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Ageing Canada Geese

Determining the age of a goose can be helpful for identification, and can also reveal some interesting behavioral and ecological information by enabling you to sort out family groups and subflocks. Given good views it's not hard to distinguish Canada Geese that are still in juvenal plumage from those that are in adult plumage. By October many immatures (hatched in the summer a few months earlier) will have molted most of their body feathers into adult-like plumage, while others have not yet begun to molt. In general, consistent with other species of birds, the late-molting juveniles are long-distance migrants from far northern breeding grounds, while local Lower-48 resident Canada Geese molt in early fall.

Juvenile (top) and adult (bottom) Canada Goose. 19 Oct 2009. Concord, MA. Photos copyright David Sibley.

Differences apparent in these photos are:

• Juvenile overall has lower contrast markings, especially blurry and obscure pale edges on back feathers
• Juvenile has all feather tips narrow and rounded, vs adult feather tips broader and more square or flat-tipped. This creates a strongly barred pattern on the adult with pale lines straight across the back and well-marked pale and dark bars on the flanks.
• Juvenile has neck not quite as dark blackish as the adult, and the dark neck blends into the paler breast color; vs the adult has a truly black neck (in shadow in the lower photo here) with very distinct edge and no blending to pale breast (but in some dark western subspecies the black neck may blend into a dark brown breast even on adults)

Similar differences in feather shape and pattern should allow ageing of other species of geese as well.

Obsolete Bird Names

Have you seen any Field Plovers lately? Blue Nutcrackers? Day Owls? These are all alternate common names of North American birds. Richard Banks has assembled a complete list of outdated English names of North American birds along with the current official names for those species, and it makes a great resource to find out what early authors meant, as well as just fun browsing. You can read it at Obsolete English Names of Birds and their Modern Equivalents. 

If only there was a similar resource for North American plants.

Corrections to The Sibley Guide to Trees

updated 16 Oct 2009

Here are page-by-page corrections and changes for the Sibley Guide to Trees. This listing will be updated periodically as issues come to my attention. Please feel free to leave comments or send me an email if you notice anything that is not listed here.

p 3 - California Torreya, the common and scientific names should be justified left
p 28 - Red Pine needs a new name to distinguish it from Japanese Red Pine. I propose American Red Pine.

p 146 - Black Hickory caption should say "husk very similar to Pignut..."; Sand Hickory, captions should read "fruit similar to Pignut..." and "twigs similar to Pignut..."

p 179 - Tanoak - caption at bottom right should specify “pale underleaf conspicuous among dense, dark foliage”
p 189 - Southern Red Oak leafy twig, the caption saying “acorn identical to Southern Red Oak” should instead say “acorn identical to Cherrybark Oak”
p 227 - Tung-Oil Tree - leaves should be larger
p 252 - Glossy False-buckthorn includes the three leaves at the top of the column and the map at the bottom. The yellow box of text and the three leaves immediately below that are Ceanothus. The map should be moved up above the box text to make clear that it represents the range of Glossy False-buckthorn.
p255 - Rose Family Intro, near bottom of column 1 should say "Plums and Cherries (Prunus) page 256" [not page 254]
p 302 - Slippery Elm, in the third sentence "fragrant" is misspelled.
page 332 - Intro to maples, the third paragraph begins "All maples have palmately compound leaves..." This should instead say "Nearly all maples have palmately lobed leaves..." And could go on to elaborate that a few species have the leaves so deeply lobed that they are compound, and Boxelder is unique among the maples in having pinnately compound leaves.
p 345 - Mountain Maple underleaf should be rotated with stem down, (same for Vine Maple)
p 392 - First line of text - capitalize Paulownia family
p 393 - Aralia Family, add a sentence saying "Castor-Aralia (p 322) is also a member of this family and should be placed here." [and in a future edition it will be]

Index:
Pignut p 145
Rose Family p 254
And it is suggested (see comments below) that species like Northern White-Cedar and Western Redcedar should have an entry in the index under "cedar". [and presumably there are other examples like this]

Trees with opposite leaves

In the past, tree identification guides have emphasized the presence of opposite leaves as one of the most important field marks. In the Sibley Guide to Trees I used a more holistic approach, like modern bird identification, giving equal weight to all parts of the tree. A tree might catch your attention because of its flowers, twigs, bark, fruit, etc., and I don’t think it’s helpful if the field guide then asks you to check whether the leaves are alternate or opposite. It’s better to get to know all of the distinguishing characteristics of oaks and maples, for example, so that you can recognize them by multiple features, rather than having to check leaf arrangement.

In some cases, however, when you encounter a confusing tree, the presence of opposite leaves can be a useful pointer to help narrow the range of possibilities. So below I’ve put together a list of trees with opposite leaves. Interestingly, almost all of these species show up in the last 80 pages of the guide.

Definition from p xxiv of The Sibley Guide to Trees:

Leaves that grow singly from the twig, without another leaf directly across the twig, are called alternate, as they usually grow from alternate sides of the twig. Leaves that grow in pairs from opposite sides of the twig at the same level are called opposite. If three or more leaves all grow from the same level on the twig they are called whorled.

