After a week of pretty good success on the windows, today was cold with light snow, and the bird feeder was very active. I realized last week that one of many variables I need to consider when I record bird-strikes-per-hour is bird activity, but I haven't tried to record that yet other than excluding long periods when no birds were present. Obviously, if there are few birds visiting, there are fewer chances for collisions. At the other extreme, like today, when the feeder gets crowded there seem to be birds in the air all the time - hovering and jostling for a perch. In these conditions there are many more chances for collisions.
So today I started observing and recorded 6 window strikes in 1 hour 40 minutes - about one every 16 minutes. Thinking that this was happening because of the faded highlighter I reapplied the lines, and in the next 3 hours 30 minutes there were 8 strikes, or about one every 33 minutes - about half as frequent but still pretty distressing and not really a significant improvement. However (one can always find a hopeful angle) five times during that period birds flew in and landed scratching at the windowsill. Maybe these were birds that would have crashed into the glass, but recognized the danger at the last second and fluttered harmlessly down to the windowsill.
A physics lesson
Some of my assumptions about UV light and what birds perceive were wrong, and I've been educated by some posts on the NikonGear UV photography forum, and some follow-up research. What we see under the black light is fluorescence. Certain compounds are "excited" as they absorb UV energy and then - when electrons return to their normal state - they fluoresce: releasing energy as light in the visible range. So this is why day-glo colors appear intensely bright in sunlight - UV energy from the sun causes fluorescence, and the colors actually glow.
Therefore my experiment with the black light has very little to do with UV other than as the light source. The black light is good for finding fluorescent things, and fluorescence begins with UV absorption, but many things absorb or reflect UV without fluorescing and we simply can't see it. A search for UV-visible substances to mark windows would require much more specialized equipment. You can see some really cool examples of UV photography here.
The fluorescent highlighter should still be visible to birds, because the fluorescent ink will simultaneously absorb UV and release visible light. But the visible fluorescence in daylight may be about as obvious to the birds as it is to us (i.e. not very). So if the highlighter works it may work largely because it absorbs UV, or maybe the combination of absorbing UV and releasing visible light is more obvious to the birds. Either way, that process requires a UV light source, and another issue that I think might explain today's poor results (still searching for that hopeful angle) is that UV wavelengths are blocked by clouds. Apparently "thin" clouds allow about 60-80% of UVA (the longest wavelengths of UV and the range that birds can see) to pass through, but thicker clouds block most UVA. So with little or no UV, such as during today's snowstorm, the highlighter marks would neither absorb UV nor release fluorescence, and the birds' vision would rely on the same visible spectrum that we see. If this is true then all efforts to use UV-related markings on glass will only have limited effectiveness (but don't take my word for it). So I'll have to note weather conditions in the future as I record window strikes to see if the highlighter is more effective on sunny days.
By the way, window glass blocks some shorter UV wavelengths, but at least 90% of UVA apparently does pass through ordinary glass.
So what does this mean?
Well, clearly the highlighter is not the "magic bullet" that everyone is hoping for. I'm still anxious to hear from others who have tried it. So far I have two responses indicating that it works, and I'd like to hear more, but if anyone has tried it without success I'm especially interested to hear about that.
If it does work, it will presumably work best in sunlight, and worst in low light or on overcast days, and unfortunately bird feeders are generally most active at those times.
As I said previously, we can keep trying to find ways to make the reflection in the glass look unattractive to the birds, but there will always be things (like hawks) that look even less attractive and cause birds to try to escape through the window. To truly prevent window strikes will require a barrier such as the BirdScreen.
Tuesday, November 20, 2007
Thursday, November 15, 2007
A Potential Simple Method for "Bird-Proofing" Windows
Update 16 November - There are a couple of points I think I should clarify. First - and I guess this may be clear already - I'm still not convinced this will work, or how well it will work, and it will probably work in some situations better than others, and never be 100% effective since the hard glass surface is still exposed. If you try it please let me know how it works, good or bad.
I should have mentioned the Bird Screen, which apparently does offer nearly 100% protection, and might be the best solution for a lot of situations. I suggest the potential of the highlighter as an easy, cheap, and possibly effective solution, but if you're really interested you should check out the Bird Screen as a proven, reliable method of preventing window strikes.
Update 17 November - It's definitely not 100% effective; I've had two bird strikes in the last few hours, but that's still only two in a total of about 16 hours, which at the previous rate would have resulted in about 20 strikes.
Update 19 November - A potentially serious flaw in the "highlighter method" of preventing window strikes has come up - the UV color fades quickly.
Here (left) is a window just 20 minutes after applying the highlighter and (right) another window after the highlighter has been on for six days. (Both photographed at night with 1 sec exposure, same distance and position of black light). The six-day-old highlighter is not as bright and obvious as the fresh ink, especially to the right in the less intense UV light, so effectiveness for preventing bird strikes presumably decreases. In order to maintain the effectiveness one would have to reapply the highlighter frequently, maybe weekly.
