Post by Gord on Mar 10, 2017 21:59:57 GMT -8
As I promised in the Thayer's and Herring Gull thread, I'd do a bit on Glaucous-winged Gull and Western Gull; most notably hybridization between the two.
In our area, and down into Washington, (and probably further by now) hybrids between the two species are very common and are increasing in frequency. Hybrids can outnumber pure birds in a flock around here these days. Pure Western Gulls seem to be less common lately than they were in years past; possibly falling victim to hybridization. I think it's realistic to suggest that pure Glaucous-winged Gulls may slowly decrease as well but will be a more gradual process. Since hybrids are able to breed as well, backcrosses are very common and it can be quite subtle to notice it in some individuals depending on species (or hybrid!) the hybrid breeds with. Some hybrids can look like a Herring or Thayer's Gull and it is quite common that these hybrids are misidentified. Hybrids between Herring and Glaucous-winged Gull also occur but I've not seen (or at least identified) a lot of these individuals but I do see them annually. These combinations also can cause confusion especially if trying to make the odd-looking bird into a Thayer's Gull.
Anyway, I thought I'd show some photos progressing from a pure Western Gull down to a pure Glaucous-winged Gull and some examples of hybrids in between as they progress.
A pure Western Gull. A tad petite which makes me suspect a female. Either way, shows classic bulbous bill, clean white head, dark gray back colour and very black wing tips. When close to the observer, the orbital ring on a Western Gull is yellow. It is purple/pink on Glaucous-winged Gulls. Western Gull adults should have almost completely white heads and necks in all seasons. Too much in the way of dark streaking is almost a guarantee of Glaucous-winged Gull in the family tree. In the spring, when the gulls start to molt to breeding colours, even the Glaucous-winged who have strong streaks in the winter will turn white for breeding. Take care at this time of year with identifying Western Gulls based just on the lack of head streaks. Your bird may be a hybird in molt.
Here's an individual that may have backcrossed with a Western Gull thus appearing fairly dark backed and pretty black wing-tips. The head streaking came through strongly in the genes though! The back colour is too dark to be a Thayer's or Herring.
Similar to above. These specimens are the ones, I believe, that cause many to ID as Herring or Thayer's. Usually, the back colour is not as dark but the wingtips are quite dark. Happily, on the vast majority of these hybrids, the parentage shows through strongly as both Western and Glaucous-winged are big hefty gulls with the apple not falling far from the tree resulting in their hybrids looking likewise. The problem is when the bird as pictured below is a small female which can then be similar size to a Thayer's Gull. I don't have wing pattern photos here but a hybrid's wing pattern will be different from a Thayer's. The guy below is well on its way to losing head streaks.
At this point the wing tips are far from black which should easily eliminate any worry if this is a Herring or Thayer's.
This hybrid is mostly Glaucous-winged with just a touch of Western in it from a couple generations back. The reason it's not a pure Glaucous-winged is the wingtips are a big darker than the back. A pure Glaucous-winged should have wing tips and back the same colour.
Finally, a pure Glaucous-winged Gull as far as we can tell in the field. It wouldn't shock me, however, to learn that a DNA analysis of this bird could show some faint Western Gull in it from many generations back. This will no doubt be more common in years to come as more of these hybrids enter the gene pool.
Here are two side-by-side for comparison. Pure Glaucous-winged on the left. Note that the hybrid's back colour is a tad darker yet still the wingtips are darker still. Here's a good time to mention lighting conditions when it comes to determining colour of gulls; especially their backs. Depending on the light, back (or what is more formally called mantle) colour can vary slightly. A bright overcast day is probably the best for gulling in terms of determining back/mantle colour. The shot below is nice as it has the birds in the same light so conversation about colour is more suitable.
Hope this was useful and helpful! Questions? Please ask!
In our area, and down into Washington, (and probably further by now) hybrids between the two species are very common and are increasing in frequency. Hybrids can outnumber pure birds in a flock around here these days. Pure Western Gulls seem to be less common lately than they were in years past; possibly falling victim to hybridization. I think it's realistic to suggest that pure Glaucous-winged Gulls may slowly decrease as well but will be a more gradual process. Since hybrids are able to breed as well, backcrosses are very common and it can be quite subtle to notice it in some individuals depending on species (or hybrid!) the hybrid breeds with. Some hybrids can look like a Herring or Thayer's Gull and it is quite common that these hybrids are misidentified. Hybrids between Herring and Glaucous-winged Gull also occur but I've not seen (or at least identified) a lot of these individuals but I do see them annually. These combinations also can cause confusion especially if trying to make the odd-looking bird into a Thayer's Gull.
Anyway, I thought I'd show some photos progressing from a pure Western Gull down to a pure Glaucous-winged Gull and some examples of hybrids in between as they progress.
A pure Western Gull. A tad petite which makes me suspect a female. Either way, shows classic bulbous bill, clean white head, dark gray back colour and very black wing tips. When close to the observer, the orbital ring on a Western Gull is yellow. It is purple/pink on Glaucous-winged Gulls. Western Gull adults should have almost completely white heads and necks in all seasons. Too much in the way of dark streaking is almost a guarantee of Glaucous-winged Gull in the family tree. In the spring, when the gulls start to molt to breeding colours, even the Glaucous-winged who have strong streaks in the winter will turn white for breeding. Take care at this time of year with identifying Western Gulls based just on the lack of head streaks. Your bird may be a hybird in molt.
Here's an individual that may have backcrossed with a Western Gull thus appearing fairly dark backed and pretty black wing-tips. The head streaking came through strongly in the genes though! The back colour is too dark to be a Thayer's or Herring.
Similar to above. These specimens are the ones, I believe, that cause many to ID as Herring or Thayer's. Usually, the back colour is not as dark but the wingtips are quite dark. Happily, on the vast majority of these hybrids, the parentage shows through strongly as both Western and Glaucous-winged are big hefty gulls with the apple not falling far from the tree resulting in their hybrids looking likewise. The problem is when the bird as pictured below is a small female which can then be similar size to a Thayer's Gull. I don't have wing pattern photos here but a hybrid's wing pattern will be different from a Thayer's. The guy below is well on its way to losing head streaks.
At this point the wing tips are far from black which should easily eliminate any worry if this is a Herring or Thayer's.
This hybrid is mostly Glaucous-winged with just a touch of Western in it from a couple generations back. The reason it's not a pure Glaucous-winged is the wingtips are a big darker than the back. A pure Glaucous-winged should have wing tips and back the same colour.
Finally, a pure Glaucous-winged Gull as far as we can tell in the field. It wouldn't shock me, however, to learn that a DNA analysis of this bird could show some faint Western Gull in it from many generations back. This will no doubt be more common in years to come as more of these hybrids enter the gene pool.
Here are two side-by-side for comparison. Pure Glaucous-winged on the left. Note that the hybrid's back colour is a tad darker yet still the wingtips are darker still. Here's a good time to mention lighting conditions when it comes to determining colour of gulls; especially their backs. Depending on the light, back (or what is more formally called mantle) colour can vary slightly. A bright overcast day is probably the best for gulling in terms of determining back/mantle colour. The shot below is nice as it has the birds in the same light so conversation about colour is more suitable.
Hope this was useful and helpful! Questions? Please ask!
