Adult 1 March 2005

Adult 2 January 2006

Adult 3 February 2006

Adult, Alviso, Santa Clara County, January 2006


Third cycle - March 2006 - Bay Area location.

Third cycle - February 2006

Third cycle - January 2005


Second cycle January - February 2005

Second cycle - December 2005 - January 2006, I also think the bird on March 8, 2006 was the same one.

Second cycle #2 - January 2006

Second cycle #3 - February 2006


First cycle - February 2005

First cycle - January 2006

First cycle - January - February 2006

An apology first, I realize this page is getting unwieldly but I will wait until the winter is over until I do a re-design. I never expected to have to add so many birds to this! Also a note, the most recently observed birds tend to be at the top.

For some historical Slaty-backed Gull reports from California, see the end of this page.

WINTER 2005-2006


Unfortunately, this bird was in private land accessed through work, and I can't divulge the actual site of occurrence. It is in the San Francisco Bay Area, and is a new county record. The large, dumpy body and "keel" behind the legs is obvious here as are the short pink legs. The mantle was a dark, slate grey and the broad white tertial and scapular crescents were very obvious. Streaking was fine on the head, and blotchy on nape, breast sides, and underparts. The streaking had a characteristic warm brown color, which other Slaty-backs have shown. The pale eye was surrounded by dark streaking ("mascara") and the orbital could be seen to be developing a red color. The bill was large on this individual, with a good gonydeal angle and lots of dark on the bill. The retention of dark on the bill to later immature plumages appears to be common to Slaty-backed, and is unlike Western which shows a bright yellow bill base by the second cycle...usually.

Below an open wing shot, showing the largely adult like primaries. The pale tongues inside of the black primary tips form the pattern known as the "string of pearls." Here that pattern can be seen extending to primary 8 (P8). There is no mirror on P9, and a moderate sized one on P10; this wing pattern will likely change once this bird is an adult, getting more white patterning. The trailing edge on the secondaries is very broad, the secondaries look entirely white from this angle. The dark bases are actually hidden by the greater coverts. Shots of the tail show extensive black, but with a white base.

A portrait from the back, showing the very obvious tertial and scapular crescents, dark upperparts, streaking pattern on face, pale eye, reddish orbital, and short pink legs.


This bird appears to be the same individual which was here on December 19, click here to see photos of the bird on that date.

Today Ron Thorn found two adult Slaty-backed Gulls in the Venice Beach flock, he gave me a call but by the time I arrived they had flown. One of the adults, Ron thought was the same one with dark on the bill observed earlier in the year in January. After a few minutes of looking for the adults, I spotted this dark mantled bird sleeping and once it opened its eye it was clear that it was another Slaty-backed Gull. Below you can see the dark mantle, more slate than blue-gray, contrastingly pale coverts, large (huge!) white secondary crescent, whitish-yellow eye, dark "mascara"" around the eye. The bird also showed fine streaking on the crown and cinnamon streaking on the back of the neck and breast sides, but they are not clearly visible in this photo.

Below, the bird standing up, showing the short legs, bulky-bokied but long-winged appearance and aggressive look due to the pale eye and dark "mascara." the bill was largely dark, paler at base and with a whitish tip. The two arrows point to slate (second generation) coverts on the inner medians (right arrow) and outer lessers (left arrow). These are of interest as they are the very same second generation coverts shown by the second cycle bird first observed in December 2005 (see lower photo). I think these two birds may be the same one, the photo from today makes the bird look a bit longer than it did in the field due to the posture, it was indeed a short-legged, pot-bellied bird like the December bird. The tertials were speckled on today's bird, and upon checking photos of the December individual the same speckling could be seen. The outer median coverts also shoed oval dark centers at the tip in both birds. Today's bird shows a flatter forehead, but I wonder if this is an effect of the posture and way the bird was holding the head? Other plumage features like the pale streaks on the mantle are on both birds.

Here is the bird again. The different looking head shape is the only thing that makes me hesitate in calling the two birds the same one. I guess it pays to be conservative and count them as one?



Feb. 6 - Adult found by Todd McGrath, also seen by Mike San Miguel, David Vander Pluym, Ryan Terrill and Dan Singer. Photo below by Ryan Terrill. This adult lacks the streaking typical of winter Slaty-backed Gulls. The string of pearls wing pattern is visible on the near wing, and the pale underwing shows up on the opposite wing.

Lower two photos by David Vander Pluym, showing more features of wing, a small amount of streaking around the eye is visible.


Feb 4 - This was the jackpot for Slaty-backed Gulls in Half Moon Bay, a record breaking day! I was able to see and photograph three different individuals, but what was insane was that two of the birds were brand new for this winter. On Feb 4 the count was up to: 2 ads; 1 3d cycle, 3 second cycles, 2 possible first cycles = 8 individuals!!!!!!

This is the third cycle bird, the first one of this age documented during the winter of 05-06. Great photos of this individual are available at Eric Preston's website, Eric notes that the wing pattern differs between right and left wing. Other observers included Dan Singer, Les and Cindy Liurance, Al Eisner, Eric Preston and several other folks (let me know who you were!).

Below, the yellowish white eye and streaking pattern on the head, along with the extensive dark retained on the bill suggests a Lesser Black-backed Gull. However the back is paler than graellsi, and tertial and scapular crescents are broad. The bill is also more massive than on a classic Lesser Black-backed Gull. When we had the bird zoomed up in the scope a reddish tint could be observed on the poorly developed orbital ring. Note that if you look just above the innermost white primary tip a sliver of pale can be seen, this is part of the pale "tongue" on the adjacent primary, in other words part of the "string of pearls" patten classic on Slaty-backed Gull.

