August - is
ALL about molt, molt, molt and one of the most exciting times for
banders. It can also be a confusing time for inexperienced banders
trying to age hatch year birds which have completed their 1st
prebasic molt but are retaining very fresh juvenal feathers.
An example of this is illustrated below showing the wing of a hatch
year (HY) male Yellow Warbler. On first glance at the photo below
left it could be fairly easy to age this bird as an adult given the
very fresh appearance of the wing, the edged primary coverts and
fairly truncate remiges (primaries and secondaries). However once
the wing is examined under magnification (photo below right) it is
easy to see the difference between the replaced lesser, median,
greater coverts and carpal covert and the retained juvenal primary
coverts and alula, the molt limit shown with the red arrow between
the outer GC and inner PC. The replaced feathers are better quality
feathers, more darkly pigmented with darker rachis and more
interlocking barbules and, therefore, tighter barbs, giving them a
more solidly structured appearance compared to the adjacent retained
juvenal feathers. Notice too the subtle difference between the
replaced greater alula covert A1 (indicated with the black arrow)
and retained lower alula feathers A2 and A3.
For this reason, especially after
adults of these same species begin to show signs of approaching the
end of their complete prebasic molt banders should always confirm
age by additional criteria such as skull ossification.
One of these
additional criteria which is helpful in Wilson's Warblers is the
variation in the extent of the crown patch illustrated on the two
males below being glossy black on adults (left) and extending
further forward and backward than on hatch year birds (right) which
are less extensive and show greenish yellow mottling.
This hatch year
(HY) male Orange-crowned Warbler (OCWA) had also completed its 1st
prebasic molt replacing lesser. median, greater coverts and carpal
covert. As in the Yellow Warbler example above the primary coverts,
alula and remiges are all retained but still fresh juvenal feathers
the molt limit indicated with the red arrow between the outer GC and
Molt limits in the making!
Birds in active molt give us an opportunity to see molt as it is
happening. This is particularly helpful to new banders who have an
opportunity to learn the sequence of events in both complete and
less than complete molts.
The photo below left shows a hatch year (HY) Orange-crowned Warbler
undergoing its 1st partial prebasic molt with lesser coverts
replaced and median and greater coverts in sheath. In many species
of warblers, sparrows and vireos, all lesser, median & greater
coverts but no tertials, retrices or other flight feathers are
The photo below right shows an adult Lincoln's Sparrow in the midst
of its definitive adult prebasic molt. This bird is replacing all
body and flight feathers. This sequence starts with the lesser and
median coverts, then tertials and innermost primaries, primary
replacement proceeding distally towards the outermost primary (P9 or
P10). Primary coverts are molted with the corresponding primary.
Greater coverts which are in sheath here commence after the start of
the primaries and proceed proximally towards the birds body with the
innermost GC10 the last replaced. The carpal covert is replaced when
the GCs complete and is not yet molted in the photo below. After the
tertials the remainder of the secondaries will be replaced beginning
with the outermost and proceeding proximally towards the birds body
with secondary 6 (S6 indicated with the red arrow) being the last
flight feather replaced.
The alula covert (indicated with the blue arrow) is molted at the
same time as the median coverts and is a molted feather in this
photo. However the alula feathers are molted during molt of the
primaries and are among the last feathers to be replaced.
prebasic molt like this adult birds can still be aged second year or
after second year based on the contrast between the molted alula
covert and as yet unmolted alula. Here all are worn but too brightly
coloured to be juvenal feathers. This bird was therefore aged after
second year (ASY) i.e. an adult bird going through at least its
second definitive adult prebasic molt.
female Yellow Warbler in the last stages of its adult prebasic molt
was aged as a second year (SY) on the basis of the as yet unmolted
alula. The molt limit is clearly visible between the darker and more
greenish-edged alula covert and retained and now very worn dull
brown juvenal middle and lower alula feathers.
Within another week or so the alula will be molted in both of these
birds which would then simply be aged as after hatch year (AHY).
This hatch year
(HY) Yellow Warbler had completed its 1st prebasic molt which
included lesser, median and 9 inner greater coverts (the red arrow
pointing to the single retained outer GC 1), carpal covert, greater
alula covert A1 (indicated by the blue arrow) and all 3 tertials
S7-9 (indicated by the black arrow).
The 1st prebasic
molt in Purple Finches (PUFI) normally include 3 to 10 greater
coverts but no flight feathers. This hatching year (HY) PUFI was
replacing 9 inner GCs showing a molt limit in the making between GC
2 in sheath and the retained outermost GC 1.
Many birds in the
midst of prebasic molt look pretty scruffy and that was certainly
the case with this male Purple Finch.
PUFI males have delayed plumage maturation meaning they do not
acquire male plumage traits until they are more than one year old
(i.e., at the time of their definitive prebasic molt, which is their
first complete post-breeding molt).