These patterns can be detected even more easily in winter, as buds and leaf scars on the twigs match the arrangement of the leaves (either opposite or alternate), and branching tends to be opposite or alternate as well. Also note that twigs with alternate leaves tend to grow in a zigzag pattern, while trees with opposite leaves generally have straighter twigs.

Species counts only include those illustrated in the guide.

North American Trees with Opposite Leaves

• Katsura, Genus Cercidophyllum (p. 101) – one introduced species [the only species in its family]
• Eucalyptus, Genus Eucalyptus (p 109) – three introduced species have juvenile foliage opposite, but adult foliage alternate [Crape-myrtle, in the same family, has alternate leaves]
• Paper Mulberry, Genus Brousonettia (p. 248) – one introduced species [other genera in the Mulberry family do not have opposite leaves]
• Lyontree, Genus Lyonothamnus (p. 293) – one native species [other genera in the Rose family do not have opposite leaves]
• Beebee Tree, Genus Evodia (p. 321) – one introduced species [related to Corktree, but other species in the Rue family do not have opposite leaves]
• Corktree, Genus Phellodendron (p. 323) – one introduced species [related to Beebee Tree, but other species in the Rue family do not have opposite leaves]
• Buckeyes, Genus Aesculus (p. 326-331) – six native and one introduced species [related to maples, but other genera in the Soapberry family do not have opposite leaves]
• Maples, Genus Acer (p. 332-351) – 13 native and ten introduced species [related to buckeyes, but other genera in the Soapberry family do not have opposite leaves]
• Dogwoods, Genus Cornus (p. 355-358) – three (out of four) native and one introduced species have opposite leaves [Dove Tree, in the same family, does not]
• Buttonbush, Genus Cephalanthus (p. 374) – one native species [the only North American tree in the Madder family]
• Ash, Genus Fraxinus (p. 376-385) – 17 native and four introduced species [all other genera in the Olive family also have opposite leaves]
• Japanese Tree-lilac, Genus Syringa (p. 386) – one introduced species [all other genera in the Olive family also have opposite leaves]
• American Fringetree, Genus Chionanthus (p. 387) – one native species [all other genera in the Olive family also have opposite leaves]
• Common Olive, Genus Olea (p. 388) – one introduced species [all other genera in the Olive family also have opposite leaves]
• Devilwood, Genus Osmanthus (p. 388) – one native species [all other genera in the Olive family also have opposite leaves]
• Desert-willow, Genus Chilopsis (p. 389) – one native species with opposite or whorled leaves [related to Catalpas, other genera in the Trumpet Creeper family also have opposite leaves]
• Catalpas, Genus Catalpa (p. 390-391) – two native and one introduced species have opposite or whorled leaves [related to Desert-willow, other genera in the Trumpet Creeper family also have opposite leaves]
• Royal Paulownia, Genus Paulownia (p. 392) – one introduced species [the only species in the family]
• Elders, Genus Sambucus (p. 397) – many native species mostly shrubs [related to Viburnums, all other genera in the Muskroot family have opposite leaves]
• Viburnum, Genus Viburnum (p. 397) – many native species mostly shrubs [related to Elders, all other genera in the Muskroot family have opposite leaves]

Probability in bird identification

One of my regular birding spots is a small farm field near my house in Concord, Massachusetts. I can walk around the entire place in about 20 minutes, but I usually take about two hours and get in some good sparrow-study. The clump of taller vegetation shown here is always a good spot to study birds that come up out of the grass and weeds and perch a little more conspicuously, so I usually spend a lot of time standing here looking at sparrows through my telescope.

On one visit in September 2008, I noticed that the three common species of sparrows – Savannah, Song, and Swamp – were using different parts of the vegetation, and I made a note to watch for this on future visits. It seems to be fairly consistent, so I can now produce a kind of "map" of sparrow-regions within the shrub thicket.

I've divided the thicket into three zones that I'll call the margins, the middle, and the depths. I was seeing mainly Savannah, Song, and Swamp Sparrows, and those are the species I'll discuss here.

• The Margins are occupied by Savannah Sparrows and are rarely used by the other two species (almost never by Swamp)
  
• The Middle zone was used by all three species, although I would say it was preferred by Song Sparrow, and was used rarely by Swamp Sparrow.
  
• The Depths were the home of Swamp Sparrows, which rarely venture into the other zones. Song and Savannah sparrows would also go deep into the shrubs when alarmed (e.g. if a hawk flew by), but their typical behavior when flushed by me was to land on the outer edges of the thicket.

Of course, in real life this thicket is three-dimensional, but the zones I've drawn are more like a cross-section. So a Savannah Sparrow could head for the lower parts of the thicket and still land in the margins of that shrub.

This may seem trivial, but it's really no different from habitat and other "soft" identification clues. You certainly can't identify a bird solely by its chosen perch, but we should never doubt the capacity of the human mind to discern subtle differences in probability (just look at baseball batting averages). The more I watched the more I realized that these are helpful clues to identification, just as date and habitat are helpful clues. A sparrow that flies right up into the highest twigs of the cherry sapling is almost certainly a Savannah, and it doesn't take much more to confirm that. A sparrow that goes straight into the deep cover and then barely pokes its head out is likely to be Swamp (or White-throated, or sometimes Song, but at least we can start with some idea of the likely species).