I'm investigating some sunlight-stable UV pigment, but it's said to be less bright, and it's much more expensive and can't be delivered by pen. More on that, hopefully, later.
In the meantime, if you need immediate bird collision prevention try the Wisconsin Humane Society online store.
I live in a house with lots of windows, and I like to keep lots of bird feeders. This is good for me as a birder, but often bad for the birds. Over the years I have tried various methods of making the windows either more visible or less harmful, but sometimes it just doesn't help. Birds fly very fast and at times (for example, when startled by a predator) will try to fly through things they would normally avoid. Occasionally, Cooper's and Red-tailed hawks seem to learn that they can pop around the corner of the house, cause a panic at the bird feeder, and then have easy pickings from under the window.
I found lots of helpful info on the web. Groups like FLAP have good suggestions about how to minimize the danger of window strikes here, and New York City Audubon has a detailed guide to Bird-safe building. Some of that worked for me, but some of it was either impractical or unsatisfactory for my situation. For several years I had pretty good success with simple lengths of white string hanging in front of the worst windows. This cut down on collisions, but did not eliminate them, and the string was unsightly and distracting, tricky to install, and required some tedious maintenance. I wanted a better solution.
Methods: In the darkened kitchen with a black light and piece of plexiglass, my kids and I tested various household products to see what, if anything, might meet the twin requirements of being visible to birds and invisible to humans.
Results: Various juices and cleaning supplies all proved to be non-UV-reflective: Pledge, Simple-Green, Windex, Rain-X, Dawn, Orange Juice, Apples, Shampoo, Conditioner,... all no.
Olive oil, yes! Drops of it look like red curry sauce under the black light, but once it's spread thin the color is so faint it would presumably not be obvious to birds (plus it's messy and hard to see through).
Thinking beyond "fluids" we wondered about dry-erase markers, but no, they don't glow under the black light either.
Then I noticed the brilliant orange light from a supermarket price tag reflecting the UV. I thought of fluorescent colors (duh) and wondered about a thin wash of diluted day-glo paint, then I thought of highlighters. My son found one in the desk drawer, and... Bingo! Under the black light we could draw a pattern of brilliant yellow lines on the plexiglass, but under normal light the lines were almost invisible. Now we needed to test it on an actual window with real birds....
Comments:
Markings inside vs outside the glass: The first test was done with highlighter drawn on the outside of the window. That seems to work very well to deter birds but the ink I used washes right off with water. I tested the highlighter on the inside of another window and the markings appear to be equally visible from the outside. So I assume that marking the inside - where the glass is generally easier to reach and the marks will be protected from weather - would be just as effective at stopping bird collisions. Testing that now, and so far so good.
Grid size and pattern: In this first trial I've drawn a rough grid with squares about 2.5 to 3" across. I'll try to test some other designs to see if less marking or different designs give the same benefit. You could be really creative and draw architectural patterns or write 'secret' messages on the glass, as long as you don't leave big parts of the window unmarked. From other research it seems that the "openings" should be no larger than 4 inches high by 2 inches wide, so maybe my grid is about right.
Other inks: It would also be interesting to test other colors of highlighters or other kinds of fluorescent ink or paint. I notice that there are commercially available "invisible" fluorescent inks, the kind that are used for admission stamps at concerts, etc. Those could be even better than the highlighter, being clear in normal light, and there's probably a formulation that would be water-resistant for outdoor use. I'll try to check that out too. But there's almost no disadvantage to the highlighter, and it's so simple and readily available.
Disclaimers: These are preliminary results, and it's possible that further trials won't be quite as successful, but these early results are so promising (and it's so easy and low-risk) I wanted to get this information out there so that other people could try it and hopefully save some birds. The highlighter that I used seems to wash off easily with water, and does not stain the window frames here, but I make no warranty against staining or other damage to windows or adjacent materials that might be caused by following the above instructions.
Let me know how it works for you.
I should have mentioned the Bird Screen, which apparently does offer nearly 100% protection, and might be the best solution for a lot of situations. I suggest the potential of the highlighter as an easy, cheap, and possibly effective solution, but if you're really interested you should check out the Bird Screen as a proven, reliable method of preventing window strikes.
Update 17 November - It's definitely not 100% effective; I've had two bird strikes in the last few hours, but that's still only two in a total of about 16 hours, which at the previous rate would have resulted in about 20 strikes.
Update 19 November - A potentially serious flaw in the "highlighter method" of preventing window strikes has come up - the UV color fades quickly.
Here (left) is a window just 20 minutes after applying the highlighter and (right) another window after the highlighter has been on for six days. (Both photographed at night with 1 sec exposure, same distance and position of black light). The six-day-old highlighter is not as bright and obvious as the fresh ink, especially to the right in the less intense UV light, so effectiveness for preventing bird strikes presumably decreases. In order to maintain the effectiveness one would have to reapply the highlighter frequently, maybe weekly.I'm investigating some sunlight-stable UV pigment, but it's said to be less bright, and it's much more expensive and can't be delivered by pen. More on that, hopefully, later.
