Blackbeards Cove

My co-pilot, Bertin d'Eon, and I had been discussing a trip to Blue Island, Shelburne County, for a while. We often fly virtually around Nova Scotia on Google Maps in search of interesting coastal areas and islands to visit. Online we could see that Blue Island is a 1 km by 0.5 km island with a great landing area on the northern side and large cliffs the rest of the way around. The most interesting features are the deep crevices on the eastern cliffs and Blackbeards Cove on the southern shore, facing the open Atlantic.

On July 5, 2015, Bertin and I left the wharf at West Green Harbour, passed the tiny rocky island named the Thrum Cap and after a short, but choppy ride, we reached the northern beach of Blue Island. We lugged the 200 pound inflatable Zodiac up far enough so that we could leave it for a few hours without risk of it washing away. It was decided to try to circle the island clockwise by foot. Once we left the northern open area, the woods constituted of short coniferous trees and short grass. We noted the fact that there was no understory and that walking was easy. We thought that this island likely has sheep on it, or at least had in the past. There is a narrow trail that led the way south along the eastern coast that we were happy to follow. We soon made it to the tall cliffs that we had seen from above on Google Maps.

The first view of the eastern coast cliffs on Blue Island.

Bertin looking down one of the many crevices on the eastern side of Blue Island.

Most large wooded islands that I visit in s.w. Nova Scotia are home to Swainson's Thrushes, this island was no exception. As we approached the southeast corner of the island we got a brief glimpse of two goats as they vanished around the bend. I was later informed that these goats as well as a sheep were placed on the island by Leroy d'Entremont.

The vista at the southeast corner of Blue Island.

The most impressive feature of the island is Blackbeards Cove. It is a large cove created by a grassed headland to the east and a formidable, almost vertical, rock structure to the west. This western border is almost unnaturally straight. This is very evident in the satellite image above once it is zoomed in.

The impressive Blackbeards Cove on Blue Island.

Bertin on a swing crafted from a large buoy at Blackbeards Cove on Blue Island.

We completed our trek around the island before 10 am, so we decided to head towards Jordan Bay Gull Rock. This is a substantial sized rock and is similar in length to Yarmouth County's Gannet Rock, but looks much taller. On our way we got great looks at a sunfish which wasn't much smaller than our boat. Gull Rock is home to hundreds of Double-crested Cormorants. I was pleased to also find four Razorbills and a colony of Great Cormorants also using this impressive rock. I've submitted a checklist to eBird with all of my observations.

Razorbills on Jordan Bay Gull Rock.

Great Cormorants on Jordan Bay Gull Rock.

Eric Mills had sent me a paper a while back entitled The Nesting of the Great Cormorant (Phalcrocorax carbo) and the Double-crested Cormorant (Phalacrocorax auritus) in Nova Scotia in 1971 (A.R. Lock and R.K. Ross). Jordan Bay Gull Rock was known as Blue Gull Rock back then and the paper states that there were 20-30 Great Cormorants and 400-430 Double-crested Cormorants. It is wonderful to know that the Great Cormorant colony on this gigantic rock of an island still has numbers on par with the 1970s.

Before summer's end I'd like to visit another Gull Rock east of Ingomar. It looks like more good habitat for Great Cormorants. Click here to view this island on Google Maps.

A Second-Year Least Flycatcher

On May 25, 2015, I photographed a Least Flycatcher at Cape Forchu, Yarmouth County. Since it was silent, I had to scrutinize the images to confirm its identification. Confident identification of Empidonax flycatchers that are not vocalizing is one of the toughest challenges for birders. A helpful article entitled Identifying Empidonax Flycatchers: A Ratio Approach by Forrest Rowland illustrates important proportional differences between these very similar species. Kenn Kaufman's Field Guide to Advanced Birding also provides useful descriptions and comparisons.

Why is it a Least?

This flycatcher is clearly an Empidonax, and not an Eastern Wood-Pewee due to its relatively short primary projection and lack of dusky chest sides. It is not a Yellow-bellied Flycatcher since it is lacking a yellowish throat. The most likely candidates based on our location that we are left with are the Alder and Least Flycatchers.

