McGILL BIRD OBSERVATORY

PHOTO LIBRARY

Red-eyed Vireo / Viréo aux yeux rouges (Vireo olivaceus)

 Seasonal status at MBO:

JAN
       
FEB
       
MAR
       
APR
       
MAY
       
JUN
       
JUL
       
AUG
       
SEP
       
OCT
       
NOV
       
DEC
       
  common
  fairly common
  uncommon
  rare
  occasional
  no records
 
QUICK TIPS:
1) Check the iris colour - it is grayish-brown on HY/SY birds, and red on AHY/ASY birds; note that this is only reliable from summer through March; eye colour should not be used to assess age during spring migration.

2) Look at the upper mandible lining - it is pinkish-gray to white on HY/SY birds, and dark gray on AHY/ASY birds; note that this is only reliable from summer through February; mouth colour should not be used to assess age during spring migration.

3 In spring, look for molt limits among the secondaries - on SY birds there is little contrast in wear between the tertials and middle secondaries (all of which are fairly worn), while on ASY birds the tertials are considerably more worn and abraded than the middle secondaries (but all of which are relatively fresh).

Ageing and sexing guidelines:

January - May:

ASY - U
Sexes identical.  Broad primary coverts with green edging, often a visible contrast among secondaries at s6/s7.

SY - U
Sexes identical.  Primary coverts narrow with minimal edging, secondaries relatively worn and uniform in age.

-

May - December:

AHY - U
Similar to ASY-U (see above); roof of the mouth dark gray, iris red.
HY - U
Similar to SY-U (see above); roof of the mouth pale pinkish-gray, iris gray to brown.
JUV - U
Similar to HY-U, but with weak wing bars, and generally more brownish in appearance.
     
 

Ageing and sexing details:

after-second-year unknown

In spring, all ages and sexes of Red-eyed Vireo have a similar overall appearance, and it is necessary to view the wings and tail to distinguish among them. 


Photo by Marcel Gahbauer, May 2005
 


One of the key distinguishing features of ASY Red-eyed Vireos is the presence of distinct green edging on fairly broad and rounded primary coverts, as shown in the photo below.  Also sometimes useful, though not visible in this photo, is a contrast between secondaries 1-6 (fresher) and 7-9 (older and more faded). 


Photo by Peter Pyle, Howell Woods (NC), May 2006
 


ASY Red-eyed Vireos have relatively broad, truncate, and fresh rectrices.


Photo by Marcel Gahbauer, May 2005

RETURN TO AGE/SEX OVERVIEW

 

second-year unknown

In spring, all ages and sexes of Red-eyed Vireo have a similar overall appearance, and it is necessary to view the wings and tail to distinguish among them.  However, sometimes SY birds will retain a somewhat brownish tone to the iris, as in the bird below.


Photo by Marie-Anne Hudson, May 2007


The primary coverts on SY birds are narrower and more tapered than on ASY individuals, and with little or no greenish edging.  The secondaries are uniform in age.


Photo by Marie-Anne Hudson, May 2007


The rectrices on SY birds tend to be somewhat narrower and more tapered, and of weaker quality than those on ASY birds.


Photo by Marie-Anne Hudson, May 2007

RETURN TO AGE/SEX OVERVIEW

 

after-hatch-year unknown

In fall, Red-eyed Vireos are generally indistinguishable with regard to sex, aside from exceptionally small females or large males (as measured by wing chord).  However, ageing is easily done by iris colour:  red in after-hatch-year birds, and brownish in hatch-year birds.  Additionally, the roof of the mouth is dark gray in adults, noticeably different from the pale gray or pink in hatch-year birds.


Photo by Marcel Gahbauer, August 2005


Photo by Seabrooke Leckie, August 2006


Photo by Marie-Anne Hudson, McGill Bird Observatory, August 2007
 


Red-eyed Vireos are somewhat unusual in that the prebasic moult commences on the breeding grounds, but in adults the majority of it takes place during winter.  As such, there may be moult limits in the wing of older birds, whereas they are unlikely in younger birds (the reverse of the usual pattern).  In practice, however, they are relatively infrequently seen, and other features (iris, mouth lining, and tail) are all easier and more reliable.. 


Photo by Marie-Anne Hudson, McGill Bird Observatory, August 2007


Photo by Seabrooke Leckie, August 2006


Photo by Seabrooke Leckie, August 2006
 


AHY Red-eyed Vireos may have a uniform tail comprised of relatively broad and truncate rectrices.  However, some begin replacing the central rectrices prior to migration (as shown in the second photo below), and this is a reliable indicator of age, as hatch-year Red-eyed Vireos do not replace any rectrices in their limited prebasic moult.


Photo by Seabrooke Leckie, August 2006


Photo by Marcel Gahbauer, August 2005

RETURN TO AGE/SEX OVERVIEW

hatch-year unknown

In fall, Red-eyed Vireos are generally indistinguishable with regard to sex, aside from exceptionally small females or large males (as measured by wing chord).  However, ageing is easily done by iris colour:  red in after-hatch-year birds, and brownish in hatch-year birds.  Additionally, the roof of the mouth is pale gray or pinkish in hatch-year birds, noticeably lighter than the dark gray of adults.


Photo by Marcel Gahbauer, August 2005


Photo by Seabrooke Leckie, August 2006
 


Hatch-year Red-eyed Vireos undergo only a very limited prebasic moult, and that of the adults is also not very advanced by the time of migration, therefore the wings are not particularly informative with this species.


Photo by Marie-Anne Hudson, McGill Bird Observatory, August 2007


Photo by Marcel Gahbauer, September 2008
 


HY Red-eyed Vireos do not replace any rectrices during their first prebasic moult, therefore all tail feathers are expected to appear relatively uniform.  They tend to be more narrow and tapered than those of AHY birds.


Photo by Marie-Anne Hudson, McGill Bird Observatory, August 2007


Photo by Seabrooke Leckie, August 2006

RETURN TO AGE/SEX OVERVIEW

 

2002- The Migration Research Foundation Inc.