It is once again bird-a-thon season. Each spring birders across the North American landscape secure pledges and then head out to comb their local haunts in an effort see as many bird species as possible in a single day. Their efforts raise money for many worthy bird conservation projects. One could make the case that no conservation effort is more urgent or important than the race to save the rapidly declining Atlantic population of Red Knots.

Over the last several decades, this population has crashed, in part due to the loss of a critical mid-migration food supply provided by spawning horseshoe crabs in Delaware Bay. The Delmarva Ornithological Society (DOS) is one of several organizations spearheading an effort to acquire and preserve critical crab spawning grounds in the bay. The centerpiece of this effort is the Delaware Bird-a-thon, which has raise approximately $190,000 and helped purchase and protect 274 acres of vital crab/shorebird habitat on Delaware Bay. 

Staggering numbers of shorebirds take advantage of the bountiful food supply at Delaware. This photo, taken at Mispillon Harbor, Delaware on 13 May 2007, includes a variety of gull and shorebird species. Many of the birds in this image are Red Knots. (Photo by Chris Bennett).

Red Knots are long-distance migrants that come to Delaware Bay from as far south as Tierra del Fuego. They arrive having shed as much as 50% of their total body weight and devoid of the fat reserves needed to complete the final 3000-mile leg to their Arctic breeding grounds. Their migration timing brings them to the Mid-Atlantic coast just as horseshoe crabs come ashore to deposit their eggs. The knots then spend many days gorging themselves on the crab eggs, building up their weight and fat reserves before continuing north. Without this important refueling stopover, Red Knots would likely not have the energy required to reach their breeding grounds, let alone reproduce once they got there. 

The Atlantic population of Red Knots has maintained fairly stable numbers over the past few years, but DOS Conservation Chair Bill Stewart, who founded the Delaware Bird-a-thon, informs us that the latest winter surveys (2011-2012) suggest that the fragile Atlantic Red Knot population is once again declining. Despite this sobering news, Delaware birders remain committed to doing all they can to help these attractive shorebirds. The best way to lend your support is to make a direct contribution to the Delaware Bird-a-thon, which can be done directly via this secure web connection:

http://www.dosbirds.org/birdathon2012

Editor's Note: Since 2009, BirdFellow has proudly endorsed the efforts of the Delmarva Ornithological Society and specifically promoted the Delaware Bird-a-thon. DOS Conservation Chair Bill Stewart provided much of the information above via his annual bird-a-thon letter asking for our support. To learn more about the plight of Atlantic Red Knots, I would encourage you to read "Help the Delmarva Ornithological Society Help the Red Knot" by Elizabeth J. Rosenthal. Rosenthal's piece was published in the BirdFellow online journal on 28 April 2009. As always, we can't overemphasis the importance of your support in preserving shorebird and crab spawning habitat on Delaware Bay. This year's bird-a-thon runs 5-13 May. Please join me in making a contribution today!

By Ann Nightingale

One of the great things about being a nature lover is that your powers of observation seem to improve. While others are walking by, oblivious to the activities going on all around them, naturalists notice the creatures and the behaviors, especially if they are out of the ordinary.  

The Ogden Point Breakwater is a popular spot with folks out for a weekend stroll. (Photo by Craig Spence, sourced online at Flickr.com)

Such was the case on March 24, 2012, a sunny Saturday morning, when Ginger Morneau, her husband Ken, and brother Lou Baker were walking along the Ogden Point Breakwater in Victoria, BC. The breakwater is a favourite spot for locals and visitors, reaching out about a half mile from the waterfront south of downtown. The area is also popular with divers as it is a marine park, populated with interesting fish, marine plants and invertebrates. Walkers strolling along the top of the breakwater can often see marine wildlife in the water below.  

