20 November 2014

How to find the South Hills Crossbill

Last weekend my wife and I took a little mini vacation to the South Hills of Idaho in search of a very unique finch.  The South Hills Crossbill (Loxia [curvirostra] sinesciurus) is an endemic species or subspecies that is found only in two isolated mountain ranges in southern Idaho.  It has been described in the scientific literature as a full species, but so far the American Ornithologists' Union and the American Birding Association have yet to adopt this change, so it is currently considered a subspecies of Red Crossbill (Loxia curvirostra).  Many people have speculated that this is only temporary, though, so last weekend we set out to put a lifer species "in the bank" in case of a future split.

There are lots of great resources online about the South Hills Crossbill, and I don't intend to repeat all that information here.  Briefly, the crossbill evolved from a fascinating ecological situation where the symbiotic relationship that keeps cones easy to access in the presence of squirrels breaks down in these isolated squirrel-free mountains, resulting in an evolutionary arms race between well-defended Lodgepole Pines and specially adapted crossbill bills.  The original paper is a great reference, but summaries are also available here and here, for example.  Rather than reiterate the details of ecology and identification that have been published better elsewhere, I will provide here the story of my search, in hopes that it will help others find this cool bird.

In November, the road to the crossbills was snowy but plowed.  My little Toyota made it just fine, but I was glad to have the chains on.  Don't park on the shoulder like I did - despite the very wide road, the sheriff came by and made me move my car to a parking lot.
We started by driving up Rock Creek Road into the South Hills.  From I-84 take Exit 182 and head south.  Just after you cross the river gorge, turn left onto 3800E.  This becomes Rock Creek Road and takes you right into the hills and up to the crossbills!  Watch the landscape change as you ascend, first valley agriculture, then sagebrush, then junipers, and finally Lodgepole Pines.  These pines are the preferred habitat of the South Hills Crossbill.

Beyond the Diamondfield Jack Campground, the road was not plowed, but we could still walk it.  Snowshoes would have been helpful.  A local told us that the road is usually plowed beyond this point.

When we visited (in late November), the road was plowed to Diamondfield Jack Campground but not beyond.  Despite the plowing, I was glad to have snow chains for the tires, but a four-wheel-drive vehicle would have probably been fine without them.  We had crossbills several times between the ski area and the Diamondfield Jack Campground, always perched in the top of Lodgepole Pine or flying over, calling in flight.

If you're looking for South Hills Crossbills, you're looking for this: their preferred habitat, Lodgepole Pine.

I suggest studying the calls well, because South Hills Crossbills are not the only crossbill type present.  Better yet, make some audio recordings and study the sonograms to be absolutely sure you got the right birds.

Is this a South Hills Crossbill?  It sure could be--it was foraging on Lodgepole Pine in the South Hills.  But, I only recorded audio from two individuals in this flock of nine birds, and both of those ended up being Type 2, "Ponderosa Pine Crossbills."
Fortunately, my audio recordings confirmed that several other crossbills we saw and heard were indeed South Hills Crossbills, a lifer subspecies that will potentially be a lifer species some day!
Overall, we had three types of crossbills, including multiple individuals of our main target.  Good luck if you go, and be sure to enter your sightings in eBird!

04 September 2013

Predicting a Clark's Nutcracker Irruption

I photographed this Clark's Nutcracker in northern Utah on 28 July 2013, but if it can't find enough pine nuts, it might be headed to your neighborhood.
I've seen two unusual events in the last few days that make me think this year might be a big one for vagrant Clark's Nutcrackers in the ABA area.  On Sunday, I was birding in typical Clark's Nutcracker habitat at about 8,100 ft. elevation near my home in northern Utah.  This is a species that is relatively common here, but we were doing a big day, and it's not so common that it is guaranteed to be found in the two or three hours we could afford to spend in its habitat.  In two or three hours of birding, we would expect to probably run in to a few of them.  Our expectations were off: in just a few hours last Sunday, we counted almost a hundred, moving around high overhead in flocks of up to 40.  Although the species is expected here, these kinds of numbers are not typical for this area and time of year in my experience.

