Nova Scotia's 4th Dusky Flycatcher

Our Fourth Dusky

On Dec. 2, 2014, Bernard Forsythe found what was later identified as a Dusky Flycatcher in Greenwich, Kings County. The Greenwich Empid spent its time at field edges and in orchards owned by Harold Forsyth. It was observed by many Nova Scotia birders over the next few weeks.

Greenwich Empid on Dec. 13. 2014 - Photo by Keith Lowe

This bird is only the 4th confirmed Dusky in Nova Scotia. Information about the previous three records is found below.

Oct. 6, 2014 - banded on Bon Portage Island, Shel. Co. (NS-RBA post)

Oct. 12, 2012 - banded on Bon Portage Island, Shel. Co.  (NS-RBA post)

Nov. 26 - Dec. 27, 1996 - Near Port Williams, Kings Co.

Details of early observations of the Greenwich Empid can be found at NS-RBA and a blog post by Owl and Marmot.

Challenging Empids

Identification to species of members of the genus Empidonax can be troublesome. Our North American empids are all small, gray (tinged olive, brown or yellow) birds with wing bars and eye rings.

NS has a history of hosting western flycatchers in late fall and early winter. The overall structure and colour of the Greenwich Empid points to one local breeder (Least Flycatcher) and 2 western vagrants (Dusky and Gray Flycatchers) as potential candidates. As compared to the other empids, these three have relatively short primary projections, and similar wing length divided by tail length ratios. This wing length (wg) over tail length (tl) ratio (wg/tl) supplies us with a number that represents how long winged, and thus, how sleek or stubby the bird appears. Below are these ratios for our three candidates.

Wing over tail ratios (wg/tl)

1.17 - Least

1.12 - Dusky

1.17 - Gray

Other empids such as Alder Flycatchers are relatively longer winged and short tailed, giving them a wing over tail ratio of  1.26. These ratios were calculated using average measurements as given in Identifying Empidonax Flycatchers: The Ration Approach found in the March 2009 edition of Birding. This Birding article makes use of differences between wing and tail lengths. Ratios are more useful when measurements aren't available.

Some early participants in the discussion on identification of this bird have suggested Hammond's Flycatcher. Due, in part, to the quality of the initial photos and videos, Hammond's Flycatcher was also a contender. Bruce's Dec. 9 photos showed a bird with drooped wings which made assessment of primary projection difficult.

Not a Hammond's

Hammond's Flycatchers are described as a relatively colourful empid. All individuals (HY or AHY) would already have completed their body moults by now. This means that a Hammond's would be at its most colourful at this time of year. Plumage colour can be difficult to assess, but the photo below does show the Greenwich Empid as looking less vibrant in comparison to a Hammond's.

Hammond's Flycatchers have the longest primary projection of the 4 species in question. This is quite obvious in the following photo.

Greenwich Empid by Keith Lowe (Left) and Hammond's Flycatcher on Seal I. on Sept. 30, 2014 by David Bell (Right)

A Hammond's usually shows a steep forehead and un-curved crown. These features are shown by the Seal I. Hammond's in the photo above. The Greenwich Empid typically shows a continuous curve from the forehead through the crown.

The bill of a Hammond's is the shortest of the four species in question at 6.0-8.0 mm (tip to nares). Least, Dusky and Gray are 6.3-8.4, 6.5-8.9 and 7.6-10.4 mm respectively. Without measurements and from photos, bill length differences in millimeters or fractions of a millimeter are tough to estimate. According to an article in the March 2009 issue of Birding by Forrest Rowland called Identifying Empidonax Flycatchers: The Ratio Approach, even bill length differences of only two millimeters can translate into discernible differences in the field. Bill size contributes to the overall impression of a bird's head. A small bill makes the empid's head appear large and rounded.

I am of the opinion that this bird has a medium length bill. It does not give the impression of a large, rounded head caused by a very short bill.

Greenwich Empid on Dec. 13, 2014 - Photo by Keith Lowe

There is a relatively long gap between the 5th and 6th primaries of the Hammond's folded wing. A Dusky Flycatcher shows two long gaps of equal length between P4/P5 and P5/P6. This characteristic of wing morphology in favour of Dusky can be seen in the following image.

