31st January 2021 – Maine Stay

In bright sunlight, colors and subtle buff hues in the supercilium where burnt out. Note the somewhat robust appearance with diffuse brown streaks extending down past the red flanks. The legs are pinkish-horn with darker brownish toes which are pro-coburni. Nominate Eurasian iliacus usually have paler, more flesh-pink tarsi. The “tooth” shaped white tip to the top tertial and pointed rectrices age it as a SY.

The last time I was in Portland, Maine was in January 1997. It was one of my first winters in New England after migrating here from the UK. I saw an Ivory Gull. It was fantastic. A rare denizen of the ice floes of the Arctic north it performed as they often do – with unabashed boldness that belied its appearance.

I nearly made it to Portland again in the winter of 2018; on a half-hearted sojourn to see the Great Black Hawk that had put Portland back on the avian map once again. Late in its stay, this resident of Central and South America had become difficult and unpredictable. So we paused to bird at Salisbury, Massachusetts, but with no news by noon, we turned around and headed back to CT, only to hear news of its reappearance as we crossed the Nutmeg state line. Too late now.  The bird was taken into captivity soon after and succumbed to frost bite. A sad event, but the squirrels of Dearing Park were reported to have uttered a combined sigh of a relief.

So, with news of a Redwing (a Eurasian thrush) being found at Capisic Park, Portland Maine, by Brendan McKay on the afternoon of 29 Jan 2021, it galvanized a few local CT birders into Twitch Mode. It was a yard bird for me, albeit in my hometown of Bolton, UK.  In my boyhood days on the Isles of Scilly, I had scoured flocks of Redwings, Song Thrushes and Fieldfares looking for something rarer, like an American Robin. Now I spend my time scouring flocks of American Robins looking for Fieldfares, Redwings and Song Thrushes. Somebody’s havin’ a larff!

So, since I had not seen one for many years, it would be rude not to go check it out, if only to perform a meditative overhaul of my COVID-induced isolation. And…there was a chance it might be from the Icelandic population coburni, a subspecies tick for me.

Nick Bonomo, Glenn Williams, Dave Provencher, Anthony Viccarelli, Jason Rieger, Phil Rusch and myself, masked up and socially distanced, arrived to find the bird on-show immediately. That’s how I like my rare birds these days – UTBBB (Under the belt before breakfast).

The CT Dream Team onsite!

It was associating with a flock of American Robins, apparently attracted to the sumac and multiflora rose fruit in the park and was performing well at close range in nice sunlight. It was a bit of a pain initially, in that it would always be obscured by twigs and branches, but on the odd occasion, it did manage to find itself out in the open for some nice photo opps.

Showing the red flanks and underwing coverts and brownish-washed flanks.

In shade, the upperparts showed the darker, oily-look to them and the subtle buff tones to the fore and rear of the supercilium became a little more obvious. Here the underparts look more heavily marked with darker centres with diffuse brownish edges fitting coburni.

The feathers of the vent have large dark centres, recalling a Black and White Warbler, a feature noted by Garner et al. as pro-coburni.

Strangely enough, with no recent Redwing experience with which to compare,  it did appear to be a robust individual, appearing closer to American Robin in size, with a big bill and sturdy legs. Not as dark below as some coburni, it was nevertheless an interesting bird showing several traits of Icelandic Redwing more than the nominate European iliacus. In the bright sunlight, it looked bright with a whitish supercilium, and pale mid-belly, but when the bird retreated to the shadows and out of the bright sunlight, it looked a darker, more oily-olive brown color above, with more diffuse brown feather edges to the dark brown streaking that extended way down the flanks beyond the reddish breast sides. The most compelling feature for me was the dark-centered undertail coverts which are described as being typically paler and less well-marked in iliacus. This was a feature mentioned in my old friend Martin Garner’s excellent Birding Frontiers Winter Challenge book.

When I returned home, I had some good discussions with local birder Louis Bevier, and then I reached out to sharp Icelandic birder Yann Kolbeinsson who replied, “To me there is little doubt, this has to be a coburni. Bulky looking bird with darkish legs, heavy streaking on breast (not in the heavier end) but more importantly brown base/streaking down alongside the flanks beyond where the red stops. The streaks also being more arrow/droplet shaped than actual streaks.”

