The Many Molt Limits of Common Yellowthroats

CAPTAIN SAMS

Another day of migrants at Captain Sam's. Common Yellowthroats continue to arrive at the banding station. Most of them were less than a year old, making their first journey to the wintering grounds.

Hatch year Common Yellowthroats have molt limits (i.e. generational differences in their feathers). For example, here is a Common Yellowthroat with juvenile alula feathers that were grown in the nest, and a carpal covert that was replaced shortly after fledging. Molt limits on this species can be subtle and I got lots of practice today aging them carefully.

Common Yellowthroat (hatch year, unknown sex)
The juvenile alula feathers, labeled A2 and A3, have a lighter and browner center than the formative carpal covert, labeled CC.

Common Yellowthroat limits are variable. Individuals can replace none to all alulas. They may show limits between the lesser and greater alula feathers, within the tertials, between the tertials and secondaries.

Individuals can also replace flight feathers eccentrically. Below is another Common Yellowthroat hatch year. Because the bird had an extensive preformative molt, it does not have the limit between the alulas and the carpal coverts. Instead, it has a limit within the primaries, and a limit within the secondaries.

Common Yellowthroat (hatch year, unknown sex)
The innermost primary and the outermost secondary are juvenile/retained (labeled s1 and p1), as the shaft color is brownish and green edging is duller compared to all other flight feathers

However, most hatch year Common Yellowthroats we aged today showed a molt limit within the alula feathers. The alula covert (A1) will be replaced, formative and darker. The lesser and greater alula (A2 and A3) will be lighter, browner and juvenile.

Common Yellowthroat (hatch year, unknown sex)
On this bird, the alula covert (A1) is replaced, and has a darker center than the other alula feathers (A2 and A3).

Jasmine

LITTLE BEAR

The heat on the island the last two days has been much more tolerable which has been quite nice. Today out at Little Bear we had 21 new birds and 7 recaps. The highlight for the day was Little Bear's second Mourning Dove. Liz had to make a mad dash to stop it from getting out of the net but she was able to secure the fella. Songbird nets are designed to catch small birds around warbler size by tangling them so they can't escape without getting some fancy new jewelry. Since the nets mesh is so small, larger birds can often escape after hitting it since they don't really get tangled, so whenever we get anything pretty big it's always exciting and lucky!

The migration forecast is looking more promising over the next couple days compared to most of the season so far, so hopefully our days of catching under 10-20 birds is behind us and numbers keep going up!

-Aiden

Species	Captain Sam's		Little Bear
	New	Recaps	New	Recaps
Mourning Dove	1	-	1	-
Red-eyed Vireo	1	-	1	-
Gray Catbird	-	-	1	-
Carolina Chickadee	-	-	-	1
Northern Waterthrush	3	-	2	1
Common Yellowthroat	47	1	5	-
American Redstart	-	-	1	-
Northern Yellow Warbler	1	-	7	-
Black-throated Blue Warbler	2	-	1	-
Western Palm Warbler	1	-	-	-
Prairie Warbler	1	-	-	-
Northern Cardinal	-	2	1	-
Painted Bunting	3	2	1	5

Today's Banding Stats	Captain Sams	Little Bear	TOTAL
# Birds Banded	61	21	82
# of Recaptures	5	7	12
# of Species	10	11	12
Effort (net-hours)	161.7	115.65	277.35
Capture Rate (birds/100 net-hours)	40.8	24.2	33.9
# of Nets	33	28	61

2026 Fall Cumulative Banding Stats	Captain Sams	Little Bear	TOTAL
# Birds Banded	783	440	1223
# of Recaptures	172	91	263
# of Species	39	40	48
Effort (net-hours)	4333.7	2574.1	6911.8
Capture Rate (birds/100 net-hours)	22.0	20.6	21.5
# of Days	32	25

Banding Staff

Aaron Given (CS)

Michael Gamble (CS)

Liz Held (LB)

Olivia DeMarchi (LB)

Jasmine Fu (CS)

Aiden Gifford (LB)

Note:  All banding, marking, and sampling is being conducted under a federally authorized Bird Banding Permit issued by the U.S. Geological Survey’s Bird Banding Lab.