Greenwich Empid on Dec. 13. 2014 - Photo by Keith Lowe

On Dec. 13, 2014, I was able to record audio of the Greenwich Empid's call. The files were sent to Andrew Horn at the University of Dalhousie in Halifax for analysis. He concluded that my recordings best matched the calls of a Dusky Flycatcher.

Listeners in the field described it as sounding like "whit" - this looks like a simple upsweep on a sonogram. The Hammond's call is described as a "peep" or "pip", which is represented on a sonogram as an upside-down "v". We can conclude that the Greenwich Empid's call is dissimilar to that of a Hammond's.



Audio Spectrograph comparing the Greenwich Empid with a Hammond's Flycatcher

All audio spectrographs were created using the free software Audacity. The y-axis is frequency in Hz and the x-axis represents time in seconds. The Hammond's call was sourced from XenoCanto.



The strongest arguments against Hammond's are most likely the dissimilar calls and lack of a long primary projection.

Not a Gray

On Dec. 9, Bruce Stevens was able to capture excellent video of the empid in question. This video clearly shows that the bird's tail movements are not similar to that of a Gray. Gray Flycatchers show a very distinctive down flick of the tail. From rest, the tail is usually raised ever so slightly then lowered slowly. It is then, more quickly, brought back up to its rest position.

The video clearly shows the tail being flicked upwards from rest. Below are two stills taken from the Dec. 9 video. The left photo shows the tail at rest while the photo at right shows the tail at the very top of the upwards flick.

Stills from a Dec. 9, 2014 video by Bruce Stevens

Below is the Dec. 9, 2014 video recorded by Bruce Stevens.

It terms of colouration, Grays generally look paler than any other empid. In Identification guide to North American Birds, Pyle describes the upperparts of a Gray Flycatcher as uniformly pale grayish or brownish gray (adult) to grayish olive (juv-HY). Kaufman (2011) states that Grays have upperparts and face as medium gray, with faint olive wash on the back but not on the head. This can be compared to a Dusky, in which Pyle describes as having a usually grayish head contrasting with grayish-olive or grayish-brown back.

A Dec. 9 photo by Chris Peters below shows obvious contrast between the darker olive back and grayish nape and face. Photos on the internet show Grays as a much paler bird than our Greenwich Empid (see All About Birds).

Greenwich Empid on Dec. 20 - Photo by Chris Peters

A Gray will always show a distinctly defined dark tip. This feature is missing on the Greenwich Empid, as seen below.

Greenwich Empid on Dec. 13, 2014 - Photo by Keith Lowe

The photo below is of the Dusky Flycatcher that was banded on Oct. 6, 2014 on Bon Portage. It shows the same mandible colouration as the Greenwich Empid. It shows gradual fading to a dark tip on the lower edge.

Dusky Flycatcher on Bon Portage - Oct. 6, 2014 - Photo by Avery Bartels

Birds of North America Online describes the Gray's call as a dry "pit" or "wit", with less of the thick, initial "wh" quality in calls of Least and Dusky. The Greenwich Empid shows a gradual upsweep that is missing in Gray. The Gray's call was sourced from XenoCanto. The second line that is parallel to the primary call for the Gray is a harmonic at twice the frequency of the main call.

Audio Spectrograph comparing the Greenwich Empid with a Gray Flycatcher

Our best anti-Gray arguments are incorrect tail movement, lack of defined dusky tip and differences in calls. 

Not a Least

One difference between a Least Flycatcher and the three western empids (Hammond's, Gray and Dusky) is the wing contrast. A Least has relatively dark flight feathers that contrast more with the pale edging and wing bars than the western species. The composite photo below demonstrates how the Greenwich Empid has less wing contrast that the Least Flycatcher to the right. 

Greenwich Empid by Keith Lowe (Left) and Least Flycatcher on Aug. 30 by Ronnie d'Entremont (Right)

The Greenwich Empid also shows a grayish head that contrasts with a grayish olive back. In comparison, the Least is fairly uniform olive above (see above photo).