This view of Cache Valley is from a point almost high enough to expect Clark's Nutcrackers.  That species is also expected across the valley, in the peaks covered with snow in this picture.  To find one down in the bottom of the valley, where you can see Cutler Reservoir shining, is very unusual, and is unheard of any time other than winter.

On Tuesday, a couple friends and I were birding in the middle of Cache Valley, at about 4,500 ft. elevation.  This is well below typical CLNU habitat, especially in summer.  In the seven years I've lived in this area, I know of just a few credible reports from the valley, almost all from the "benches" very near the mountains and all between October and December.  Yesterday, we saw a flock of 28 Clark's Nutcrackers flying over the middle of the valley, barely in to September.

This is what a Clark's Nutcracker can look like in a good year, with a crop full of pine nuts that it will cache around the area to feed on in the winter.  I photographed this one in 2011 in northeastern Nevada.
The Birds of North America account for the species indicates that Clark's Nutcracker irruptions are most likely to happen when two years of above average pine cone production is followed by a year of very poor production.  In years of good pine nut production, Clark's Nutcrackers are successful in raising young and mortality is low.  Two years of good production can build up population sizes well above normal.  When a bad year follows, there are way more Clark's Nutcrackers than nutcracker food, and the birds have to wander widely to find the nuts they need to survive.

In both 2011 and 2012, pine cone production by whitebark pines, one of the nutcracker's two main food sources, was higher than average.  The very dry winter last year (about 60% of typical snowpack locally, and around that or lower in much of the inland west) has caused poor production by whitebark pines this year, in Wyoming the lowest since about 2002.  Coincidentally, in 2002, Clark's Nutcrackers were reported from as far out of range as Alabama and Missouri.

This figure shows the standardized whitebark pine production from the Greater Yellowstone ecosystem for the last 24 years.  Note that both 2011 and 2012 were above average years, but 2013 is about the lowest since 2002.  This figure is from here and is in the public domain.
Based on my observations over the last few days, and the current status of whitebark pine production compared to previous years, I'm guessing that this will be a good year for vagrants of this species in North America.  Most movements of Clark's Nutcrackers are relatively local, so this is most likely to affect birders who live near Clark's Nutcracker habitat, but are a bit outside their usual range.  However, there is also potential for long-distance wandering, perhaps well outside of the species' expected range.  It might be helpful to study the call, and to be sure you're familiar with this species, so you're prepared if a Clark's Nutcracker should find its way near you this winter.

26 August 2013

County Big Year, again: How I found myself chasing my own tail

If you've been with this blog since the start, you might remember that it began as a way to chronicle my attempt at a county big year in 2008.  My goal at the time was 200 birds, an achievement that is honored by membership in the Bridgerland Audubon Society's 200 Club.  I met that goal early in the year, earlier than I expected, and ended up making it a full-scale Big Year.  By the end of the year, I had broken the county record.  At the time, I knew that my number of 242 species was good.  For comparison, there are THREE other birders tied for second place, each having maxed out at 235 species in separate years.  But, I also knew I had missed many species I might have found if I had known where to look, or if I had spent less time out of the county doing field work for my dissertation.

Four Common Redpolls is about double the total records from Cache County before the winter of 2012/2013.  These four were part of a flock of about 40 that I photographed in the first week of February, 2013.  (Photo copyright Ryan O'Donnell.)

Fast-forward to last winter, 2012-2013: It was shaping up to be a record-setting year.  For the first time since my big year in 2008, there was a Bohemian Waxwing irruption going on.  This normally tough-to-find-species was everywhere.  There was also an unprecedented irruption of Common Redpolls going on: a species that had less than five previous records in the county was showing up in flocks of dozens.  A few individual birds were noteworthy, too: a vocal Blue Jay was spending the winter in Smithfield and a White-throated Sparrow was coming to a feeder in Logan, for example.  These great birds and many others helped the Logan count circle break their Christmas Bird Count record in late December 2012, and indicated a good winter for birding in the county.

This Blue Jay was first reported from Smithfield, Utah, in the middle of November, 2012.  It was only the third or fourth record from the county.  It stayed in the area through at least March 2013.  (Photo copyright Ryan O'Donnell.)

