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Cavity Nesting Raptors

The North American Kestrel
Male American Kestrel

Formally called sparrow hawk, the kestrel has always been a favorite with American ornithologists. The kestrel is probably our most beautifully marked hawk. Females are uniformly rufous brown in color, while males have blue-gray wings and a rufous brown back. Both male and female have a mustached black and white face pattern. About the size of a blue jay, the kestrel is primarily a bird of open country and woodland borders. It is commonly seen in the characteristic pose of falcons; hunched up on high, exposed perches scanning the ground below for prey. They also hunt by pointing into the wind and hovering over fields, looking for prey and then shifting to hover in another spot if nothing is seen. The kestrel has been nicknamed “Killy Hawk” because of the sharp cry it emits when it has spotted an intruder. The kestrel is a highly beneficial bird, eating large numbers of insects and meadow mice. They have a very widespread range throughout the western hemisphere. They breed from above the Arctic Circle in Alaska and northwestern Canada, south through Canada and the United States into Mexico, parts of Central America and most of South America. In the spring the male selects a nesting site (usually a cavity within a tree) and waits for the female to appear and approve the site. The kestrel normally lays 4-5 eggs which hatch in about 30 days. Although both parents incubate the eggs, the female does the majority of the incubation, while it is up to the male to bring in food. Within 30 days of hatching the young kestrels are fully fledged and have plumages very similar to the adults. The kestrel is one of few species of raptors where the juvenile plumage differs between the sexes and resembles the respective adult plumages. Starting early in September the kestrel moves southward in large numbers from the northern parts of its range. The Migration peaks in late September and early October with the largest number of birds moving along the coast.

The Screech Owl
Screech Owl

The Screech owl regularly haunts old orchards, cemeteries, suburban parks and open deciduous forest . They are our most “suburban” owl, but are rarely noticed because of their small size and ability to blend in with their surroundings. There are three species of screech owls native to North America; the eastern screech owl (Otus asio), the western screech owl (Otus kennicotti) and the whiskered screech owl (Otus trichopsis). Screech owls have two color phases, red and gray. This color variation is independent of age, sex or season; however the red phase seems to be more predominant in the southern part of the owls range. The screech owl’s diet consists of a wide range of species including shrews, mice, voles and other small rodents, small birds and various insects. These owls are strictly nocturnal, skimming over fields, meadow, apple orchards and along the edges of wood lots in search of food. Screech owls have two distinctive calls which vary somewhat depending on the species. The one most often heard is a long, single trill in one pitch or a series of two trills, one short , one long. The other call, sung as a duet by male and female is a mournful, descending whinny, similar to a horse. Screech owls raise their young in natural cavities, abandoned nesting holes of flickers and pileated woodpeckers and man-made nest boxes. In April, four to six pure white eggs are laid and by July the young owls have left the nest and are scattered in the surrounding woodland. The screech owl is a permanent resident throughout it’s range. They are essentially non migratory although some birds do move southward in winter.

American Kestrels
Female American Kestrel

American kestrels have experienced a decline in population, reducing their numbers by almost half over the last 45 years. The reason for the decline is unclear but may be due to changes in land use practices, competition from European starlings, predation by Cooper's hawks, or pesticides. One way we can help these cavity nesting falcons is to provide them with additional nesting opportunities by building and erecting nest boxes.

Both the American kestrel and screech owl will readily accept nest boxes as places to lay eggs and raise their young. Studies seem to indicate that these species even prefer them to natural cavities. The placing of nest boxes in suitable locations is a very effective way of significantly increasing population sizes of these birds in areas that lack natural cavities. For kestrels, boxes should be placed 10 feet up or higher on a pole or in a dead tree located in a field or on a field edge. The box should face south or southeast. If the box is placed on a tree, metal flashing should be placed around the trunk of the tree at least 3 feet above the ground to prevent predation by racoons or snakes. Nest boxes for screech owls should be placed 10 feet up or higher on pole or in a dead tree located at a field edge or in an orchard. Screech owls seem to prefer groves of low lying hardwoods with a stream nearby.

Cleaning Old and Placing New Nest Boxes

Kesstrel Nest Box

Each year it is important to remove old nests/nesting material to minimize parasite infestation in the spring.  The best time of year to put out new nest boxes for all cavity nesting species and to clean out old nests from existing boxes is the Fall.  However, boxes can also be placed and/or cleaned up until the end of March in most areas.  Instruction for building and placing nest boxes for American kestrels or screech owls can be found on our facebook posts or complete kits can be ordered on our website.

Great Horned Owl

About Owl Pellets
11/02/18  Michael J. Gaylo

All birds of prey consume quantities of bone, feathers, and fur when eating prey.  Owls tend to swallow small prey such as voles, mice and shrews whole. Prey is swallowed head first and moves down the owl's esophagus and then through the proventriculus which is the glandular part of the stomach. Here, the owls food gets coated with digestive enzymes and then moves to the muscular part of the raptor’s digestive tract called the gizzard. After the soft tissue has been digested, the remaining bones, fur and/or feathers are rolled and compacted to form a pellet or casting. This is regurgitated by the owl several hours after eating or before the next meal.

Accuracy in making counts of prey items depends on the type of pellet that is being worked with.  Because of differences in feeding habits and physiology, hawks and owls produce pellets that differ in their ability to be examined quantitatively.  Owls usually swallow small prey whole and don’t take the time to pluck their prey.  Also their digestive tract does little or no damage to the bone consumed.  This results in pellets that usually contain whole skeletons that are relatively undamaged.  Hawks on the other hand, pluck their prey before eating and then tear it into small pieces before swallowing, consuming varying amounts of fur and feathers.  They also digest bones more completely than owls so that their pellets often contain little osseous remains.  Identification of prey species must be made by pairing incisors which are usually present.  Fairly accurate counts can be made in this manner by someone trained in their identification .

It isn’t known how many pellets a wild raptor produces per day so that accurate figures on daily intakes are unavailable.  However, they do yield information as to the type of prey consumed.   By comparing bones, feathers, and fur with the same material in an identified collection, identification of the dissected items is fairly easy.  In many cases if a large enough sample of pellets is examined it is possible to obtain a fairly accurate record of the diet of one raptor or the diet of a species.  It is also an indication of population densities and vulnerability of the prey species identified, since prey is taken in proportion to it’s relative density.

Owl pellets are in stock!