This flycatcher was found in a habitat better suited for an Alder Flycatcher. Cape Forchu is predominantly covered by young coniferous trees with sections of alders. Leasts are typically found in mature deciduous forests.

A few key features separate this bird from the similar Alder Flycatcher. Compared to an Alder Flycatcher, the Least has a more conspicuous eye ring and a shorter primary projection (Alderfer & Dunn, 2014). Rowland (2009) describes the Least Flycatcher as a short-winged and long-tailed Empidonax. This structure may be appreciated in Fig. 1. The wing chord of the Least appears shorter in comparison to the Alder Flycatcher.

The tail of an Alder Flycatcher looks broad compared to that of other smaller Empidonax. Kaufmann (2011) describes the tail of the Least Flycatcher as narrow (see Fig. 1). The Alder's wing contrast is lessened by the dull wing bars and tertial edgings in comparison to the typically more white wing bars and tertial edgings of the Least (see Fig. 1). In fresh spring plumage, Alder shows olive upperparts with a contrastingly gray face. The Least Flycatcher has fairly uniform brownish gray upperparts with darker crown and forehead and is washed olive only on the back. This difference in  colour between the head and back in Leasts is visible in Figure 1, Alders appear to have more similar coloured heads and backs. Leasts also appears to have a relatively larger head than Alders (Alderfer & Dunn, 2014).

Figure 1. Least Flycatcher (L) versus Alder Flycatcher (R). Photos by Alix d'Entremont.

How old is it?

After analysis of this Least Flycatcher, I conclude that it is a second-year bird, born in 2014. Below are supportive arguments.

A bird born in 2014 (typically in July) would have gone through a first prebasic molt from Jul-Oct 2014 on the breeding grounds. The extent of this molt is variable, but it typically involves the body plumage and occasionally the secondaries and a few upper wing coverts. The primaries, primary coverts and a variable number of secondaries and secondary coverts will not be replaced during this molt. (Tarof & Briskie, 2008)

The first prealternate molt would have occurred on the wintering grounds from Feb-May 2015 and involves the body plumage, some inner secondaries and their corresponding greater and middle coverts along with a variable number of rectrices. Again, no primaries, primary coverts and outer secondaries and secondary coverts are not replaced. (Tarof & Briskie, 2008)

Pyle (1997) describes Least Flycatchers in their second year (SY) during Apr-Sep as having marked contrast between the retained, outer coverts that are brown and abraded compared to the duskier and lemon-tipped, replaced inner coverts. Second year birds also show strong contrast between the tertials and the adjacent secondaries. These features are clearly visible in Figure 2. After second year (ASY) birds show less contrast.

The primaries of this Least Flycatcher also appear very worn and brown as compared to the relatively fresh primaries that would be seen in an ASY bird. The rectrices appear tapered, also indicating a SY bird. The primary coverts are worn, brown and have no green edge. An ASY would show broader green edging to fresher and duskier primary coverts.

Figure 2. Least Flycatcher. Photos by Alix d'Entremont.

SY birds can replace 1-3 tertials during their prealternate molt. This bird appears to have replaced the longest tertial. There is slight, but apparent differences between this longest tertial and two inner ones. The inner tertials show slight wear on the feather edges while the longest shows a smooth edge (Fig. 3).

Figure 3. Least Flycatcher. Photos by Alix d'Entremont.

Summary

The retained juvenile feathers that were not replaced during the prebasic (Jul-Oct 2014) or prealternate (Jan-May 2015) molts show strong contrast with the newly replaced feathers. The primary coverts show no green edging. The rectrices are apparently tapered. These features indicate that this Least Flycatcher is a second-year bird, born in 2014. The differences between a SY bird and an ASY bird in spring arise due to the partial first prebasic molt compared to the complete prebasic molt of an AHY (after hatch year) bird.

References:

Alderfer, J. & J.L. Dunn. 2014. (Ed). Complete Birds of North America, 2nd Edition. National Geographic Society. Washington DC, USA.

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

Pyle, P., S.N.G. Howell, R.P. Yunick, and D.F. Desante. 1997. Identification guide to North American Birds, Part 1, Columbidae to Ploceidae. Slate Creek Press, Bolinas, California.