Ebird Checklist with more pix:
https://ebird.org/checklist/S80340150

There is some obvious individual variation between the races, but this bird seems to fit within the paler end of coburni and would not fit a typical iliacus. For example, here’s a bird from Vancouver in Jan 2016 that is classic iliacus on plumage and would be the expected race to show up on the west coast of North America.

Note the greyer-brown tone to the small amount of upperparts we can see, coupled with the whitish ground color to the breast and unmarked belly. The dark streaking breaks up into small delineated droplets on the flanks. Note also the relatively whitish vent. Again, there is variation within iliacus with birds being more heavily marked, but had this bird shown up in eastern North America, it would easily be assignable to iliacus rather than coburni.

After our fill, we searched briefly for the western Black-headed Grosbeak that had been frequenting the park. It was the presence of this vagrant that had been the catalyst for the Redwing being found, but we drew a blank, but managed to see a wintering Dickcissel nearby with a flock of House Sparrow.

Then it was off to Arundel Cemetery, spending time en route looking in vain for Pine Grosbeak, a lifer for Jason. We soon arrived at the cemetery and found the flock of feeding Red and White-winged Crossbills. They weren’t as photogenic as we expected, but it was cool to see these niche-feeders plying their cone-destroying trade. It was at this point that we got an unexpected first for Maine – one that wasn’t on anyone’s radar I don’t think. Crossbills had been calling all the time we were there, and just as we convened to leave, the crossbills flushed in one group, giving their flight calls. Immediately one bird’s call stood out.  It was a Type 4 Red Crossbill! The first recorded in Maine. Woot!! In that moment, Nick Bonomo deserves full credit for having the presence of mind to keep his phone running so he was able to capture the call. We weren’t sure if it was Type 4 or perhaps Type 3, both seemed quite similar, especially when trying to compare the timbre of calls from different quality of recordings with real-world audible experiences. Tom Johnson quickly provided us with calls from a fly-over in New Jersey, but still it was hard to decide for sure which Type we had heard, although we suspected, and hoped it would be Type 4, which Nick later confirmed  by audio-spectrographic analysis.

Red Crossbill – Type 4

Info here:
https://ebird.org/checklist/S80340831

Yeah, I know. You were expecting something sexier! Me too!

Jeff Groth’s landmark work in 1993, laid out the idea that each taxon gives a unique, identifiable call type when in flight. As many as 10 “call types” of Red Crossbill can be found across North America (Groth 1993, Benkman 1999, Irwin 2010), each of which may represent a different incipient species (Parchman et al. 2006).

More great in-depth and helpful info on Crossbills by Matt Young and Tim Spahr here:

We continued on towards Ogunquit to try for a long-staying Rock Wren, another western stray that had taken up residence at Perkins Cove. We had one last shot at Pine Grosbeak at Ogunquit, and it was while we had pulled over to reconnoiter the area, I spotted a female-type Pine Grosbeak perched up along the road. A few minutes later, we got great looks at this bird, ABA numero 600 for Jason!

We failed to see the Rock Wren, but the weather was beautiful and the cove was Maine-scenic. Small flocks of Harlequin’s and the odd eider loafed offshore, but the highlight was the Thick-billed Murre that Jason spotted close inshore.

Brunnich’s Guillemot aka Thick-billed Murre

It had appeared seemingly out of nowhere and showed well. Brunnich’s Guillemot as they were known back in the homeland, was a highly-sought after rarity. Most of the early British records involved dead or moribund individuals showing up on the tide wrack of the Orkney or Shetland Isles. I’ve never seen one in the UK, but I always transport myself back home when I see one here and watch it vicariously through a young twitcher’s eyes.

https://ebird.org/checklist/S80232021

A fantastic day out with good friends and good birds!

Common and Roseate Terns in Flight

Juvenile Common Tern (left) and juvenile Roseate Tern, West Haven, CT August 2020 (composite: Julian Hough). Note the stout, blackish bill and hood of the Roseate and the body proportions compared to the Common Tern and the paler mid-wing panel, broader white trailing edge to the primaries and the diagnostic whitish outer web to the outermost tail feather on the Roseate. Click to view hi-res.

A good number of juvenile terns are mixing in with the post-breeding flocks at Sandy Point, New Haven, CT. Juvenile Roseates are not frequently seen here, but several have been present and afforded me a nice chance to study them.