In the meantime, if you need immediate bird collision prevention try the Wisconsin Humane Society online store.
________________________________________
Estimates of the number of birds killed in window collisions each year in North America run as high as nearly a billion birds. It's the biggest source of direct human-caused mortality in wild birds. But a simple means to prevent birds from hitting windows on your house or office could be in your desk drawer, or at least as close as your local office supply store, costing only a couple of dollars and a few minutes of your time. This needs further testing, but it appears that an ordinary yellow highlighter can be used to draw lines on the window, and those lines may be visible to birds, warning them away from the window, but are almost invisible to people.________________________________________
Windows like the one below can be deadly for birds. This is my window with a bird feeder I recently set up. Placing the feeder within one meter of the window prevents the birds from picking up much speed before they hit it, so any bird collisions are supposedly non-lethal, but this reflection was so deceptive that an average of nearly two birds every hour were hitting it in early November - incredible and distressing! I left the feeder empty after a couple of days but kept thinking it would make a good opportunity to study bird-window 'interactions'.
I live in a house with lots of windows, and I like to keep lots of bird feeders. This is good for me as a birder, but often bad for the birds. Over the years I have tried various methods of making the windows either more visible or less harmful, but sometimes it just doesn't help. Birds fly very fast and at times (for example, when startled by a predator) will try to fly through things they would normally avoid. Occasionally, Cooper's and Red-tailed hawks seem to learn that they can pop around the corner of the house, cause a panic at the bird feeder, and then have easy pickings from under the window.
I found lots of helpful info on the web. Groups like FLAP have good suggestions about how to minimize the danger of window strikes here, and New York City Audubon has a detailed guide to Bird-safe building. Some of that worked for me, but some of it was either impractical or unsatisfactory for my situation. For several years I had pretty good success with simple lengths of white string hanging in front of the worst windows. This cut down on collisions, but did not eliminate them, and the string was unsightly and distracting, tricky to install, and required some tedious maintenance. I wanted a better solution.
Experiment 12 Nov 2007
Hypothesis: Since birds can see ultraviolet wavelengths of light and we can't, it must be possible to add a UV-reflective coating to windows that would make them more or less opaque to birds but still transparent to humans.Methods: In the darkened kitchen with a black light and piece of plexiglass, my kids and I tested various household products to see what, if anything, might meet the twin requirements of being visible to birds and invisible to humans.
Results: Various juices and cleaning supplies all proved to be non-UV-reflective: Pledge, Simple-Green, Windex, Rain-X, Dawn, Orange Juice, Apples, Shampoo, Conditioner,... all no.
Olive oil, yes! Drops of it look like red curry sauce under the black light, but once it's spread thin the color is so faint it would presumably not be obvious to birds (plus it's messy and hard to see through).
Thinking beyond "fluids" we wondered about dry-erase markers, but no, they don't glow under the black light either.
Then I noticed the brilliant orange light from a supermarket price tag reflecting the UV. I thought of fluorescent colors (duh) and wondered about a thin wash of diluted day-glo paint, then I thought of highlighters. My son found one in the desk drawer, and... Bingo! Under the black light we could draw a pattern of brilliant yellow lines on the plexiglass, but under normal light the lines were almost invisible. Now we needed to test it on an actual window with real birds....
13 November 2007
Here (above) is the window and new bird feeder that had been combining for an average of nearly 2 bird strikes per hour until I left it empty. I've already drawn on the window with a highlighter, but the lines are invisible in this photo. Below is the same window illuminated with the black light to show the grid of highlighter lines (window shades inside are glowing blue). Presumably the birds see something like this. I filled the bird feeder and went inside to observe.
14-15 November results:
As I write this on 15 November, I have spent 11 hours monitoring steady bird activity at the feeder. After nine hours with NO window-collisions, a light rain started. The highlighter markings were getting washed away and a goldfinch hit the window. So I wiped off the outside of the glass and drew new lines on the inside. That's working so far, with no strikes in about two more hours of bird activity. Not enough data to really say anything conclusive, but testing continues....Comments:
Markings inside vs outside the glass: The first test was done with highlighter drawn on the outside of the window. That seems to work very well to deter birds but the ink I used washes right off with water. I tested the highlighter on the inside of another window and the markings appear to be equally visible from the outside. So I assume that marking the inside - where the glass is generally easier to reach and the marks will be protected from weather - would be just as effective at stopping bird collisions. Testing that now, and so far so good.
Grid size and pattern: In this first trial I've drawn a rough grid with squares about 2.5 to 3" across. I'll try to test some other designs to see if less marking or different designs give the same benefit. You could be really creative and draw architectural patterns or write 'secret' messages on the glass, as long as you don't leave big parts of the window unmarked. From other research it seems that the "openings" should be no larger than 4 inches high by 2 inches wide, so maybe my grid is about right.