The great birds stuck around into the new year, and even more locally rare species started turning up.  In the second week of January, Gray-crowned Rosy-Finch, Snow Bunting, and Lapland Longspur were all found.  I had found all of these in 2008, but considered myself very lucky to have found them after quite a bit of effort.  A flock of Pine Grosbeaks (a rare year-round resident that I missed in 2008) was found feeding on the USU campus on January 15th.  On the same day, Black Rosy-Finches were reported from North Logan; I had never seen this species in the county.  On January 26th, two Greater Scaup were found, another species I missed in 2008.  A Harris's Sparrow was found on January 29th, a species I had in 2008 but only once or twice since.  Then, on February 1st, a Snowy Owl was found, only the second in the state since 1967!  A great winter was turning into an incredible one.

Pine Grosbeaks probably breed in Cache County, but they can be very tough to find.  I missed them entirely in my big year in 2008.  A small flock of three, found by Leah Lewis on the USU campus in January, was quite obliging and was a great addition to any Cache County big year.  (Photo copyright Ryan O'Donnell.)

This Black Rosy-Finch was one of several coming to a feeder in North Logan.  I had never seen this species in the county before this year.  (Photo copyright Ryan O'Donnell.)

After noticing abrupt changes in the birding habits of a few of my friends, I was starting to realize that my Big Year record might be in jeopardy: at least two people were doing big years in the county, and they had picked the perfect year to do it.  So, around the beginning of February, I decided to join them: to take advantage of a great winter to try to improve on my Cache County Big Year record.  I didn't really WANT to do a big year, but I also didn't want an opportunity like this record-breaking winter to pass me by.

Well, that was unexpected!  A friend of mine had this bright red bird show up at her feeders, and asked for help identifying it online.  She soon learned it was a Summer Tanager, the first record in Cache County of a species that is usually found far south of here.  I saw the record on eBird and was able to see the bird later the same day at her feeders. (Photo copyright Ryan O'Donnell.)
This bird was a little less unexpected: Neotropic Cormorants have been moving in to Utah from the south in recent years.  This species was on my radar to find in Cache County, because they've become almost easy to find just a few hours south of here.  I've been carefully checking all cormorants in the area for a few years now.  Still, it was quite satisfying to finally find one last month (the smaller dark bird in this photo), the first record ever for Cache County.   (Photo copyright Ryan O'Donnell.)

Now, seven months later, I see that I made the right decision.  The good birds have kept coming, including several new species for the county, like Summer Tanager, Neotropic Cormorant, and Least Flycatcher.  And I'm really happy to be taking another shot at a big year now that I have five years' more experience of birding the area under my belt.  I'm finding my birding trips more efficient, now that I know most of the calls of the regular species and I can pass them by in search of rare ones.  I know the birding locations better, so I know where to find each species, and I know the changes of the seasons better, so I know when to look for rare species.  I also know the people of the area better, so I have more friends to go birding with, more people to give me tips, and more people to share their land with me.  In all, I'm glad to be able to give a big year another effort, because it would always bother me knowing that I could improve on my number of 242.

And, improve on that I will.   In fact, yesterday was a special day because I surpassed my previous record: my friend Andy and I found a Northern Waterthrush, my 243rd species of the year.  I can't wait to see how high a record I can set, a record I know I'll be proud of for years to come.

This Northern Waterthrush is among the most regular of the rare warblers that can be found in Utah.  It was a satisfying way to break the record: this bird, photographed on 25 Aug 2013, was my 243rd species in Cache County this year, breaking my old record of 242.  (Photo copyright Ryan O'Donnell.)

04 August 2013

Ten Best Birds from St. Paul Island, 2012

Last summer (2012) I had the privilege of working as a guide on St. Paul Island, Alaska, with Scott Schuette and Doug Gochfeld.  St. Paul Island is one of the Pribilof Islands, a small group in the middle of the Bering Sea.  Its unique geographic location makes it a famous birding destination: it is slightly west of the easternmost tip of Russia, and so it frequently gets old-world vagrants.  Plus, it is a great spot to see some of the endemic Bering Sea species like Least Auklets, Crested Auklets, and Red-legged Kittiwakes.

