Mark B Bartosik
Well-known member
Hi All,
A few months ago (during spring migration) I posted many examples from Texas of what I think are hybrids between Cabot’s and Cayenne Terns that, at least some of them, are most likely breeding in North America. In those posts I included some pointers of possible recent invasion of Cayenne Terns (including intermediate forms) in recent years. I also tried to summarize what is known about distribution of this subspecies and its taxonomy. During this summer I was able to collect indirect evidence that indeed these intermediates are most likely breeding here. There were, this year during breeding season, Cayenne-type birds in Texas attending freshly fledged juveniles. But that is not a subject of this post.
Here I have a couple examples of a very interesting cases, at least to me, that I am interested to hear opinions about from others with field experience who had a chance to observe large number of Cayenne and Elegant Terns. One bird molting into winter plumage with mostly orange bill (with only areas of darker smudges in the center and small areas of black at the bill base and nostrils). In my opinion it is Cayenne-type tern although if seen in Caribbean or South America it would pass as a ‘pure’ Cayenne - based on many Cayenne photos from Caribbean many birds reported from there as Cayenne show even more black coloration on their bills. BTW Olsen and Larsson described Cayenne bill as yellow, varying from orange to straw-yellow, often with darker central areas, and in extreme cases (illustrated) black bill base and center but with broader yellow tip to bill than in Cabot’s Terns. These authors included photos of birds with varying amount of black in their bills as ’pure’ Cayenne. Again, in my opinion, at least some of these birds are intergrades but without genetic studies it would be not possible to be sure. One more trait - this bird has red soles - but this is nothing unusual.
Usually when this type of bird is found outside of its normal range three possibilities are considered: Cayenne, Elegant and Lesser Crested. A few will try to add one more possibility: Cabot’s mutant. I think Lesser Crested can be excluded not only because of the bill pattern but this bird has white rump and tail. There are one more thing I want to disclosure to have a full picture of this bird; is not easy to see this trait in the photos. Breast, belly, flanks and underwing areas show a faint pink flush It is often seen in Cabot’s Terns during spring but not so often during the fall. But I see it from time to time, even more intensive in a few Cabot’s during prebasic molt. Area right behind the eyes is sort of more dark than one would expect during this part of the year in Cabot’s but it happens sometimes and this bird is still molting feathers. I found many Cayenne Tern photos from South America showing similar pattern in winter plumage. Also the bill structure fits Cabot’s and not so Elegist’s bill; even in birds presented by Velarde and Royo as presumed Elegant x Cabot’s hybrids (with dark smudges on the bill).
Photos illustrating this tern
http://www.pbase.com/mbb/image/161543970
http://www.pbase.com/mbb/image/161543971
http://www.pbase.com/mbb/image/161543973
http://www.pbase.com/mbb/image/161543974
http://www.pbase.com/mbb/image/161543975
Also I want to show for possible discussion examples of a few older juveniles. The bill coloration in Cabot’s chicks and juveniles are poorly studied and not illustrated in bird guides. Chicks with yellow/orange bills change coloration to black with small pale (yellowish) tip. By now practically all have black bills - I spend a lot of time with terns for several years now and Cabot’s Terns are common around here so I had opportunity to see thousands of them. In this example juvenile shows bill pattern that it could be seen a few weeks earlier; so one or even a few birds now are still look as quite possible. But look at the another HY juvenile in this composite photo
http://www.pbase.com/mbb/image/161543969
http://www.pbase.com/mbb/image/161543972
Not only it seems to be too late but the pattern is weird for HY Cabot’s; but it could be a good match for Cayenne type (intermediate form) candidate.
Well, one thing is for sure - it is never ending fun when studying terns. We are (in most cases) reporting any bird with excessive yellow coloration as Cayenne in South America without even mentioning bill coloration pattern. On the other hand in North America we are undecided what to do with them. Sure we need genetic study to solve this problem correctly but in meantime we should make a call to collect more detailed data (especially from SA) that can be useful for future references.