Here is a photo of the bird in flight. The brown tones on the wing, and black on tail identify this as a third cycle bird. The white trailing edge is broad, very broad. In fact on the near wing you can see that the secondaries extending past the greater coverts are entirely white, on a Western Gull the dark would be noticeable beyond the greater coverts, these coverts are popping up due to turbulence in this photo. Following the white trailing edge out on to the primaries you can see that it eventually invades inward from the black primary tips, this in effect is the "string of pearls" pattern. On this bird it reaches to P7, but with pale ghosting which suggests that in an older age it will reach farther out on the wing. Only a mirror on P10 is visible, most third cycle Western Gulls show now mirror or only a very small one.

The large breasted and bulky bodied shape here is quite unlike that of a Lesser Black-backed Gull. The pale eye, dark around the eye, warm brown streakign which is crisp and blobby on the nape is quite unlike that of Western or Western x Glaucous-winged hybrids. Western Gulls at this age typically show a bright banana yellow bill with a dark tip. The dusky shins on this bird is a mark that is not typical of Slaty-backed Gull, but then it is not typical of Western Gulls either and you do see this sometimes.

This shot shows the menacing pale eye, as well as the more blobby streaking on the nape. Some of the pale tongues on the primaries can be seen here, just left of the tertial tip of the right wing. The dark, almost purplish pink legs and feet can be seen here. The huge white tips to the tertials are shown well.


Feb 4 - This was the first bird I found today, and at first I wondered if it was the same individual observed and photograhed by Dan Singer, and Matt Heindel (see below), but it is not, it is indeed a new bird for this winter. The third second cycle bird of this winter can be seen lower down on this page.

This new bird shows the classic Slaty-backed Gull shape, bulky and deep at the chest and belly (keel), but somwehat small headed, small bill for size of bird and long wings. I have noticed that often the Slaty-backed Gulls that we have seen here in Half Moon Bay droop the wings and tilt the axis of the body up, so that they seem to sit a bit more high headed, and low-tailed than the more horizontal Western and Glaucous-winged gulls. This individual has good crisp head streakign, again some dark around the eye, short and bright pink legs. The back was a tad darker than Western Gulls near it, but not by much. I would not have picked it out by looking at the back alone, the second winter bird from December was obviously darker backed than this one. The coverts on this individual were not all that pale, but they did show almost no patterning at all. The tertials were broadly tipped white, one of the features that stood out most about this bird. The eye looks dark in this photo, but it was becoming pale, with the iris noticeably paler than the pupil.

Here it is preening, the palish eye might be visible on some monitors. The back color is not that different from that of the 3d cycle Western Gull in front of it. Like most of the Slaty-backed Gulls which have shown up here, the streaking on the breast, neck and nape was a warmer brown color than that of Western Gull, it almost has a cinnamon tone to it.

A closer look at the streaking on the head, and neck, with the dark "mascara" around the eye quite prominent.

this photo shows the unmarked secondaries, and the broad tertial ends. Again, one can see that more vertical stanse of this bird, than is typical of Western Gulls. As well, the short legs are obvious on this photo.

A bit of a yawn, and a view of the warm brown streaking on this bird. The somewhat vertical stance, short and dark pink legs, as well as the deep "keel" on the vent.

This shot from behind shows the broad scapular crescents, as well as the tertial crescents. It is an angle that allows for a nice comparison to the next photo of the second cycle bird that was here last week, this is definitely a different bird. The Feb. 3 individual shows more grey on the back, and a more worn covert pattern.


This bird was found by the CBRC folks on their outing before their annual meeting, I gather it was first spotted by Marshall Iliff. Thanks to Marshall and Matt Heindel for allowing me the use of these photos. This is the same bird on Dan Singer's page.

Photo below by Matt Heindel, taken on January 27, 2006.

The two next photos are by Marshall Iliff. Below, this bird is almost Herring Gull like, except for the darker back color and the classic short-legged and bulky-bodied shape of Slaty-backed Gull.

Here is the bird in flight, the right primaries flexing almost to the breaking point! The left wing shows the start of the string of pearls pattern, the dark grey on the upperparts can be compared to a Westen Gull and Glaucous-winged Gull here and it is clearly dark.

FIRST CYCLE - HALF MOON BAY - JAN. 20, 2006, FEB 3 and 4, 2006.

Feb. 4 - This bird appears to be the same one first found by Luke Cole on Jan. 7.

More discussion below, this is a first cycle bird which is a fine candidate for Slaty-backed Gull. Here the broad white tertial tips, with little white on the tertial edges is seen. The large size, but rather parallel sided bill and nicely streaked head and neck with substantial dark around the eye. The rather pale greater coverts are quite unlike that of Western Gulls. Note also that the primaries and tail are quite blackish-brown, contrasting strongly with the pale coverts.

Some new scapulars are coming in on this bird. The crisply streaked pattern on the neck is visible here.

In the scope, the iris of the eye could be seen to be paler than the pupil, it seemed as if the eyes on this bird were becoming pale. Note the underside of the primary on the far wing, showing substantial pale.