Other inks: It would also be interesting to test other colors of highlighters or other kinds of fluorescent ink or paint. I notice that there are commercially available "invisible" fluorescent inks, the kind that are used for admission stamps at concerts, etc. Those could be even better than the highlighter, being clear in normal light, and there's probably a formulation that would be water-resistant for outdoor use. I'll try to check that out too. But there's almost no disadvantage to the highlighter, and it's so simple and readily available.
Disclaimers: These are preliminary results, and it's possible that further trials won't be quite as successful, but these early results are so promising (and it's so easy and low-risk) I wanted to get this information out there so that other people could try it and hopefully save some birds. The highlighter that I used seems to wash off easily with water, and does not stain the window frames here, but I make no warranty against staining or other damage to windows or adjacent materials that might be caused by following the above instructions.
Let me know how it works for you.
My new Birder's World column
I'm pleased to join my friends Kenn Kaufmann, Pete Dunne and others as a contributor to Birder's World magazine, and editor Chuck Hagner promises that I will "reveal the real secrets" of bird identification. I don't know if everyone's really ready for that, but each of my columns will be a short illustrated discussion of bird identification challenges from a more general perspective. The first one is about using flocking habits as a field mark, the second one - due out in February - will be about wingbars. Currently this is available only in the paper magazine, not on the web, so I can't offer a link to it yet. But I'll be interested in any discussion, comments, or suggestions. You can leave those here, or on the Birder's World forum, or just send me an email.
Wednesday, November 14, 2007
More rare bird news and a correction
The latest Siberian highlight was California's first Eurasian Kestrel banded in Marin Co. CA on 23 October 2007 but not seen again (photos here). About 10 North American Records.
Otherwise, in addition to what I listed previously, a Dusky Warbler and four Eastern Yellow Wagtails in CA, and a Rustic Bunting in BC are the only Siberian birds that I've heard of that seemed to find their way down from Alaska. A little above average, perhaps, but my earlier excitement about watching for Eye-browed thrushes, etc hasn't really panned out. Although there's still time....
A well-seen adult Ross's Gull November 10-11 at Vanderhoof, north-central BC ( the 2nd for BC, with a very late and rare-inland Arctic Tern). There was an earlier report of an adult Ross's Gull in September in eastern Colorado! So this is another species for southern birders to keep in mind.
Probably unrelated to the Ross's Gull, but quite a coincidence in timing, an Ivory Gull was reported on 11 November just inland from Vancouver, BC.
The Green-breasted Mango continues in Georgia, and the Wisconsin bird now survives in captivity. See my previous post about mangos for more.
Correction - I said in a previous post that a Tristram's Storm-Petrel off southern California in July this year was the first ever reported in North America, but there are photos of an apparent Tristram's Storm-Petrel trapped on the Farallons, off San Francisco, CA on 22 Apr 2006 (photo here) and currently under review by the California Bird Records Committee.
Otherwise, in addition to what I listed previously, a Dusky Warbler and four Eastern Yellow Wagtails in CA, and a Rustic Bunting in BC are the only Siberian birds that I've heard of that seemed to find their way down from Alaska. A little above average, perhaps, but my earlier excitement about watching for Eye-browed thrushes, etc hasn't really panned out. Although there's still time....
A well-seen adult Ross's Gull November 10-11 at Vanderhoof, north-central BC ( the 2nd for BC, with a very late and rare-inland Arctic Tern). There was an earlier report of an adult Ross's Gull in September in eastern Colorado! So this is another species for southern birders to keep in mind.
Probably unrelated to the Ross's Gull, but quite a coincidence in timing, an Ivory Gull was reported on 11 November just inland from Vancouver, BC.
The Green-breasted Mango continues in Georgia, and the Wisconsin bird now survives in captivity. See my previous post about mangos for more.
Correction - I said in a previous post that a Tristram's Storm-Petrel off southern California in July this year was the first ever reported in North America, but there are photos of an apparent Tristram's Storm-Petrel trapped on the Farallons, off San Francisco, CA on 22 Apr 2006 (photo here) and currently under review by the California Bird Records Committee.
Paintings on exhibit
Six original plates from the Sibley Guide to Birds will be exhibited at the Cahoon Museum of American Art in Cotuit, MA now through December 31, 2007 as part of their show "In Fine Feather: Excellence in Contemporary Bird Carving and Avian Art"
Monday, November 5, 2007
"Great White" Heron - not just a color morph
Great White Heron Ardea herodias occidentalis
updated 13 Nov 2007, thanks to all those who have commented publicly and privately. I've backed off a bit from my criticism of the TBRC decision, the more I learn the less clear-cut this seems, although I still think it's at least a good subspecies. Shaibal Mitra sent me a copy of a paper he and John Fritz published in the Kingbird a few years ago, which reaches the same conclusion that Great White Heron is a distinctive subspecies, but points to my book as one of the sources unfortunately labeling the Great White Heron "simply a color morph". Oops, I guess it does. That's not quite what I meant!