Hammond's, Dusky and Gray Flycatchers all have bills with fairly straight sides. Least Flycatchers have bills with curved sides. The photo below shows that the Greenwich Empid has a straight sided bill.

Greenwich Empid on Dec. 9, 2014 - Photo by Bruce Stevens

A Least Flycatcher's call is described as sounding like "pwit" or "pit" (or "whit" by Birds of North America Online). The sonogram for the Least's call below shows more than a simple upsweep. There is another element to the call that is not shown by the Greenwich Empid. The Birds of North America Online's sonogram shows the Least's call as an upwards sloped line followed by a shorter down sloped line. The Least's call below was sourced from XenoCanto.

Audio Spectrograph comparing the Greenwich Empid with a Least Flycatcher

Strong arguments again Least are the contrast between the back and head, a straight sided bill and differences in call. 

Definitely a Dusky

We are now left with Dusky Flycatcher as the best fit for this bird. Wonderful photos, audio and video of this bird's behavior, sound, structure and colour have enabled us to be confident in our identification. The composite image below shows the Greenwich Empid with a Dusky that was banded and measured on Bon Portage in 2014.

Greenwich Empid by  Keith Lowe (Left) and Dusky Flycatcher by Avery Bartels (Right)

The final supporting argument lies in the audio recording. Both the Greenwich Empid and Dusky Flycatcher calls below show a gradual upsweep. This upsweep is what produces a "whit" instead of a "wit". The Greenwich Empids sonogram matches the Dusky Flycatcher's call very nicely as seen below. Again, the second line that is parallel to the primary call and higher in frequency for the Dusky is a harmonic at twice the frequency of the call.

Audio Spectrograph comparing the Greenwich Empid with a Least Flycatcher

 Note: A robust sonogram analysis would require comparing a large sample of recordings. The limited analysis of sound in this post should be taken simply as further evidence and not diagnostic due to the possible variability in calls.

References:

Rowland, F. 2009. Identifying Empidonax Flycatchers: The Ration Approach. Birding. March 2009.

Birds of North America. Online. http://bna.birds.cornell.edu/bna/

Pyle, P., S.N.G. Howell, R.P. Yunick, and D.F. Desante. Identification guide to North American Birds, Part 1, Columbidae to Ploceidae. Slate Creek Press, Bolinas, California.

McLaren, I.A. 2012. All the Birds of Nova Scotia: status & critical identification. Gaspereau Press Ltd, Kentville, N.S., Canada

Sibley, D.A. 2014. The Sibley Guide to Birds 2nd Ed. Alfred A. Knopf, New York, N.Y.

Kaufman, K. 2011. Field Guide to Advanced Birding. Understanding What You See and Hear.Houghton Mifflin Harcourt, New York, NY.

Cory's Shearwaters in 2014 - A Record Year

2014 was a banner year in Nova Scotia for Cory's Shearwater (COSH) sightings. The first and last reports of Cory's were from Bon Portage (Aug. 15 - Oct. 21).  The one day high count from Bon Portage was 18 on Oct. 18. During a NSBS near shore (~ 23 km) pelagic trip out of Sambro on Sept. 16, a crew of experienced birders observed an unprecedented 57 Cory's Shearwaters. See the links below for more information and photos from this historic day.

Owl and Marmot Blog
NS-RBA Post
eBird Checklist

 

This northern hemisphere breeder is a rare visitor to NS during summer and fall. In All the Birds of Nova Scotia, Ian McLaren describes how COSH is almost annual in warmer waters off our Atlantic coast. The many sightings of COSH in 2014 (137 from eBird) combined with the single day high count of 57 leads one to wonder what factors lead to this exceptional year.

 

Cory's Shearwater - Sept. 16, 2014 - Bruce Stevens

 

There were only ten provincial sightings of COSH in 2013 and twelve in 2012. 2011 had a high count of 19 during the Sept. 25 NSBS pelagic trip out of Sambro. In the Winter 2012 edition of NS Birds, Eric Mills explained that the unusually warm waters on the Scotian Shelf contributed to the high number of Cory's in 2011 (NS Birds Winter 2012). COSHs feed mainly on fish and squid in warm open ocean waters.