While the undersides of the primaries are pale, the uppersides are quite dark, certainly as dark as that of a similar aged Herring Gull or Western Gull.

Feb. 3 - It is now substantially paler and more contrasting and the bill base appears to be getting paler. The tertials have very broad white tips, but very narrow edges. The pale, almost whitish greater coverts now strongly contrast with the darker tertials and the blackish-brown primaries. The nice streaks on the head and neck are apparent here as is the dark around the eye, the "mascara."

Below a shot showign the extensive pale inner vanes to the primaries, giving it a Thayer's Gull like underwing pattern, with only the tips of the undersides of the primaries being dark. The very pale tail coverts can be seen here contrasting with the ege of the entirely dark tail. More photos from Jan. 20 below.

Jan. 20 - backlit, evening light. Today at Venice Beach a whole lot of Marin Birders were out looking very hard for Slaty-backs, but unfortunately this bird showed up after most had gone (sorry guys). At about 4:45 near the south end of the gull flock we (myself, Dave De Sante and Jim White) saw this following first cycle bird that appears to be another Slaty-backed Gull. This bird was backlit in low sun, it was getting close to sunset, but the photos came out much better than expected. Two cameras were used with different resolutions, one digiscoping and the other with a 400 lens, this is why the bird appears slightly different in color in separate photos. What struck me about this individual, was that for a first cycle bird it was quite different from all of the local birds in showing a good whitish background color to the head, neck and breast, highlighting the much more crisp streaking than on a Western or Glaucous-wing of similar age. Once again, this bird had dark around the eye, giving a furrowed/menacing appearance that was apparent even though this bird had a dark eye. In structure this was a large and bulky bird, but in the field the short legs did not make it stand out as larger than the other birds although I think it was marginally bigger. It showed a pot-bellied, short-legged and thick-necked look. Dave pointed out that the pot-bellied and bulky structure was balanced out by the long wings, such that this bird did not appear stocky and truncated, but stocky and attenuated at the rear end. The overall effect was a structure quite unlike that of the common gulls that are out there, we had been enjoying several hours of watching them previous to this find. The bill was long and parallel sided, not showing much of a gonydeal angle at all, reminiscent of some smithsonianus Herring Gulls. The bird was mostly in juvenal plumage, except that some of the mantle looks to be of a new generation. We did not have an extensive and long look at this bird, but we did see it well, it was one of the closest birds to us at the time. It sat perhaps just over 5 minute for us as we all got on it, talked about it a bit, and I snapped photos but we would have wished for a much longer view to get more details down. Eventually it flew along the beach to the north, and I was able to get some distant flight shots as it did so. In the photo below, it is with Glaucous winged (both dark bird to left and pale bird to right) as well as Western farther back, and hybrid Western x Glaucous-winged to the far left.

Here is a closer view of the bird, showing the distinctive bulky, short-legged and long winged look with the parallel sided bill. The dark around the eye, and nicely defined streaking on the head and neck, partially due to the pale background color. The wings and tail were dark brown, the primaries showing thin pale fringes. The greater coverts were not worn, but they were rather pale, contrasting clearly with the darker tertials and primaries. The pale panel on the greater coverts was very different from that of any Herring, Glaucous-winged, Western or the various hybrids we had seen on this day. The tertials showed large white tips and a narrow pale edge.

This shot of the bird preening shows the dark tail and contrasting whitish rump. The pale tips to the tertials are visible as well. .Here the pink leg color is shown better than in the previous shots. It was not as vibrant dark pink (bubblegum) as that of some of the other Slaty-backs that have shown up, but it was a deeper pink than that of the nearby Glaucous-wings.

A good shot of the great contrast from the dark brownish-black primaries to the paler tertials and the very pale greater coverts. The mottled pattern on hte back was rather unique. The tertials showign large pale tips and no notching on the edges seems to be a good clue for Slaty-backed, Herrings tend to show notching and the Herring x Glaucous-winged hybrids often do as well. Glaucous-wings on the other hand, like the bird to the right, tend to show smaller pale tips to the tertials. I don't know that it would be a regular feature for any Glaucous -winged x Herring hybrid to show tertials such as these.

Here is an enlargement of the bird in flight. It is too bad that the angle does not allow for a good assessment of the pale inner vanes of the primaries. In flight this bird was quite striking, with contrasting dark outer primaries, dark secondary bar, pale inner primaries, pale greater covert panel, dark tail and contrasting pale rump and lower back.

This shot was just lucky, as it shows the underwing on the left wing. This is a bird showing extensive pale inner vanes to the primaries, as is classic of Slaty-backed Gull (and similar to Thayer's Gull). The "wrist" can be seen here and it is much darker than the primaries. Other photos of underwings of Slaty-backed that I have seen seem to show this quite consitently, so while pale on the undersides of the primaries, the wing linings and wrist are dark. I need to look at this feature in more hybrids (Western x Glaucous-wing, and Glaucous-winged x Herring) but from memory they tend to be more unicolored below, not showing the contrasting darker linings. On the right wing the pale inner primares are clarly visible, to at least P6 it seems. The angle is not good for seeing the actual pattern on the outer primaries.