Until this time they resemble the brown-streaked females.
Thus, a male PUFI that is replacing brown juvenal and first basic
feathers with new raspberry-colored feathers is an SY, while one
replacing old purplish feathers with new ones is an ASY.
Now you should be able to age this bird! (Answer at the end of the
Molt is a protein
and energy demanding process so birds do not undertake molt when
they are engaged in other energy demanding activities such as
breeding or migration. Most species of passerines molt after the
breeding season either on their summer (breeding) grounds or after
migration on their winter (non-breeding) grounds.
One exception to
this is Swainson's Thrushes (SWTH) which overlap their molt with
migration in a phenomenon called molt-migration. SWTH are long
distance migrants breeding as far north as Alaska and wintering as
far south as Argentina.
The term molt-migration is given to individuals that leave their
breeding grounds and head south to find a suitable location to
undergo their annual prebasic molt before continuing southward
migration. Birds may continue to migrate while actively molting or
they may initiate and/or complete their molt in an area south of
their breeding grounds.
Where arid conditions on the breeding grounds in late summer are not
especially conducive to molting, adults routinely migrate
substantial distances to special molting areas. In general, their
movement away from increasingly drought-stricken breeding habitats
is timed for their arrival somewhere in the desert Southwest or
Mexico during the period of monsoon rains. The flush of insects
associated with these rains constitutes a bumper-crop resource for
the energy and protein-demanding molt process.
Our research at Colony Farm has shown that many birds caught for
banding after the breeding season are in molt suggesting the site
could be a special molting area for this species. Interestingly,
following the breeding season we see an influx of unbanded birds and
we suspect these are birds leaving their breeding grounds further
north and undertaking molt here before continuing southbound
The photos below
show a hatch year (HY) SWTH (left) molting inner greater coverts
(GCs) as part of its partial 1st prebasic molt, the molt limit is
between the 4 retained outer GCs and 6 inner GCs in sheath and an
after hatch year (AHY) SWTH (right) molting inner primaries as part
of it's complete adult prebasic molt.
This hatching year
(HY) SWTH had completed it's 1st prebasic molt showing a clear molt
limit (indicated with the red arrow) between the replaced inner 3
greater coverts and the retained 7 outer greater coverts.
Notice the buffy
tipping or 'tear-drops' on the retained outer greater coverts and
the chocolate brown edging on the replaced inner coverts.
Notice also the replaced feathers are longer than the retained ones
producing the visible 'step-in' between replaced and retained
coverts typical of Catharus thrushes.
In many species the
1st prebasic molt is incomplete meaning that not only are contour
feathers replaced but additional flight feathers can also be
replaced. This hatching year (HY) Lincoln's Sparrow had replaced
lesser, median, greater coverts, carpal covert and the two inner
most tertials (S8 & 9) - molt limits are indicated between the
replaced outer greater covert and retained inner primary covert
(green arrow), between the replaced greater alula covert (A1) and
the main alula feather A2 (blue arrow) and the two tertials S8
and S9 (blue arrow). When tertials are replaced like this central
retrices are also sometimes replaced which was the case with this
As many birders know summer and fall
can also be a confusing time trying to identify hatch year birds in
juvenal and first basic plumages especially when they may only get a
fleeting glimpse and don't have the benefit of the bird in the hand
as banders do. The two birds below are good examples of this looking
very different from their adult counterparts - answers at the end of
We conduct several
studies at Colony Farm involving colour banding birds. One such
study in association with Wildlife Rescue Association of BC (WRA)
involves releasing some WRA rehabilitated birds in the park to see
if survival rates can be determined through recapture and resighting
of colour banded birds.
At this time of year WRA are inundated with
nestlings and recently fledged birds brought in to the shelter by
members of the public and WRA staff and volunteers do an amazing job
of hand rearing and caring for these birds until they are ready to
be released. We have banded and released 8 fledgling American Robins
this year and have posted signs in the park requesting sightings of
colour banded birds.
Upon release one baby Robin promptly flew
and landed on the VARC truck maybe
trying to convince us that our logo should include a Robin and not a
hatching year female Cooper's Hawk was a nice surprise and had
everyone running back to the station from net rounds when the radios
announced her arrival!
Flycatcher had us scratching our heads again this month and thinking
'Alder'! We band so many Willow Flycatchers which breed in the park
that when a bird shows up like this one it just doesn't 'feel'
right. These 'odd' birds have much whiter throats and breasts than
our WIFLs, much paler lores and narrow, white, albeit faint
According to other banders familiar with ALFL they also tend to
'whine' in the hand which our WIFLs never do. This bird constantly
whined! This trait is definitely not in 'Pyle' but an interesting
When the breeding range of Alder Flycatcher is considered it's
inconceivable that all of the birds breeding in northern BC migrate
eastwards and none return down the coast and we'd be interested to
hear the thoughts of any other banders who have experience with this
Less confusing was
this hatch year (HY) Pacific-slope Flycatcher.