Check it out in your local area. I'd be interested to hear how it works in other places and with other species. And of course the same principle should be applicable to lots of other situations.

Correction to maples, page 332

Reader Sherman Dunnam sent me a note about an error in the introduction to maples on page 332. The third paragraph begins "All maples have palmately compound leaves..."

This should instead say "Nearly all maples have palmately lobed leaves..." And could go on to elaborate that a few species have the leaves so deeply lobed that they are compound, and Boxelder is unique among the maples in having pinnately compound leaves.

Updates to the Tree Guide

I have spent the last seven years working intensively on my new Guide to Trees, but of course a few misstatements and errors somehow managed to creep in. I'm always interested in learning more, correcting my mistakes, and passing along to you - the reader - newer, better, more accurate information.

So if you notice any errors, or anything that seems to be missing or misleading, please don't hesitate to let me know, either by leaving a comment here or sending me an email. I'll be posting additions and corrections as time allows. (And the same goes for any of my bird guides, of course)

Thanks!

Tree Guide news

Two events related to The Sibley Guide to Trees: It is the featured product today on the Daily Grommet website. I’ll be checking in periodically, responding to comments and answering questions through noon tomorrow (Wednesday Sep 23rd) .

And “The Art of Identification” - a show of my artwork and field sketches at the Massachusetts Audubon Society’s Visual Arts Center in Canton, MA, will be opening this coming Sunday Sep 27th, and showing until January 2010. More details are here.

My latest project

After seven years of work, my new Guide to Trees goes on sale officially on September 15th (but those who live near Philadelphia can get it as early as Saturday the 12th when I'm there for book-signings). I'll be traveling quite a bit this fall to book-signings across the US and Canada, doing a variety of publicity-related things, and adding tree identification to the topics I cover here on this blog. Coming soon...

More information about the book can be found at the Knopf website, and a list of my confirmed book-signing events for the fall is here.

More vocal copying by American Goldfinch, Purple Finch, and Ovenbird

After listening carefully to Pine Siskins this year to pick out the calls of other species (see my earlier post) I have run across several other mimics. In early June in Arlington, Massachusetts I heard a remarkable American Goldfinch song that incorporated several phrases of a Song Sparrow song along with Northern Flicker and I suspect other species were being copied but I couldn't pick them out. This is the first time I've heard an American Goldfinch that included copies of other species in its song, and these were very clear and obvious copies, but as Dan Lane pointed out in comments on my previous Siskin post American Goldfinch seems to be exceptional – the one American member of the genus that does not copy. Apparently they do, at least occasionally.

In western Massachusetts in late June 2009 I heard a male Purple Finch giving its territorial song. This territorial song began with a bright warble like a typical Purple Finch song, then continued into a longer and more varied section – a jumble of short song phrases and copies of other species. I was able to pick out copies of American Robin, Tufted Titmouse, Eastern Towhee, and Hairy Woodpecker, and again I suspect there were more. In this case the copying has been previously reported in the literature, with the BNA account mentioning Barn Swallow, American Goldfinch, Eastern Towhee, and Brown-headed Cowbird.

Several years ago I noticed a few copies in the flight song of an Ovenbird, and I've heard a few others since then. Over several days in late June 2009 I was able to hear many flight songs from one Ovenbird in Colton, New York, which included copies of Red-eyed Vireo song phrase, Robin tut note, and a Purple Finch song phrase. There are very few recordings of the flight song (since it is given at such long intervals) but one on the Stokes Guide to Bird Songs: Eastern includes a lot of mimicry. Listening carefully to that I can hear a snippet of Winter Wren song, the trill of Eastern Towhee song, Red-eyed Vireo song phrase, and ending with White-eyed Vireo song. It's such a jumble of calls that (like the Siskin song) it's very hard to pull out all the copies, so I suspect there are others, and this whole performance – other than the few typical Ovenbird song phrases in the middle – might be copies. This is another instance of vocal copying that has never been reported before, as far as I know. The BNA account for Ovenbird makes no mention of it.

It's interesting that both the Purple Finch and Ovenbird use copies in these sort of extended or auxiliary songs, and not in the more frequently heard "typical" songs.

I should point out a very interesting new blog by Nathan Pieplow about bird vocalizations, with a comment on the Pine Siskin issue here, and lots of other good stuff. And another blog about bird voices by Paul Driver, with a recent post about Mimicry here.

References:

McGraw, Kevin J. and Alex L. Middleton. 2009. American Goldfinch (Carduelis tristis), 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/080

Van Horn, M. A. and T.M. Donovan. 1994. Ovenbird (Seiurus aurocapilla), 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/088

Wootton, J. Timothy. 1996. Purple Finch (Carpodacus purpureus), 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/208

Promising new window film may prevent bird collisions

The most recent research by Dr. Daniel Klem, who has been studying the problem of bird/window collisions since the 1990s, has just been published in the June 2009 Wilson Bulletin. It is available, along with lots of other bird/window resources, at his website here.