 

The Coastal Ocean Observation Laboratory of Rutgers University in New Jersey produces, and keeps an archive of sea surface temperature (SST) models of the Gulf Stream. The most striking trend found in the Sept. 2014 data is that the temperature of the majority of the Scotian Shelf is constant throughout the month (16 - 20 degrees Celcius). Previous years show much more variability in temperature, from 10 to 23 deg. Celcius.

 

After passing Cape Hatteras, the Gulf Stream turns towards the east and some of its meanderings break free and keep heading northward. These warm cores are typically 100 to 200 km across and can be up to 1.5 km deep. The usual alternating warm and cold waters on the Scotian Shelf can be attributed to this warm core mechanism.

 

The model below shows a cool Scotian Shelf in Sept. 2013 that never occurred in Sept. 2014.

 

SST for Sept. 27, 2013 from Rutgers Coastal Ocean Observation Laboratory

 

The following model depicts what the Scotian Shelf was like throughout all of Sept. 2014. The models do not show any days with substantial amounts of cold waters over the shelf (less than 16 deg. C.).

 

SST for Sept. 17, 2014 from Rutgers Coastal Ocean Observation Laboratory

 

We can hypothesise that continuous warm water conditions on the Scotian Shelf may have allowed warm water prey to make its way close to Nova Scotia. The variability of the temperature in previous years may not have been consistently warm enough to entice the Cory's Shearwaters's prey.

 

The sparse sampling of the abundance of Cory's Shearwater off of Nova Scotia's southern coast does not allow for a robust analysis of trends. There are probably a multitude of factors that influence the abundance of COSH that occur near NS but we can assume that food location and thus sea temperature is high on the list.

 

 

References:

 

McLaren, I.A. 2012. All the Birds of Nova Scotia: status & critical identification. Gaspereau Press Ltd, Kentville, N.S., Canada.

 

Sibley, D.A. 2014. The Sibley Guide to Birds 2nd Ed. Alfred A. Knopf, New York, N.Y.

 

Thurston, H. 2011. The Atlantic Coast: a natural history. Greystone Books, Vancouver, BC, Canada.

Chebogue Point - Sparrowville

Cape Forchu was the Yarmouth County warbler/vireo hotspot in September and Chebogue Point has been the sparrow mecca in October and early November. Chebogue is another of Yarmouth County's many peninsulas. It is situated directly south of the Town of Yarmouth. The Chebogue Point Rd runs down the eastern side of this fairly elevated grassy headland. The entire road is a great birding spot but the best birding usually happens near the southern tip.

Each time I visited Chebogue it was either raining or windy so all of the photos in this post are taken by other people. Below is a photo of one of two Dickcissels that were present at Chebogue Point on October 30.

Dickcissel by Ervin Olsen - Oct. 30

The aerial photo below shows Chebogue Point with Chebogue Point Road running along the eastern side of the point. The areas that I've seen the most birds during this fall are annotated.

 

• Willow Trees - a fairly large group of trees next to a small pond.
• Lobster Traps - a pile of lobster traps in front of a residence. Sparrows hide in the traps and come out to feed near the road.
• Farm - many sparrows feeding on the road in front of the farm.
• Driveway - this driveway has been a junco hotspot every time I've been there this year.
• Shrubs/Trees - when driving down the road many sparrows hide in these shrubs near the last house on the road.
• Shore - I've seen shorebirds and American Pipits there.

 

Google Maps

 

Below is a list of interesting birds found at Chebogue Point this fall. The highlight birds were Lark Sparrow, Vesper Sparrow, House Wren, Dickcissels, Indigo Bunting, and Field Sparrow. Observations were made by Ronnie d'Entremont (RD), Alix d'Entremont (AD), Ervin Olsen (EO), Laurel Amirault (LA) and Larry Neily (LN). Vagrants are annotated with double asterisks (**).  