Today, I want to show you the ten best birds of my 2012 season on the island.  There are many ways to define the "best" birds.  This is not a science.  The ranking here is strictly based on how much I enjoyed seeing them.  That is of course strongly affected by rarity, but these are not necessarily the ten rarest birds.


10. Wood Sandpiper.  This species is major rarity anywhere in the contiguous 48 states, but annual in small numbers at St. Paul.  I saw up to three individuals in a day, and photographed both juveniles (like this one) and an adult.

This juvenile Wood Sandpiper paused in Town Marsh on St. Paul Island while trying to find its way to Australia or southeast Asia. (copyright Ryan O'Donnell)



9. Gray-tailed Tattler.  Like the Wood Sandpiper, this species is annual on St. Paul but very rare in the contiguous 48: a bird in Massachusetts last fall was only the third North American record away from Alaska.  We had multiple sightings of this species in their fall migration, up to two in a day.   

This adult Gray-tailed Tattler was photographed on the sandy beach on the north side of the island, probably the first land it had seen since leaving Siberia on its way south. (copyright Ryan O'Donnell)

8. Little Stint.  Also rare in the contiguous 48, with total records probably around 50 sightings, and less than annual on St. Paul.  We had up to two individuals at a time on the island last year.

This juvenile Little Stint (at front right) joined a few juvenile Western Sandpipers to snack in the mudflats on St. Paul as it was headed south. (copyright Ryan O'Donnell)

7. Hawfinch.  This was high on my list of dream birds when I was preparing for my summer in the Pribilofs.  This bird, first spotted on May 23rd and still present a week later when our access to the area where the bird was found was closed for the fur seal breeding season, was the 10th record for the Pribilof Islands.  There are no North American records of this species outside of Alaska, and it is less than annual in Alaska.

This Hawfinch, with dirt on its bill from picking at seeds in the grass, is a Eurasian relative of our Evening Grosbeak. (copyright Ryan O'Donnell)

6. Tundra Bean-Goose.  This species is "casual" (less than annual) in Alaska, and unrecorded elsewhere in North America.  Many earlier records of "Bean Goose"from Alaska had to remain unidentified when the species was split into the Tundra Bean-Goose and Taiga Bean-Goose.  This was an exciting find as our first real Asian rarity of the season, on May 12th.

After we accidentally flushed this Tundra Bean-Goose from a small melt pond, I was afraid we wouldn't see it again.  A few minutes later, it circled back past us and I was able to take a few photos, including this one.  (copyright Ryan O'Donnell)

5. Terek Sandpiper.  Another of my dream birds before arriving on the island, this fall migrant hung around for several days and pleased many visiting birders.  This species is named for the Terek River where it was first discovered, a tributary of the Caspian Sea.

I love the unique head shape and upturned bill of this Terek Sandpiper.  (copyright Ryan O'Donnell)

4. Eurasian Bullfinch.  Wow, what a charmer!  This adult male was found coming to some seed spread by a local resident between houses in the center of town.  Imagine having this on your yard list in North America!  This was the first spring record for the Pribilofs, but there had been a handful of fall records.

The bold and beautiful male Eurasian Bullfinch, peeking up from a meal of millet.  (copyright Ryan O'Donnell)

3. Dark-sided Flycatcher.  Flycatchers in general are among my favorite groups of birds, pushing this drab juvenile into the top three.  This was the seventh of this species reported from the Pribilof Islands.

This juvenile Dark-sided Flycatcher probably found plenty of bugs in the leeward side of an old volcanic cone on St. Paul.  (copyright Ryan O'Donnell)

2. White-tailed Eagle.  This Asian counterpart to North America's Bald Eagle was first found early in the season and continued, off and on, for the rest of the year.  It would sometimes go missing for weeks at a time, and we suspected it might be moving between the Pribilof Islands.  It was frustrating at times because it never seemed to develop much of a pattern, making it hard to track down, but it was thrilling any time it happened to fly past as it hunted around the island.  This was the first time this species had been seen in the Pribilofs.

