McGILL BIRD OBSERVATORY

NOTE: This species account has been moved to Piranga to allow for improved comparison among examples.  
The updated profile is located at:  http://www.natureinstruct.org/piranga/view.php/Canada/A6C0C4A9DCB84453

Introductory notes: Although common in much of its range, there appears to be a lot of individual variability among Yellow Warblers (some of it perhaps tied to subspecific differences).  As such, caution should be exercised when ageing and sexing, taking into account as many features as possible.

Ageing and sexing guidelines:

January - July:

ASY - M Yellow to golden plumage; bold reddish streaks on breast; very little brown on outer rectrices ASY - F Fairly strong yellow; light to moderate streaking on breast; molt limits absent; outer rectrices broad, with fair amount of brown SY - M Easily confused with ASY-F, but usually has molt limit between primary and greater coverts; outer rectrices mostly yellow and fairly tapered SY - F Usually pale yellow; breast streaks faint to absent; rectrices fairly tapered and with relatively extensive brown

June - December:

AHY - M Yellow to golden plumage; may have distinct reddish streaks on breast; primary coverts with distinct yellow-green edging; outer rectrices broad with very little brown AHY - F Yellowish-green; primary coverts with distinct yellow-green edging; outer rectrices broad with relatively extensive brown  HY - M Generally yellow; sometimes with faint reddish streaks on the breast; minimal edging to primary coverts; rectrices tapered but mostly yellow HY - F Yellowish-green with distinct grayish wash; lacking reddish streaks on breast; rectrices tapered and with extensive brown HY - U Yellowish-green to yellow, minimal reddish streaks on breast; minimal edging to primary coverts; rectrices tapered, somewhat brown JUV - U Mostly gray, with some yellow on the face, as well as the wings and tail

SY males have a rather variable amount of reddish streaking on the breast, from as little as on an ASY-F to nearly as much as on a typical ASY-M.  The crown tends to be more yellow than on females, contrasting less with the face, but this too can be variable.  The tail and/or wing usually need to be studied to confirm SY males.

A typical SY-M with fairly strong breast streaking, but browner wings than ASY individuals.
Photo by Marie-Anne Hudson, McGill Bird Observatory (QC), May 2007

A particularly boldly streaked SY-M, also with a tinge of orange in the crown.
Photo by Marcel Gahbauer, McGill Bird Observatory (QC), May 2010

An especially pale SY-M, with only faint breast streaks.
Photo by Marcel Gahbauer, McGill Bird Observatory (QC), May 2005

Identifying molt limits on the wing is often the most reliable way to distinguish SY-M and ASY-F Yellow Warblers.  This can be confounded somewhat by the alternate molt of the greater coverts, but in general the more brownish, faded, and abraded juvenile feathers of the primary coverts, primaries, and secondaries are apparent in terms of both quality and colour (note too the more limited yellow edging).

A typical SY-M wing, with all greater coverts and tertials replaced during the prealternate
molt, contrasting strongly with the brown juvenile feathers on the rest of the wing.
Photo by Marcel Gahbauer, McGill Bird Observatory (QC), May 2010

A stronger contrast in this example, with the inner secondaries more worn and showing
even less yellow edging. Note also that in this case the prealternate molt did not replace
all of the greater coverts, as the outermost two are still formative plumage. The presence
of three generations of plumage (juvenile, formative, alternate) as on this bird is also
indicative of SY birds.
Photo by Marcel Gahbauer, McGill Bird Observatory (QC), May 2005
 

Rectrices of SY Yellow Warblers are typically narrower and more tapered than on ASYs, and may also show more wear.  The extent of brown on the inner web tends to be more restricted on males than females, as with ASY birds.

An example showing relatively little wear, and colours only slightly paler than what would
be expected on ASY-M.
Photo by Marie-Anne Hudson, McGill Bird Observatory (QC), May 2007

A paler tail (note the contrast with the more yellow uppertail coverts), also showing a bit
more fraying near the tips of some rectrices.
Photo by Marcel Gahbauer, McGill Bird Observatory (QC), May 2010

A somewhat unusual case, where most of the rectrices (except for r3 and r5-r6 on the right)
appear to have been replaced, showing the contrast between the paler retained juvenile
feathers and the darker replaced feathers.
Photo by Marcel Gahbauer, McGill Bird Observatory (QC), May 2005

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SY females are generally quite easy to recognize by their overall appearance, which is generally more greenish-yellow than other age/sex combinations, and with hardly any reddish streaks present on the breast.