Cheers,
Mark
http://www.pbase.com/mbb/from_the_field
A few months ago (during spring migration) I posted many examples from Texas of what I think are hybrids between Cabot’s and Cayenne Terns that, at least some of them, are most likely breeding in North America. In those posts I included some pointers of possible recent invasion of Cayenne Terns (including intermediate forms) in recent years. I also tried to summarize what is known about distribution of this subspecies and its taxonomy. During this summer I was able to collect indirect evidence that indeed these intermediates are most likely breeding here. There were, this year during breeding season, Cayenne-type birds in Texas attending freshly fledged juveniles. But that is not a subject of this post.
Here I have a couple examples of a very interesting cases, at least to me, that I am interested to hear opinions about from others with field experience who had a chance to observe large number of Cayenne and Elegant Terns. One bird molting into winter plumage with mostly orange bill (with only areas of darker smudges in the center and small areas of black at the bill base and nostrils). In my opinion it is Cayenne-type tern although if seen in Caribbean or South America it would pass as a ‘pure’ Cayenne - based on many Cayenne photos from Caribbean many birds reported from there as Cayenne show even more black coloration on their bills. BTW Olsen and Larsson described Cayenne bill as yellow, varying from orange to straw-yellow, often with darker central areas, and in extreme cases (illustrated) black bill base and center but with broader yellow tip to bill than in Cabot’s Terns. These authors included photos of birds with varying amount of black in their bills as ’pure’ Cayenne. Again, in my opinion, at least some of these birds are intergrades but without genetic studies it would be not possible to be sure. One more trait - this bird has red soles - but this is nothing unusual.
Usually when this type of bird is found outside of its normal range three possibilities are considered: Cayenne, Elegant and Lesser Crested. A few will try to add one more possibility: Cabot’s mutant. I think Lesser Crested can be excluded not only because of the bill pattern but this bird has white rump and tail. There are one more thing I want to disclosure to have a full picture of this bird; is not easy to see this trait in the photos. Breast, belly, flanks and underwing areas show a faint pink flush It is often seen in Cabot’s Terns during spring but not so often during the fall. But I see it from time to time, even more intensive in a few Cabot’s during prebasic molt. Area right behind the eyes is sort of more dark than one would expect during this part of the year in Cabot’s but it happens sometimes and this bird is still molting feathers. I found many Cayenne Tern photos from South America showing similar pattern in winter plumage. Also the bill structure fits Cabot’s and not so Elegist’s bill; even in birds presented by Velarde and Royo as presumed Elegant x Cabot’s hybrids (with dark smudges on the bill).
Photos illustrating this tern
http://www.pbase.com/mbb/image/161543970
http://www.pbase.com/mbb/image/161543971
http://www.pbase.com/mbb/image/161543973
http://www.pbase.com/mbb/image/161543974
http://www.pbase.com/mbb/image/161543975
Also I want to show for possible discussion examples of a few older juveniles. The bill coloration in Cabot’s chicks and juveniles are poorly studied and not illustrated in bird guides. Chicks with yellow/orange bills change coloration to black with small pale (yellowish) tip. By now practically all have black bills - I spend a lot of time with terns for several years now and Cabot’s Terns are common around here so I had opportunity to see thousands of them. In this example juvenile shows bill pattern that it could be seen a few weeks earlier; so one or even a few birds now are still look as quite possible. But look at the another HY juvenile in this composite photo
http://www.pbase.com/mbb/image/161543969
http://www.pbase.com/mbb/image/161543972
Not only it seems to be too late but the pattern is weird for HY Cabot’s; but it could be a good match for Cayenne type (intermediate form) candidate.
Well, one thing is for sure - it is never ending fun when studying terns. We are (in most cases) reporting any bird with excessive yellow coloration as Cayenne in South America without even mentioning bill coloration pattern. On the other hand in North America we are undecided what to do with them. Sure we need genetic study to solve this problem correctly but in meantime we should make a call to collect more detailed data (especially from SA) that can be useful for future references.
Cheers,
Mark
http://www.pbase.com/mbb/from_the_field
