Introduction
On 13 May 2013 at roughly 0640 EDT, we were birding just south of the Sparrow Field at Point Pelee National Park, Essex, when we spotted an unusual chickadee in close proximity to a typical Black-capped Chickadee (Poecile atricapilla). Our attention was immediately drawn to its grayscale, low-contrast appearance and slightly atypical GISS (general impression of size and shape). Our impression was that this was a Carolina Chickadee (Poecile carolinensis), yet both of us knew that there was only one previously accepted record of this species for Ontario and Canada: a single bird observed on 18 May 1983 at Long Point (Tip), Norfolk (Weir 1983, James 1984). This prompted us to begin taking sample photographs in an attempt to properly document the individual. Although we each had previous experience with Carolina Chickadee in the species’ core range, the identification is notoriously difficult (Kaufman 1990). After several minutes of observation, the bird remained silent and we continued onwards with the morning’s birding.
Later that day at
the park’s visitor centre, we queried the available references for new insight
into this difficult identification. The popular field guides focused heavily on two features: a white
vs gray nape and brighter vs paler edging on the flight feathers for
Black-capped and Carolina, respectively (Sibley 2000, Peterson 2008). Review of
our photographs revealed a bird with faint feather edging, suggesting Carolina,
but inconclusive as the lighting and angle in various photographs seemed to
change the appearance dramatically. Feeling stuck, we did little more in the
short term, other than Holden posting some photos with a request for opinions
on his web log (Holden 2013a).
We continued to
bird in the Point Pelee area over the next two days and discussed the sighting
with other birders. On 14 May, Peter S. Burke commented that the amount of
white edging on the greater coverts was an excellent mark for helping to
identify individuals of this complex, and that the bird in our photographs looked
much better for Carolina. On the morning of 15 May, we were witnessing a
moderate reverse migration
at the Tip of Point Pelee when various
observers (including Peter S. Burke) began arriving and informed us that they
too had seen the subject chickadee at various times around the Tip area. All
agreed that it was easily detected among Black-capped Chickadees due to its
relatively distinctive appearance.
At roughly 0800 EDT
on 15 May, we had the opportunity to observe the subject chickadee at the
extreme Tip with two typical Black-capped Chickadees. Once again it stood out
immediately due to its greyscale, low contrast appearance and different GISS.
It was present for a short period of time before flying northwards away from
the Tip. Alan Wormington had independently recognized the bird from some distance
to the south and simultaneously pursued the bird northwards.
As various
observers moved north, multiple Black-capped Chickadees were detected around
the Point causing considerable confusion. Regrettably the subject chickadee was
not observed again.
After additional
information from the 15 May sighting was posted online (Holden 2013b), we
received photographs of the subject bird taken just north of the Tip of Point
Pelee on 12 May by Hayden J. Bildy. He was birding with R. Gordon Payne at the
time, who also observed the bird (Burrell and Charlton 2015).
Over the next
several months, we conducted extensive research on this difficult
identification. Presented below are the results of that research and why it
supports the identity of this bird as a Carolina Chickadee.
Identification
In this section, we highlight the following identification criteria, derived from numerous sources: head size and shape, bill size and shape, bib size and shape, nape colouration, cheek patch vs breast colouration, secondary and tertial edging, greater coverts base shade and edging, tail feather edging and tail length/wing chord ratio. Regrettably no vocalizations were heard by any observers. Our analysis compares the Point Pelee individual with the criteria for known Carolina Chickadee and Black-capped Chickadee. A detailed comparison of each trait with photo examples was submitted to the OBRC (Holden 2013b, Holden 2013c, Holden and Bell 2014) and is archived at the Royal Ontario Museum (ROM).
Head Size and Shape: A review of many photographs of
Black-capped and Carolina chickadees showed that Carolina frequently appears to
have a smaller and rounder head in contrast to Black-capped Chickadee which
frequently shows a proportionately larger head, appearing as a horizontal oval
in shape. The Point Pelee individual was a better match to known Carolina
Chickadees (Figs. 1, 2).
Bill Size and Shape: This is difficult to properly quantify
from photos. After reviewing hundreds of Black-capped Chickadee photographs
from southern Ontario, our impression was that the Point Pelee bird had a
smaller and shorter bill (Figs. 1, 2). It does not appear to show any dramatic
differences from known Carolina Chickadees when compared to photographs from
various online sources. Pyle (1997) lists the exposed culmen of Black-capped as
measuring 7.6-10.5mm and of Carolina as 6.6-9.5mm.
Bib Size and Shape: In some identification guides, Carolina
Chickadee is described as having a smaller and more sharply defined bib than
Black-capped Chickadee (e.g., National Geographic 2002). Approximately 100
photos were taken of the Point Pelee individual by the authors, which revealed
a remarkable range in bib size and shape. This range was most pronounced during
periods of activity, with the bird stretching or twisting its neck to obtain
food or move to a new perch. During the few moments when the bird was at rest,
the bird’s bib size and shape was well defined and small and was a better match
for Carolina Chickadee than examples of Black-capped Chickadee (Fig. 3).