White-tailed Eagle soaring over St. Paul Island. (copyright Ryan O'Donnell)

1. Pin-tailed Snipe.  Easily the rarest bird, this was our only Code 5 bird (five or fewer North American records), and this was the fifth North American record.  The previous four records were all from Attu Island, at the western end of the Aleutians.  Attu is far enough west to be in the eastern hemisphere, so including one record from a remote part of the Hawaiian Islands, this was the second record for the western hemisphere.  This photo is about the best I could manage, but fortunately Doug was able to take some better ones!


Out-of-focus Pin-tailed Snipe flushing from the tundra of St. Paul Island (copyright Ryan O'Donnell)

04 July 2013

Black Swifts on nests

Yesterday, I had the chance to visit a well-known nesting site of Black Swifts in northern Idaho on my way back from another trip.  Black Swifts are a very unique species that can be tough to find if you don't know where to look.  Here's one big hint: they nest exclusively behind waterfalls or in ocean-misted cliffs.  This was an exciting species for me because it was an "eBird lifer," that is, I had seen them only once before (June 2000), and it was before I was keeping detailed enough notes that I could later enter the sighting into eBird.  Black Swifts are a mysterious species as birds go: only about 200 nesting sites are known, and they made big news last year when their wintering range was finally discovered in western Brazil.  The total population is estimated at about 15,000 individuals worldwide, and is declining at about 6% per year.  Here are a few photos from my recent trip to see this intriguing bird at a nesting colony.






04 June 2013

Utah's West Desert Migrant Traps

On Saturday I led a trip for the Bridgerland Audubon Society to the west desert of Box Elder County, Utah.  Our main goal was to visit some of the famous "migrant traps" in the area.  This area, north of the Great Salt Lake, is well known in the state for being one of the most consistent places to find rare eastern birds in migration.  There are several small freshwater springs surrounded by miles and miles of sagebrush, salt flats, and hypersaline water.  As migrating birds pass over the area, they are drawn like magnets to these migrant traps in search of a drink, a snack, and some rest before continuing north to their breeding grounds.

We met early, 5:00 AM, so that we would have a full day of birding despite a nearly three-hour drive to our first stop.  We chatted about some of our rare bird fantasies for the day, discussed the plan of attack, and then headed west as the sky was starting to get light.  After a brief stop for gas in Snowville, our first birding stop was along Highway 30 in one of the best areas for FERRUGINOUS HAWKS in the state.  We got close looks at an adult light morph here, the first of about four in the next couple of miles.  After this brief stop, we continued on to Lucin, our first migrant trap.

Part of the BAS field trip party scoping a distant Golden Eagle nest from Lucin.
The flycatchers at Lucin set the tone for the day: while we called this trip "West Desert Migrant Traps" we might as well have called it "Identification of Difficult Flycatchers."  Several of the easier species were present, including SAY'S PHOEBE, WESTERN KINGBIRD, and WESTERN WOOD-PEWEE, but there were impressive numbers of Empidonax flycatchers, including at least FOUR WILLOW FLYCATCHERS, a DUSKY FLYCATCHER, a GRAY FLYCATCHER, and at least two other unidentified Empidonax sp.  Warblers were also pretty diverse, including ORANGE-CROWNED WARBLER, YELLOW WARBLER, YELLOW-RUMPED WARBLER (AUDUBON'S), WILSON'S WARBLER, and COMMON YELLOWTHROAT.  Here is a link to the complete eBird checklist: http://ebird.org/ebird/view/checklist?subID=S14315363

One of at least four WILLOW FLYCATCHERS at Lucin.  This is not a rare species in northern Utah, but it felt odd to find them perched on barbed wire and surrounded by sagebrush and greasewood!