This hatch year
male Common Yellowthroat (COYE) was actively undergoing its first
prebasic molt with the greater coverts, carpal covert and upper
alula (A1), or alula covert, in sheath and flakes of sheathing from
pin feathers coming in all over its head and body.
At this time of the year birds like this one with blackish in the
lores and auriculars can be sexed male although birds without
blackish in the lores and auriculars should not be sexed female as
apparently a small proportion of males lack blackish after the 1st
We have never seen evidence of this with the many COYE banded at
Colony Farm with retrap data showing hatch year birds without
blackish in the lores and auriculars are indeed females.
weather for most of the month Vancouver was looking at its stunning
best and the hot, sunny summer days gave us time for a quick sun
bathe between net rounds - well all this banding can wear a guy out!
this month as we bid farewell to British ringer Gabriel Jamie a
student from Cambridge University who spent the summer working at
the University of British Columbia (UBC) and his spare time at
weekends volunteering for VARC. Gabriel is an accomplished ringer,
was a fantastic help and although he looks really serious in this
photo was also a lot of fun!
He learnt a bit from us on molt (well maybe more than a bit!) and
how to use the body grab method for net extractions and despite his
tender years was able to teach us a new net furling technique!
This method (photo
below right) involves furling as normal where the lower shelves are
spun in to the top shelf and furled as normal but then rather than
being tied with trail tape or pegs the net is spun by standing in
the centre of the net using two hands in a pedaling motion to wind
the net tightly on either side of the furler and then simply tied
off to a nearby piece of brush. This is difficult to describe and
even more difficult to do at first but once mastered really is quite
None of us have seen this net furling method at any stations we have
ever visited but we would highly recommend it especially if nets are
being used in open and/or windy areas. The net ends up very tightly
furled avoiding any loose strands and is exceptionally easy to
unfurl in the mornings as it requires no trail tape or pegs and even
more importantly makes net furling by one person much easier and
less time consuming. We may try to video the process and put it up
on U-Tube for anyone interested in learning the technique.
I'm not sure
Gabriel is going to miss us all that much as his travels now take
him on a birding expedition to Peru - We're all very jealous! Thanks
for all your help Gabriel - we'll miss you! (P.S. Nice hat!)
Hatch year Cedar
Waxwings (CEDW) were much in evidence this month as berries ripened
throughout the park. Young CEDWs like these are not only among the
cutest of all the baby birds we see they are also among the most
confiding often remaining perched on fingers (photo below right) and
refusing to leave when released!
This hatch year (HY) male
Sharp-shinned Hawk provided an opportunity for us to see the
nictitating membrane, the translucent 'third eyelid' present in
birds that can be drawn across the eye for protection and to moisten
it while maintaining visibility.
Unlike the upper and lower eyelids, the nictitating membrane moves
horizontally across the eyeball. In birds of prey like this
Accipiter, it also serves to protect the parents' eyes when
feeding nestlings. According to one raptor expert when Peregrine
Falcons go into their 200 mph dives, they blink repeatedly with the
nictitating membrane to clear debris and spread moisture across the
This hatch year
(HY) male Hairy Woodpecker was a nice surprise too. Downy
Woodpeckers (DOWOs) are common in the park but HAWOs less so
preferring to forage along main branches and trunks of larger trees
which are absent in the banding area.
arrangement of toes in passerines is 3 toes in front and 1 in back
in a configuration termed anisodactyl. Toes are numbered 1 to
4, 1 being the hind toes or hallux and 2 to 4 are front toes
numbered from inner to outer.
In woodpeckers toe
4 has shifted to the back in a configuration termed zygodactyl
with 2 toes forward and 2 back to aid in climbing.
We talked last month about the
red juvenal crown patch in hatch year male
DOWOs and how the red nuchal patch (on the back
of the head) characteristic of 'adult' males molts in during the
birds 1st prebasic molt. This hatch year male HAWO in the midst of
its 1st prebasic molt is showing the last remnants of its red
juvenal crown molting in to the red nuchal patch of an 'adult' male.
Thanks to Mark
Habdas, Kerry Kenwood, Carol Matthews, Jason Jones, Marg Anderson,
Jerry Rolls, Debbie Wheeler, Sarah Gray, Marianne Dawson, Mike
Nutter, Marguerite and Chris Sans and Gabriel Jamie for their help
with banding this month.
- The two birds above in juvenal plumage are White-crowned
Sparrow (left) and Savannah Sparrow (right).
- The Purple Finch wing belongs to a second year (SY) male Purple
Finch undergoing its first definitive prebasic molt.