Nape Colouration: Although this
character is frequently referenced in field guides (e.g., Peterson 2008), we
had a difficult time assessing this feature when using images. Variations in
exposure settings yielded results from pure white to neutral gray. We felt that
this feature was not useful when studying photographs although perhaps it would
be a better feature when scrutinized with a live specimen in hand.
Cheek Patch vs Breast Colouration: During formal review of the record by
the OBRC, Peter S. Burke identified a potential feature of Carolina Chickadee
on the Point Pelee individual stating that the breast appeared to be a duller
gray than the bright white cheek patches (Sibley 2014). Photos of Black-capped
Chickadee often show a breast that is as bright/white as the cheek patches.
This feature was not examined on skins or as extensively with photographs as other
field marks noted here, yet it appears to support the identification of the Point
Pelee bird as a Carolina Chickadee.
Secondary and Tertial Edging: Examination of photographs online and
of the Point Pelee bird shows that this
feature is variable depending on angle and camera settings, even with a single
individual. Carolina Chickadee is reported to show a more muted pattern,
compared to Black-capped Chickadee (Sibley 2000). When considering the approximately
100 images of the Point Pelee individual, our overall impression was of a bird
that fell within the range for Carolina Chickadee (Fig. 2), but appearing as an
outlier in the variation observed in Black-capped Chickadee.
Greater Covert Base Shade: A field mark rarely referenced is the
base shade or colour of the centres of the greater primary and secondary coverts.
It is reported to be gray in Carolina Chickadee, whereas in Black-capped
Chickadee it is black (Crossley 2011). The greater coverts in photographs of
the Point Pelee individual in which the bird had spread wings are a medium
gray, matching Carolina Chickadee (Fig. 4), although the sample size was small.
Holden studied nearly 300 skins of both species at the ROM and found that this
feature is not reliable in direct comparison. We presume it is simply a
difference in impression, with Black-capped appearing more contrasting than the
uniform gray of Carolina.
Greater Covert Edging: Another field mark that is occasionally
referenced is the contrasting white edges to the greater coverts of Black-capped
Chickadee whereas Carolina shows a uniform gray edge. While it appears possible
for Black-capped Chickadee to lose these white edges due to feather wear
(especially in spring as chickadees do not do a pre-alternate molt (Pyle 1997)), our examination of photographs has
shown it to be rare. The Point Pelee individual shows a uniform gray edge on
all feathers on each wing, matching known examples of Carolina Chickadee (Fig. 5).
Rectrices: Pyle (1997) states that Black-capped Chickadee can be separated from
Carolina Chickadee “by the [presence of] white edging to the outer rects”. Despite only
retaining three rectrices, the Point Pelee individual clearly shows a white
edge, which was originally identified as a problem in the identification of
this bird as a Carolina Chickadee. We set out to confirm the validity of this
feature and discovered that many Carolina Chickadees from the central and
northern parts of the species range show white edges on the rectrices (Holden
2013d). Thus the white edging on the Point Pelee bird appears well within the
variation shown by pure Carolina Chickadee and does not contradict that
identification. Review of specimens at the ROM also showed that this is a
feature frequently shown by Carolina Chickadee including the first provincial
record (Holden 2014). Review of Black-capped Chickadee photographs has shown a
bolder and more prominent edge to the rectrices than Carolina Chickadee.
Tail Length/Wing Chord ratio: Pyle (1997) states that tail length is
the most useful character in separating Black-capped from Carolina chickadees. Although
impossible to accurately measure without a bird in-hand, tail length relative
to wing chord can be useful as the “tail/wing ratio can then provide further
means for separation: 0.886-1.032 (usually >0.9) for Black-capped,
0.819-0.922 (usually <0.9) for Carolina” (Pyle 1997:335).
Using photographic samples of 10 known Black-capped Chickadees, 10 known
Carolina Chickadees and 15 of the Point Pelee bird, we set out to see if the
tail/wing ratio could be useful in this case. For this analysis to be
conducted, photos that showed the bird in profile were chosen because the wing
and tail were held at approximately the same angle to the photographer. We used
the ruler tool in Adobe Photoshop CS4 to determine lengths of wing chord and
tail for each photo. These values were then inserted into a Microsoft Excel
spreadsheet which calculated the tail/wing ratio (tail length divided by wing
chord). We then sorted the values into Black-capped Chickadee (BCCH), Carolina
Chickadee (CACH) or intermediate (Figure 6).
Four (of 10) photos
of Black-capped Chickadee resulted in values that were within the overlap
range, but still above the ‘usual’ cut-off of 0.9.
