73

Slaty-backed Gull at Toronto

Bob Yukich and Juha Varella

The DiscoveryOn 2 January 1999, I (BY) was bird­ing the Toronto waterfront withJuha Varrela, a friend from Finlandwho was visiting over the holidays.It was a cold, cloudy day (-lrC),with a few flurries and a raw north­east wind. We were just finishing upa morning's birding and were look­ing over the gulls and waterfowl atSunnyside before our return home.At about 1200h, as we approachedfrom the west, we saw a small groupof gulls sitting on the ice inside thebreakwater between the foot ofEllis Avenue and Colborne LodgeDrive. While they were still in thedistance, I raised my binoculars togive them a quick scan beforeapproaching any closer. The majori­ty appeared to be Herring Gulls(Larus argentatus) , but I immediate­ly noticed a dark-backed gull amongthem which I thought was a LesserBlack-backed Gull (L. fuscus)because it had a lot of dark streak­ing on the head. I pointed it out toJuha, and we continued toward ituntil we were almost opposite thespot where the gull rested.

We were now fairly close to thebird and, looking through mybinoculars, I could see it sitting onthe ice, its legs hidden from view. Itappeared to be in definitive basic(adult winter) plumage. However,the mantle looked too dark and thesmudge around the eye did not

seem dark enough for the graellsiirace of Lesser Black-backed Gull. Ibegan to think that it was just aGreat Black-backed Gull (L. mari­nus), but that was not right either,not with all the dusky streaking onthe head. Next I thought of theintermedius race of Lesser Black­backed Gull. The mantle colour wasperfect for it. But, this gull lookedtoo large, about the same size asnearby Herring Gulls, and the over­all structure, especially the headand bill, was not right for any raceof Lesser Black-backed Gull. Juhawas very familiar with all of thoseraces from Europe, and especiallyfrom Finland. He also had experi­ence with many of the darker OldWorld races of Herring Gull, butthis bird did not match anythingthat he was familiar with.

I began to think that it might bea hybrid. Whatever it was, it wasgood! I asked Juha if he had his cam­era. He said that he did, and ran to hisvan to get it. Meanwhile, I startedstudying the bird through my scope(60 mm Kowa with ED glass and a27x eyepiece), from a distance of 30to 40 m. I now began to considerSlaty-backed Gull (L. schistisagus)after noticing that this bird had quitea large white tertial crescent. I alsorealized that the chances of thisspecies showing up here were quiteremote. Juha returned with his cam­era (35 mm, hand held with a 300 mm

VOLUME 18 NUMBER 2

74

lens and fast film). Positioning him­self as close to the shoreline as possi­ble and opposite the bird, he begantaking photographs. I continuedstudying the bird. Then the gull stoodup, revealing bright pink legs - apromising sign.

After noting as much as I couldon the bird, I was hoping to see it flyso that we could see whether it hadthe diagnostic "string of pearls" pat­tern of white spots that Slaty-backedGull shows on the outer primaries.At one point, several of the gulls,including our dark-backed bird, flewup briefly and landed almost imme­diately. Juha was still clicking butwas not sure whether he had gottena good flight shot or not. It hap­pened so quickly that I really didn'tsee much more on the bird. Finally,several of the gulls flew off, but ourmystery bird remained with a fewHerring Gulls. A short time later,after he had taken about 30 expo­sures, Juha began walking backtowards me. Suddenly our gull flewup and eastward. Juha did not havetime to get another shot, and I triedin vain to see the wingtip pattern asit moved away from us. After flying ashort distance, it turned and begancoming back toward us. I was hopingthat it would fly over our heads so

• that we could see the pattern on theunderside of the primaries, but itveered northward and continued fly­ing over the Gardiner Expresswayand High Park, all the while gainingaltitude. Finally it disappeared fromour view. Total observation time hadbeen about 20 to 25 minutes.

When it first flew, I had a

ONTARIO BIRDS AUGUST 2000

micro-second view of the undersideof the primaries. I sensed theymight have had the pattern I waslooking for, but I could not be sure.In flight, it had a slightly heavybearing, and the wings did notappear particularly long. Not muchelse was noted. We then continuedwalking a short distance in an east­ward direction, checking out thevarious ducks and gulls. Afteranother 15 minutes or so hadpassed, we returned home, but firstwe checked the gulls sitting on theice at the south end of GrenadierPond. Our bird was not there.

One week later, on 9 January,Glenn Coady and Patrick Stepien­Scanlon saw what they believed tobe the same gull farther to the easton the ice inside the breakwateropposite the Boulevard Club. Theirdescription fit the bird that we saw.Patrick also had a paler mantledLesser Black-backed Gull nearbyto compare with. Unfortunately, thegull in question was on privateproperty with no public access andboth observers had to contentthemselves with somewhat distantviews. They watched the gull fly outover the lake at dusk, and it was notreported again.

Juha was returning to Finlandin a couple of days after our sight­ing and would not have time to gethis slides developed here. Weagreed that once he had themdeveloped in Finland he would sendme duplicates of most of them. Westill were not sure whether he hadcaptured anything on film that wehad not already seen in the field.

After the slides were developed inFinland, Juha e-mailed me sayingthat he had one good flight shot ofthe upper wing. When he comparedit with photographs of known Slaty­backed Gulls, the primary patternmatched perfectly. Everything elsehad matched up also. We were pret­tyexcited!