After a meeting today at the Environmental Education Center I scoped the gulls and saw this blackish backed gull in with the Herring Gulls. It was a ways away, but in the scope it stretched the wings and I could see the string of pearls perfectly in the scope. I could not believe it! I sneaked up closer to it on the levees and got 4 shots before a Harrier came by and scared the gulls. I was still not close enough to get good photos, but here is one below with a blow up of the bird. This bird was a full adult and showed the following features: Yellow eye with reddish orbital ring; dull yellow bill with red gonys spot, some streaking around eye but not much streaking on head at all; warm cinnamon-brown blobby streaks on the base of the neck; bright pink legs; bold primary pattern with string of pearls well out towards the outer primaries; p10 appeared to show a large mirror; very broad white trailing edge to secondaries which was extremely prominent in flight; large white primary tips. The mantle was very dark grey, blackish-grey, noticeably darker than a few Western Gulls that were nearby and lacking the bluish tone of Western Gulls. IN size this was a bulky bird, larger than most Herring Gulls near it, but not by much, had a thick-necked appearance, long neck, and pot-bellied look. I apologize for the poor photos, but it is all I could get!


Exactly a year after the first Slaty-backed of 2005 was found, Ron Thorn located an adult Slaty-backed Gull in the flock. He saw it approximately at 11:30 in the morning, and I had it in the late afternoon (thanks for the call Ron!) at about 4:45 pm. There have been a minimum of 4 Slaty-backed Gulls observed here this winter, up until January 13th, Ron has found two adults, and add to this the first cycle and second cycle bird below. A potential fifth bird, a first cycle bird, was photographed approximately a week ago and observers are firming up the identification at this time. Here are photos by Luke Cole from Jan. 16, 2006.

It is not certain to me if this is the same bird as the adult type from last year, but I would bet it is. The fact that both are adult birds and retaining a lot of black on the bill is unusual, making it more likely that they are the same bird. Looking at photos of last year's adult type bird it seems to have a similar head shape in some views and the same bill size. In addition, both appear to have the mirror on P10 united with the white tip, and both have a smaller mirror on P9. While it is not unusual for Slaty-backed Gull to have a mirror on P9, it is somewhat unusual (based on photos on the web) for the P10 mirror to extend to the primary tip. These features, in addition to the dark in the bill and general proportions make me think it is the same bird as last year. Interestingly it now has yellow at the bill tip, and the dark on the bill is less extensive. Perhaps it was a 4th cycle bird last year, and 5th this year? The orbital ring was reddish pink, that is not clearly visible in the photo here but it is in the blow-up of the original. The extensive white on P10 can be seen here on the folded wing, note how similar in length P9 and P10 are, just like the adult bird last year.

Another shot of the bird with various common gull species (Western, Glaucous-winged and a young Herring). The mantle color of the Slaty-backed is darker and less blue than that of the adult Western Gull in the front and right.

I obtained only poor flight shots, this enlargement of the wing shows the entirely white tipped P10, mirror on P9 and pale inner tongue (string of pearls) going out at least to P8.


This is the third different Slaty-backed Gull reported from the Half Moon Bay flock this winter, as of Jan. 3 the three birds had each been seen once on a single occasion. Note (Feb. 5, 06 - this first cycle bird was seen the one time, no resightings yet).

This individual was a rather large one, noticeably larger than most Western Gulls and overlapped with some Glaucous-winged Gulls in size. Again, the structure of this bird was noticeably different than that of Western and Glaucous-winged gulls it was with. Although a longer-legged bird than most of the others Slaty-backed Gulls which have occurred at this site, in proportion the legs were short on the tibia and tarsus and well spaced apart, giving it a characteristic waddle as it walked. The neck was long,with the head often resting far back on the back, when fully retracted. The body was rotund and deep at the breast and belly, this in addition to the waddle and long neck gave the bird what I have come to think of as a "goose like" look to the bird. It was immediately separable from the dark first winter Western Gulls due to its pale neck as well as a general cinnamon tone to the plumage. This cinnamon tone was also present in last winter's possible first cycle Slaty-backed Gull.

Another shot, showing the generally bulky body, rather big bill on this individual and widely set apart strongly pink legs. The legs were noticeably pinker than those of similar aged Western or Glaucous-winged Gulls. The head is moderately pale with crisp streaking (unlike Western Gull), with the streaking concentrated around the eye and in a furrow behind the eye. The greater wing coverts were noticeably dull and lacking contrasting markings, something that seems to be typical of Slaty-backed Gulls. The primaries were blackish with pale fringes (like Thayer's Gull) and moderately dark tertials, but not quite as dark as the primaries.

A better view of the primaries, coverts and tertials. The tertials show large white tips, very little white edging. The dull, pale greater coverts lacking much contrast were suggestive of what one sees in second cycle plumage of other large gull species. The flanks and many of the mantle feathers appear to be new, with some rather dark centered mantle feathers coming in.

Here the dark centered mantle feathers can be seen. This seems to be advanced for a first cycle bird, but similarly dark based mantle feathers were seen in photos of birds in the Japan Gull Site. The dark tail can just be seen poking through between the wings here. The streaky pattern on the crown, cheeks and nape is not typical of either Glaucous-winged or Western gulls which are more heavily vermiculated or barred rather than streaked, or show obscured, blobby streaks or even a dark wash rather than crisp streaking.

The upperwings show an interesting pattern with only a slight difference between the paler inner primaries and darker outer primaries as all primaries have a dark bar along the rachis. This is different from the Herring pattern where the inner primaries are obviously paler than the outers. This bird also differs in the fact that the inner vanes of the primaries (what is visible on the underside) are pale, visible to primary 8 in this photo. Note also the contrasting whitish rump of this bird, a feature that is common in Slaty-backed Gulls (and similar aged Kelp Gulls) but not in young Western or Glaucous-winged which are more uniform on the rump.