As the group headed out along the walkway, Ginger noticed a gull acting strangely a short distance ahead of her. The bird was on the inside of the breakwater, where the water is clear and can be quite still. The gull appeared to be feeding on something underwater, but it didn’t raise its head. As they approached, they could see a red-orange shape in the water below the gull. When they got to the spot directly above the gull, they could see that it was an octopus. And Ginger’s camera was in her hand.

The Giant Pacific Octopus can be seen regularly patrolling the shallows of the shorelines around Victoria. They primarily feed on crustaceans, but are known to occasionally take fish and even birds. Octopi are extremely intelligent animals, and great problem solvers. Although they live only about four years, they can grow to have a span of more than 20 feet and to weigh more than 100 pounds. This one wasn’t that large, but it was still an impressive individual. What was even more impressive, though, was that it had one of its tentacles wrapped around the head of the gull, holding it under water.

When first spotted, it appeared that the young Glaucous-winged Gull was feeding on something just under the surface...but on further inspection it became clear that the gull was was the prey item. (Photos by Ginger Morneau)

The first winter Glaucous-winged Gull was struggling, flapping its wings in an attempt to break the octopus’s grip, but without success. The octopus’s eight tentacled arms allowed it to cling firmly to the rocks and simultaneously maintain its grasp on to the gull. Initially, air was bubbling to the surface, but within a minute, the struggle was over. More tentacles came out of the water to grab the body of the gull and pull it completely under. Other gulls flew overhead, noisily checking out the scene as if to see if there were going to be any scraps, but disappeared once the victim had been pulled from the surface.  

In less than one minute the gull was drowned, fully submerged and appeared to partially ingested with only its wings still visible. (Photos by Ginger Morneau)

Ginger described the battle as “primal” and although she wanted to rescue the gull, it wouldn’t have been possible due to the sheer drop from the walkway–not to mention that the writhing tentacles of the octopus were more than a little intimidating. So she snapped a few more pictures, aware that she was witnessing a rarely-seen event. There wasn’t time for more–from her first picture to her last, only 53 seconds had elapsed. A couple of others watched the spectacle, but most people just walked on by, unaware of the struggle just fifteen feet below them.  

Gulls will eat octopus, given the opportunity. There’s a decent possibility that the victim in this story might have even been pecking at the octopus before Ginger and her family happened by. We’ll never  know who started this battle, even though we definitely know who won! There are other records of octopus catching and eating sea birds, including reports of one with a den near a boat ramp on Whidbey Island that was seen catching both gulls and Pigeon Guillemots. However, Ginger’s are the only photos we’ve found that document this behavior.  

To commemorate witnessing and photographing this amazing event, Ginger, Ken and Lou went out for a calamari lunch.  

Literature Cited:

Mather, Jennifer A., Roland C. Anderson and James B. Wood (2010). Octopus: The Ocean's Intelligent Invertebrate (2010).

Sazima, Ivan and Lisandro Bastos de Almeida (2008). The Bird Kraken: Octopus preys on a sea bird at an oceanic island in the tropical West Atlantic. Marine Biodiversity Records, 1 , e47 doi:10.1017/S1755267206005458

This winter season "Sooty" Fox Sparrow shows the fairly bright corn-yellow lower mandible that I expect to see on this Fox Sparrow type. (Photo by Glenn Bartley). 

It remains to be determined whether Fox Sparrow is one highly variable species or up to four closely-related species (Zink and Kessen 1999). Even within the four major subspecies groups the 18 recognized subspecies of "Red, Thick-billed, Slate-colored", and "Sooty" Fox Sparrows present  so much individual plumage variation as to cause birders to scratch their heads in befuddlement. Where I live in the Pacific Northwest, one can readily see 20+ Sooty Fox Sparrows during a winter day, with no two looking exactly alike in terms of plumage (Mlodinow et al. 2012). 

My experience with Red and Sooty Fox Sparrows led me to believe that their most consistent aspect is bill coloration, which consists of mostly dark horn color on the upper mandible and bright corn-yellow along the basal cutting edge of the upper mandible and most of the lower mandible. I've always thought that this bill coloration was universal among Sooty and Red Fox Sparrows, with Slate-colored Fox Sparrows showing lesser amounts of duller yellow on the bill.