On the deck

• Standing juvenile Common Terns have pale orange bill bases and pale orange-flesh legs with a clean white forehead.
• Juvenile Roseate Terns have dark blackish-brown legs, a complete black bill and a finely streaked blackish forehead that often extends all the way to the bill base, giving them a characteristic “hooded” look.

In Flight

In flight, especially at a distance, they can be hard to identify in a large mixed flock of flying terns. Their distinctive, di-syllabic “Chrr-uitt” call is often a clue to their presence and it is definitely a call any would-be searchers should memorize.

In flight, like adult Roseates, juveniles often look a bit skinnier and more “pure white” compared to Common Terns. With experience, they look slightly longer-necked, narrower winged and longer-tailed behind the wing (probably due to their shorter wings than longer tails) compared with the more even proportions of Common Tern. The more whiter plumage, especially the rump and tail and the paler mid-wing contrasting a bit more on average with the dark outer wing may be noticeable. These features will be hard to discern in a mixed flock, flying around, so look for the more rapid, shallow wingbeats of Roseate that is often helpful with experience. The dark, hooded look should also be noticeable at a distance helping cement any identifications.

On closer views, some minutiae, that helps differentiate these two species are:

• the outer web to the outermost tail feather is blackish-gray in Common Tern and white in Roseate (both adult and juvenile). If the tern you are looking at has a dark outer edge of the outermost tail feather it isn’t a Roseate.
• on Roseate, the tips to the secondaries and particularly the primaries are broadly edged white unlike in Common Tern.
• the upperpart markings in Roseate are more contrasting, giving a “black and white” pattern formed by broad blackish “c” marks to the rear scapulars. In Common, the dark subterminal marking are less dark and often the whole mantle is washed with ochre-brown.
• the outer primaries often contrast with a paler mid-wing panel in Roseates while in Common Tern the whole wing tends to be a more even gray.

Long Tales

During the past couple of years, I have been lucky enough to see a handful of first- and second-cycle Long-tailed Jaegers from pelagics off Massachusetts. I have been intrigued by some of the molt and ageing issues presented by these and put some images and thoughts together.
READ MORE…

Yellow-bellied kingbird tail patterns

A self-found Western Kingbird, New Haven, CT October 2010. Nice dark tail and pale grey head identify it quickly as a Western, but note the white tail edges are not visible in this view. (Julian Hough)

Vagrant kingbirds such as Tropical, Couch’s and Cassin’s have all been recorded in the north-east and it is only a matter of time before one of these “Western” kingbirds in Connecticut turns into something a bit more exciting.

While Western Kingbird is the expected species, Cassin’s has been recorded in Massachusetts in 2010 (https://www.flickr.com/photos/bonxie88/6686022777/in/photostream/)
and recently as last week in Brooklyn, although this was a one-observer sighting and couldn’t be refound.
Pictures clearly solidify the identity (https://www.flickr.com/photos/123166253@N05/sets/72157646979944483/); the second record for NYS after one at Montauk in October 2007 ( http://citybirder.blogspot.com/2014/11/new-brooklyn-rarity.html)

The Mass bird was mis-identified as a Western by virtue of its tail pattern, which was blackish and showed prominently white outer webs to the tail feathers, a key id feature of Western. That Cassin’s can show this too means that any yellow-bellied kingbird with a blackish tail and white outer edges may not necessarily be a Western.

A reported Western Kingbird in Bridgeport, without any details of other potential species being systematically ruled out, set off the spidey senses.  Questioning several observers, it seems the bird was distant but the ”white tail edges were apparent” The only pictures we saw seemed somewhat ambiguous – indeed the darkness of the head and tail pattern in one image suggested better photos need to be obtained to rule out Cassin’s. Further images revealed the bird to be a Western, as reported, but it spotlighted some tail features that needed to be expounded upon should observers be faced with a fall, yellow-bellied kingbird.

Tropical (left two birds) and Western (right two birds). Yale Museum (Julian Hough). Note tail and wing color.

Note the greenish band across the breast in the two Tropicals (left) compared with the more extensive grey breast of the Westerns. The Tropicals also show a cleaner white throat. Also, note the pale edge to the tail feather of the rightmost tropical, but compare with the more broader, whiter outer web of the Westerns. From below, the dark charcoal-gray underside to the tail is darker than the pale gray of the Tropicals.