Here the underwing is visible, a rather pale silvery brown below, with darker tips to the primaries. This pattern is similar, but not identical to that of Thayer's Gull.

Another side view, showing structure, lack of contrast on coverts, blackish primaries, pale tipped tertials and generally quite a different look from Western or Glaucous-winged, or their hybrids.

Close up of the upperparts, dark centered feather obvious in upper mantle. Lower rows of scapulars appear to be retained, faded juvenal feathers.

The upperpart pattern of darker new feathers is obvious here where the back is stretched. Also the crispness of the streaking one the head is clear, compare it to the similar aged Western Gull to the right.

The Slaty-backed with a mix of Wester and Glaucous-winged gulls, showing pot-bellied, thick-necked structure and distinctive cinnamon tone to the plumage.

Another flight shot showing the pale inner vanes of the primaries (pale underwing) as well as the moderate difference in darkness of inner and outer primaries on upperwing. Tail is dark to base with contrasting whitish tail coverts and rump.

I wish I had gotten lucky and caught the undersides of the outer primaries, oh well. In any case the pale underwings are clear here, as are the bright pink legs. I don't know if the contrasting dark wing linings are a typical mark of Slaty-backed or not.

Upperwing with paler inner primaries, but not as clearly contrasting as on a Herring Gull. Pale inner vanes of primareis visible to outer most feathers. All dark tail, with pale tail coverts and rump. Here are some images of flying first cycle Slaty-backs from Japan.


Note that another second cycle individual was observed by various observers, and photographed by Dan Singer on January 27, 2006.

This is the second Slaty-backed Gull reported from the Half Moon Bay flock during this winter (still present Jan. 31 - Ron Thorn), a couple of weeks ago Ron Thorn saw an adult there. This is therefore a new bird for this winter, as it is a second cycle (second winter) individual. During the winter of 20042005, an adult or 4th cycle, third cycle, second cycle and a possible first cycle bird were seen (see links at top of page). Given the age of the Dec. 19, 2005 bird, it cannot be any of the birds from last year other than the possible first cycle. The problem is that the identification of first year Slaty-backs is not reliable given current knowledge, so of last year's birds it is the one that is least convincing of all. Do have a look at the bird here, I am biased on this but I find the structure of the first year bird from last year and this second cycle bird to be quite close. They both have that thick-breasted, goose-keeled and short legged look as well as somewhat similar median covert pattern. Of course we can never be sure, but I wonder if it is not the same bird?

This Slaty-backed had what I am now learning to be a classic structure of being short-legged, with an obvious waddle while walking, a large body and thick neck, and a deep chest and deep "keel" just behind the legs. The deep keel makes me think of a goose, and compared to the other gulls nearby (Western, Glaucous-winged and Herring, it looks real different). Other features to mention are the yellow eye and dark around the eye and furrow behind the eye which gives the bird an angry expression. The bold streaking that is concentrated on the back on the neck and breast sides. The dark mantle, darker than adjacent Western Gulls and more of a true grey rather than a blue-grey. The belly retains a lot of dark smudging, this is reminiscent of the third cycle bird from 2004-05.

Mean looking, smallish bill and short legged (compare to Glaucous-winged top left).

Upperwing and tertials shown here, pale tongues visible on inner primaries. On a second cycle bird one would not expect the string of pearls effect to be well developed yet.

Underwing here, dark extensive on outer primaries, less so on others. Median covert pattern can be seen here, just a dark stripe on a largely buffy feather. Western Gulls of similar age show a darker and less contrastingly pale edged covert pattern.

Here flanked by two species, a Western adult behind it and a Glaucous-winged adult in front of it. The Slaty-backed is obviously darker mantled than the Glaucous-winged, and slightly darker and less blue than the Western Gull. Check out the different facial proportions from bill size, eye size and eye placement.

The white breasted bird in the middle is the Slaty-backed, almost at sundown with various Half Moon Bay gulls (Western, Glaucous-winged, Glaucous-winged x Western, and Herring Gulls).

WINTER 2004-2005


A brand new individual, right at the end of the winter gull season! At this point, it is ridiculous and it makes me wonder if there was a huge Slaty-backed Gull invasion to the West Coast that was not clearly detected north of us.

Here is the new bird, effectively an adult except for the dark on the bill. I assume it is a fourth calendar year bird. This shot shows the spread wing with the "string of pearls" which are clear to P8, and even present on P9. The outer primary, P10, of this bird has an almost entirely white tip, due to the mirror and the tip blending together. A hint of a dark division exists, and there is a clear mirror on P9.

Side view of this bird, showing the pale eye and dark mascara. In life the orbital ring was clearly seen as reddish in colour. The upperparts were similar in darkness to most of the Western Gulls, but slighly darker in direct comparison and less blue-grey, more slate-grey. Again, structurally this Slaty-backed Gull was short-legged, deep bodied (keeled look), and long-winged. In terms of size, this individual was distinctly larger than nearby Western Gulls, but due to the shorter legs it did not stand much taller. The head and neck had lost most of the streaking, but there was a good amount of streaking at the base of the neck.

