Redstart-ing Migration

 Captain Sam's:

This morning surprised us with some cooler (by our standards) weather, so we were able to keep our nets open for longer and catch a good number of birds! We ended the day with 37 individuals, split almost down the middle between new captures and recaptures. Along with the usual Northern Waterthrushes and Painted Buntings, we had a male Downy Woodpecker, Ovenbird, and female Black-throated Blue Warbler - all hatch years - fly into our nets. Our favorite birds of the day, however, were 2 adult male American Redstarts. Highly distinguishable from other warblers by their orange and black color-blocked plumage, they are always a treat to see. While it is easy to tell the difference between an adult male and female for this species, it can be tricky to sex hatch-year individuals. Keep reading to learn how we do this in the field from the Little Bear crew!

Adult male American Redstart. Check out that vibrant orange flank!
Photo by Sarah Mueller

- Sarah S. 

 

Little Bear:

Well its good to be back. Good to see some old friends, avian and human. I enjoyed my first day back at Little Bear with Josh and Kristin and got my hands on some of the usual suspects like Painted Buntings, Northern Waterthrushes, Prairie Warblers and a Carolina Wren. Josh deployed a couple more radio-tags on the Painted Buntings for the Motus project that he mentioned yesterday and we enjoyed Little Bear's first of the season Black-throated Blue Warbler that was an After Hatch-year Male. We were also able to get a pair of Prairie Warblers and American Redstarts for some nice in-hand comparisons. 

After Hatch-year Black-throated Blue Warbler (Photo: Josh L.)

 

As Sarah mentioned above, determining the sex for Hatch-year American Redstarts can be a bit more subtle than when they are adults. In the photo below we are comparing the color in the "armpit" of the birds as well as down the flank. The bird on the left is a male and shows more of an orange hue than the female that is on the right, which is more yellow. This is one characteristic we look at when aging Hatch-year American Redstarts, but we will also use other characteristics like black feathers on the head or face (indicating male) as well as wing length. Caution! Mature adult females can begin to show the orange hue seen on this young male. This is why it is critical to first look for a molt limit before sexing!

 

Hatch-year male American Redstart (left) and Hatch-year female (right) (Photo: Josh L.)

 

For another comparison, we delve deeper into the intricacies of what I like to call "the feather map". Here we are looking at two male Prairie Warblers. The one on the left is a Hatch-year (immature) and the other is an After Hatch-year (adult). The top arrow on the left bird is pointing to the first alula feather or as we call it, the A1. Its a tiny feather, but if you can make it out, you'll see that it's actually darker and contrasting with the adjacent feather to the right, which is the A2. This is the molt limit we used to age this bird. The A1 is a newer and fresher feather than the A2. You can see that the bird on the right is showing the same density and darkness of the A1, A2 and A3 feathers that are pointed out by the blue arrows. That's because there is no molt limit here. All the feathers are the same age. The bottom arrow on the immature bird (left) is pointing at the primary coverts. These feathers are more faded and paler than the row of greater coverts to the left that are pointed out by the blue line. Compare them to the adult's primary coverts. Notice they are also rounded whereas the adult's primary coverts form a straight edge accented by the red bar and arrow. This is a shape difference we note when aging warblers. The photo below demonstrates the shape difference in the tail feathers. Again the immature (Hatch-Year) bird is on the left and the adult (After Hatch-year) is on the right. The tail feathers of the adult are more rounded and truncate where the immature tail is much more pointed.

 

Hatch-year Prairie Warbler (left) and After Hatch-year Prairie Warbler (right) (Photo Josh L.)

Hatch-year Prairie Warbler (left) and After Hatch-year Prairie Warbler (right) (Photo Josh L.)

Happy trails and birding!

- Dan E.

Species	Captain Sam's		Little Bear
	New	Recaps	New	Recaps
Downy Woodpecker	-	1	-	-
Red-eyed Vireo	-	-	2	-
Carolina Chickadee	-	2	-	-
Carolina Wren	2	2	1	-
Ovenbird	1	-	-	-
Northern Waterthrush	6	8	5	4
American Redstart	5	-	2	-
Black-throated Blue Warbler	1	-	1	-
Prairie Warbler	-	-	5	-
Northern Cardinal	-	-	1	1
Painted Bunting	5	4	2	2

Today's Banding Stats	Captain Sam's	Little Bear	TOTAL
# Birds Banded	20	19	39
# of Recaptures	17	7	24
# of Species	8	8	11
Effort (net-hours)	155.17	108	263.17
Capture Rate (birds/100 net-hours)	23.8	24.1	23.9
# of Nets	30	20	-

2020 Fall Cumulative Banding Stats	Captain Sam's	Little Bear	TOTAL
# Birds Banded	309	118	427
# of Recaptures	128	25	151
# of Species	30	23	35
Effort (net-hours)	1687.92	650.55	2338.47
Capture Rate (birds/100 net-hours)	25.9	21.98	24.7
# of Days	15	7	-

Banding Staff
Aaron Given (CS)
Sarah Mueller (CS)
Sarah Stewart (CS)
Kristin Attinger (LB)
Josh Lefever (LB)
Dan Errichetti (LB)