Gulls, and birds in general, are known to host a tremendous amount of ectoparasites that generally have a negative effect on feathers and fitness. Preening is just one of the obvious day-to-day activities that birds engage in to combat these parasites.
Earlier this week, I noticed this young Great Black-backed repeatedly scratching its face. Face scratching has become a good reason for me to further inspect the head and face of a gull:
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| Juvenile Great Black-backed Gull. Cape May, NJ; 06 August 2012. Photo by Amar Ayyash |
A specific ectoparasite which parasitizes birds is "chewing lice". These lice usually feed on the feathers, skin and/or blood of their host. Without getting into any specific louse species, they can sometimes be detected on the surface of a gull's feathers by what look like small dark ovals concentrated together:
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| Note the dark spots on the lower cheek. This region is difficult to preen, hence the need for scratching. |
Some amounts of lice are generally tolerable and not detrimental to a bird's health unless an unusual infestation occurs. An unmanageable "load" is usually a secondary consequence of much more serious health problems. That is, a bird that's unable to control its louse problem is probably suffering from malnourishment, stress and/or disease.
The Black-legged Kittiwake pictured below spent several weeks at Montrose Harbor in Chicago early last year. It shows louse spots that were overlooked when I photographed it. Indeed, this bird was in trouble at the time (click
here for that story) and it ended up dying shortly after being picked up on 31 March 2011.
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Juvenile Black-legged Kittiwake. Chicago, IL; 31 March 2011. Photo by Amar Ayyash.
Note the dark gray spots above the back of the eye. |
I think my evaluation of this bird's health would have been better informed had I known more about these spots when I first observed it earlier that month. This is not to say the cause of death was lice, but these spots should serve as fitness indicators to the field observer, especially when found on lingering individuals that are out-of-place.
An example of an adult with lice spots is Minnesota's first recorded Slaty-backed Gull:
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| Adult Slaty-backed Gull. Grand Marais, MN; 22 July 2006. Photo courtesy of Laura Erickson. |
I recently inquired about this bird after finding its photos online and was not at all surprised to learn that it was found dead on 14 August 2006. It lingered for over 3 weeks and was unusually tame (very similar to the Black-legged Kittiwake's story). Again, these spots could have served as an obvious red flag regarding its condition. It's this message that I hope my readers take from this post.
Here are a couple more examples of gulls showing lice spots:
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Juvenile Iceland Gull. Osøyro, Norway; 01 January 2012.
Photo by Urban Ringing. |
Interestingly, all 8 of the gulls that I've personally observed with louse spots have been 1st cycle birds (the number of online photos of juveniles with lice spots also reflects my experience). A provisional conjecture of mine is that "fully" fledged juveniles have less of an advantage at combating these lice, possibly due to an absence of allopreening. Although, this doesn't answer why I haven't seen any intermediate-aged birds (2nd-3rd cycles) with lice spots - they don't regularly engage in allopreening. Perhaps having been afforded an opportunity to molt is also advantageous? Also, fully fledged juveniles may have just recently acquired their lice on the nest (not very uncommon to come into various parasites while flightless). Being in their first year of life, 1st cycle birds may lack the experience to deal with these parasites. More to come on this later.
A special thanks to Jason Weckstein, an ornithologist at Chicago's Field Museum, who provided me with engaging information on this subject. Weckstein was able to confirm for me that the spots on the GBBG and BLKI are indeed louse spots, and are very likely of the genus Saemundssonia (living specifically on the head and neck of birds).