The photo above shows a good comparison of shape with Western Gull. The Western is longer legged (note the amount of leg showign above joint, and the deep keel of the Slaty-backed Gull (goose-like) rather than the more slender body of the Western Gull. The eye of the Slaty-backed is larger and has a different placement on the head. Not much of the uppperparts are visible on the Slaty-back, but you can see that the colour was similar to the Western, although a bit darker and less blue. The legs were darker on this individual than on most Western Gulls, many of which are getting a yellowish or orange tone to them at this time of year.

Above is another side by side comparison with Western Gull. this shot shows the slightly darker and less blue colour of the Slaty-backed, appropriately it is slightly more slate-grey in colour. There are some missing coverts, not sure if this is due to moult, or loss for another reason. The head does appear to be in moult though. Back to the comparison, note the much wider white trailing edge on the secondaries of the Slaty-backed. The bill is thick, but not blob-ended and thus more parallel sided than on Western Gull.

Profile of the bird, showign head and bill structure and pale eye. The complex wing pattern can be seen in the stack of primaries here. A nice wide tertial crescent was wider than the average one on Western Gull.

The bird preening, showign some of the primary pattern. The entirely white tail, different P10 pattern, and larger primary tips of this bird absolutely rule out the possibility that this is the same bird as "Bird 2" below. The bird should have the same wings and tail in March as it had in January. I don't have any photos of the underwing but they showed the classic Slaty-backed Gull pattern with medium grey undersides of the primaries inside of the "string of pearls" and a narrow black stripe outside of the "string of pearls". The fact that there have been this many Slaty-backed candidates at one site in California is nuts!


This is the individual that people who came to chase Slaty-backed Gull in Half Moon Bay saw. More photos here.

Today, at the local gull flock while birding with David VanderPluym we located what appears to be a third cycle (third winter, Four calendar year) Slaty-backed Gull (Larus schistisagus). The bird just popped out in the binoculars, and in the scope it was strikingly different from all of the gulls in this flock. Given that there is no accepted record for Slaty-backed Gull in California, we were just amazed. A week after a great candidate shows up here in Half Moon Bay, one in an even more distinctive age shows up - crazy!!!!

Structurally this bird was not huge, it was roughly the size of the nearby Western and Glaucous-winged Gulls, perhaps slithgly smaller. The bill was parallel sided, with little gonydeal angle. It was a smaller and slimmer bird than last week's bird. My guess is that this is a female, last week's bird a male. Otherwise it did share structural similarities to last week's bird, being bull-necked, but long-ecked when alert. It also had a distinctive pot-bellied appearance. Something I had not noticed on last week's bird, but was similar and obvious in this bird is that it was short-legged.

One of the other similarities between the two birds is the menacing appearance, due to the pale eyes which contrast with the dark "mascara." The upperparts on this bird were very dark, just slightly paler than the black primaries. Sitting next to occidentalis Western Gulls, this bird was quite dark. This photo shows the retained dark belly markings, similar to the second winter bird last week. However, this individual retained markings and streaking on the breast, and neck.

This photo of the bird while alert shows the thick, yet long, neck of the bird. As well the menacing look of the head is obvious due to the eye and dark streaking around the eye, but also due to the shallower forehead as compared to Western and Glaucous-winged Gulls. Also note the adult occidentalis Western to the left and lower right of the bird, not only is the Slaty-back darker it is a different colour, lacking the blue tones obvious in Western Gull. The short legs were brigh pink, slightly more bubblegum than the Western Gulls near it. Check out that large scapular crescent.

Unfortunately I did not get a photo of the fully spread wing. This photo shows the bill pattern, dull pinkish at the base, with a dark tip and white nail. Note that the dark of the base bleeds basally along the cutting edge. In addition the extreme base of the lower mandible, the gape, is noticeably paler. Surprisingly this is practically the same bill pattern as that of last week's bird, although in this case the base is much paler, making the general pattern contrast more than in the second cycle bird. On the spread wing note that the inner secondaries are white right to the ends of the greater coverts. The tail also showed a substantial amount of black, widest in the central rects and narrower on R6.

This photo shows the broad white tertial and scapular crescents. As well you can see that P10 has a moderate size white mirror. But more importantly look at the pattern on the closed primaries on the near wing. The white tip of the primary closest to the tertials is an odd shape, witht a white "spur" on it. This is a pattern that you often see in photos of Slaty-backed Gulls, the spur is not part of the tip of that feather but is the white tongue showing through from the next feather out on the stack. In effect, this is a tongue that contributes to the "string of pearls" pattern. When the bird opened its wing, David and I could clearly see the string of pearls pattern, unfortunately I was not able to get this in a photo. Now if the outermost primary tip visible is P10, then this tongue is on P8, if P9 and P10 are really similar in length and in fact the outermost feather visible is P9, well its on P7. Peter Adriens (through e-mail) suggested that other than in long-winged large Larus (Lesser Black-backed for example) P9 and P10 are practially the same length, and that P6 tends to be the first primary to fully poke out of the tertials. Thus, this white tongue is likely on P7. Also look right up against the tertial tips, you can see the next white tongue up on the stack of primaries (P6).

This one is for those skeptical of the last analysis of the primary pattern. The primaries have moved a bit here and you can see that the white tongue of P8 (or P7?) is now showing through the leading edge of the adjacent primary tip, and the spur pattern is not present.

A nice side view image of the bird, showing the distinctive menacing look, thick neck, and short legs. I should point out that the orbital ring was weakly developed, but it was definitively pinkish-red, easiest to see above and below the eye. I have many more photos but I don't think any show features not shown by these. I hope that this second and more distinctive bird will be easier to find than the first, which was a one day wonder. Thanks to David for calling me up and giving me a reason to go out and do some gull watching!


