Raptor Natural History, Handling and Housing

Class by Alida Morzenti, Fall 2003, Santa Rosa Bird Rescue

This series of four lectures was broken out into a Natural History section and a Handling/Housing section. Jump to Handling and Housing.

  • Migration and Movements

    • Types of Movement

      • Dispersal: the young moving out and away from parents

      • Nomadic

        • Unpredictable and variable from year to year

        • Burrowing owls, Harriers and Kites

      • Migrations: leaving a breeding area and traveling to a wintering area

        • May be complete (~95% of birds in the species migrate): examples include Swainson's Hawks, Broad-winged Hawks, and Rough-legged Hawks

        • Other species migrate in varying degrees...for example, Arctic Peregrine Falcons leapfrog other PEFA and go further south

    • California's temperate climate may contribute to more undefined movements (there's no great pressure to head south if the weather is ok and prey is plentiful).

    • Insectivores may need to travel further for prey (SWHA) although some may switch their prey source to rodents (American Kestrel) SWHA have smaller feet, they can't switch prey source, so they must migrate.

    • Movement can be caused by dams, which create areas of open water and no ice; this changes patterns of Bald Eagles and Osprey.

    • In general, adults tend to take more direct routes and juveniles tend to wander. Juvs also tend to hug the coasts (water is an obstacle)

    • Some species can fly long distances over water and may be found far at sea or on the wing for days: PEFA, Merlins, OSPR.

    • Veracruz, Mexico

      • 1992, 2.5 million total counted, .5 million in one day.

      • 1994, 3.2 million total, 900k in one day

      • Attracts migrants who are heavily dependent on thermals

    • Mountain ranges create updrafts which can be exploited

    • Highways tend to get hot, causes thermals (particularly attractive to Turkey Vultures.

    • Falcons are more likely to migrate near water, buteos are less likely

    • Weather and winds have strong effects on specific sites

    • The young usually migrate ahead of the adults (possibly due to dispersal); different sexes may migrate at different times

    • The fall migration is larger, and it is triggered by the weather.

    • Spring migration is smaller...60-80% of the young have died during the year. Adult males usually return first to establish territory. Then come the females, then the 1st year birds.

    • Some, especially PEFA, may not return the first year (may wander)

    • Eating and migration is not well understood, though it appears that some species gorge before migration (SWHA)

    • Minnesota Raptor Center has transmitter birds you can follow online

  • Turkey Vultures (TUVU)

    • New world vultures in general are not as close genetically to raptors as they are to storks.

    • Vultures tend to gorge when they can (since they are not predators, they are not in control of their own food supply). They will regurgitate when threatened (possibly this lets them move faster if they have just gorged).

    • At night their body temperature drops by about five degrees and they go into hyperthermia. They need to warm in the morning before moving. In the winter, they will roost where the sun hits first.

    • They grunt and hiss but otherwise don't vocalize

    • Carrion circling signals food availability to others

    • Defecating on feet in summer cools them (feet appear white in summer); storks do this also

    • Usually nest on cliffs or in trees; adults usually stay and juvs migrate; may move to ridges in the winter because of lack of thermals

    • They do have a sense of smell, but older food doesn't necessarily smell better

    • Their sight is comparable to other raptors; they can find food by sight or by smell (old world vultures don't find food by smell)

  • Peregrine Falcons (PEFA)

    • Often take ducks and used to be called the "duck hawk"

    • Love water, love to bathe

    • Falconers where the first ones to recognize that the DDT crash was happening

  • Golden Eagles (GOEA)

    • Feathered all the way to the toes

    • Tend to lighten with age

    • Some nest in eucalyptus trees on Lakeville Highway

  • Bald Eagles (BAEA)

    • Get more white feathering as they mature

  • Osprey (OSPR)

    • Used to be ground nesters in some places, especially islands, but cat predation probably contributes to this changing

    • Big River Beach in Mendocino usually has a nesting pair

  • Northern Harriers (NOHA)

    • Often appear smaller when standing and larger when flying due to long wings

    • Males are much more agile due to slightly different wing loading; mailes will hunt birds more often in brushy areas while females tend to hunt rodents in open fields.

    • The reddish/pumpkin color in juvs starts to go away right away

    • Very slender legs are good for hunting in tall vegetation and for hunting by sound (don't have to see prey to reach into grass and grab it).

    • Bird-hunting raptors tend to have long, slender toes for penetrating feature cover, and male Harriers have longer toes than females

    • Ground nesters; the young will scuttle away from the nest on their hocks before they can walk

    • Males rarely go near the nest; the female flies away from the nest for a food transfer -- female turns upside down and male drops the food; this happens during courtship as "practice", but becomes necessary for successful nesting.

  • White-tailed Kite (WTKI)

    • "The commuter bird" because it's often hunting near highways during commute hours

    • Can hover for up to five minutes at a time

    • Has a very large mouth -- gape goes all the way under the eye

    • In rehab situations, cardboard box with pine shavings is good housing -- other materials will let them damage their feathers

    • After they leave the nest, they will stay on the ground for 4-5 days (let them be!)