Rowland, F. 2009. Identifying Empidonax Flycatchers: the Ratio Approach. Birding 41(2): 30-38

Tarof, Scott and James V. Briskie. 2008. Least Flycatcher (Empidonax minimus), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/099
doi:10.2173/bna.99

A Little Egret in Nova Scotia

On May 14, 2015 Rachel Hoogenbos found a small white egret behind her house at Daniel's Head, Cape Sable Island, Shelburne. Johnny Nickerson was notified and he identified it as a rare Little Egret (Egretta garzetta) which is very similar to the relatively more common Snowy Egret (Egretta thula).

Figure 1. Little Egret at Cape Sable Island on May 15, 2015. Photo by Alix d'Entremont

Little Egrets are common and widespread in Eurasia and Australia (Alderfer & Dunn, 2014). These white egrets have bred in Barbados since the mid-1980s, and 15-20 pairs currently breed there each year and fledge 3-4 young per nest. In 2008 they were also found to be breeding on Antigua (Howell et al., 2014).

This Little Egret at Cape Sable Island represents the seventeenth record of this species in Nova Scotia. The last was one at Eastern Passage, HRM present April 21-27, 2013 (NS Birds Vol 55, No 3 Spring 2013). Birds occurring in North America could be from Western Europe or the Caribbean. Little Egrets will likely be found in greater numbers in e. North America as the Caribbean population increases. Individuals from this recently established population could reach us by migrating north in association with returning Snowy Egrets, Little Blue Herons and Tricolored Herons (Howell et al., 2014).

I was privileged to have seen a Snowy Egret at Melbourne on April 19, 2014, so photos of that bird will be used to compared to the Little Egret. For most of the year, Little Egrets have grayish to greenish-yellow lores compared to bright yellow on Snowy. At the height of courtship (only for a short period), the lores of Little Egrets are bright red and rarely bright yellow (Howell et at., 2014). Snowy Egrets also show red lores in high breeding (Alderfer & Dunn, 2014). Both of the birds below do not show bare part coloration consistent with breeding flush. The Cape Sable Island Little Egret shown in Fig. 2 shows grayish lores with a reddish tinge to the anterior region and maybe a slight blueish tinge to the posterior area. This coloration is consistent with the description of the lores as blue-pink at the onset of breeding given by Parsons & Master (2000). This contrasts strongly with the bright yellow lores shown in the Snowy Egret from 2014. Two more field marks to notice in Fig. 2 are the longer bill of the Little Egret and facial feathering that seems to project further at the base of the bill (Howell at al., 2014).

Figure 2. Pale lores and longer bill of the Little Egret compared to the yellow lores of the Melbourne Snowy Egret and its slightly shorter looking bill. Photos by Alix d'Entremont

The two white occipital plumes are clearly visible in Fig. 3 as they are blown about by the wind. Compare this to the numerous breeding plumes of the Snowy Egret that look much more bushy and filamentous. (Howell at al., 2014)

Figure 3. The two lancelot plumes of the Little Egret compared to the bushy, filamentous head feathers of the Melbourne Snowy Egret. Photos by Alix d'Entremont

Svensson et al. (2009) describe the Little Egret as having black legs and dull yellow toes while the Snowy Egret invariably shows distinctly yellowish rear to the lower tarsus and more saturated yellow feet. The extent of the foot colour can be appreciated in Fig. 4. We see the the Little Egret shows only yellowish toes, while the Snowy has the entire foot as well as a small portion of the rear tarsus coloured in a saturated orangish-yellow.

Figure 4. Little Egret and Melbourne Snowy Egret legs and feet. Photos by Alix d'Entremont

On April 11, 2014 during an NSBS field trip led by James Hirtle, an interesting Snowy Egret was discovered at Blanche, Shelburne. It initially caused some excitement due to its atypical lore colour. All other features appear typical of Snowy Egret. Fig 5 shows the similarity in lore colour in both the Cape Sable Island Little Egret and the Blanche Snowy Egret.

Figure 5. Little Egret at left and Blanche Snowy Egret at right with somewhat similar coloured lores. The Snowy Egret photo has been flipped horizontally to allow for easier comparison. Photos by Alix d'Entremont (L) and Keith Lowe (R)

Another interesting Snowy Egret was photographed in Newfoundland on May 14, 2015 which again showed the variability in lore colour of Snowy Egrets. Check Bruce Mctavish's blog post for photos and some discussion.