Most of the images of Thick-billed Fox Sparrows that I looked through showed no yellow on the bill, when their over-sized bills are a uniform grayish horn color. It should be noted that all the photos I found were taken during the spring and summer months. My experience with Thick-billed Fox Sparrow is limited to seeing birds on their central Oregon breeding grounds (May-July). None of the Thick-billeds that I've seen or photographed showed yellow on the bill. This article does include one March photo of a Thick-billed (see below) that shows a restricted area of dull yellow on the lower mandible. Additionally, Kimball Garrett told me of an Allan Brooks painting of a "Yolla Bolly Fox Sparrow" (references P. i. brevicauda) that was painted from a January specimen taken in Los Angeles County. Brooks' illustration shows "bright yellow-orange on the basal two-thirds" of the lower mandible according to Garrett.

A day spent sorting and captioning Fox Sparrow images for the BirdFellow  Social Field Guide has revealed that bill color–at least in Red and Sooty Fox Sparrows–may change seasonally, adding another confounding element to sorting them out. 

This "Thick-billed" Fox Sparrow photographed in May (California) shows the deep all-grayish horn-colored bill typical of this subspecies group. (Photo by Robert Royse). 

Robert Royse, Mark Szantyr, and Glenn Bartley have provided BirdFellow with a nice assortment of spring and summer season images of all four subspecies groups. Several of Royse's Sooty and Red Fox Sparrows were photographed on their northerly breeding grounds. It came as a surprise to me that these birds show no yellow on the lower mandible. I also found several early spring (March-April) images in which it appears that some of the bright yellow that is typically seen on winter birds had been lost or was fading and that that bases of the lower mandible had in some cases faded to a paler bone or horn color.

Conversely, fall and winter images provided by Szantyr, Bartley and others, along with those found elsewhere online, generally show birds with bright corn-yellow on the lower mandible and along the cutting edge of the upper mandible. I looked to the Birds of North America Online account for enlightenment on this topic. Weckstein et al. (2002) suggest that seasonally variability in the bill color of Fox Sparrows is in need of further study, a sentiment echoed by Garrett (pers. comm).

If one peruses the more popular illustrated field guides of North American birds (Sibley, National Geographic, and Peterson), it is easy to conclude that Red and Sooty Fox Sparrows have entirely yellow lower mandibles or even mostly yellow bills. Similarly, the David Beadle plate that accompanies Zink and Kessen (1999) depict Reds and Sooties with all-yellow lower mandibles. The Beadle, Sibley, and Peterson illustrations of Slate-colored Fox Sparrows show them to have duller yellow on the lower mandible, while the 5th edition National Geographic Guide plate includes a Slate-colored with no apparent yellow on the bill. 

The Beadle plate and the illustrations of Thick-billed Fox Sparrow in all three of these guides depict them as having no yellow on their bills. They are shown to have more grayish or dusky horn-colored bills. Beadle's plate along with the Peterson and National Geographic guides show this subspecies group to have a somewhat bi-colored bill, with the upper mandible being noticeably darker than the lower mandible. I have some poor quality photos of Thick-billeds with distinctly two-toned bills (darker upper mandibles) that were taken in June 2009 on the east side of the Cascades in Jefferson County, Oregon. Sibley's illustration of Thick-billed Fox Sparrow shows it to have a mostly uniform grayish bill with a darker culmen, closely matching the bill pattern of the bird in the Royse photo above. Zink and Kessen (1999) and Garrett et al. (2000) discuss the cline that exists between the Thick-billed and Slate-colored Fox Sparrows, which frequently hybridize along the the "Great Basin-Sierra Nevada interface." Both articles describe birds in the White Mountains of California that are morphologically intermediate in terms of bill size and plumage.

