DBQ answers

2 12 2014
Bird A as it might have looked in life. (Photo: Wikimedia Commons)

Bird A as it might have looked in life. (Photo: Wikimedia Commons)

I could well have termed this quiz “The yellow on the mandible edition” as that feature is telling in both these birds. All my respondents identified Bird A as a Yellow-billed Cuckoo, and I included that one not because it was tricky overall, but mainly because it’s an oddity. It’s not that this species is so rare, but its occurrence on a Maine beach might be considered notable for two reasons: Maine wildlife authorities report that the bird does occur in the south and central regions of the state, but is quite uncommon in the northern part of the state. We, then, are seeing this bird roughly at the northern limit of its range. Already less common in Maine than its cousin, the Black-billed Cuckoo, population estimates on the Yellow-billed Cuckoo show it declining, likely due mainly to habitat fragmentation (the birds prefer dense undergrowth for foraging). Maine lists the YB Cuckoo on its list of of species of special concern, and in the western and southwestern regions of the U.S., the species has been in precipitous decline, with some discussion of endangered status.

A deceived reed warbler attempts to keep fed a gigantic European Cuckoo chick in its nest. (Photo: Per Harald Olsen)

A deceived Reed Warbler attempts to keep fed a gigantic European Cuckoo chick in its nest. (Photo: Per Harald Olsen)

Interestingly, the Yellow-billed Cuckoo occasionally lays its eggs in the nest of another bird, engaging in what is known as brood parasitism, but very often builds its own nest and rears its own young. This is in contrast with the European Cuckoo, which is, as I understand it, an obligate brood parasite, much like our Brown Cowbird. It was the European Cuckoo whose actions drew the moral disapproval of medieval Europeans, giving us the term “cuckold.” It seems the Yellow-billed Cuckoo is slightly more virtuous, by those lights.

 

As to Bird B, I had hoped this one might generate a bit more discussion, and it appears that it did. All our respondents (Edward, James, Mary, and Maureen) placed this bird in the pouch bill group, which includes pelicans, gannets, cormorants, and frigatebirds, among others. These birds are distinguished by their variable throat pouch, and, in most cases, by the distinctive webbing involving all four toes. Maureen suggested Magnificent Frigatebird, though it would be pretty far north for that species, but to be sure, we do occasionally see them turn up. In fact, one of the photos of that species in our new field guide is of a bird that turned up dead on Sable Island in Canada! More importantly than geography in this case, however, is anatomy. While most pouchbills have strongly webbed, fleshy feet, frigatebirds have rather spindly toes with scarcely any webbing. This reflects their natural history as birds that do not land on the water or swim and dive as their cormorant and gannet brethren. Instead, they snatch food from the water’s surface while on the wing, or shakes down other birds for their catch, a behavior known as kleptoparasitism.

Another species of Frigatebird, but with the typical Frigatebird feet (Photo: Aviceda)

Another species of Frigatebird, but with the typical Frigatebird feet (Photo: Aviceda)

So the feet on our Bird B alone point us away from Frigatebird, as does the bill, which would be longer and more slender in a Frigatebird. The rest of our respondents identified Bird B as a cormorant, but were split as to species. We’ve been through this before, trying to distinguish Great Cormorant from Double-crested, which can be a challenging i.d. depending on the state of the carcass. I included this case because of the white appearance of the head in Bird B. Generally, a conspicuous white patch at the bill base is characteristic of Great Cormorants. Bird B shows white over much of the face, which led me to suspect that the color was an artifact of decomposition. We do see feather and skin sloughing, especially in water-logged carcasses, which this bird appears to be, so the white color on the head of this bird was not present in life. The feather sloughing is also clearly visible over the wings. We are left without the color of the skin at the base of the bill to go on, which often clinches the i.d. in this case. What we do have is the color of the mandible itself, which has a yellowish tinge in Bird B. When we look at the two candidate cormorant species, only the Double-crested shows that, and it is strongly present in juveniles, fading to gray in adults. Thus, I am with Edward on this one, identifying it as a juvenile Double-crested Cormorant.

Double-crested Cormorant showing yellowish mandible. (Photo: Hans Stieglitz)

Double-crested Cormorant showing yellowish mandible. (Photo: Hans Stieglitz)

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