Species	Date	Observer
Pine Warbler	Oct. 10	RD
Brown-headed Cowbird	Oct. 21	AD
Orange-crowned Warbler	Oct. 21	AD
3 White-crowned Sparrows	Oct. 21	AD
2 Chipping Sparrow	Oct. 21	AD
**Lark Sparrow**	Oct. 21	RD
White-crowned Sparrow	Oct. 22	EO
Eastern Bluebird	Oct. 26	EO
**House Wren**	Oct. 26	EO
**2 Dickcissels**	Oct. 26	EO
Chipping Sparrow	Oct. 26	EO
**Indigo Bunting**	Oct. 26	AD
**Field Sparrow**	Oct. 26	AD
3 White-crowned Sparrows	Oct. 26	AD
2 Ipswich Sparrows	Oct. 26	AD
Chipping Sparrow	Oct. 27	LA
3 White-crowned Sparrows	Oct. 27	AD
8 Chipping Sparrows	Oct. 27	AD
Eastern Phoebe	Oct. 28	EO
Orange-crowned Warbler	Oct. 28	EO
White-crowned Sparrow	Oct. 28	ED
**Dickcissel**	Oct. 30	EO
American Tree Sparrow	Oct. 30	EO
American Tree Sparrow	Oct. 31	AD
Chipping Sparrow	Oct. 31	AD
White-crowned Sparrow	Oct. 31	AD
Chipping Sparrow	Nov. 8	AD
Fox Sparrow	Nov. 8	AD
Snow Bunting	Nov. 9	LN
Vesper Sparrow	Nov. 13	RD
Orange-crowned Warbler	Nov. 22	EO
Eastern Bluebird	Nov. 22	EO
**Dickcissel**	Nov. 24	EO
Orange-crowned Warbler	Nov. 30	EO
Orange-crowned Warbler	Dec. 3	EO

 

House Wren by Ervin Olsen - October 26

 

Vesper Sparrow by Ronnie d'Entremont - Nov. 13

 

Hybrid Herring x Great Black-backed Gull

Gull hybridization occurs rarely, but it is most frequent in large white-headed gulls. Hybrids are highly variable and can show almost any combination of parental characters. The resultant hybrid offspring often look intermediate between the parent species. This combination of features can produce a hybrid gull that closely resembles another species entirely.

 

In Newfoundland, there are Herring x Lesser Black-backed Gull hybrids that resemble the sought after Yellow-legged Gull. Bruce Mactavish likens differentiating between a real Yellow-legged Gull and its hybrid imposter like splitting an atom in his blog.

 

On November 22, 2014 I found a rather odd gull at Dennis Point Wharf in Pubnico, Yarmouth County. It was large, perhaps about the size of a Herring Gull or larger. Its mantle was similar in shade to a nearby Lesser Black-backed Gull. Its legs were lead-pink and it had a fairly large bill.

 

Experienced larophiles on the North American Gulls Facebook Group have labelled it as a probable hybrid Herring x Great Black-backed Gull. I use the word "probable" because one can never be sure of a hybrid's exact lineage without having direct information on the parents (which would be available if a mixed pair's chick was banded). The speculation on the parent species of a hybrid are simply educated guesses.

 

HERG x GBBG - Dennis Point Wharf - Nov. 22, 2014.

 

HERG x GBBG - Dennis Point Wharf - Nov. 22, 2014.

 

The following is a list of features of this hybrid and their probable origins.

 

GBBG-like Features

• faintly streaked nape and head
• heavy bill with extreme gonydeal angle

HERG-like Features

• White mirror on P9 and P10
• Black on P5-P10

Intermediate Features

• Mantle shade (half way between HERG and GBBG)

Unique Features

• Lead pink legs 

 

The upper wing tip pattern shown below more closely resembles an average HERG. The hybrid has a large white mirror on P10 and a small one on P9 like a HERG. The black in the primaries goes from P5 to P10. A GBBG in comparison typically has fewer primaries with black (P6-P10), P10 has a completely white tip and P9 has a white mirror. See the wing tip comparison image below which shows these features.