This post is about the debate over whether the "Great White" population of Great Blue Heron is "simply a color morph" (TBRC 2006, Butler 1992), a subspecies (Mayr 1956, Meyerriecks 1957), or a full species (McGuire 2002). A few days ago in the first draft of this post it seemed clear-cut, now with additional information from many sources it seems less so. Much of what I've written here has been said before by Mitra and Fritz (2002) and by Tony Gallucci in 2004 on TexBirds here.
Butler (1992) dismisses the white population with almost no discussion, and unfortunately I labeled this the "white morph" in my field guide (Sibley 2000) even though I recognized that it was more than just a color morph. The Texas Bird Records Committee (TBRC) decided in 2006 to drop "Great White" Heron from the state review list, saying that it seemed to be just a color morph and not a distinct subspecies. This decision was apparently prompted by two records of white nestlings in Great Blue nests in Texas - an old photo from Galveston County (presumably from McHenry and Dyes, 1983) and an unpublished 2006 photo from Aransas County showing a white and dark nestling together in a nest tended by two dark adults!
I am fascinated by these records of white nestlings in Great Blue nests in Texas, but I disagree with the TBRC decision. I have always considered Great White Herons distinctive and I can't accept that this is "simply a color morph". Mayr (1956) did some actual research to confirm that "The Great White Herons are not merely albino specimens of Ward's [Great Blue] Heron, but form a mangrove population in the Key West area which differs from Ward's Heron on the mainland not only by the white coloration, but also by shorter plumes and an average larger bill." (some nice Great White photos are here).
Mayr (1956) and Meyerriecks (1957) studied the white and dark herons of south Florida and found mixed pairs, no clear differences in behavior, and subtle differences in morphology. Zachow (1983) found that measurements of Great Whites are significantly larger than Great Blues from the Florida peninsula, which in turn are significantly larger than Great Blues from farther north. Mayr and Meyerriecks both argue that the "Great White" Heron is not a separate species, but they never question the fact that it is a valid subspecies.
Looking at the measurements from a field ID perspective, however, suggests that they may not be as diagnostic as has been assumed. The following graph shows Mayr's bill/wing data in graphic form. Obviously there is lots of overlap between Great White and Ward's Great Blue from the Florida peninsula, even though there is enough difference for most birders to take away the impression that the Great White is a "much larger-billed" bird.
McGuire (2002) in a more detailed study actually does suggest that "The great white heron appears to be a good biological species". McGuire found that although some mixed dark-white pairs occur in the Florida Keys, there are fewer than would be expected by chance. DNA analysis suggests that the herons of Florida Bay and the Keys are isolated to some extent from the Great Blue Herons of the Florida Peninsula. [McGuire suggests that one possible isolating mechanism is time of breeding, with the peak of nesting in the Keys from October to April, and the nesting season on the mainland beginning in Feb-Mar].
The map below shows the breeding range as recorded in the Florida Breeding Bird Atlas. I added the green color to show the Great White records. Note that the green dot far north on the Gulf Coast represents a solitary Great White among Great Blues. The red dot at the upper end of Key Largo might represent one or more nests of true Great Blue Herons or an intermediate "Wurdemann's-type". Interesting to note on this map is the small but obvious gap between breeding Great Blues and Great Whites.
One of the most interesting facets of this is that the dark birds in the keys are intermediate in plumage and known as "Wurdemann's Heron". These are found only in the Florida Keys with Great White Herons, and according to McGuire, Mayr, and Meyerriecks all of the dark birds breeding in that area are typical of "Wurdemann's" rather than the mainland subspecies of Great Blue Heron. So when researchers in the Keys report dark-white pairs and also dark-dark pairs with some white offspring, the dark birds are "Wurdemann's" and not typical dark mainland Great Blues. Among nesting colonies in Florida Bay and the Keys, white birds (Great White) outnumber blue (Wurdemann's) about 4:1 (McGuire 2002).
McGuire shows that "dark" birds in the keys are slightly smaller than white ones, but not significantly, and emphasizes that color of dark birds varies continuously from Great-Blue-like but (always?) with more white on the head (photo here) to mostly white with pale gray wings and back, so that it is not possible to classify the non-white birds into subgroups. In size measurements and in DNA the dark birds of the Keys are slightly but not significantly different from Great Whites, but they are significantly different from the mainland Great Blues (McGuire 2002). McGuire takes the color and size difference as evidence that "Wurdemann's" are intergrades, but it would be helpful to know if measurements are correlated with size. That is, are the birds with the most Great-Blue-like plumage in the keys also the smallest? Assortative mating supports the intergrade hypothesis.
I may not go so far as to endorse McGuire's view that the Great White Heron is a separate species, but there does seem to be plenty of evidence that this population is distinctive and at least somewhat isolated. A vagrant outside of the normal range should be identifiable with a high degree of certainty, and Great White and "Wurdemann's" can be reliably distinguished from albino Great Blue Herons.