It is important to point out that artists charged with creating a single example of a particular species or subspecies for a field guide are left to present a general representation that approximates what you or I perceive when we see that species in the field. Thus, it is unrealistic to expect their illustrations to be letter perfect or to capture the range of variation we might see. Both Red and Sooty Fox Sparrows are northerly nesters, whose breeding ranges are far-removed from where most of us spend our time birding. Those who buy and use these field guides are mostly observing Red and Sooty Fox Sparrows on their wintering grounds, hence the illustrations in these guides represent what we are likely to see outside of the breeding season. Below is a series of head only crops of various subspecies of Fox Sparrows. My apologies to the photographers for the heavy cropping of these images, which compromises the quality of their otherwise wonderful uncropped images. 

From to to bottom, the four Sooty Fox Sparrows above were photographed in Alaska in May (by Robert Royse), in Barrington, New Hampshire during January (by Mark Szantyr), at an unknown location in January (by Glenn Bartley), and near Clatskanie, Oregon during April (by Dave Irons). Note that the summer bird has no yellow on the bill, while both of the winter season birds show extensive yellow, particularly on their lower mandilbles. Interestingly, the April bird has a bill that appears to be in transition, presumably losing the yellow and becoming more horn-colored.

From top to bottom, the three Red Fox Sparrows above were photographed in Manitoba during June (by Robert Royse), in New England during April (by Mark Szantyr) and in Hamden, Connecticut in March (by Mark Szantyr). The top two birds–photographed April or later–lack yellow on the bill, while the March bird has conspicuous yellow on the bill. Also note that the bird from Connecticut, where P. i. iliaca is the presumed subspecies, is unlike the other New England bird in appearance and looks more like the Manitoba bird, which is presumed to be P. i. zaboria. Szantyr and Louis Bevier compared the appearance of this bird to other photos and museum specimens of P. i. zaboria and came away convinced that it is likely of that subspecies.

The bird above was thought to be a Thick-billed Fox Sparrow by Robert Royse when he photographed it in California's San Diego Mtns. during March. To my eye the bill on this bird seems, perhaps, not quite deep enough for Thick-billed, but making such determinations from photos is a challenge. Note that the yellow on the bill of this bird is more limited and has a slightly greenish cast and the base of the lower mandible is horn-colored.

This Thick-billed Fox Sparrow was photographed on territory in California during May (by Robert Royse). It shows no yellow on the bill, which matches the bill pattern of the May/June birds shown above. 

The Slate-colored Fox Sparrow in the two images above was photographed in California during March (by Robert Royse). Note that the yellow on the lower mandible does is a bit duller than the yellow exhibited by Red and Sooty Fox Sparrows and it doesn't extend all the way to the base of the bill.

Although this small sample seems to suggest that northerly breeding Fox Sparrows (Red and Sooty) have bright yellow lower mandibles away from breeding season and show more uniform gray to pinkish horn-colored bills on the breeding grounds, there is, to date, no solid science to support this idea. In multiple captions Zink and Kessen (1999) emphasize that bill coloration is not reliable as a  field mark when separating Fox Sparrow subspecies or subspecies groups. It would be great to hear from folks with experience handling these birds at banding stations to learn if they notice any seasonal variations in bill color. One thing seems clear, this question warrants further investigation. I will certainly be looking more closely at Sooty Fox Sparrows in my area, particularly the latest departing northbound and earliest arriving southbound individuals.

This article would not have been possible without the collection of photos provided by Glenn Bartley, Robert Royse, and Mark Szantyr. Their images were a pleasure to look at and inspired me to delve into this question further. Kimball Garrett offered a prompt and informative response to several questions that I posed to him and confirmed my notions about some of the taxa with which I'm less familiar. Szantyr and Royse both responded promptly to my queries and provided valuable additional information about the circumstances of their respective observations. Royse was also able to supply higher resolution head shots for a couple of his birds.