 

Wing tip comparison

 

This hybrid gull is superficially similar to a Slaty-backed Gull. A few missing features are the bright pink legs, broad white tertial crescent, broad white secondary tips and dark streak through the eye. A Western Gull would show much less white on the wing tips and an even whiter head and neck.

 

A similar gull also believed to be a HERG x GBBG was found in Glace Bay in the spring of 2002. The initial thoughts of it possibly being a Slaty-backed Gull soon vanished after the gull was thoroughly analyzed. The lack of deep pink kegs and extensive window in the outer primaries ruled out Slaty-backed and it was then presumed to be a hybrid. [NS Birds, Vol. 44, No. 3]

 



HERG x GBBG at Glace Bay - March 7, 2002 - Ian McLaren Photo

 

References

 

Howell, S.N.G. and J. Dunn. 2007. Gulls of the Americas. Houghton Mifflin Company, New York, N.Y.

My First Red-shouldered Hawk

On November 16, 2014 I observed my first Red-shouldered Hawk (RSHA) on Cape Sable Island, Shelburne County. This buteo was flying Northeast over the road near the intersection of the Centerville South Side Road and the Daniel's Head Road.

 

Red-shouldered Hawk - Cape Sable Island - November 16, 2014.

From the mid-1960's until the end of 2010 there have been 106 reports of this bird in Nova Scotia. Many of the 65 fall sightings have occurred during large hawk movements over Brier Island. [All the Birds of Nova Scotia, Ian McLaren]

 

There are 5 subspecies of RSHA but three of them are essentially indistinguishable from one another and they occupy most of the eastern states. Southern Florida and California birds are separable from the eastern subspecies group. [Hawks in Flight, Dunne et al.]

 

All About Birds

 

This hawk most closely resembles the expected eastern subspecies group. A juvenile California RSHA would have thick black bars on the tail and dark rufous underwing coverts. The Florida subspecies would not show such an evenly patterned underside and would have smaller light bands and wider dark bands on the tail. [The Sibley Guide to the Birds 2nd Ed, Sibley]

 

Juvenile Red-shouldered Hawks are somewhat similar to juvenile Broad-winged Hawks (BWHA). There are a few field marks that allow an observer to easily differentiate between both species given clean views. 

 

Both have quite different wing tip shapes. The BWHA shows pointed wings reminiscent of a candle-flame. The wings of a RSHA are described as looking like a rectangular plank. BWHAs show narrow dark tail bands in comparison to the RSHAs evenly wide light and dark tail bands. The pale crescent windows produced by the translucent outer primary bases are only found on RSHAs. [Hawks in Flight, Dunne et al.]

 

The Sibley Guide to the Birds 2nd Ed, Sibley (added annotations)

 

The annotated photo of my Nov. 16th RSHA below shows all of the field marks that differentiate it from a BWHA.

 

Red-shouldered Hawk with annotations

 

My First Swainson's Hawk

Ervin Olsen and I were driving on the Melbourne Road in Pinkney's Point on November 8, 2014 when we spotted an interesting hawk flying above the road. My initial impression was of an Osprey. It had the characteristic "M" shape that an Osprey often shows. I stopped the car and took a few photos as it flew by. By then I had noticed that this bird was in fact not an Osprey and I couldn't make it match with any raptor that I knew.

 

It was only once I put it on the computer and lightened the image to see the details that I knew I had something great. I searched through Sibley and landed on Swainson's Hawk. I sent the image to David Currie and was pleased to hear that he agreed with the ID.

 

Swainson's Hawk - Pinkney's Point - November 8, 2014

The Swainson's Hawk is a rare buteo for Nova Scotia. It breeds in western North America and is rare further east. All the Birds of Nova Scotia by Ian McLaren which is current until the end of 2010 describes only 11 sightings of this hawk in Nova Scotia. 

 

The following are the diagnostic characteristics that are discernible from the photos that were taken on November 8 accompanied by an annotated photo afterwards.

 

1. Light patch at the base of the tail

2. Body and underwing linings are a light buffy colour
3. Patchy chest markings (differing from an adult's solid chest bib)
4. Flight feathers darker than underwing lining.
5. Pale outer primaries

 

Annotated Photo

 

This bird, as all other Swainson's that have been found in Nova Scotia has not yet reached adult plumage. See below for a photo of a light morph juvenile Swainson's Hawk from Hawks in Flight by Dunne et al showing an Osprey-like "M" shape.

