Wednesday, December 24, 2014

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.

video
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.

Wednesday, December 10, 2014

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.

Wednesday, December 3, 2014

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 SparrowHouse 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
 

Monday, November 24, 2014

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.