Literature Cited:

Garrett, K. L., J. L. Dunn, and R. Righter. 2000. Call notes and winter distribution in the Fox Sparrow complex. Birding 32:412-417.

Mlodinow, Steven G., Bill Tweit and David Irons. 2012. Photo Essay: The Sooty Fox Sparrows of Washington's Puget Trough. Birding Vol. 44:2 46-52.

Weckstein, Jason D., Donald E. Kroodsma and Robert C. Faucett. 20o2. Fox Sparrow (Passerellailiaca), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds. cornell.edu/bna/species/715doi:10.2173/bna.715

Zink, R. M. and A. E. Kessen. 1999. Species limits in the Fox Sparrow. Birding 31:508-517.

Other sources on this topic:

I recommend taking a look at a lively and informative exchange that occurred on the ID Frontier's listserv back in 1997. Joining in this discussion were the likes of Louis Bevier, P. A. Buckley, Jon Dunn, Kimball Garrett, Alvaro Jaramillo, David Sibley and Mark Szantyr. Greg Gillson created a link to this thread, which can be viewed at: http://thebirdguide.com/fox/frontier.htm

Birds that use thermal uplift to conserve energy as they gain altitude typically have long broad wings and a comparatively short broad tails. This Black Vulture was photographed in Montgomery County, Texas. (Photo by Scott Carpenter).

In our first investigation of avian flight strategies we explored dynamic soaring and how some birds are able to take advantage of wind gradients (differences in the speed of two air masses) to cover great distances with nary a wingbeat. 

In this piece we will explore how soaring birds exploit the temperature differences in neighboring air masses. Vultures, hawks, pelicans and cranes are among the species one most often sees gliding in tight circles and using thermal uplift to gain altitude with very little wing flapping.

Rising columns of warmer air (thermals) are created by the solar heating of the Earth's surface. Areas with the most exposure to the sun warm more rapidly than areas that are shaded, thus the air masses above exposed areas also warm more rapidly. 

Since warm air masses are less dense, they rise while the dense cooler air masses descend, in essence adding a push to the already rising columns of warmer air. When a soaring bird encounters these rising air masses it starts circling in an effort to remain within narrow column of rising air, which carries it upward. Other soaring birds or flockmates recognize that they are riding a thermal and join in to form a "kettle." It is not unusual to see multiple species of vultures (Black and Turkey Vultures in North America) and hawks together in a single kettle. When birding in south Texas in Winter one of the best ways to find Zone-tailed Hawks is to look for kettling vultures as they make their mid-morning departures from roost sites. Roost sites are often located along rivers or other bodies of water. The land heats up quickly while the water absorbs most of the insolation rather than reflecting heat back into the atmosphere, presumably creating a significant difference in the temperatures of neighboring air masses (see illustration below).  

This graphic illustrates the interaction between warm columns of rising air (thermals) and descending masses of cooler air. (Image source: http://www.aerospaceweb.org)

If one watches long enough, kettling birds will reach the apex of the rising column and start peeling off the top of the thermal in a long gradual straight-line descent until they find another thermal, where the process is repeated. On 16 September 1993, near Danville, Hendricks County, Indiana, I watched as a southbound group of 103 Broad-winged Hawks followed the pattern shown in the graphic above. The birds streamed single-file into a thermal and formed a kettle almost directly overhead. The hawks were perhaps 200 feet up when they entered the thermal. They then spiraled upward several hundred feet before peeling off the top of the updraft single-file. They glided south about a half mile or so, caught another thermal and kettled up again. It was amazing to watch. I envisioned this process being repeated over and over again all the way to their South American wintering grounds. On many other occasions I've observed transient flocks of American White Pelicans and migrant Sandhill Cranes move along from thermal to thermal.

The airborne grace of soaring American White Pelicans belies their bulk, which may approach 20 pounds. These pelicans were photographed over Othello, Adams County, Washington on 7 August 2010 (Photo by Steven Mlodinow). 