Three (of 10) photos of Carolina Chickadee resulted in values that were
similarly within the overlap range (0.886-0.922), with one being
above the ‘usual’ cut-off of 0.9 but still within variation for Carolina Chickadee
(Figure 1). All other photos fell within the expected range for their
respective species. The 15 photos of the Point Pelee bird showed an average tail/wing
ratio of 0.8667 and a standard deviation of 0.0086 (1%) showing that measuring
error (possibly due to differences in posture) was minimal. The same average
and standard deviation statistics cannot be applied to the known photos of
either species as they represent different individuals. The values obtained for
the Point Pelee bird are all within the variation for Carolina Chickadee, and
more importantly, all are below the minimum ratio for Black-capped Chickadee.
General Impression (GISS): A final thought, which is once again
difficult to quantify, we and other observers were readily able to detect the
bird when it was present, due to its a distinctive GISS. The general colour,
low contrast appearance and atypical shape combined to produce a very
noteworthy individual. Many field marks presented here were unknown to us at
the time of observation, and have been correlated with the Point Pelee bird only
after additional research was conducted.
Conclusion: While many features listed above are overlapping, there is no single
feature present on the bird that is outside the range of Carolina Chickadee.
Subspecific Identity
Pyle (1997) noted that geographic variation in Carolina Chickadee is weak and clinal where the ranges of subspecies meet. Mostrom et al. (2002) list four subspecies, following Snow (1967) and Philips (1986) which are detailed below.
P. c.
atricapilloides A large, gray subspecies that occurs from south Kansas through
central Texas.
P. c. agilis A medium sized, gray
subspecies occurring from south Arkansas to southeast Texas and south
Louisiana.
P. c. carolinensis A small, dark gray subspecies with an
olive tinge occurring from north Arkansas-southeast Louisiana through to southeast
Virginia-Florida. Synonymous with P.c. impiger.
P. c. extima A
large and slightly more colourful subspecies, noted as having more extensive
white on the secondaries, sides and flanks. This subspecies occurs north of P.c.
carolinensis west to eastern Missouri. Subspecific name formerly “extimus”
(AOU 2000).
We compiled approximately
300 photos of Carolina Chickadees from various online and published sources.
Study of P.c. carolinensis reveals the strongest differences from the
Point Pelee individual, being darker and less contrasting overall. An
examination of birds from within the ranges of P. c. atricapilloides and
P. c. agilis also showed differences, especially as few individuals
showed white on their outer retrices as well as showing a more uniform gray
appearance overall. The white on the outer rectrix of the Point Pelee Carolina
Chickadee matches known individuals from the northern tier of the species range
such as Illinois, Ohio, Indiana and Pennsylvania – all of which would
fall within the range of P. c. extima. After further examination, there
were no differences between the Point Pelee bird and photos of birds within the
range of P. c. extima; leading us to believe that it is the appropriate
subspecific identification for this bird.
Hybridization
Hybrids between the
Black-capped and Carolina Chickadees have been detected wherever the contact
zone between them has been studied (Sibley 2009). The same article states that
hybrids are less fit than pure birds, leaving hybrid populations small and
stable. Given that the Point Pelee bird shows no outward sign of hybridization
in the form of intermediate characteristics of head size and shape, bill size
and shape, bib size and shape, cheek patch vs breast colouration, secondary and
tertial edging, greater coverts base shade and edging, tail feather edging and
tail length/wing chord ratio; the authors felt it was reasonable to identify it
as a pure Carolina Chickadee.
Discussion
Canada’s first Carolina Chickadee record, initially listed as P. c. impiger by James (1984), was later published as the synonymous subspecies P. c. carolinensis by Gustafson (1987). After a thorough examination of the specimen, Parkes (1988) changed the subspecific identity to P. c. extimus (now P. c. extima), which is the same as our identification of the Point Pelee individual. A query of the eBird database shows the stable northern boundary of the Carolina Chickadee range surprisingly close to our observations at Point Pelee, measured to as little as 80km SSW at Findlay, Ohio (eBird 2014). With other records of vagrants occurring in northern Illinois (American Ornithologists Union 1998), southeast Michigan (Reinoehl 1997), northern Ohio (Williams 1944) and western New York (Bent 1946), the Carolina Chickadee has a well-established pattern of short-distance vagrancy in the Great Lakes region. The contact zone between Carolina and Black-capped chickadees has been slowly moving northwards (Taylor et al. 2014) and has a female biased dispersal. While impossible to know, the quiet nature of the Point Pelee bird may have been due to the possibility that it was a wandering female. It is not outlandish to suggest that future records will materialize in southern Ontario. Perhaps the only limiting factor is the high degree of difficulty in detecting, identifying and properly documenting any future observations.
The sighting from
12-15 May 2013 at Point Pelee National Park was accepted by the OBRC as the
second record for Ontario and Canada (Burrell and Charlton 2015).
Side Note. A possible occurrence of Carolina
Chickadee in Ontario has been published (Jarvis 1965), based on song only, the
bird was never seen. However, this report was not accepted by the OBRC
(Wormington 1985).
Photo: David Bell
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Accessed 2 February
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