Klem tested the effectiveness of various window treatments confirming, for example, that single decals on a window are not effective at preventing bird collisions, and that the non-reflective Collidescape film is nearly 100% effective at preventing collisions. Several different UV-absorbing films were tested with small to moderate success.

Beginning in 2007 Klem tested a new film developed in collaboration with Dr. Tony Port, a chemist at CPFilms. This film has vertical strips that reflect UV wavelengths alternating with vertical stripes that absorb UV wavelengths. The UV reflection and the alternating pattern seems to be very effective at deterring birds – only a few birds collided with the windows treated with this film, and none of those collisions were fatal. The real promise of this film lies in the fact that it appears clear to humans, and should be relatively easy to apply to existing windows!

Hopefully the company, CPFilms, can be convinced that there is a market for this window film, and start producing it commercially. I can think of dozens of windows that I would put it on.

Klem, Daniel, Jr. 2009. Preventing Bird-Window Collisions. The Wilson Journal of Ornithology 121:314 –321

Identification of Belding's Savannah Sparrow

In early March 2009 it was my pleasure to spend a few days in California at the San Diego Bird Festival. On my first morning in San Diego I headed straight out to the Tijuana River National Estuarine Research Reserve hoping to spend a few hours studying Savannah Sparrows (who wouldn't, right?). I had seen some Belding's Savannah Sparrows in March 2008 in Orange County, California, and realized that the treatment of this endangered subspecies in my field guide was not very good, so I was anxious to learn more.

I succeeded in seeing dozens of the resident Belding's, with many birds singing and territorial around the marsh. I also saw quite a few of the migratory northern subspecies of Savannah Sparrows (ranging from grayish to brownish) in weedy areas around the margins of the marsh.

The image below compares two of my photos showing the most obvious differences between the subspecies. Compared to northern birds, Belding's has:

• longer and thicker bill with curved culmen
  
• darker and much thicker streaks on the underside
  
• darker streaks on the upperside and coarser and darker markings on the face
• Belding's never (as far as I could see) raises a crest, while the northern birds often look slightly crested and show a distinct peak on the rear crown
  

Belding's (left) and Northern-type Savannah Sparrows. Photos 5 and 8 March 2009, San Diego, CA 

 copyright David Sibley (digiscoped with Nikon Coolpix 4300 handheld to Swarovski telescope)

Differences in behavior, habitat, and molt were also fairly obvious, and should be very helpful for identification (but bill and plumage features should be checked to confirm). 

• Belding's in early March were singing and territorial, chasing each other across the marsh, while the northern birds were in small, loose flocks moving together widely across dry grassy and weedy areas around the marsh
• Belding's flight was low and weak, with round body and fluttering wingbeats, reminding me of Sharp-tailed Sparrow, unlike the stronger, higher, more "bounding" and undulating flight of northern Savannahs
• in early March the Belding's were all in clean fresh plumage, while the northern birds were molting and scruffy with missing feathers all over the head and body

I could not hear any difference in the song of Belding's compared to Savannah Sparrows from farther north.

I was struck by how much stockier and larger-billed the Belding's looked in comparison to the northern subspecies, in many ways intermediate between northern and "Large-billed" Savannah Sparrows. Apparently some populations intermediate between Belding's and northern birds are resident farther north along the California coast, but alongside the migratory northern subspecies the Belding's Savannah Sparrows in southern California seem quite distinctive.

Vocal copying by Pine Siskins

[10 July 2009 - update added at end]

In July 1990 I spent several weeks birding in west-central British Columbia, where Pine Siskins were one of the most conspicuous birds, and I became convinced that Pine Siskins were copying the sounds of other species of birds and incorporating these sounds into their songs. I was able to identify American Robin (squeal call), Evening Grosbeak (“krrr” call), Warbling Vireo (scold call and a song phrase), White-winged Crossbill (flight call and trill), and even House Sparrow (calls).

Since then I’ve heard this in many other places, and come to expect it whenever I hear siskins singing. From late March to early April 2009 I had the opportunity to listen to several individuals repeatedly in my yard in Concord, Massachusetts, and I was able to identify the following 14 species in the siskins’ songs:

Evening Grosbeak “krrr” call

American Robin, flight squeal and single “pup” call

Eastern Bluebird, rattling flight call

Eastern Towhee, “chewink”

Black-capped Chickadee, a single “dee” note

Northern Flicker, “kew” call

Hairy or other woodpecker, “wika” call

Dark-eyed Junco, soft “tew-tew-tew” call

Eastern Phoebe, song phrase and chase call

Blue-headed Vireo, two syllables of scolding call

Red-eyed Vireo, scold call

Song Sparrow, “jimp” call

Ruby-crowned Kinglet, two-syllabled whistled song phrase

Common Redpoll, flight call

These sounds can be very challenging to pick out, since the song moves along so rapidly that the bird is already singing other sounds while your brain struggles to process and identify the previous sound. The Evening Grosbeak call is commonly used and distinctive enough to stand out each time, but other calls like the Eastern Bluebird rattle simply blend in with the staccato jumble of sounds.