Our next stop was Rabbit Springs, where the habitat is spread out over a wider area and the trees are not as large.  Three COMMON NIGHTHAWKS calling in flight here seemed unusual in the heat of the middle of the day.  We added one warbler species to our list for the day here, with a couple of MACGILLIVRAY'S WARBLERS.  Sparrow diversity was higher here, too, including many BREWER'S SPARROWS, two LARK SPARROWS, and a SAGE SPARROW.  We had lunch in the shade of a Russian Olive tree here and enjoyed some great looks at a couple of lizard species, a WESTERN WHIPTAIL and a LONG-NOSED LEOPARD LIZARD.  Here is the eBird checklist: http://ebird.org/ebird/view/checklist?subID=S14315422


Western Whiptail.

Bob, Craig, Terry, and Leah eating lunch in the shade.

Long-nosed Leopard Lizard
The next stop was at Owl Springs.  Here, we had a few more flycatchers, including DUSKY, WILLOW (singing), WESTERN WOOD-PEWEE, and a pair of WESTERN KINGBIRDS at a nest.  Our only migrant thrush of the day was a late HERMIT THRUSH here, and we also had our only LAZULI BUNTING of the day here.  eBird checklist: http://ebird.org/ebird/view/checklist?subID=S14315556

A migrating HERMIT THRUSH stopped for a rest at Owl Springs.
Our next and last stop of the day was at Locomotive Springs Wildlife Management Area, about an hour away.  This area has more open water, so we were able to add a few more species here, including FORSTER'S TERN, GADWALL, CINNAMON TEAL, AMERICAN WHITE PELICAN, PIED-BILLED GREBE, and AMERICAN AVOCET, for example.  A few LONG-BILLED CURLEWS were seen.  eBird checklist: http://ebird.org/ebird/view/checklist?subID=S14315760

Overall, we had a great day of birding in some very unique locations.  While we weren't able to pick up any rare eastern vagrants, we saw impressive numbers of some expected western species in habitats where they are not found except in migration.  Along the way, we got some great experience identifying a lot of Empidonax flycatchers and learning other valuable tips about how to identify sparrows from tail patterns, how to tell some of the female yellow warblers apart, and how to identify Catharus genus thrushes.  On the way out of our last stop, we added the highlight of many people's day, a large adult DESERT HORNED LIZARD.  It was great to end a good day in the desert with this popular and iconic species.

Desert Horned Lizard near Locomotive Springs WMA.

Kendal posing with the Desert Horned Lizard.

Terry holding the Desert Horned Lizard.





04 May 2013

A Hybrid Dusky Grouse x Sharp-tailed Grouse

A Dusky Grouse x Sharp-tailed Grouse hybrid, photographed by the author in northern Utah on 7 Apr 2013.

I love hybrids.  Some birders can be disappointed by hybrids, especially when a locally rare species turns out to not be "pure" (and thus can't go on a list).  But for me, they have everything you could look for in a bird: They are generally very rare: even the more common hybrids are rarer than their parent species.  They are often a challenge to identify.  And they give us a peak into the process of evolution: why don't we see more hybrids, and if two species can produce hybrids, why are they considered species?

I was hiking around a local birding spot (Hardware Ranch W.M.A.) a couple weeks ago, and I saw what I thought at first was a Sharp-tailed Grouse.  This bird was running through the sagebrush, with its tail held high, showing bright white undertail coverts, like Sharp-tailed Grouse do.  It had a slightly crested head, and an overall yellowish tone, also fitting Sharp-tailed Grouse.  But when I got my binoculars on it, I could see the black tail feathers with broad charcoal tips, a clear mark of a Dusky Grouse.  I was able to grab a couple photos before the bird flushed, and flew off through the sagebrush.

Later, I became suspicious that I had photographed a hybrid.  Hybridization between these species had been documented once before, by Allan Brooks in 1907 (illustration below).  I sent the photos around to a few grouse experts I knew, and a few people who knew grouse experts, and all the replies came back that this was indeed a hybrid Dusky Grouse x Sharp-tailed Grouse.  Interestingly, although I haven't been able to find any other photographs of this hybrid, one biologist indicated that this is the most frequently observed hybrid combination between wild grouse.  Local biologists have told me that they have seen a male Dusky Grouse displaying among a lek of Sharp-tailed Grouse about 25 miles (40 km) north of where I photographed this bird.  That same male Dusky, in fact, even tried to mate with a Sharp-tailed Grouse while the biologists had it caught in a trap!