 

 

There have been two other fall 2014 sightings of Swainson's Hawks in Nova Scotia. Both were of light morph juvenile birds at Brier Island. The first sighting was on September 25th by Rick Whitman and the second on October 31st by Richard Stern, Rick Whitman and Bernard Forsythe. We may be able to better compare my November bird with the October bird since flight shots of both were obtained.

 

All photos of the Oct. bird were taken by Richard Stern. The comparison below seems to show that my Nov. bird has lighter markings on the underside than the Oct. bird.

 

My Nov. bird (L) vs. the Oct. bird (R)

 

The next composite shows that the Nov. bird has much cleaner flanks than the Oct. bird.

 

My Nov. bird (L) vs. the Oct. bird (R)

 

My distant photos certainly don't allow for accurate colour and contrast comparisons, but we can

accurately compare moult between the two birds. My Nov. bird shows more moult.

Swainson's Hawks take 2 years to reach adult plumage. This gives us the possibility of distinguishing between 3 ages in the field - juvenile, sub-adult and adult. [Nemesis Bird]

The Oct. bird looks like a bird born this year (juvenile) because of the lack of a dark trailing edge to the wing and tail and its very fresh plumage. Juvenile plumage is retained on most birds for their first year of life [Nemesis Bird]. For these reasons I believe that the Oct. bird is a freshly plumaged juvenile born in 2014.

We can clearly see that the Nov. bird is moulting because of the missing feathers. The trailing edges of the wing and tail appear much less neat as opposed to crisp as would be seen in a juvenile. During fall migration, Swainson's Hawks showing symmetric wing and tail moult, while exibiting juvenile body plumage, are sub-adults [Hawks at a Distance, Ligouri]. Since my Nov. bird does show symmetric wing moult, I believe that my sighing on Nov. 8th is of a sub-adult. A flight feather where the primaries meet the secondaries (it looks like P1 to me) seems to be missing from both wings on my Nov. bird. The Nov. bird also looks to have dropped P7 in both wings.

 

This kind of primary dropping is attributed to stepwise moult which involves simultaneous waves of primary moult. Birds with stepwise moult have one or more of the following characteristics: long distance migrants, spends time in open habitats, are relatively long-winged and large mass [Molt in North American Birds, Howell]. Ninety percent of after hatch year (AHY) / after second year (ASY) birds show this stepwise moult in the primaries and secondaries [Identification Guide to North American Birds, Pyle]. This moult pattern is also known as staffelmauser moult (in Pyle) or serial moult (this paper).

 

Nov. 8th bird - left wing and right wing moult

 

Molt in North American Birds by Howell mentions that Swainson's Hawks suspend their wing moult during migration so it is unlikely that the Oct. bird with all its flight feathers would start moulting before reaching its wintering grounds. The time period of one week between sightings isn't enough to produce the feather wear and moult differences between the Oct. and Nov. birds.

In my opinion it seems clear that there have been at least 2 Swainson's Hawks in Nova Scotia in 2014. There is a continuum of plumages from light to dark in Swainson's Hawks [Hawks at a Distance, Ligouri]. I believe that the Oct. bird has slightly more and darker markings than my Nov. bird. A more convincing argument is that the Oct. bird is a juvenile and my Nov. bird is sub-adult.

Cere position on Sharp-shinned & Cooper's

On September 23, 2014 with the sighting of a Cooper's Hawk in Argyle, Yarmouth County, I could finally say that I've seen all three North American accipiters - the Sharp-shinned Hawk, the Cooper's Hawk and the Northern Goshawk.