Clearly, there is a significant conservation of energy that comes from utilizing this strategy.  According to Knopf and Evans (2004), the weight of most American White Pelicans likely ranges from 5.4 to 9.0 kg (12-20 lbs). Getting that amount of mass airborne and keeping it there would require a lot more energy in the absence of thermal updrafts. Like vultures and many hawks, pelicans have comparatively long, broad wings and relatively short, broad tails. They do most of their commuting and longer flights between mid-morning and mid-afternoon when the most direct sun angles increase surface heating. It is always impressive to watch as these massive birds rise almost out of sight with almost no expenditure of effort.

Literature Cited:

Knopf, Fritz L. and Roger M. Evans. 2004. American White Pelican (Pelecanus erythrorhynchos), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online; http://bna.birds.cornell.edu/bna/species/057doi:10.2173/bna

On 28 March the first egg was laid. (Image sourced online at http://www.allaboutbirds.org/page.aspx?pid=2433.)

Just this morning, I received an e-mail from The Cornell Lab of Ornithology announcing a new Great Blue Heron nest cam (they also have a Red-tailed Hawk nest cam this season). The nest is on the property at the Lab's "Sapsucker Woods" campus. In addition to point-blank nest views, the nest cam provides an audio feed so you can hear various other birds calling and singing in the background. It should be fun trying to pick out warbler songs over the next few weeks.

The best feature of the nest cam site is a live chat stream, which allows for a fun exchange among the many folks who are watching. Questions come fast and furious as some of those watching admit to knowing very little about birds. During the 4-5 minutes that I followed the chat stream there were questions/discussions about plumes, incubation, sexing the adults, and a resident Canada Goose named "Sweetie."

The questions and answers about plumes included mention of plume hunting and how that was in part responsible for the formation of the The National Audubon Society. Some chat participants were unaware of the impacts of plume-hunting and how it inspired early bird conservation efforts.

On this day, it's cold and blustery in Ithaca, New York, so the moment-to-moment video and audio provided by the camera are a far cry from scintillating. One of the adults has been standing essentially motionless over a single egg (looks like an over-sized American Robin egg) as the wind ruffles its feathers. During the time that it took me to write this short article, the adult heron has moved just twice. First it turned to face the opposite direction, stepping on the egg briefly as it did so and then, finally, it sat down on the egg.

Finally, after many minutes the adult heron sat down on what had to be one very chilly egg. (Image captured online at http://www.allaboutbirds.org/page.aspx?pid=2433)

Despite the general lack of activity in the nest, the chat remains lively. In addition to feeding our voyeuristic nature, this nest cam fosters a wonderful opportunity for birders and non-birders to share and learn together in real time. Over the next several weeks I will likely be one of many who pop in occasionally to see what the birds are doing and sample what everyone is talking about. I can't wait to see the baby herons and hear their incessant "walla walla walla" vocalizations.

This map shows the April pattern of distribution of Black-throated Gray Warbler eBird reports for all years 1900-2011. (Image sourced online at  http://ebird.org)

On 9 March 2012 a Black-throated Gray Warbler was reported from Bandon State Natural Area on Oregon's south coast. There was modest debate on the local listserv over whether this bird was overwintering or, perhaps, an early northbound migrant. I was in the overwintering camp.

Just a week earlier, I was melding together the Oregon and Washington sections of the Fall 2011 report for North American Birds when I noted that my co-editor, Brad Waggoner, had characterized a November 1st Black-throated Gray at Vancouver, Washington as being "a month tardy."

It's important to note that Brad lives on Puget Sound about 180 miles north of where this bird was seen. Vancouver is just across the Columbia River from Portland, where I live. Since low numbers of Black-throated Grays are still passing through Oregon during the first two weeks of October, I would have described this bird as being about two weeks late.