We should also entertain the possibility of hybrids for these non-characteristic birds. When discussing the Blanche egret, Ian McLaren commented on the typological thinking that a certain species, subspecies or hybrid must have a well defined list of features. Hyrbids may show different characteristics than what are currently documented in the literature. The genetic dilution of the first filial generation of hybrids by further breeding can introduce further complications.

References:

Alderfer, J., J.L. Dunn. 2014. (Ed). Complete Birds of North America, 2nd Edition. National Geographic Society. Washington DC, USA.

Howell, S.N.G.,  I. Lewington & W. Russell. 2014. Rare Birds of North America. Princeton University Press

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

Parsons, Katharine C. and Terry L. Master. 2000. Snowy Egret (Egretta thula), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/489

Svensson, L., K. Mullarney & D. Zetterstrom. 2009. Collins Bird Guide. 2nd Ed. Princeton University Press, Princeton, New Jersey.

Two Ross's Geese in Nova Scotia

Ross's Geese (Chen rossii) breed in northern Canada and winter in a fragmented range from the Atlantic to the Pacific coast of the US. It typically migrates through central North America. Since the 1950s, this small white goose's breeding and wintering grounds have been expanding eastward. This expansion is thought to have resulted in more contact with Snow Geese and thus more hybridization. (All About Birds, n.d.)

The first Ross's Goose in Nova Scotia was found by Mike King at Hartlen Point, HRM and was present from Dec 31, 2012 to Jan 13, 2013 (King, 2013). The next was at Truro and was found by Cliff Sanderson on Oct 10, 2013. This second bird is likely the same that was spotted at Windsor from Oct 19 - Dec 3 (Hall, 2013).

On April 3, 2015, Karel Allard noticed two small white geese from his home at Mavilette, Digby. Further inspection with his scope confirmed his suspicion, these were two Ross's Geese that represented the third and fourth records of this species in Nova Scotia (Fig. 1).

Figure 1. Two Ross's Geese with two Canada Geese at Mavilette, Digby 5 April, 2015. Photo by Alix d'Entremont.

Johnny and Sandra Nickerson picked me up later in the day on April 3 and we met Karel Allard and Ervin Olsen at Mavilette (Fig. 2). Soon after, Laurel and Kevin Amirault arrived and we all got to see these very rare birds.

Figure 2. Johnny Nickerson, Karel Allard and myself (Alix d'Entremont) at Mavilette, Digby 3 April, 2015. Photo by Ervin Olsen.

The Ross's Goose is very similar to the Snow Goose, but smaller with a relatively small bill, round head and short neck. Hybrids between Ross's Goose and Snow Goose also occur, and these should be considered when presented with a small white goose. In comparison to a Snow Goose, the Ross's Goose has a rounder head with a steeper forehead, no grin patch, a blueish/gray bill base, and a more vertical border at the base of the bill (Fig. 3). Hybrids are intermediate between the two species. (Sibley, 2014)

Figure 3. Ross's Goose at Mavillette (left) and Snow Goose in Pubnico (right). Photos by Alix d'Entremont.

The head shape of the Ross's Geese seemed to change between photos. Some images show a less steep forehead. The birds seemed to flatten their foreheads when actively feeding, making the bill look larger (Fig. 4).

Figure 4. Variability in head shape shown by one of the Ross's Geese at Mavilette, Digby 3 April, 2015. Photos by Alix d'Entremont.

The relatively short necks, rounder bodies and less elongated heads shown by the Ross's Geese are apparent in Figure 5.

Figure 5. The two Ross's Geese at Mavillette, Digby 5 April 2014. Photo by Alix d'Entremont.

Nova Scotia saw its first ever Ross's Goose at the end of 2012 and less than 2 and a half years later we've added another 3 to the provincial total. We can likely attribute the eastwards expansion of this goose's range to the spike in recent records.  