So, just because it has pale outer tail feathers it doesn’t automatically make it a Western (see the Mass individual). So what should you key into when you chance upon a distant yellow-bellied kingbird?

Tropical Kingbird, Panama, February (Julian Hough). Note the long, notched tail, not darker than the wings and long, stout bill. Note the obvious pale edges to the tail – easily could be mistaken for those shown by Western?

Western Kingbird, New Haven, CT (same as title photo). Note broad white edge to the tail which is blackish and clearly darker than the wingtips (Julian Hough)

• Bill size and shape and tail seem to be the two main features to concentrate on.  Calls are also invaluable in separating kingbirds, so recording and/or a clear description of the call is important in identifying and documenting the record from a historical point of view.
• Any yellow-bellied kingbird with a blackish tail that is darker than the wings, is either a Western or a Cassin’s.
• Both Western and Cassin’s show whitish tail sides, but Cassin’s often lacks this and has pale tips to the tail forming a pale terminal band. They are typically more obvious and include the entire outer vane of the outer tail feather in Western. Sometimes in the field this may not be obvious, so continued observation of an individual may be required to determine the presence and amount of white in the tail.
• Any kingbird that has a paler brownish tail, that is concolorous with the wings is likely a Tropical or Couch’s. Note that some Tropicals can show paler edges to the outer tail feathers, but this is narrower and less well-defined that Western. Tropicals in particular seem to show a disproportionately long and notched tail.
• Tropical and Couch’s both show a long, broad and hooked bill tip, larger than either Western or Cassin’s but sometimes, bill size and shape can be hard to determine on lone individuals.
• Cassin’s and Western have a smaller bill, but compared to Western, Cassin’s have a short, but deep-based bill, often with a curved culmen that gives the bill a stouter, more conical-appearance.

So, a distant kingbird that has an obvious blackish-tail, darker than the wingtips, should get you into the Cassin’s/Western camp and a bird that has a tail concolorous with the wingtips should get you thinking about Tropical/Couch’s.

Separating them from here requires more observation about plumage and how dark the grey areas are on the head, underpart color and tail pattern. This post isn’t meant for covering that in detail, but I found a similar and more in-depth look at this problem by Kevin McGowan here at http://www.birds.cornell.edu/crows/kingbirdsX.htm

Northern Goshawks-problems and pitfalls

We are getting into that time of year where well-manned hawk watches begin to see the occasional Northern Goshawk. Here in Connecticut, they are a late migrant, generally occurring in late October into November – all reports are typically of juveniles and not adults (I’ve never seen an adult away from the breeding grounds in CT).

Our well-known, in-state watchpoints (Lighthouse Pt. and Quaker Ridge) are manned everyday, all day, at this time of year and there are few reports of Northern Goshawk. The math is simple. Goshawks are uncommon.

Goshawks are  big buteo-like birds, impressive to see both during the breeding season and on migration. They are also frequently misidentified. The time-honored identification pitfall being big Cooper’s Hawks –  it is these birds that you are likely to see  at Hawkwatches in September; in your backyard, attacking birds at your feeders; or just hanging out at Hammonasett in winter. Could you see a Northern Goshawk in September, in your backyard, or at Hammonasett in winter. Sure, it’s possible…but really, it’s just a big Cooper’s Hawk. CLICK FOR LARGER IMAGE.

Juvenile Northern Goshawks (left) and Cooper’s Hawks (right) (Julian Hough). Large juvenile female COHA can be very similar to NOGO, but note the broader body, tail and wings of NOGO. Underpart markings are variable in both, but typically heavier, darker and more extensive in NOGO.

We’ve all made that mistake, been spooked initially by that huge female Coop’s, but when you finally see a Goshawk, it’s often a case of “You know it when you see it”.

 

Status of “Northern” Red-tailed Hawk in Connecticut

An adult  Red-tailed I photographed at Lighthouse Point, Ct on the 14th November 2011 was particularly well-marked that I mused about it having some Western influence. I admit I am not familiar enough with that race to know, but it was distinct enough from typical Eastern (borealis) Red-tails to be noticeable. I recently came across the photo while updating my file library and with some basic research it fits as a typical example of a “Northern” Red-tail, the so-called abeiticola. While not a recognized sub-species, these birds inhanit the boreal forests from Alberta east to Nova Scotia.