Birders in Texas and elsewhere should be encouraged to watch for this distinctive subspecies, and the Texas Bird Records committee should put it back on the state review list. That of course reopens the question of what to make of the white nestlings photographed in Texas. They should not be accepted as "Great White" Herons just because they're white. Similarly, their mere existence does not negate the distinctiveness of true Great Whites from the Florida Keys. The true status of those white nestlings will have to remain a mystery for now, awaiting further study.
Questions:
It is interesting that white nestlings have been found twice in Texas but full-grown white birds have been seen very rarely there, and only as brief visitors. We still don't know what these white nestlings look like as adults.
Have white nestlings been found elsewhere in Great Blue nests?
White morph Great Blues are also said to occur in Cuba, Jamaica, the Yucatan, and off Venezuela but are apparently smaller than the Keys birds and scarce (not a majority). What do these birds actually look like and what is their status?
Just how big and short-plumed are Great Whites? I didn't do a thorough search but couldn't find a good set of published measurements. I found no published measurements of head plumes, only the repeated assertion that Great White has shorter plumes. So I can't confirm the identification features, only that I have the impression that Great Whites are distinctive, and should be more distinctive the farther one gets from Florida (as the size of Great Blues decreases clinally).
Does it make more sense to consider the variable "Wurdemann's" Heron as an intergrade swarm, or simply as the dark morph of Great White Heron - making Great White a dimorphic, large, short-plumed subspecies of Great Blue Heron?
--------------------------------------------
Distribution:
There are isolated records of Great White Heron nesting north to the Tampa area (Bancroft, 1969; Florida Breeding Bird Atlas map), and nonbreeders wander regularly to northern Florida (not mapped) and less often but still regularly to coastal Georgia.
Aberrant "Wurdemann's-like" herons:
A bird photographed in Washington County, PA in 2004 and present every year since then is clearly not a "Wurdemann's" Heron, and likely a Great Blue x Great Egret hybrid.
Another odd bird photographed in MA in Sep 2005 was clearly a leucistic Great Blue based on size and plumage details, and not a "Wurdemann's". (Thanks to M. Rines for the photo)
--------------------------------------------
References:
Bancroft, G. 1969. A great white heron in great blue nesting colony. Auk
86:141–142. pdf here
Butler, Robert W.. 1992 . Great Blue Heron (Ardea herodias), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online
Mayr, E. 1956. Is the great white heron a good species? Auk 73:71–77. pdf here
McGuire, H. L. 2002. Taxonomic status of the great white heron (Ardea herodias occidentalis): an analysis of behavioral, genetic, and morphometric evidence. Final Report. Florida Fish and Wildlife Conservation Commission, Tallahassee, Florida, USA. pdf here
McHenry, E. N., and J. C. Dyes. 1983. First record of juvenal “white-phase”
great blue heron in Texas. American Birds 37:119.
Meyerriecks, A. J. 1957. Field observations pertaining to the systematic
status of the great white heron in the Florida Keys. Auk 74:469–478. pdf here
Mitra, S. S. and Fritz, J. (2002) Two Great White Herons (Ardea (herodias) occidentalis) in NewYork,Sept-Nov 2001.Kingbird 52 (1):27-34.
Sibley, D. A. 2000. The Sibley Guide to Birds. Chanticleer Press.
Texas Bird Records Committee. 2006. Minutes of Annual Meeting.
Zachow, K. F. 1983. The great blue and great white heron (Aves: Ciconiiformes: Ardeidae): a multivariate morphometric analysis of skeletons. Thesis, University of Miami, Coral Gables, Florida, USA.
updated 13 Nov 2007, thanks to all those who have commented publicly and privately. I've backed off a bit from my criticism of the TBRC decision, the more I learn the less clear-cut this seems, although I still think it's at least a good subspecies. Shaibal Mitra sent me a copy of a paper he and John Fritz published in the Kingbird a few years ago, which reaches the same conclusion that Great White Heron is a distinctive subspecies, but points to my book as one of the sources unfortunately labeling the Great White Heron "simply a color morph". Oops, I guess it does. That's not quite what I meant!
This post is about the debate over whether the "Great White" population of Great Blue Heron is "simply a color morph" (TBRC 2006, Butler 1992), a subspecies (Mayr 1956, Meyerriecks 1957), or a full species (McGuire 2002). A few days ago in the first draft of this post it seemed clear-cut, now with additional information from many sources it seems less so. Much of what I've written here has been said before by Mitra and Fritz (2002) and by Tony Gallucci in 2004 on TexBirds here.
Butler (1992) dismisses the white population with almost no discussion, and unfortunately I labeled this the "white morph" in my field guide (Sibley 2000) even though I recognized that it was more than just a color morph. The Texas Bird Records Committee (TBRC) decided in 2006 to drop "Great White" Heron from the state review list, saying that it seemed to be just a color morph and not a distinct subspecies. This decision was apparently prompted by two records of white nestlings in Great Blue nests in Texas - an old photo from Galveston County (presumably from McHenry and Dyes, 1983) and an unpublished 2006 photo from Aransas County showing a white and dark nestling together in a nest tended by two dark adults!
