are indistinguishable when in this plumage.  

Indigo Bunting (hatch-year, sex unknown)
The next two photos show examples of birds that has already undergone their presupplemental molt exhibiting an eccentric molt pattern with some outer primaries and inner secondaries being replaced.  They also has replaced their greater coverts which when compared to the greater coverts in the photo above are darker and have much wider and browner edging to them.  This first individual is probably a female based on the minimal amount of blue in the lesser, median, and greater coverts.  The second is a male because it has a substantial amount of blue in the lesser and median coverts (trust me - my finger is covering most of it up), and some blue in the greater coverts.      
Indigo Bunting (hatch-year, probably female)

Indigo Bunting (hatch-year, male)

Adults do not undergo a presupplemental molt and will replace all of their feathers once in late summer during its prebasic molt.  Adult females will look similar to hatch-year males and females except that the replaced primary coverts, primaries, and secondaries will be darker and have a slight blueish edging to them.

Indigo Bunting (after hatch-year, female)
 Adult males will have a lot of blue in the lesser and median coverts and all/most of the greater coverts, primaries coverts, primaries, and secondaries will have bright blue edging.

Indigo Bunting (after hatch-year, male)

1 Eastern Phoebe
1 Ruby-crowned Kinglet
74 Gray Catbird
1 Black-and-White Warbler
22 Common Yellowthroat
1 American Redstart
1 Northern Parula
2 Black-throated Blue Warbler
3 Palm Warbler (Western)
16 Yellow-rumped Warbler (Myrtle)
1 Swamp Sparrow
1 White-throated Sparrow
3 Indigo Bunting
1 Painted Bunting

1 White-eyed Vireo
1 House Wren
13 Gray Catbird
1 Black-and-White Warbler
2 Common Yellowthroat
1 Eastern Towhee

# of New Birds:  128
# of Recaptures:  19
# of Species:  17
Effort:  133.4 net-hours
Capture Rate:  110.2 birds/100 net-hours
# of Nets:  23

Aaron Given
Mattie VandenBoom
Libby Natola
Matt Zak
William Oakley