From left to right: juvenile Eastern (borealis), adult Northern (abeiticola) and adult Eastern (borealis) Red-tailed Hawks, Lighthouse Point, CT Oct/Nov 2011. (Julian Hough)

Birds show overlap in many plumage traits, juveniles in particular being harder to pigeonhole as abeiticola than adults. Compared to borealis, they are generally darker-throated, have more densely marked belly bands due to more globular streaks and are often more buffy-toned on the underparts, particularly the upper breast.

These features are all noticeable on the CT bird, together with more lightly-marked secondaries and darker tips to the outer primaries, giving a more Broad-winged-like wingtip pattern (though I don’t believe this is a separating feature, it does stand out).

As  increased buteo migration through Lighthouse Point ramps up in October and November, hawkwatchers should look out for these birds so we can try and assess their occurrence compared with more typical Eastern birds.

Thanks to Jerry Liguori for discussion and comments.

Confusing Calidrid, Milford, CT July 16th 2006

I came across these photos I had saved in my “unknown” folder.  It is an adult bird that I came across while scouring through a big flock of Semi-ps.

It didn’t instantly stand out as anything I could put my finger on, except that it resembled both Semiplamated and White-rumped Sandpiper to me, but I don’t believe it either of those species. I considered the bird might be a hybrid, but the obvious one White-rumped x Dunlin doesn’t fit this bird, and if it is possibly a hybrid, does it looks more like White-rumped x Semiplamated Sandpiper?

I believe these images were digiscoped by Nick Bonomo. Although he did well to get any images, they are not of the highest quality but some key features can be seen.

Long-bodied, quite horizontal in stance with an attenuated body.

Bill, at least in one image looks quite long and fine-tipped.

Upperpart feathers and wing coverts dark-centered and pale-fringed and fairly uniform.

Off-white underparts with obvious and well-marked streaks.

Dark tail and rump in flight.

Comments?

The German harrier – some comments

HY male Northern Harrier, Milford, CT, USA (Julian Hough)

So, after looking at the images, here’s my thoughts on this particular bird:

• eye-crescents look too white and bulbous, especially toward the rear of the eye .
• the nape is perhaps not as dark, or solid as I might like, even though it appears somewhat hooded at a distance
• the streaking across the breast and along the flanks seems more in line with a young male, since females, generally from what I can gather, tend to be the less streaked. The streaking along the flanks seems well-marked, so that doesn’t mesh well with the age as a young female.
• the color of the underparts looks fine for hudsonius.

Primary Barring

Females can show less bars and a wider middle secondary bar compared to males. Primary bars (excluding the dark tip) of 15 banded female Northerns in Cape May had the following:

•  P9-7 varied on both male and female. Males averaged 6 bars (lowest 5, highest 7) while females averaged 5.6 bars (lowest 5, highest 8).

The German bird shows 4 bars on these feathers and thus fits better with Hen Harrier

Vent Pattern

One feature I need to look at is do juv Hen harriers often (always??) show dark-centered under tail coverts while hudsonius tend to have uniformly rufous vents (hair-like shaft streaks in young males, but not really visible in the field). This bird appears, from the images, to show a hudsonius-like vent, but again I am not sure based on my knowledge, if Hen Harriers frequently show this. Northern’s, as far as I have seen, never show dark, redpoll-like markings on the undertail coverts which makes the German bird better for hudsonius – or a hybrid? -than perhaps a Hen.

I often find I change my mind when re-examining images of these kinds of birds (!) and also wonder about a hybrid  possibility and whether that can be ruled out, especially if the under tail coverts in juv. (HY) Pallid and Montagu’s  are unstreaked and Hen’s are streaked. I do not go to the hybrid theory quickly, but the head pattern and underpart streaking strike me as odd for that age class of a putative hudsonius and overall fit better with Hen.

It is an interesting bird, but in my opinion doesn’t fit neatly the criteria for a vagrant Northern Harrier . Further in-depth info on Northern Harriers can be found here:

http://birdingfrontiers.com/2010/12/20/marsh-hawk/

Thanks Ralph for the shots!

Julian

Interesting “orange” harrier in Germany

Ralph Aumueller kindly sent me these images of an interesting harrier.