I am fascinated by these records of white nestlings in Great Blue nests in Texas, but I disagree with the TBRC decision. I have always considered Great White Herons distinctive and I can't accept that this is "simply a color morph". Mayr (1956) did some actual research to confirm that "The Great White Herons are not merely albino specimens of Ward's [Great Blue] Heron, but form a mangrove population in the Key West area which differs from Ward's Heron on the mainland not only by the white coloration, but also by shorter plumes and an average larger bill." (some nice Great White photos are here).
Mayr (1956) and Meyerriecks (1957) studied the white and dark herons of south Florida and found mixed pairs, no clear differences in behavior, and subtle differences in morphology. Zachow (1983) found that measurements of Great Whites are significantly larger than Great Blues from the Florida peninsula, which in turn are significantly larger than Great Blues from farther north. Mayr and Meyerriecks both argue that the "Great White" Heron is not a separate species, but they never question the fact that it is a valid subspecies.
Looking at the measurements from a field ID perspective, however, suggests that they may not be as diagnostic as has been assumed. The following graph shows Mayr's bill/wing data in graphic form. Obviously there is lots of overlap between Great White and Ward's Great Blue from the Florida peninsula, even though there is enough difference for most birders to take away the impression that the Great White is a "much larger-billed" bird.
McGuire (2002) in a more detailed study actually does suggest that "The great white heron appears to be a good biological species". McGuire found that although some mixed dark-white pairs occur in the Florida Keys, there are fewer than would be expected by chance. DNA analysis suggests that the herons of Florida Bay and the Keys are isolated to some extent from the Great Blue Herons of the Florida Peninsula. [McGuire suggests that one possible isolating mechanism is time of breeding, with the peak of nesting in the Keys from October to April, and the nesting season on the mainland beginning in Feb-Mar].The map below shows the breeding range as recorded in the Florida Breeding Bird Atlas. I added the green color to show the Great White records. Note that the green dot far north on the Gulf Coast represents a solitary Great White among Great Blues. The red dot at the upper end of Key Largo might represent one or more nests of true Great Blue Herons or an intermediate "Wurdemann's-type". Interesting to note on this map is the small but obvious gap between breeding Great Blues and Great Whites.
One of the most interesting facets of this is that the dark birds in the keys are intermediate in plumage and known as "Wurdemann's Heron". These are found only in the Florida Keys with Great White Herons, and according to McGuire, Mayr, and Meyerriecks all of the dark birds breeding in that area are typical of "Wurdemann's" rather than the mainland subspecies of Great Blue Heron. So when researchers in the Keys report dark-white pairs and also dark-dark pairs with some white offspring, the dark birds are "Wurdemann's" and not typical dark mainland Great Blues. Among nesting colonies in Florida Bay and the Keys, white birds (Great White) outnumber blue (Wurdemann's) about 4:1 (McGuire 2002).
McGuire shows that "dark" birds in the keys are slightly smaller than white ones, but not significantly, and emphasizes that color of dark birds varies continuously from Great-Blue-like but (always?) with more white on the head (photo here) to mostly white with pale gray wings and back, so that it is not possible to classify the non-white birds into subgroups. In size measurements and in DNA the dark birds of the Keys are slightly but not significantly different from Great Whites, but they are significantly different from the mainland Great Blues (McGuire 2002). McGuire takes the color and size difference as evidence that "Wurdemann's" are intergrades, but it would be helpful to know if measurements are correlated with size. That is, are the birds with the most Great-Blue-like plumage in the keys also the smallest? Assortative mating supports the intergrade hypothesis.
I may not go so far as to endorse McGuire's view that the Great White Heron is a separate species, but there does seem to be plenty of evidence that this population is distinctive and at least somewhat isolated. A vagrant outside of the normal range should be identifiable with a high degree of certainty, and Great White and "Wurdemann's" can be reliably distinguished from albino Great Blue Herons.
Birders in Texas and elsewhere should be encouraged to watch for this distinctive subspecies, and the Texas Bird Records committee should put it back on the state review list. That of course reopens the question of what to make of the white nestlings photographed in Texas. They should not be accepted as "Great White" Herons just because they're white. Similarly, their mere existence does not negate the distinctiveness of true Great Whites from the Florida Keys. The true status of those white nestlings will have to remain a mystery for now, awaiting further study.
Questions:
It is interesting that white nestlings have been found twice in Texas but full-grown white birds have been seen very rarely there, and only as brief visitors. We still don't know what these white nestlings look like as adults.
Have white nestlings been found elsewhere in Great Blue nests?
White morph Great Blues are also said to occur in Cuba, Jamaica, the Yucatan, and off Venezuela but are apparently smaller than the Keys birds and scarce (not a majority). What do these birds actually look like and what is their status?
