Friday, December 21, 2007

Species profile: American Kestrel

I haven't done a species profile in a while. And I am avoiding the ungodly amount of gift wrapping I should be doing right now.

American Kestrel

The American Kestrel (Falco sparverius) is a small falcon. An old colloquial name for the kestrel was "Sparrow Hawk", which was misleading because it seemed to imply a connection to the Eurasian Sparrowhawk (Accipiter nisus), where they is no connection. (Sparrowhawks are accipiter hawks, not falcons) And kestrels are neither sparrows or hawks. I hate colloquial names.
You can find kestrels throughout the Americas. Most of the northern birds (Canada and the northern states) migrate south in winter, thought some males may stay as year-round residents. There are at least 15 sub-species.

Just like all raptors, kestrels are sexually dimorphic. Females are larger than males:
Females: 9 to 11 inches in length, wingspan 21 to 24 inches, weight averages at 4.2 ounces.
Males: 8 to 10 inches in length, wingspan 20 to 22 inches, weight averages at 3.9 ounces.
These differences are hard to discern in the field...but kestrels are unique from most raptors in that the males and females are colored differently. Males have blue-gray wings, and the females have barred, rusty colored wings. Tails are different, too. Males have a striking rufous tail with the outer rectrix set in white with a black terminal band. Females have a striped rufous tail. All this makes them undoubtedly the most colorful raptor.

back of AK
(RAPTOR, Inc's male kestrel)
*This next part comes from Wikipedia...I tried to condense it. This is a new bit of information I came across*
This bird is apparently not a true kestrel. mtDNA cytochrome b sequence analysis indicates a Late Miocene split between the ancestors of the American Kestrel, and those of the Common Kestrel and its closest relatives. The color pattern with its large areas of brown is reminiscent of kestrels, but the coloration of the head - notably the black ear patch, which is not found in any of the true kestrels - and the male's extensively gray wings are suggestive of a closer relationship with the hobbies, an informal grouping of falcons of usually average size.

Species such as the Merlin and the Aplomado Falcon may be possible close relatives. The Merlin is a highly polymorphic bird and although its grey tail and back are distinctive, certain morphs are the only birds that might conceivably be confused with American Kestrels. Conclusive evidence is lacking, and what can be said at present judging from the fairly noninclusive DNA sequence studies is that the general relationships of the present species seem to lie with a number of rather basal "hobby" lineages, such as the Merlin and Aplomado Falcon mentioned already, or the Red-footed and Amur Falcons - or even the Peregrine Falcon lineage with its large species.

The American Kestrel is not very closely related to any of these groups, although it might be closer to the Aplomado Falcon (and its presumed close relatives, the Bat and Orange-breasted Falcons) than to any other living species - an association that is also supported by biogeography than a close relationship with the exclusively Old World true kestrels. It is nonetheless highly distinct in morphology from any of these and, interestingly, has a syrinx similar to the Peregrine and the hierofalcons.

In conclusion, until better evidence is available, it is best considered part of a radiation of falcon lineages that diversified around the North Atlantic at the end of the Miocene. Though several fossils of small falcons arte known from North America at roughly the correct time, the earliest testimony of the American Kestrel lineage is Pleistocene remains of the living species.

Confused? Yeah, me too. Let's move on....

Kestrels are birds of open spaces...parks, suburbs, open fields, forest openings and edges and highway corridors. They are the only North American falcon to routinely hover, and they can keep their heads motionless as they beat their wings against the wind. (I do a cute thing with our kestrel at RAPTOR...I bounce him gently up and down and show how he can do a "bobble-body")

A "klee-klee-klee"...Click here to listen.

In summer, kestrels feed largely on grasshoppers, dragonflies, lizards, mice, and voles. They will also eat other small birds. Wintering birds feed primarily on rodents and birds. They hunt along roadsides from telephone wires, fence posts, trees or other convenient perches when not flying in search of food. Just before diving in to catch something, they will bob their heads and pump their tails.

Kestrels are cavity nesters. They will use holes in trees, rock cavities, small spaces on buildings and artificial nest boxes. No nest is built inside the cavity.
Pairs nesting in boxes on poles have much higher nesting success than pairs using boxes on trees. Both sexes will share the job of incubation, a very rare situation among North American birds of prey. Between 3 and 7 eggs are laid and they hatch about 30 days later. The young fledge around day 30.

American Kestrels, along with the Red-tailed Hawk, are one of two raptors almost universally used by new (apprentice) falconers in the United States. They are considered a harder bird to care for, due to its small size, quick metabolism and fragility. Their weight must be carefully monitored and maintained to within a few tenths of a gram.
Kestrels can be used to hunt insects (um, WHY?) and small birds, usually non-native species like house sparrows and starlings.


Anonymous said...

wonderful profile on one of my fave falcons!

Dave said...

I think thay are the prettiest of falcons. Thier size and colors. Don't get me started on thier speed.

Mary said...

Glue some rhinestones on the edges of the wings and she'd be good to go out on the town, wearing a beautiful evening gown.

Great post!

KatDoc said...

I love kestrels. I can almost be certain of seeing one or two every day, as there is a resident pair on my country road, and a couple other ketrel territories along my daily commute. Only this morning I saw two (plus a Red-tailed hawk) just driving along the roads. (I was driving, not the raptors.)

I read once that, while a pair will share a territory during breeding season when the feeding is good, when the food supply dwindles, the female, being larger, will keep the good spot and chase off the male. This esplains why we see more male kestrels than females in the winter in southern Ohio.

Are they big enough to get starlings? I didn't think anything ate starlings by choice! I would love it if a kestrel would move in here and clear out the ones visiting my bird feeders.
As for the scientific gibberish: That's why we are birders, not ornithologists!


Gallicissa said...

Interesting post. Enjoyed reading it.