In my yard the same sounds were used repeatedly day after day, so as I became familiar with them I was better able to pick them out, and started to notice other copied sounds. I could not distinguish individual siskins, so I don’t know how many sounds were shared among birds, but the fact that the Evening Grosbeak call and American Robin call were heard virtually every time I listened carefully (and were heard years earlier in BC as well) suggests that most or all siskins use these calls, and probably share a lot of other sounds as well.

If you’d like to hear some of this, check out the recording catalog number 133352 at Cornell's Macauley Library, July 2, 2007, recorded in Newfoundland by Geoffrey Keller. [You’ll have to Search audio for Pine Siskin, and then find this recording]

The bird starts singing at about the 40 second mark, and between 47 and 56 seconds imitates Common Redpoll, Evening Grosbeak, Hairy Woodpecker, Dark-eyed Junco, American Tree Sparrow and American Robin (and probably others). Notice the clear sing-song notes of American Tree Sparrow at about 55 seconds, with the abrupt “pup” of American Robin following immediately after.

Amazingly, this vocal copying seems to have been almost completely overlooked. In Bent’s life histories (online here) copying of Evening Grosbeak and (in a captive bird) Common Redpoll and Canary, are mentioned. A study of vocal copying by Lawrence’s and Lesser goldfinches (Remsen et al, 1982, pdf here) specifically says that the song of Pine Siskin does not include any copied sounds, and the Birds of North America account makes no mention of it.

Presumably the sounds that are learned are simply the ones that are common in the siskins’ environment, so siskins from the western mountains must learn some sounds that are not heard in the east, and vice versa. Another Macauley Library recording from California (catalog number 120288) includes copies of Lesser Goldfinch flight calls, among others. Given how much siskins wander, it would make a really interesting exercise to listen for copied sounds that are “out-of-range”. Hearing, for example, Eastern Towhee in British Columbia or Lesser Goldfinch in Massachusetts would give you some idea of how far that individual siskin has traveled.

Update - in early June 2009 I spent a week at The Nature Conservancy's Pine Butte Guest Ranch near Choteau Montana, and was able to hear several Pine Siskins singing. I was able to hear copies of the vocalizations of seven species there. In addition to the now-expected calls of American Robin, Dark-eyed Junco, Common Redpoll, and Evening Grosbeak, the Montana siskins copied Western Tanager call, Mountain Chickadee dee note, and a Cassin's Vireo song phrase. Clearly these birds had learned their calls in the west, and would stand out in the east. So the challenge remains – to find a siskin that has traveled cross the continent, and recognize it based on the sounds it has learned.

More on identification of Greenland White-fronts

Coincidentally, just days after my last post about the two White-fronted Geese in Concord, two White-fronted Geese showed up in Amherst, Massachusetts (about 60 miles west of Concord, but not the same birds) that appear to be one Greenland and one North American type. James Smith has some discussion and really nice photos on his blog, and he's allowed me to post some of the photos here. 

Two Greater White-fronted Geese - 23 November 2008, Amherst, MA. Photos copyright James P. Smith, used by permission. Click for higher resolution (660 kB). In this montage the upper image shows the apparent North American bird with the Greenland-type on the left. I've resized and pasted in another photo of the Greenland type below for comparison.

This provides a great comparison of the two birds, very well-photographed, in similar light and from similar angles. The Greenland-type bird shows the following differences from the North American-type:

• neck, head and bill larger and bulkier than the North American-type
• neck and head more uniform and darker brownish
  
• scapulars with slightly narrower and less contrasting pale edges
• white border on flank feathers narrower
• pale tips on median and greater coverts narrower and less contrasting, not bright white
• pale edges on tertials slightly narrower and less white

These are all the same differences that I noticed on the two birds in Concord, and that have been described before as identification features for Greenland White-fronts in Europe. One other feature deserves mention:

• bill bright orange (and James says the color is accurate and this bird was truly very orange-billed) which may be useful even though we know how unreliable bill color can be, and the other bird happens to be a fairly obviously pink-billed individual, providing a strong contrast. One thing I noticed on the Concord birds, and again here, is that the North American bird has a fairly obvious whitish tip on the bill, while the Greenland bird does not.

And on 24 November, Taylor Yeager posted photos of another apparent Greenland White-front (scroll through the gallery to see several images of this bird), this one in Sharon, MA about 30 miles south of Concord. This bird doesn't look quite as heavy-billed as the other two, but it still looks fairly thick-necked, the bill is bright orange, and it has the dark head, narrow and low-contrast feather edges on the back, virtually no white on the wing coverts, very narrow white flank stripe, and extensive black on the belly between the legs. I'm comfortable calling this a Greenland White-front also. 

This would all seem to lead to confidence in identifying Greenland White-fronts, and I think we're getting there. But when I browse photos of White-fronts from other areas they show a bewildering range of variation. Identifying Greenland White-fronts will require excellent views and a careful assessment of all the different identifying features, preferably with direct comparison to other White-fronts, and a healthy dose of caution.

Another photo of the two birds in Amherst: Greenland-type in front showing the much larger and bulkier bill and head, and thicker neck, in comparison with the more delicate features of the North American-type bird behind. Photo by James P. Smith, used by permission. 23 November 2008, Amherst, MA.

