"Micro"-ageing Red-eyed Vireos

Captain Sam's:

After yesterday's cold front, we were anticipating that today would be busy.  However, we heard very few nocturnal flights calls overhead as we were opening the nets, and activity around the banding station at dawn was eerily quiet.  Fortunately, the birds started to move around soon after and we ended up with 180 new birds and 2 recaptures.  The day's catch was dominated by Common Yellowthroats.  In fact, they made up 53% of everything that we banded today.  Species diversity was low with only 15 species however we did get a couple first-of-the-season Palm Warblers.  

We have been catching a good number of Red-eyed Vireos since the beginning of the season.  A couple weeks ago, I captured an adult that had a molt limit within the greater coverts and within the alulas.  Red-eyed Vireo are one of the few species that will suspend their molt on the breeding grounds and finish it after they arrive at their wintering grounds.  This got me thinking that I might be able to age these adults more accurately than just assigning them to AHY (after hatch-year).  I began studying the molt pattern on many of the adult Red-eyed Vireos that were coming through the station and realized that some birds could be aged as SY (second-year) and ASY (after second-year).  AHY  basically means a bird that is at least 1 year old and includes both SY and ASY under its classification.  

HATCH-YEAR (hatched this summer - immature)

The eyes of hatch-year Red-eyed Vireos are brown. 

Unlike adults, hatch-years will molt prior to fall migration.  Their typical molt includes the replacement of upper wing covert, greater coverts, carpal covert, and the 1st alula (A1).  There is typically a molt limit between the A1 and A2 (2nd alula).  The A1 will be darker and have a brighter green edging to the feather.  

     

SECOND-YEAR (hatched last summer and bred this summer)

The eyes of second-years are reddish.  There can be some variation between bright red or a deeper maroon color as in the photo above.  

Second-year Red-eyed Vireo will suspend their molt prior to fall migration. The typical molt includes the replacement of some inner greater coverts and probably the tertials (s7-9).  The rest of the feathers will be replaced at the wintering grounds.   This gives us an opportunity to see 3 generations of feathers at this age.  The replaced inner greater covert are part of the definitive basic plumage, the outer greater coverts and A1 are from the formative plumage, and the primaries, secondaries, primary coverts, A2, and A3 are from the juvenal plumage.

AFTER SECOND-YEAR (at least 2 years old)

ASYs have bright red eyes.

The typical molt pattern is similar to SYs except that there is no molt limit between A1 and A2.  In the photo above it appears that this bird replaced the carpal covert in addition to the normal inner greater coverts.  

-Aaron

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Little Bear:

Although we weren't as busy as Captains Sams (they caught more Common Yellowthroats then we had total birds!) it was still an awesome morning at Little Bear. All of us were excited for a birdy day with some first-of-season species, and things got rolling quickly with our first Veery and Eastern Wood-Pewee of the season.

Veery

Eastern Wood-Pewee

Although we didn't catch nearly as many as Captain Sams, Common Yellowthroat was still our most common bird today and we had some other cool warbler species mixed in, like our first-of-season Palm Warbler and a striking young male Black-throated Blue Warbler.

Palm Warbler (photo by Nate Watkins)

Black-throated Blue Warbler, hatch-year male

Our most exciting bird of the day came a little later in the morning- a species that KIBS catches less than annually (a rare coastal migrant in the southeastern US), and tends to hide-out amongst the big pushes of Common Yellowthroats that move through our area every September.

Immature Mourning Warbler- similar to Common Yellowthroat at first glance, but note the pale throat and bright yellow belly.

Young Mourning Warblers such as the one we caught today are similar in size and color palate as the much more abundant Common Yellowthroats, but are most easily recognizable by the fact that their brightest yellow is on the belly, rather than the throat. The adults have distinctive gray hoods, but these drab hatch-year birds can be easily overlooked in the field. Over the past 10 years there has only been one Mourning Warbler confirmed in the Charleston region apart from the individuals that have been captured at the KIBS banding stations; which goes to the show the value of mist-netting for detecting the movements of rare and difficult to find species.

-Josh

Species	Captain Sam's		Little Bear
	New	Recaps	New	Recaps
Eastern Wood-Pewee	-	-	1	-
Acadian Flycatcher	1	-	-	-
White-eyed Vireo	2	-	2	-
Red-eyed Vireo	19	-	17	-
Carolina Chickadee	-	-	-	1
Veery	2	-	1	-
Yellow-breasted Chat	-	-	1	-
Ovenbird	1	-	-	-
Northern Waterthrush	13	-	6	-
Black-and-white Warbler	2	-	2	-
Prothonotary Warbler	-	-	1	-
Mourning Warbler	-	-	1	-
Common Yellowthroat	95	-	37	-
Hooded Warbler	2	-	-	-
American Redstart	21	-	7	-
Cape May Warbler	-	-	1	-
Yellow Warbler	1	-	-	-
Black-throated Blue Warbler	6	-	2	-
'Western' Palm Warbler	2	-	2	-
Prairie Warbler	10	-	2	-
Painted Bunting	1	2	2	1

Today's Banding Stats	Captain Sam's	Little Bear	TOTAL
# Birds Banded	180	85	265
# of Recaptures	2	2	4
# of Species	15	17	21
Effort (net-hours)	197.5	145.5	343
Capture Rate (birds/100 net-hours)	92.2	59.8	78.4
# of Nets	30	23	-

2021 Fall Cumulative Banding Stats	Captain Sam's	Little Bear	TOTAL
# Birds Banded	635	376	1,011
# of Recaptures	132	53	185
# of Species	39	37	46
Effort (net-hours)	3,394.0	1,986.9	5,380.9
Capture Rate (birds/100 net-hours)	22.6	21.6	22.2
# of Days	25	20	-

Banding Staff

Aaron Given (CS)

Kristin Attinger (CS)

Kandace Glanville (CS)

Ben Stalheim (LB)

Nate Watkins (LB)

Josh Lefever (LB)