References:

All About Birds (n.d.) Ross's Goose. Retrieved from http://www.allaboutbirds.org/guide/Rosss_Goose/id                                                                            

King, M. (2013) The Discovery of Nova Scotia's First Ross's Goose. Nova Scotia Birds. 55(2), 64-65

Hall, R. (2013) Waterfowl. Nova Scotia Birds. 56(1), 12

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

Common Gull

The Mew Gull complex (Larus canus) is comprised of four subspecies. The New World representative, referred to as the Mew Gull (L.c. brachyrhynchus), breeds in n.w. North America and winters mainly on the Pacific Coast and is exceptionally rare on the Atlantic Coast during the non-breeding season (one has been confirmed nearby in New Brunswick). The Old World birds are the Common Gull (L. c. canus & L. c. heinei) and the Kamtchatka Gull (L. c. kamtschatschensis). (Howell et al., 2014)

The canus Common Gull is regular in NS in winter in small numbers. The province's first was discovered on March 9, 1969 on Sable Island. (McLaren, 2012)

Analysis of this winter's photos of the canus Common Gulls in the Dartmouth area suggest that there have been 4 individuals. I was able to photograph the gull that was frequenting the Sobeys parking lot on Tacoma Drive in Dartmouth on February 27, 2015 (Fig. 1).

Figure 1. Common Gull in Dartmouth - 27 Feb 2014. Photo by Alix d'Entremont

Common Gulls are superficially similar to Ring-billed Gulls. In comparison, a Common Gull has a thinner, less blunt tipped bill that lacks a distinct black ring. Its eyes are dark brown compared to the pale lemon eyes of a Ring-billed as seen in Fig. 2. (Howell et al., 2014)

Figure 2. Common Gull (L) vs. Ring-billed Gull (R). Photo by Alix d'Entremont

Common Gulls have a slightly darker mantle that is clear in Figure 3, along with wider and more contrasting scapular and tertial crescents. The wider scapular crescent on the Common Gull is obvious in Figure 3 as well. (Howell et al., 2014)

Figure 3. Common Gull (L) vs. Ring-billed Gull (R). Photo by Alix d'Entremont

The relatively more extensive white mirror on P10 of the Common Gull is visible in Fig. 4. (Howell et al., 2014)

Figure 4. Common Gull (L) vs. Ring-billed Gull (R). Photo by Alix d'Entremont

The Dartmouth Common Gull was my first Nova Scotian sighting of this bird. I had previously seen Common Gulls in the fjords of Norway in July 2007. Figure 5 shows a number of them with pristine white heads and in the process of moulting their inner primaries. These would also be L.c. canus based on range.

Figure 5. Common Gulls near Flåm, Norway - July 21 2007. Photo by Alix d'Entremont

References:

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

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

Fieldfare

The Fieldfare (Turdus pilaris) is a nomadic thrush breeding in temperate and boreal forests from Iceland to e. Russia. There is also a small, fluctuating population breeding in sw. Greenland since the late 1970s. Fieldfares are also regular winter visitors to Iceland from Europe. Birds that arrive to our region are thought to originate from northern Europe, Iceland or Greenland. Cold weather winter movements of this nomad align well with Atlantic Canada sightings that are mostly in late Dec–Feb. (Howell et al., 2014)

Nova Scotia previously had 3 reports in Oct, one each in Dec, Jan and Feb and one late bird that was found in Apr. Our latest bird was discovered by Kathleen Spicer in an apple tree in her yard in Apple River, Cumberland on 31 Jan 2015, representing Nova Scotia's 8th report. (McLaren, 2012)

Figure 1. Fieldfare in Apple River, Cumberland - 27 Feb 2014. Photo by Alix d'Entremont.

This rare North American visitor scores a Code 4 (Casual) on the ABA Checklist equating to less than annual occurrence in North America. I made the 1000 km trip from Pubnico to Apple River to see the Fieldfare (Fig. 1) at the end of Feb, and was about the 100th birder to so at the time. Listers flew in from as far as the southern US to see this vagrant bird. We are all very grateful for the kindness of both Kathleen and her husband Blaine for being so accommodating to the many birders visiting their private home.

Howell et al. (2014) describe first year Fieldfares as typically duller than adults with whitish tips to retained juvenal greater coverts. The Apple River bird appears fairly vibrant but early photos do show what looks like moult contrast in the greater coverts indicating that it is likely a first-winter bird.