Finally, one further mystery: It's not at all clear how we can tell that the smaller bird in Amherst is a North American White-front rather than a Eurasian bird. I don't think I've ever seen a discussion of that identification issue, but Eurasian White-fronts show up rarely in Iceland, and could easily wander into North America from there or from Siberia, so it is a potential vagrant to North America. All I can dig up in a cursory search is that Eurasian birds are consistently pink-billed, and may average smaller-billed, and may average less white on the wing covert and tertial edges, but those things are all vague, subjective, and variable. So while I've called the smaller bird in James Smith's photos a North American-type, I can't actually rule out the possibility that it is a Eurasian bird. Any comments or suggestions welcome. 

Identification tips for Greenland Greater White-fronted Goose

The Greenland Greater White-fronted Goose (Anser frontalis flavirostris) is known to be a rare visitor to northeastern North America, but I have never been satisfied with a reliable, objective way of distinguishing it from the North American subspecies of Greater White-fronted Goose, also a rare visitor to the northeast.

Bill color is the most frequently-mentioned field mark – supposedly orange on Greenland birds and pinkish on North American – but this has been refuted multiple times (see Kenn Kaufmann's note in Birding 1994, my blog post here). I suspect this is a mark that works in Europe, where local White-fronts are reliably pink-billed, but not in North America, where lots of the local birds look more or less orange-billed.

Over the last few weeks a single adult White-fronted Goose has been frequenting farm fields near my home in Concord, Massachusetts, and about a week ago it was joined by a second bird (well... "joined" is an overstatement since they pay no attention to each other and keep apart in the big flock of Canada Geese). 

These two individuals, in their details, are really strikingly different, and the differences all lead me to the conclusion that the new arrival is a Greenland bird, and the other a North American bird. On 19 November I was able to get some photos of the Greenland-type bird, and I've annotated a photo here with the differences between it and the North American-type bird. The differences are listed simply from front to rear, not in order of importance. (I'll try to get some photos of the other bird to post here for comparison).

Presumed Greenland Greater White-fronted Goose, 19 November 2008, Concord, MA. Photo by David Sibley

1. bill color slightly more orange, with yellow base (vs. orange with pale pink base on the other bird); but this is very very difficult to judge and essentially worthless as a field mark (see my post from last fall about judging bill color).
   
2. whole head nearly uniform dark brownish, sometimes looking paler on the cheeks but still with solidly dark crown above the eyes (vs. paler gray-brown head and neck with narrow dark crown stripe and contrasting dark border along white front). This is highly dependent on lighting, and would be difficult to judge on a lone bird, but the Greenland-type bird does look consistently darker, and may show a contrasting dark hind-neck that the other bird doesn't, but I need to check that in more lighting conditions.
   
3. neck strikingly thick and heavy, no thinner than the head (vs. neck slender, obviously narrower than the head and looking graceful and slim). This is one of the most obvious differences on these two individuals.
4. margins of mantle and scapular feathers pale brownish, not strongly contrasting (vs. margins whitish, more strongly contrasting).
5. white border on flank feathers narrower and not extending as far forward (vs. broader and longer)
6. pale tips on median coverts narrow and not white, relatively inconspicuous (vs. broader, whitish, conspicuous)
7. greater coverts without pale edges, and with narrow and inconspicuous whitish tips (vs. obvious narrow white edges and broad white tips forming a conspicuous narrow white band across edge of folded wing). This is another obvious difference between these two individuals.
8. black smudges all over the small feathers of the belly between the legs and extending well behind the legs (vs. this area virtually all white). This is separate from the irregular black bands before the legs and up onto the flanks, which are marked similarly in both birds.
9. white tips on the tail feathers seem to be narrower on the Greenland-type, but this is very difficult to see in the field.

Overall the Greenland-type bird appears bulkier, heavy-billed and thick-necked, and darker, without the elegant white fringes that are prominent on the rear upperparts of the North American-type.

Here's another photo of the Greenland-type bird, showing the heavy orange bill, dark and thick neck, and the lack of contrasting edges on the feathers across the shoulders. But none of that is very helpful in a single photo without another bird for comparison, nor is it likely to be very helpful on a single bird in the field. 

I know that some of these things have been described before, and they are still pretty subjective, and it's not safe to generalize from a single individual, but if this is a typical Greenland White-front, then I feel more hopeful about identifying the subspecies.

notes:

Martin Reid's website has some other discussion, photos, and lots references

Sungrebe – New for North America!

Stunning news from Bosque del Apache NWR in New Mexico: a female Sungrebe was photographed there on 13 November 2008, those photos here. It was correctly identified on 17 November from the photos, then refound and photographed more on 18 November. This is not only a new species for North America, but a whole new family.

A map of the species' whole range can be seen here at InfoNatura (scroll down for the detailed map).

Of course, birders are already debating whether this is a wild, naturally-occcurring bird or an escape from captivity. On one hand, it's a secretive species that is rarely seen flying, with no known history of vagrancy or even real seasonal movements, making the prospect of one appearing nearly 1000 miles northwest of the closest known population seem very unlikely. On the other hand, it's not kept in any zoos, and doesn't seem like the kind of species that would be illegally transported by an individual, which makes the escapee theory unlikely also.