FEBRUARY 20, 2005

Thanks to Dan Singer for re-locating this bird after more than a month's absence today and letting me know (via Joe Morlan) that it was there. I had really wanted to see this bird again as I figured that more of the upperpart colour would be coming in through the winter, and as I figured this bird would help me learn more about Slaty-backed Gull than seeing the third cycle individual again. Indeed, 5 weeks had made a difference:

The bird looks quite different now, and is a striking Slaty-backed Gull, more obviously so than it was back in January. I have carefully checked the pattern of the coverts, flank streaking, as well as the "proto-mirror" pattern visible on the underside of the longest primary with the bird in January, and they match very well. I am convinced that this is the same individual, although its appearance has changed to a great degree. Most obvious is that more adult like upperpart feathers have come in. Somewhat surprising, but logical once I thought about it, was that the head streaking has actually increased in extent on the head. Immature large gulls lose streaking on the head through wear and fading, not through moult. Newly moulted feathers replacing worn whitish head feathers, are going to be largely streaked at this age. So what the increase in head streaking tells me is that there has been head moult, in addition to the back and scapular moult. The coverts on the other hand have faded and become more worn, creating the classic contrasting pale coverts of Slaty-backed Gull. The earlier photos suggested that the bird was odd for Slaty-backed Gull due to apparently blob-tipped bill, too long a leg length, and apprently uncharacteristic whiteness of the breast. The thought of Glaucous-winged genes went through my head more than once. However, the blob-ended bill shape was something that I thought was more of an illusion, due to the pale blaze along the base of the lower mandible. This new observation confirmed that this was true for the most part, this bird is structurally fine for Slaty-backed Gull, the blob-tipped bill is more of an illusion than a reality, and in fact the bird is not all that long-legged. It also has some of the pot-bellied structure typical of Slaty-backed, although less so than the third cycle and first cycle candidate. The new views erased any thoughts of Glaucous-winged genes, particularly since the primaries remain black and fresh, and the upperparts are coming in nice and dark. The dusky legs are unusual for Slaty-backed Gull, and this bird has them now and during the first sighting.

Here is a closer view of the bird. It still retains a bit of the dark on the belly, particularly above the leg. The coverts have bleached out, and interestingly the areas which often are hidden in the flank feathers (the bend of wing, and outer greater coverts) are darker and probably less sun bleached due to protection by the flanks. The mantle colour coming in was as dark as that of nearby adult Western Gulls. The eye was yellow, lacking dark flecks, and no orbital ring colour was evident. The new head streaks that have come in on the head are crisp and narrow, with a distinct dark area around the eye, the "mascara" look.

An underwing shot, unfortunately with a lot of vignetting around the edge of the photo. This makes the wing pattern difficult to see, I have cropped out the outer wing and enhanced it a bit and show it below. In this shot, look at the real nice and blackish scapulars coming in, and the very pale underside of the secondaries and inner primaries.

This is an enhanced and enlarged image of the wing, taken from the image directly above. Here you can see the start of the P10 mirror, and some internal markings that appear like the beginnings of the "string of pearls" out to P6.

Dan Singer sent me the shot shown above. The tip of the wing is off the frame, but the start of thte string of pearls pattern can be seen in this photo with what looks to be P5 having a darker tip, and a paler crescent inside (proximal) of that. P6 shows the same pattern. The new blackish-grey scapulars and back can even be seen on this shot. The pale inner primaries and secondaries are shown, and quite distinctive. On the near wing, what I have called the "proto-mirror" can be seen on P10. I don't know why I call it that, it just sounds cool. Proto-mirror.

Here it is on the left, with a similar aged Western Gull to the upper right, and a first cycle Glaucous-winged Gull to the lower right. Comparing to the Western, note the difference in head streaking, and the darker upperpart feathers coming in. Part of an adult Western Gull can be seen to the left of the Slaty-backed Gull, the mantle colours were similar in the field although in the photo vignetting along the edge of the shot is making the Western Gull look darker.

Above is a shot of the bird with Western Gulls below and to the upper right, and a Glaucous-winged to the right. This shot shows how the bill is expanded at the gonys, but the expansion appears greater than it really is, due to the pale blaze at the base of the lower mandible, as well as the paler colour on the upper mandible, near the nostril. The strikingly pale eye, unlike on any Western Gull shows up well, even from a distance. The pale eye and mascara add up to a fierce expression, quite unlike the more gentle expression of young Western and Glaucous-winged gulls. Note that the Western Gulls show their classic bandit mask appearance, with evenly dark auriculars andn a pale area behind the auriculars. This look is typical of Western Gull, and not seen in the other gulls usually about in this part of California. It is most obvious in first cycle Western Gulls.

Thanks again to Dan Singer for finding this bird, and to Joe Morlan for letting me know.

JANUARY 13, 2005

Below are photos of the same bird, 5 weeks earlier.

Today, at the local gull flock I located what appears to be a second cycle (second winter, Third calendar year) Slaty-backed Gull (Larus schistisagus).

Below I will quickly outline some of the features which led me to this identification.