This European visitor (Turdus pilaris) is closely related to our American Robin (Turdus migratorius), both are members of the genus Turdus. They are structurally similar (Fig. 2), but the Fieldfare is slightly larger.

Figure 2. American Robin (L) vs. Fieldfare (R). Photos by Alix d'Entremont.

References:
Howell, S.N.G.,  I. Lewington & W. Russell. 2014. Rare Birds of North America. Princeton University Press

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

Hoary Redpoll

The two species of redpoll are similar, but careful study is usually diagnostic. Nova Scotia's regular species is the Common Redpoll (Acanthis flammea) while the Hoary Redpoll (Acanthis hornemanni) nests farther north and is much rarer. Pyle (2007) recognizes two subspecies for each, A.f. flammea and A.f. rostrata for Common and A.h. hornemanni and A.h. exilipes for Hoary. McLaren (2012) states that we observe mainly flammea Common Redpolls and exilipes Hoary in our province - this article will focus on these two subspecies.

On February 4, 2015 I found a redpoll that stood out from the group at Laurel Amirault's feeder in Lower West Pubnico, Yarmouth County. It was clearly much paler than the Common Redpolls that it was travelling with. This bird was my first Hoary Redpoll (Fig. 1).

Figure 1. Hoary Redpoll in Pubnico - Feb 4, 2015 - Photo by Alix d'Entremont

Confidently identifying a Hoary Redpoll in a flock of Common Redpolls requires analysis of a number of characteristics, some of which are quite subtle. Fig. 2 shows how the Hoary Redpoll is paler overall as compared to the two Common Redpolls. There is plumage variation in both species, but first-winter birds are consistently darker than the adults. The infusion of buff in the face, molt limit in the greater coverts and tapered outer rectrices of this bird make it a first-winter. This immature bird is considerably lighter than the nearby adult male Common Redpolls (the palest sex and age of that species) in other photographs, providing strong evidence in favour of first-winter Hoary rather than first-winter Common.

Most field guides illustrate a few other major differences. Sibley (2014) mentions the bold white edging to the secondaries, stubby bill and fine underside streaking of a Hoary that are all appreciable in Fig. 2. Hoaries often look larger due to their tendency to fluff their feathers, but they are extremely similar in size (McLaren, 2012). The Hoary in Fig. 2 looks much more plump than the Commons due to its fluffed up feathers.

Figure 2. Hoary Redpoll with Commons and a Goldfinch in Pubnico - Feb 4, 2015 - Photo by Alix d'Entremont

The relatively stubby bill of the Hoary Redpoll is evident in Fig. 3. Pyle (1997) gives us another way to appreciate this bill difference by describing the comparatively longer bill of a Common as more acutely angled versus the obtuse bill tip of a Hoary.  Hoary Redpolls typically show less extensive black in the chin and lores (Brinkley et al., 2011). Fig. 3 also shows how the light crown of the Hoary contrasts much more with the red forehead.

Figure 3. Hoary Redpoll (L) vs. Common (R) - Feb 4, 2015 - Photo by Alix d'Entremont

Hoary Redpolls show no or very limited streaking on the undertail coverts while Common Redpolls have more extensive streaking. First winter birds show the most pronounced streaking for each species. The longest undertail covert of first-winter Commons have heavy and distinct streaks while Hoary shows no or narrow streaks. Fig. 4 shows the single narrow streak found on the undertail coverts as is expected for a first-winter Hoary. (Pyle, 1997)

Figure 4. Hoary Redpoll in Pubnico - Feb 4, 2015 - Photo by Alix d'Entremont

A very useful article that appeared in North American Birds called Photo Essay: Redpolls from Nunavut and Greenland visit Ontario is available online as a PDF. It describes the four redpoll subspecies with text and photos and is worth reading in preparation for your next redpoll flock.

References:
Brinkley, E.S., Buckley, P.A., Bevier, L.R. and A.M. Byrne. 2011. Photo Essay: Redpolls from Nunavut and Greenland visit Ontario. North American Birds 65(2): 2-11

Pyle, P., S.N.G. Howell, R.P. Yunick, and D.F. Desante. 1997. 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.