“When we found the bird on jan. 5th, our initial impression was of a pallid harrier, an impression what we had to reject immediately as we found the bird five-fingered, broad winged and so on. So it´s a Hen Harrier of some kind, but ruling out hudsonicus causes us quite a headache.

Almost all id-features neatly fit in the pattern awaited for a Northern Harrier (hudsonius), but we are much too inexperienced with that taxon. We are aware, however, that the underwing-pattern seems not to suggest a hudsonicus, with the barring on the outer primaries at the very lower (too low?) end of its range of variability. Additionally the middle secondary bar seems to be to wide. However we found in the literature that females tend to show a more cyaneus-like pattern in this respect. So we really reached the point to need  the help of an expert on that topic. May I therefore kindly ask you for  your opinion on the bird´s id? That would be fantastic!

Best wishes,

Ralf

S0, in light of the recent British and Irish records of vagrant Northern Harrier (C.c hudsonius), this bird seems quite striking and scary. What do others think of this bird and what would you call this if you saw it. Be interested to hear people’s opinions on this before I post my comments I had sent to Ralph.

 

An interesting “Buff-bellied” pipit, Cheshire, UK, January 2014

American Buff-bellied Pipit (rubescens), Connecticut, USA, Jan 2008

A vagrant Buff-bellied Pipit (aka known as American Pipit or confusingly Water Pipit here in the US) is being seen at a coastal marsh in the north-western part of the UK. Buff-bellied Pipits, of the race japonicus, also occur in Asia and winter in the Middle East and this race and the Nearctic race rubescens show a great deal of variation and so separating these two in a vagrancy context may be difficult with some individuals.

While Buff-bellied Pipit, of the Nearctic race rubescens (American Buff-bellied Pipit) has occurred several times in Britain and Ireland, the Siberian race japonicus (Siberian Buff-bellied Pipit) has not, so it is worth noting the plumage features of any vagrant Buff-bellied Pipit to determine race.

Basically, the dumb-down cliff notes are that Siberian birds are:

• pale-legged
• rather pale below with a noticeable eyering
• large, club-ended malar and streaked blackish below with rather tear-shaped spots/streaks.

American birds are:

• darker-legged
• rather plainer above,
• being less streaked, more buff-below with rather more brownish, blurry streaking.

However, individual variation and wear and geographical variation across their ranges makes the “simple” criteria just mentioned somewhat useless in a vagrancy context, and identification is often easier if you are standing in Israel or Connecticut respectively!

The individual in Cheshire can be seen at (scroll down for the images if necessary) :
http://www.surfbirds.com/gallery/display.php?gallery=gallery9

Initially, on a comment I posted on Martin Garner’s Birding Frontiers site I had thought the bird seemed fine for American Buff-bellied Pipit, but further photos seemed to show a bird with rather contrasting upper wingbar, rather large blobby malar and well-defined dark streaks on the underparts. I was cautious and wondered if the bird could be a Siberian Buff-bellied, but having no field experience of that race, I was in unchartered waters and wanted to add some caution to my initial support of the bird.

So, I dug up some pictures I had taken of a bird here in New Haven for comparison (see below) and also a link to Siberian Buff-bellied Pipit here:
http://www.birdsofsaudiarabia.com/20…f-bellied.html.

All three images, American Buff-bellied Pipit (rubescens), New Haven, CT, January 14th 2008.
Based on Pyle et al., 1987,  the pointed centres to the median coverts and the blurry, non-indented edges to the greater coverts makes this bird a first-winter (HY). The Cheshire bird is a first-winter by the same features.

 

Overall a buff-brown bird, with non-contrasting wingbars and dull buff underparts. Underpart streaking is brown, not blackish and there is no pale contrasting eyering or large, dark, ‘blobby’ malar. Note the dark brown, not pale legs.

After reviewing images, and taking into consideration variability, with all things considered, the Cheshire bird is more likely American based on the overall plumage tones, plainer mantle and underpart color but it is certainly not straightforward. If the bird had been the rather white-below, heavily streaked Siberian birds, perhaps it would be easier, but since they vary so much, a vagrant may often be hard to assign to race.

American Buff-bellied’s have a distinctive, di-syllabic “pip-it”, “pip-it” calls that may help distinguish it from Siberian birds but I have no experience with that race.

A great educational bird that has generated some insightful discussions in the UK for those that want to read more on this bird:
http://www.birdforum.net/showthread.php?t=273086