STRUCTURE - A large, long-necked and pot-bellied gull. Compared to the Western Gulls and Glaucous-winged Gulls it was as large or larger than some but was very heavy in the chest and belly, making it look heavier. It was not a particularly long-winged Gull. The head had a flat forehead, not as round as most Western or Glaucous-winged Gulls near it, and the eye was not so centrally placed on the head. Head structure was similar to that of a large smithsonianus Herring Gull. Otherwise the only structural oddity was that this gull was long-necked, although it tended to keep the neck recoiled. When alert, the long neck was obvious.

Bill - The bill was large and comparatively long. It was as deep at the base as that of Western Gulls, but did not widen out at the gonys. In fact the gonydeal angle was not that striking, in other words it was comparatively shallow. The length of the bill masked the fact that the bill was actually rather large and deep, compared to smithsonianus Herring Gulls this bird was larger billed.

PLUMAGE - I will detail some of the features I saw which point to Slaty-backed Gull using the photos I took of this bird.

This photo shows the dark grey mantle coming in. Compared to Western Gulls, the darkness of the mantle was similar, however the new mantle feathers of this bird were tipped pale, making the overall colour look paler than it likely will look once these tips wear away. Note some dark lesser coverts coming in as well. The folded primaries were black with thin pale tips, contrasting with the paler tertials which were broadly tipped white. Western Gulls and smithsonianus Herring tend to show nearly as dark as the primaries, the paler tertials (like that of Thayer's Gull) are a good feature for Slaty-back. As well, note that the coverts are rather pale and unmarked, suggesting a "white-winged gull," in fact the paleness of the coverts was similar to that of several similar age Glaucous-winged Gulls, but distinctly paler than that of all similar aged Western Gulls I could see. The tertials were nicely dark centered, not vermiculated. Finally, the scapular crescent was very broad, and although not clearly visible in this photo the tertial crescent was broad and white, much more striking than on any similar age Western Gull.

This photo shows thte dark mantle coming in, as well as the very crisply streaked crown and dark patches around the eyes.

This shot shows the gleaming yellow eye, which in conjunction with the flat forehead, large bill and dark patch around the eye, gives this gull a menacing expression. As well, note the very crisp and bold streaking on the crown. Some streaking was presnet on the neck sides, but most appeared to have either been molted away or worn off. The rather white breasted look of this bird was something that I was not expecting, but I do not think it is a problem for the identification as a Slaty-backed Gull. The bird retained a dark belly, and this did not appear to be staining, but was brownish feathering, note how it is present on only the centers of the flank feathers. The blackish primaries are obvious, and you can see the start of the pale inner wing panel here, as the innermost primary has a distinctly paler base than tip. Note also the small mirror already present on the underside of P10, on the opposite wing. The legs were dark pink, not bright, not dull, just dark. The unpatterned greater coverts can be seen in this photo, as well as the frosted appearance of the upperparts due to pale tipping on the mantle feathers. Finally, the light or my scope may have been playing tricks, but at one point the very dark orbital ring could be seen to have a very dark carmine colour to it.

I have no photo of the spread wing, but this shows that the black of the primaries was concentrated on the outer vane, and tips. A few seconds later when it opened up the wing a tad more, the dark vanes of the primaries could be seen to form a pattern of dark stripes on a paler background. From below the wing pattern was reminiscent of Thayer's Gull, the undersides of the primaries were pale, not black, and they contrasted with black tips forming a narrow dark trailing edge. In flight the inner primaries were obviously paler than the outers. Look at the huge white scapular tip which creates the scapular crescent!

This photo shows the bill pattern pretty well. From a distance it looked blackish, but in detail one could see that the base of the upper mandible out to the nostril was paler. The tip was indeed black, as was a stripe along the cutting edge, but the very base of the lower mandible was once again paler. The extreme tip, the nail, was pale. The yellowish eye is obvious here. The mirror on the undeside of P10 is somewhat visible.

This photo shows thte black and unicolored tail, and the white uppertail coverts. The black tail excludes many other Old World contenders, such as Lesser Black-backed Gull, although that species is structurally very different from this bird. In flight this bird has a contrasting white rump and whitish uppertail coverts with some dark markings.

This photo hints at the rather long necked structure of this bird. The large and long bill and yellow eye are prominent.

A back shot, to show the mantle, blackish primaries, paler tertials, tert and scap crescents etc.

A good structure shot, bulky, pot-bellied, not long-winged, menacing appearance. Note that the darkness of the mantle is not obvious in side view, due to pale tipping and the fact that the dark is restricted in extent.


Ventura, California 1996- Don DesJardin's second cycle individual. There is no doubt in my mind that this was a Slaty-backed Gull. Given the current new information on Slaty-backed Gull in the state, historical records will likely be re-reviewed by the CBRC.

Davis, California - 1998. First cycle bird. - The contrasting white head, structure and well marked coverts make me think this may be a Herring hybrid of some type. This is a gut feeling, I did not see the bird myself.

Half Moon Bay, California. No photos on the web. A second cycle bird photographed by Ron Thorn (approximately 4 years ago) is clearly a Slaty-backed Gull. This bird has not been reviewed by the CBRC.

Folsom Lake, Placer County - 1998. No flight shots, but it looks like an adult Slaty-backed Gull.

Salton Sea, 1998. This is a tough one, several good points, several bad points. The molt during late February, and some aspects of shape and maybe even a yellow tone to legs suggest it could be a heuglini-taymirensis, rather than Slaty-backed Gull. Broad tertial crescent and wing pattern suggest Slaty-backed.