 

Juvenile Sharp-shinned Hawk - Cape Forchu - Sept. 24, 2014

 

In Nova Scotia the Sharp-shinned Hawk is our most numerous accipiter and it breeds throughout the province. The Cooper's does not regularly breed in Nova Scotia and thus is quite rare (a handful of sightings per year). Northern Goshawks breed throughout the province as well but in smaller numbers than the Sharpie. [All the Birds of Nova Scotia, Ian McLaren]

 

Differentiation between these three species can be challenging. They all have similar shapes - short, rounded wings with long and narrow tails. Goshawks are largest followed by Cooper's and then Sharp-shinned. Juvenile birds in all three species are brown above and streaked below. The adult Northern Goshawk is quite unique compared to an adult of the two smaller accipiters. [Hawks in Flight, Dunne et al.]

 

Cooper's Hawk - Argyle - Sept. 23, 2014

 

Many reference books discourage observers from relying too much on size differences for ID purposed in the field. Female Sharp-shinned Hawks approach the size of a male Cooper's [Hawks in Flight, Dunne et al.]. Below are dimensions as given by the website All About Birds.

 

	Length (in)	Wingspan (in)
Sharp-shinned	9.4 - 13.4	16.9 - 22.0
Cooper's	14.6 - 15.4	24.4 - 35.4
Goshawk	20.9 - 25.2	40.6 - 46.1

 

For accipiters it is always best to use as many field marks as possible to come to a conclusion in its ID. Birds with contradictory field marks should be ID'd using all of its characteristics as a whole placing more weight on the stronger field marks. For example, Sharp-shinned Hawks can show a rounded tail when in flight. [Hawks in Flight, Dunne et al.]

 

Northern Goshawk - Brier Island - Aug. 30, 2014 

 

There are many great texts that provide wonderful field marks to help to differentiate these three confusing birds so I won't repeat them all here.

 

There is one field mark that I haven't yet found any direct mention of in any of my reference materials. This field mark was passed on to me by a very accomplished Nova Scotia birder named Fulton Lavender. The yellow coloured part at the base of the maxilla of a raptor is named the cere, as shown in the image below.

 

Sharp-shinned Hawk showing the yellow "cere"

 

According to this field mark, the top of the cere on a Sharp-shinned hawk is lower than that of a Cooper's Hawk. I've done some searching through images of these two birds on Flickr and it does look very consistent. The following is the same Sharpie as above with lines showing the height of the cere with the lines adjusted for the head position of the bird (looking up). The line on the top of the head is used to get an idea for the positioning of the head (looking up or down).

 

Sharp-shinned Hawk cere position in relation to the eye (mid-eye)

Sharp-shinned Hawk cere position in relation to eye (mid-eye) - photo by Sheila Briand

 

The top of the cere in the above Sharpies seems to pass through the middle of the eye. Below are photos of two Cooper's Hawks - one photographed by myself and the other by my uncle Ellis d'Entremont.

 

Cooper's Hawk position of cere compared to the eye (above eye)

 

Cooper's Hawk position of the cere compared to the eye (above eye) - Photo by Ellis d'Entremont

 

The newest version of The Sibley Guide to Birds also shows this field mark. The beak of the Cooper's seems pushed up as compared to the Sharp-shinned.

 

The Sibley Guide to Birds, David Sibley

 

Determining the position of the cere relative to the eye is somewhat subjective. The angle of the head must first be estimated. This process introduces a risk of error right from the start. A more relaxed bird may provide more accurate assessment of head angle due to flattened head feathers.

Like all other field marks used to differentiate between all three accipiters, the relative position of the cere should be used as one of the many supporting field marks. Like a Sharpie showing a rounded tail in flight, a Sharp-shinned can also have a tall cere or a Cooper's can have a low cere. These contradictions would be exceptions, but they do occur.

All the Birds of Nova Scotia by Ian McLaren makes reference to comparing the relative size of the bill (height) versus the eye diameter to help differentiate between Sharpies and Cooper's. The relatively larger bill of a Cooper's may contribute to the appearance of a taller cere which does contribute greatly to the Cooper's head shape. Dr. McLaren prefers to use the relative size of the bill compared to the eye (easily measured on a digital image). With these confusing accipiters we often need as many field marks as we can get and the cere height may be useful as another of the many characteristics that contribute to the overall look of these birds.

I'd love to hear if anyone else has heard of or is using this field mark.