These discussions, which involved highly experienced birders, demonstrate that each of us has unique notions about the migratory timing of Black-throated Gray Warblers. These perceptions are shaped by where we live and our own set of experiences with this species. 

My experiences with migrant Black-throated Gray Warblers have come primarily from the Willamette Valley in western Oregon. In the southern end of the valley–where I lived from 1984-86 and from 1998-2010–the first northbound Black-throated Grays would appear in during the first few days of April. Skinner Butte in downtown Eugene would almost always yield the earliest sightings for the valley and often for the entire state, in part because it gets daily coverage from late March through May. The first reports Portland (110 miles to the north) would come several days later, usually not until about the 10th of April or later. The fall migration of warblers through Oregon is diffuse and there are rarely weather systems that create noticeable fallouts. Along the outer, coast the southbound "passage" of warblers borders on undetectable. In the interior lowlands, focused efforts along riparian corridors, especially those bordering north-south running waterways will produced small mixed flocks of migrants that usually include a few Black-throated Grays until about 15 October.

Since my ideas about the migratory timing of this species were not the same as other equally experienced observers, I decided to compare my perceptions about Black-throated Grays with the data that one can easily mine from the eBird database. Here's what I found.

January eBird reports of Black-throated Gray Warbler 1900-2012. (Image sourced online at  http://ebird.org)

February eBird reports of Black-throated Gray Warbler 1900-2012. (Image sourced online at  http://ebird.org)

March eBird reports of Black-throated Gray Warbler 1900-2012. (Image sourced online at  http://ebird.org)

At a glance, the three maps above, which show the distribution Black-throated Gray Warbler reports for January, February, and March are remarkably similar. Compare these to the April map at the top of the article, which shows a major influx of Black-throated Grays all along the Pacific Coast during that month.

We can also look at the year-long bar graphs, which offer better resolution of what happens within each month. The bar and line graphs below provide a closer look at the migration timing in Northern California, Oregon, and Washington.

This graphic shows the annual bar and line graphs for just those counties in the northern one-third of California, basically drawing line from Placer on the eastern border (at the elbow of California) west to Mendocino. It illustrates that Black-throated Gray Warblers are reported almost year round, with the spike of spring migrants starting just before 1 April and peaking during the last two weeks of April. (Image sourced online at  http://ebird.org)

The annual bar and line graphs for Oregon shows that Black-throated Gray Warblers are essentially absent from the state November-March. The spike of spring migrants starts right about 1 April and peaks about the first week of May. Note that the number of fall reports remains pretty high into October, with a sharp drop-off after the second week of October. (Image sourced online at  http://ebird.org)

The line graph for Washington is nearly identical in shape to that of Oregon, but it is more compressed. The spring spike in Washington doesn't really kick in until about 15 April, but still peaks right at beginning of May. Note that in Fall the sharp drop-off comes about 1-2 weeks earlier than it does in Oregon. (Image sourced online at  http://ebird.org)

One of things that is exposed in looking at these graphic representations is that the spring migration of Black-throated Gray Warbler is incremental in nature. When we think about migration, we are captivated by those species that make long trans-oceanic crossings and non-stop flights that extend for multiple days. By contrast, the migrations of many passerines involve a more protracted series of short hops. In looking at the bar graphs above, it is apparent that the first influx of northbound Black-throated Gray Warblers Northern California about two weeks or more before they reach Washington. The southern end of the area represented by this set of graphs is approximately 500 miles to the south of the southern border of Washington. If we break down this distance as it relates to the number of days (about 15) between arrival dates at each end of this 500-mile divide, it translates to about 30-40 miles of northbound flight per day. Surely, this is an over-simplification, but the data does suggest that Black-throated Grays are either coming north in a series of short flights or making longer hops and then stopping to rest and feed for multiple days along the way.

In the end, this exploration confirmed my thoughts about what constitutes "early" and "late" in Oregon. More importantly, it demonstrated that the perceptions of my colleagues are equally valid given the experiences one would have living where they live.