About a month after havingseen the bird, I received the slides. Ilooked at them carefully and com­pared them with various photo­graphs of Slaty-backed Gulls. I alsoreferred to The Large Gulls ofNorth America video narrated byJon Dunn, which I found especiallyhelpful. I felt that the photographsof our bird matched Slaty-backedGull in every way. Subsequently, theOntario Bird Records Committeeaccepted our reports as confirmingthe second record of Slaty-backedGull for Ontario (Roy 2000). Thefirst Ontario sighting involved abird on the Niagara River from 24November to 29 December 1992(Bain 1993).

Identification PointsThe Slaty-backed Gull appeared tobe the same size as the HerringGulls it was with, maybe a bitchunkier, and with a similar shapedhead and bill. I believe that this gullwas probably a female because ofits relatively small size and smallbill. Slaty-backed Gulls can exhibitmuch sexual dimorphism. The man­tle colour was a dark slate, darkerthan on the graellsii race of LesserBlack-backed Gull but paler thanthat of a nearby Great Black-

75

backed Gull; it was intermediatebetween the two. The large whitetertial crescent was noticeably larg­er than that on any of the HerringGulls, and its large round-shapedscapular crescent was also largerthan on any of the nearby gulls. Thevisible folded black primaries con­trasted slightly with the dark man­tle. Each primary was tipped withwhite, beginning with a fairly smallapical spot on P10. These spotsbecame successively larger inward­ly, through to P6, the white tip ofwhich was often just visible at theedge of the white tertial crescent.At times I could see the undersideof the outermost primary, P10. Itshowed a small white tip with a nar­row band of black next to it, fol­lowed by a large, oval-shaped white"mirror" that completely coveredboth webs.

The bill was similar to that ofnearby Herring Gulls, moderate insize with little swelling at the tip,and not much gonydeal angle(almost parallel sided). The basaltwo thirds of the bill was a chalkyyellow, and the tip was a brighterorange yellow. There was a medi­um-sized red spot near the tip ofthe lower mandible, and a smalldusky mark (possibly extendingslightly onto the upper mandible)posterior to and touching this spot,suggesting a fourth year bird. Thecrown appeared rounded or slightlyflattish, depending on the bird'sposture. The eye was pale yellow asin Herring Gull. The orbital ringwas not noted.

The head, neck and breast were

VOLUME 18 NUMBER 2

76

Figure 1: Slaty-backed Gull at Sunnyside Beach, Toronto, 2 January 1999, showingdiagnostic "string of pearls" in primaries. Photo by Juha Varella.

Figure 2: Slaty-backed Gull, 2 January 1999, showing deeper chest and longer neckthan nearby Herring Gull. Photo by Juha Varella.

ONTARIO BIRDS AUGUST 2000

streaked and mottled with greyishbrowns. The dense streaking aroundthe eye formed a dark eye-patchextending posteriorly in a point,upwards and toward the rear of thecrown. It also extended in a similarfashion in front of the eye, but pos­sibly more bluntly so. This eye­patch was not as dark as is usuallyseen in definitive basic LesserBlack-backed Gulls of the graellsiirace. There were short duskystreaks on the crown that continueddown the nape, more heavily sodown the hindneck and darkest onthe lower hindneck. The front andsides of the neck were also streakeddusky, being perhaps more mottledon the lower neck. The underpartswere white with large well-spacedmottling across the entire breast.This mottling had a more brownishhue than the rest of the streaking,which was more greyish brown. Thetail was all white. The legs were abright pink, and this colour wasmatched by a few Herring Gullswith the brightest legs.

The most important photo­graph (Figure 1) reveals the upper­side of the gull in flight, showingwell the wide white trailing edge ofthe secondaries which extends intothe inner primaries, much widerthan on any of the Herring Gulls inthe photo. The wing also shows aconspicuous white leading edge.Most important is the "string ofpearls" effect created by the white

77

"tongues" in P7, P6 and P5. Theseare separated from the white tipson each feather by varying amountsof black. PI0 shows a large white"mirror", and P9 and P8 have nomirrors at all, just white tips. Theamount of white in P8 on Slaty­backed Gull is variable; it can some­times have none at all, as in thisindividual (although there could bea slight mark on the inner web ofP8, hidden by the outer web of P7).Difficult to see in this photograph,but visible upon close inspection, isthe grey inner web of the outer pri­maries (mostly covered by theblack outer web of the primary nextto it). This feather pattern (blackouter web and grey inner web) isright for Slaty-backed Gull. Alsoevident in Figure 1 are the wide­based wings, noticeably wider thanon any of the Herring Gulls.

The photograph of the birdstanding (Figure 2) shows the deep­er chest and longer (and thicker)neck of this gull when comparedwith the Herring Gull next to it. Thewide white tertial crescent andlarge scapular crescent are also vis­ible in this photograph.

Literature CitedBain, M. 1993. Ontario Bird Records

Committee report for 1992. Ontario Birds11: 46-63.

Roy, K.J. 2000. Ontario Bird RecordsCommittee report for 1999. Ontario Birds18: 53-72.

Bob Yukich, 39 Lincoln Avenue, Toronto, Ontario M6P IM7

Juha Varella, Piispankatu 1, as. 6-7, FIN-20500, Turku, Finland

VOLUME 18 NUMBER 2