Just how big and short-plumed are Great Whites? I didn't do a thorough search but couldn't find a good set of published measurements. I found no published measurements of head plumes, only the repeated assertion that Great White has shorter plumes. So I can't confirm the identification features, only that I have the impression that Great Whites are distinctive, and should be more distinctive the farther one gets from Florida (as the size of Great Blues decreases clinally).
Does it make more sense to consider the variable "Wurdemann's" Heron as an intergrade swarm, or simply as the dark morph of Great White Heron - making Great White a dimorphic, large, short-plumed subspecies of Great Blue Heron?
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Distribution:
There are isolated records of Great White Heron nesting north to the Tampa area (Bancroft, 1969; Florida Breeding Bird Atlas map), and nonbreeders wander regularly to northern Florida (not mapped) and less often but still regularly to coastal Georgia.
This map shows the resident range (purple), distribution of vagrant records (green), and general areas of reported occurrence outside the US (yellow). The two red dots represent multiple records at a single location, which might be more likely to represent color abnormalities of local Great Blues rather than wandering Great Whites (Pymatuning Lake, PA: three birds in 1938 and another in 1961); South Holston Lake, VA/TN: single bird in fall 1990, 1991, 1994, and 2002). But in general the distribution of records appears consistent with a south Florida origin. On the other hand, Marshall Iliff (pers. comm.) points out that this is a surprising number of vagrant records given that the total breeding population of Great White Heron is under 1000 breeding pairs.--------------------------------------------
Aberrant "Wurdemann's-like" herons:
A bird photographed in Washington County, PA in 2004 and present every year since then is clearly not a "Wurdemann's" Heron, and likely a Great Blue x Great Egret hybrid.
Another odd bird photographed in MA in Sep 2005 was clearly a leucistic Great Blue based on size and plumage details, and not a "Wurdemann's". (Thanks to M. Rines for the photo)
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References:
Bancroft, G. 1969. A great white heron in great blue nesting colony. Auk
86:141–142. pdf here
Butler, Robert W.. 1992 . Great Blue Heron (Ardea herodias), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online
Mayr, E. 1956. Is the great white heron a good species? Auk 73:71–77. pdf here
McGuire, H. L. 2002. Taxonomic status of the great white heron (Ardea herodias occidentalis): an analysis of behavioral, genetic, and morphometric evidence. Final Report. Florida Fish and Wildlife Conservation Commission, Tallahassee, Florida, USA. pdf here
McHenry, E. N., and J. C. Dyes. 1983. First record of juvenal “white-phase”
great blue heron in Texas. American Birds 37:119.
Meyerriecks, A. J. 1957. Field observations pertaining to the systematic
status of the great white heron in the Florida Keys. Auk 74:469–478. pdf here
Mitra, S. S. and Fritz, J. (2002) Two Great White Herons (Ardea (herodias) occidentalis) in NewYork,Sept-Nov 2001.Kingbird 52 (1):27-34.
Sibley, D. A. 2000. The Sibley Guide to Birds. Chanticleer Press.
Texas Bird Records Committee. 2006. Minutes of Annual Meeting.
Zachow, K. F. 1983. The great blue and great white heron (Aves: Ciconiiformes: Ardeidae): a multivariate morphometric analysis of skeletons. Thesis, University of Miami, Coral Gables, Florida, USA.
New products
Responding to some recent questions:
A couple of readers have asked about any plans for an updated version of my bird guides. This is something I'm always planning for and I look forward to compiling all the new things I'm learning into a new edition in the future. But there are no plans at present to create an updated version of the bird guide. Whether that will happen in two years, five years, or more will depend on a lot of other things.
In the meantime a French language edition of the Eastern Guide was published in Quebec by Michel Quintin in 2006. This was translated by an expert birder - Normand David (with help from Serge Gagne) - who painstakingly read and interpreted every word, so the translation actually offers a lot of editorial improvements and some Quebec-specific tidbits compared to the English language edition.
And while I'm at it, I'll mention the new calendars. Ronnie Sellers Publishing, Inc. has produced a wall calendar, a weekly appointment planner, and a page-a-day calendar for 2008.
A couple of readers have asked about any plans for an updated version of my bird guides. This is something I'm always planning for and I look forward to compiling all the new things I'm learning into a new edition in the future. But there are no plans at present to create an updated version of the bird guide. Whether that will happen in two years, five years, or more will depend on a lot of other things.
In the meantime a French language edition of the Eastern Guide was published in Quebec by Michel Quintin in 2006. This was translated by an expert birder - Normand David (with help from Serge Gagne) - who painstakingly read and interpreted every word, so the translation actually offers a lot of editorial improvements and some Quebec-specific tidbits compared to the English language edition.
And while I'm at it, I'll mention the new calendars. Ronnie Sellers Publishing, Inc. has produced a wall calendar, a weekly appointment planner, and a page-a-day calendar for 2008.
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