A typically pale SY-F, with only faint streaks on the breast.
Photo by Marie-Anne Hudson, McGill Bird Observatory (QC), May 2008

A slightly more yellow individual, especially on the crown, but overall still pale and
with very little reddish streaking on the breast.
Photo by Marcel Gahbauer, McGill Bird Observatory (QC), May 2010
 

AHY males are the only age/sex class that may retain distinct reddish streaks on the breast during fall migration, but this is not the case for all individuals. 

An AHY-M near the end of its prebasic molt, showing only a trace of breast streaking.
Photo by Marcel Gahbauer, McGill Bird Observatory (QC), August 2009

An AHY-M retaining distinct red breast streaks after its prebasic molt.
Photo by Marcel Gahbauer, McGill Bird Observatory (QC), September 2005
 

The wing appears similar for AHY birds of both sexes.  They lack a molt limit, have distinct yellow edging to the primary coverts, and broad yellow edging on all of the greater coverts. 

Note the broad and rounded primary coverts and the bold yellow edging to all wing feathers.
Photo by Marcel Gahbauer, McGill Bird Observatory (QC), September 2005

This individual shows similar features, but is still completing its prebasic molt; any Yellow
Warbler observed in molt can generally be assumed to be AHY, as the preformative molt
is limited to the greater coverts, alula, and tertials.
Photo by Marcel Gahbauer, McGill Bird Observatory (QC), July 2006
 

In both sexes, the outer tail feathers of AHY birds are usually fairly broad and rounded.  With males, almost the entire inner web is yellow, with usually only a small amount of brown near the tip, extending up the shaft much less than on females.  Note that the third photo is of a male at least 3 years old, showing unusually narrow and pointed rectrices, though the colour pattern is consistent with that of an older male.

A fairly typical AHY-M tail, although some individuals have even less brown on the inner web.
Photo by Marcel Gahbauer, McGill Bird Observatory (QC), August 2009

A somewhat unusual shape to the rectrices, still showign the typical broadness, but with
a distinct point at the tip. The pattern of yellow is consistent with AHY-M though.
Photo by Marcel Gahbauer, McGill Bird Observatory (QC), August 2005

The rectrices in this case are more narrow and tapered, similar to what would be expected
for HY Yellow Warblers, but this individual was at least in his third year, and the extent
of yellow is more consistent with AHY-M than HY-M.
Photo by Marie-Anne Hudson, McGill Bird Observatory (QC), August 2007

RETURN TO AGE/SEX OVERVIEW

HY Yellow Warblers are generally greenish above and yellow below, with few prominent markings.  Some males already show faint reddish streaks on the breast in this plumage, thus if these are present sex can be determined easily.  If they are absent, it may be possible to determine sex using the tail, but often it will be unknown.

Note the few reddish streaks on the breast, which a HY-F would not have.
Photo by Marcel Gahbauer, McGill Bird Observatory (QC), August 2005 

HY Yellow Warblers show minimal pale edging on the primary coverts, and these become increasingly narrow, tapered, and worn over the course of the fall.  The wing does not provide any information to assist in determining sex.

Photo by Peter Pyle, Big Sur Ornithology Lab (CA), August 2007

Photo by Marcel Gahbauer, McGill Bird Observatory (QC), August 2005
 

HY Yellow Warblers tend to have somewhat pointed rectrices; males show a relatively small amount of brown on the inner web of the outer rectrices.  This can be used as an aid to determining sex, but should be used with caution and preferably not as the only identifying characteristic.

A fairly typical HY-M tail, showing the narrow and tapered shape of fresh juvenile rectrices;
the limited extent of brown is strongly indicative of this being a male.
Photo by Marcel Gahbauer, McGill Bird Observatory (QC), August 2009

An example with slightly more brown on the tail, but still quite a bit less than would be
expected for most HY-F.
Photo by Marie-Anne Hudson, McGill Bird Observatory (QC), August 2007

RETURN TO AGE/SEX OVERVIEW

Female HY Yellow Warblers are generally greenish-yellow with a grayish tinge, and lacking reddish streaks on the breast.