A Dusky Grouse x Sharp-tailed Grouse hybrid, illustrated by Allan Brooks and published in the Auk in 1907.


The same Dusky Grouse x Sharp-tailed Grouse hybrid shown above.  This is the second of the only two photos I was able to take before the grouse flushed.

(Thanks to Mike Wolfe, Timothy Taylor, Scott Gardner, Mike Schroeder, and Jack Connelly for sharing their thoughts on this bird.)


04 April 2013

Identifying adult California Gulls and Ring-billed Gulls in flight

In much of the inland western United States and Canada, there are two common breeding white-headed gull species, the California Gull and the Ring-billed Gull.  If you live in this region, the first step in learning your gulls will be to learn to tell adults of these two common species apart.  When they are perched on the ground, it is not difficult: California Gulls have dark eyes, red and black on the bill, are slightly larger, and have a slightly darker mantle (back).  In contrast, adult Ring-billed Gulls have light eyes, a black ring around the bill without red, are slightly smaller, and have a paler mantle.

A pair of adult California Gulls in breeding plumage, showing their dark eyes, red and black on the bill, and relatively dark mantle.  Photographed 13 Apr 2009 at Logan, Utah.

An adult Ring-billed Gull in breeding plumage, showing its pale eye, black ring around the bill without red, and relatively pale mantle.  Photographed 2 May 2011 at Blackfoot, Idaho.
Even with these relatively distinctive gulls, identifying them in flight can often be difficult.  Sometimes, it is possible to make out the same features in flight, especially with close looks in good light.  Look especially for the eye color and the bill markings, because size and mantle color are particularly difficult to judge on a bird in flight.

Adult California Gull in breeding plumage.  Even in flight, the pattern of black and red on the bill and the dark eye can be obvious.  Photographed 17 Mar 2013 in Mendon, Utah.

Adult Ring-billed Gull in breeding plumage.  Even in flight, the black ring on the bill (without red) and the pale eye can be obvious.  Photographed 17 Mar 2013 in Mendon, Utah.
The real challenge, however, is in identifying these species when they are high overhead or lit in such a way that the eye color and bill pattern are impossible to distinguish.  In this case, it is helpful to pay close attention to the pattern and colors under the wing.  Both species have mostly whitish wings with extensive black near the tips and white spots at the very ends of the outer flight feathers.  But, California Gulls have duskier inner primaries contrasting more with the rest of the wing, and Ring-billed Gulls have paler inner primaries that are about the same color as the rest of the wing. California Gulls also tend to have more black in the wingtip than Ring-billed Gulls, but there is some overlap in this trait. 

Note the darker gray band that stretches from the black wingtips into the outer secondaries on this adult California Gull.  With practice and good light, this contrast could be visible from great distance on overhead birds.  California Gulls also tend to have more black in the wingtips, but there is some overlap in this trait.  Photographed 17 Mar 2013 in Mendon, Utah.

In contrast to the California Gull above, this Ring-billed Gull has much paler inner primaries and outer secondaries, which contrast less than on the California Gull.  Some slight contrast is still evident, so it might take some practice in the field to get a feel for this field mark.  Ring-billed Gulls also tend to have less black in the primaries, but there is some overlap in this trait so it should be used only as a supporting character.  Photographed 17 Mar 2013 in Mendon, Utah.


California Gull in flight.  Note again the relatively grayish inner primaries and outer secondaries, contrasting with the paler underwing coverts.  Photographed 9 Feb 2008 in Logan, Utah. 


Ring-billed Gull in flight.  The relatively pale inner primaries and outer secondaries almost lack contrast with the underwing coverts.  Note that the extent of black visible in the primaries varies to some degree with the position of the wing and the individual, so this bird appears to have about the same amount of black as the California Gull above.  Photographed 9 Feb 2008 in Logan, Utah.
The differences in underwing pattern between these two species are subtle, and take field experience to get a good understanding of them.  Of course, not every gull will be identifiable in every situation.  But with practice, you can learn to identify a higher percentage of gulls, even when they are seen only in flight high above you.