Tipping the balance in favor of natural occurrence, in my opinion, is that in South America Sungrebes are apparently quick to occupy ephemeral wetlands, even when those are isolated many miles from any other suitable Sungrebe habitat. So clearly they are capable of long-distance flight, and wander enough to discover recently-created habitat. Perhaps, like rails, or Masked Ducks, they are capable of amazing feats of vagrancy.

Unless there is some clear evidence of captivity, I would consider this a wild bird. Incredible!

Update 19 November: Jerry Oldenettel has more details and will be updating the bird's status on his website here; and apparently the original photos were taken 13 November, and identified on the 17th, so the bird has been present at least six days.

Lesser Canada Goose in the northeastern US

The primary challenge of distinguishing Canada from Cackling Goose centers on the intermediate-sized 'Lesser' Canada Goose, B. c. parvipes, which reportedly nests across the boreal forest regions of western Canada and interior Alaska (more details on my website here). I've seen a few birds that I thought were 'Lesser' in the northeast over the years, most convincingly one at Brigantine NWR in NJ that accompanied a big flock of Snow Geese rather than flocking with Canadas. But it's a pretty ambiguous subspecies. The identifying features are wholly subjective: anything that seems smaller than the regular Canadas but too big for Cackling is a candidate for 'Lesser' Canada. Recently I saw this bird (the one on the left) that I feel pretty confident is a 'Lesser':

click for a slightly larger image. 

16 November 2008, Great Meadows NWR, Concord, MA - photo by David Sibley. Taken with the 10x zoom on a Canon digital camera. The Canada on the right was a bit farther to the right in the original photo, I cut and pasted it closer for better comparison.

It was distinctly smaller than the Canadas around it, with a very short neck and short bill. In flight going away it appeared no more than 2/3 the bulk of the Canadas next to it. Whenever I scan Canada Goose flocks in the east looking for Cackling Goose, there are always a few birds that grab my attention because they look small. Often they are marginally smaller than the other Canadas, sometimes their smallness was an illusion (happened to be standing in a furrow, next to an unusually large goose, etc). After a closer study these "small" birds fit nicely into the normal range of variation of the local Canadas, and the impression of smallness vanishes. This bird stood out because its smallness held up to closer scrutiny; it was truly small with very short neck and short bill.

I called it a Canada rather than Cackling because it seemed just a little too long-billed, too large overall, and the head/bill too wedge-shaped for 'Richardson's' Cackling Goose. It also looked the same color as the Canadas around it, without the gray sheen on the back or golden cast on the breast that many 'Richardson's' show. 

There are very few reports of 'Lesser' Canada Goose in the northeast. This could be due to the difficulty and inherent uncertainty of identification: we identify only the most clear-cut examples and report those tentatively, if at all. Or maybe it's because few birders really look for them or follow-up on possibles since "it's just a Canada Goose". Or maybe they are truly rare. I have actually seen more 'Richardson's' Cackling Geese in the northeast than convincing 'Lesser' Canadas; but that could be due to any of the reasons above. Given the normal distribution of this subspecies – breeding farther south and west than 'Richardson's' Cackling, with shorter migration – I would expect it to be less frequent than 'Richardson's' on the Atlantic coast, at least in the north. The only way to figure that out is to keep watching for, and documenting, these small geese, in order to develop a better sense of the identification and status of the various subspecies.

How many rare birds did we miss before the internet?

Yesterday morning I 'found' Canada's first Lucy's Warbler... in my inbox. 

After reading my recent posts about rare birds, Cathy Mountain (whose redpoll photos were featured here last winter) sent me a series of pictures of a warbler that had been in her yard in Fort McMurray, northern Alberta, from November 8-10, 2008. 

After rejecting the possibility of a drab Yellow Warbler, she thought it might be a Virginia's or Lucy's Warbler, as did other local birders who saw the photos, but they were reluctant to call it since both of those species were so unlikely. 

photo by Cathy Mountain - used by permission

This photo is not the sharpest in the series, but it is the best for showing the identifying features: the small pointed bill, plain gray color, pale lores and eyering, and dark rusty rump just showing under the wings. (and Yes, that is snow.)

This highlights another line of evidence in the debate about how many rare birds we miss - the number of rare birds found and identified only because they are photographed. This bird, like West Virginia's Great Knot in August 2007, and countless others, would have been lost in the swirl of ambiguous possibilities if not for photography. And without the internet to allow immediate sharing, even photos might have laid in a drawer with a very low chance of ever being identified. 

Imagine the chain of events that led to this discovery:

• In all of northern Alberta, this warbler landed in the yard of a birder (maybe not entirely random since Cathy probably has some landscaping to attract birds, but still... northern Alberta's a big place)
  
• She had to notice it and take some pictures
  
• She had to realize it could be something noteworthy and go to the effort and the risk of showing the photos to other birders to try to identify it
  
• When it remained a mystery she had to continue pushing the pictures out on the internet

Judging from her email to me, I think she knew what it was, and just didn't have the confidence to say, but did have the confidence to keep trying to confirm her suspicions.