A typical HY-F, very pale grayish-yellow overall.
Photo by Marcel Gahbauer, McGill Bird Observatory (QC), August 2005

Another relatively pale HY Yellow Warbler, likely a female.
Photo by Marie-Anne Hudson, McGill Bird Observatory (QC), August 2008

HY Yellow Warblers show minimal pale edging on the primary coverts, and these become increasingly narrow, tapered, and worn over the course of the fall.  The wing does not provide any information to assist in determining sex.

A typical HY-F wing, showing the brownish primary coverts, lacking yellow edging, and
the overall grayish-brown tone of the wing.
Photo by Peter Pyle, Big Sur Ornithology Lab (CA), September 2007

Another HY-F wing, with a touch of narrow greenish-yellow edging to the primary coverts,
but much less than on AHY individuals, and still quite grayish overall.
Photo by Marie-Anne Hudson, McGill Bird Observatory (QC), August 2008 

HY Yellow Warblers tend to have somewhat pointed rectrices, and the amount of brown on the inner web is generally more extensive on females than males. 

An example with relatively little brown on the tail for a female.
Photo by Marie-Anne Hudson, McGill Bird Observatory (QC), August 2008

A more typical example, showing both the pointed outer rectrices and a greater amount
of brown on the inner web.
Photo by Marcel Gahbauer, McGill Bird Observatory (QC), August 2005

A western example, illustrating the much greater extent of brown on the inner web,
compared to the eastern birds in the previous photos. Note also the dark growth bar
visible across the entire tail.
Photo by Peter Pyle, Big Sur Ornithology Lab (CA), September 2007

RETURN TO AGE/SEX OVERVIEW

While sex can be determined for some HY Yellow Warblers (generally males with some reddish breast streaks and/or a relatively dark yellow plumage, and females that are particularly pale grayish-yellow and/or have very extensive brown on the outer rectrices), many HY Yellow Warblers are best left as sex unknown.

This HY Yellow Warbler is neither pale enough to be recognized as a female, nor yellow
enough to be reliably considered a male, so is best considered sex unknown.
Photo by Marcel Gahbauer, McGill Bird Observatory (QC), August 2005

HY Yellow Warblers show minimal pale edging on the primary coverts, and these become increasingly narrow, tapered, and worn over the course of the fall.  The wing does not provide any information to assist in determining sex.

Another example of a HY Yellow Warbler wing, with minimal edging on the primary coverts.
Photo by Marcel Gahbauer, McGill Bird Observatory (QC), August 2005
 

The shape of the rectrices are generally quite reliable for ageing Yellow Warblers, but as examples within the HY-M and HY-F sections illustrate, there is a fair amount of variability in extent of yellow and brown on the outer rectrices, and therefore this should be used with caution as a guide to sexing.

This example shows the classic narrow and tapered shape of HY rectrices.  The amount of
brown on the outer rectrices is more suggestive of a female, but may be within the range of
variation of males and would not be enough to determine sex unless all other features
were consistent with female characteristics too.
Photo by Marcel Gahbauer, McGill Bird Observatory (QC), August 2005

RETURN TO AGE/SEX OVERVIEW

Juvenile Yellow Warblers are predominantly gray.  Small patches of yellow are usually visible on the face, and there is greenish-yellow edging on the wings and tail.

Photo by Marcel Gahbauer, McGill Bird Observatory (QC), July 2005
 

The wing of juvenile Yellow Warblers is predominantly brown/gray, with dull yellowish-green edging to the primary coverts and flight feathers.   

Photo by Peter Pyle, Southeast Arizona, June 2007

Photo by Marcel Gahbauer, McGill Bird Observatory (QC), July 2005
 

Fledgling Yellow Warblers leave the nest before their tails are fully grown, thus it is fairly common to see juveniles with short tails, such as the one shown below.  Note that the feathers are pointed and largely brown, but with distinct yellow edging.

Photo by Marcel Gahbauer, McGill Bird Observatory (QC), July 2005

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