Now imagine if any one of the links in this chain had broken down. The bird didn't land in a birder's yard, didn't stay long enough or simply wasn't noticed, wasn't photographed, or wasn't 'advocated for'. This Lucy's Warbler could have landed unnoticed in dozens of yards on its trip from Mexico to Alberta. 

The digital photography revolution, and the ability to share pictures easily on the internet, means that a lot more of these birds are found (meaning confirmed), which is fantastic. But this still must be a fraction of all the rare birds that are out there.

So get out there and find something!

So how many do we find?

My last post "How many rare birds do we miss?", was simply getting at the idea that we can miss something glaringly obvious if we are not looking for it. A popular psychology quote goes "I wouldn't have seen it if I hadn't believed it". In the case of the moon-walking bear, since I wasn't looking for it, I didn't see it. 

In the comments a reader pointed to a discussion on his own blog "The Birdist" where he actually tries to answer the rhetorical question in the title of my blog post. So how many rare birds do we actually miss? The Birdist and his interviewee guess that one-third to over one-half of all rare birds are found. I disagree and I would put the percentage much much lower. 

Why do I think so few rare birds are found? Well, for one thing, I look at the very small number that are ever refound. The White-crested Elaenia in Texas last January, or the Variegated Flycatcher in Washington this September, or the European Golden-Plover in Maine in October, or the White Wagtail in the Florida Keys last week, etc etc. all share the fact that none of them was seen anywhere else in North America. Maybe a statistician can comment on the hypothetical numbers involved, but if one-half of all rare birds were being found by birders, I would expect a lot of re-finding of these ultra-rarities. It's likely each of these birds wandered slowly and spent time at many other places where they could have been discovered by birders, both before and after their actual discovery. And there must be countless others that are never found. 

The Jabiru in Louisiana July 31, 2008 could be the same one that was seen in southern Texas August 10th and 20th. But that is a big, conspicuous species that even a non-birder will notice. In fact, as I understand it, it was found in Louisiana by a local hunter who noticed it and took a few snapshots. It was refound by a birder in Texas on August 10th (if indeed the same bird) but then went missing for 10 days, reappearing on August 20th! Add to that the experience in August 2007 when a Jabiru showed up in Mississippi. Birders were alerted to it by the local farmers, but after a few days that bird vanished and was never seen again, despite intensive searching and the fact that its most likely path back to Central America would have taken it through Louisiana, past Houston and Corpus Christi, and over several hawkwatches. Rare birds being refound at a distant location are the very rare exception to the rule. 

Another interesting bit of evidence is what I will call "delayed discovery". There are many examples, as in the 2007 Mississippi Jabiru that was seen by birders only because the landowner was curious and sent out a photo. It turns out the bird may have been in the area for several weeks before that. Or the Least Grebes recently discovered in a park in Boca Raton, Florida. On September 27th self-described "recreational birders" Lee and David Hasse sent an email alerting other birders that "last Sunday" they saw two Least Grebes. This was confirmed by their photos and by "serious birders" the next day. The following day (28th of September) the nest was discovered, and on the next day (29th) the first egg hatched!

The eggs must have been laid about 3 weeks before they hatched, and nest-construction must have started at least a week before that, and probably several weeks for pair formation, etc. So those two grebes must have been at that park for at least 6 weeks, since mid-August. And if the Hasse's weren't there in late September, or hadn't taken the time to report their sighting, would the entire nesting have passed without birders noticing?

So I'll take on the question now: How many rare birds are actually found? At a place like Cape May in the fall, arguably THE most intensively birded location in North America, a Jabiru is almost certain to be seen and identified, I'd say 80 or 90% of the time, and if it sticks around for more than an hour or two the odds go up to near 100%. As we go down the scale of conspicuousness, Fork-tailed Flycatcher is fairly likely to be found (virtually all birders and even a lot of nonbirders would notice one, even from a great distance); Western Tanager is less likely to be found (much less conspicuous - you have to be within a few hundred feet to notice one); Smith's Longspur is even less likely (secretive and nondescript), etc. The odds of finding a Smith's Longspur that only stays for a day are very very low overall (although if it spends that day on the lawn by the Cape May hawkwatch, it's very likely to be found). Staying longer will increase the chances of being found, and so on.

Psychologically, birders at places like Cape May are somewhat more likely to find rare birds simply because, at known vagrant traps, we expect to find rare birds. The same observation that might set a Cape May birder running after a "possible Smith's Longspur" is more likely to be dismissed as "not worth the effort" by a birder in farm fields in upstate New York. And as soon as a historical pattern develops at a location - like Cave Swallows at Cape May in November - the tables turn and birders start actively looking for a specific rare bird.

Back to my point about birds not being refound: if each of these rarities is spending 10 or 20 or 30 days wandering around inside North America, but is only seen once, that's something like a 10% or 5% or 3% chance of being found, and that strikes me as the right range to consider for how many rare birds we actually see.

As a final note, I like to think that this makes me an optimist, since I can always convince myself that the European Golden Plover from Maine is going to show up in my local patch tomorrow, and that there must be loads of rare birds hiding in the next bush.