    • Very small feet are adapted for insects, mice and voles.

  • American Kestrels (AMKE)

    • Females have streaks on breast, males have spots (spotting tends to decrease and move down the breast as they get older, though not always)

    • Will bathe if given the opportunity

  • Merlins (MERL)

    • Females tend to be lighter in color, but different races have different light/dark coloring also

    • Flocks of birds which ball up and spread out may be reacting to a Merlin approaching and then leaving (herd mentality: group for protection)

  • Red-shouldered Hawk

    • "Bad attitude" bird -- Alida has seen them crash thru trees to go after an interloper

    • Quite vocal

  • Red-tailed Hawk (RTHA)

    • Secondaries tend to bulge out, creating a distinctive shape

    • A generalist about food; they can and will eat about anything (GHOW is the nocturnal equivalent)

  • Swainson's Hawks (SWHA)

    • Very light under-tail coverts can sometimes be mistaken for NOHA

    • Tend to have a dark bib and a white throat

    • More light-weight than a RTHA

    • Sometimes immatures will get confused and stay thru the winter

    • About equal number of light and dark morphs

    • Sometimes have up to three young, but the two larger chicks may kick out the smaller

    • Males usually leave the nest first.

  • Rough-legged Hawk (RLHA)

    • Completely migratory -- nest in arctic and move into Northern US

    • Very small beak and feet are adapted fro small rodents and insects

    • Feathered all the way to the toes

    • Covers long distances -- pointy wing like long-migrating SWHA

    • Not a perch hunter -- hover hunts (perches are not available in the tundra)

  • Ferruginous Hawk (FEHA)

    • Has a carpal coma, darkly-feathered thighs (light on juvs); sometimes a lot of color in the patagium

    • Very white on the front

    • Midwest plains states; will hover-hunt, and will sit in middle of fields

    • Very self-possessed demeanor, similar to eagles

    • Nest on the ground but do not seem to return to habitats that are restored

    • Will often migrate in pairs and return to the same places

  • Prairie Falcon (PRFA)

    • The nasal hole (nares, naris singular) on all falcons is round (it's more slit-shaped in other raptors). There is a post-like "nostril baffle" that may be used to slot air into nostrils during high-speed manueuvers (Wheeler, Raptors of Western America). This is also called a "tubercle".

    • Falcons don't tend to build nests; they usually nest on "scrapes" but will sometimes take over another nest

    • Biting is a problem when handling a falcon.

    • Very strong mandible and a "tomial tooth" that points down into a corresponding notch in the lower mandible. Falcons use the beak to kill by breaking the spine.

    • Prairie falcons adjust very well to their environment. At Tule Lake they will sometimes perch hunt. In other areas, they capitalize on pheasant populations. They will actually use NOHA by following after them...the NOHA will flush the pheasant (which is too big for it) and the PRFA will come in and grab it.

  • Accipiters: Cooper's Hawks (COHA) and Sharp-shinned Hawk (SSHA)

    • Very slender toes with long talons = bird hunters

    • The more a raptor depends on birds as prey, the greater the sexual dimorphism (accipiters and PEFA)

    • Both species get red eyes as they get older (as do Kites) -- 3-4 years as adults

    • They hide their nests in dense cover.

  • Barn Owls (BNOW)

    • HIde during the day

    • Not unusual to find the entire family dead not long after the young have fledged because they perch on fence posts near roads and are hit by cars as they go after prey crossing the road. Despite this, populations seem to be thriving.

    • Cavity nesters, so lack of proper habitat could become a problem

    • Sometimes nests are surrounded by dead rodents; males will begin hunting for the young before they hatch and experienced males may over-do it

    • The young are staggered in age (hatch days apart)

    • Facial disks allow them to hunt by sound; ears are actually offset at a different height and slightly different shape. The facial disk is completely feathers; there is no anatomy behind it.

    • Feathers grow out of a blood-filled shafted; sheaths cover the feathers and they pull it off by preening.

  • Great Horned Owl (GHOW)

    • The nocturnal equivalent of a RTHA; will eat just about anything; they are crepuscular and nocturnal

    • Second-worst bird to be footed by (Eagles are the worst)

    • Ear tufts are probably for camouflage

    • Owls in general have very short tails

    • Feathered all the way to talons

    • The only owl legally used for falconry

    • Build poorly constructed nests and often take over old crow nests

    • The young stay with the adults for 4-5 months, and will often stay on the ground for a week after leaving the nest. They then move into nearby trees while the parents hunt and bring them food (they don't start hunting right away)

    • There are windows of opportunity for release -- they won't start hunting until they are ready, but you want them to learn to hunt and it's important to not miss that stage

  • Long-eared Owl (LEOW)

    • Strictly nocturnal

    • Smaller body than a GHOW

    • Like GHOW, they will puff up turkey-like as a defense mechanism

  • Short-eared Owl (SEOW)

    • Nocturnal equivalent of a NOHA; looks like a big-headed harrier when hunting

    • Both NOHA and SEOW are nomadic and somewhat social; they sometimes gather in good hunting areas and will nest communally on the ground

  • Western Screech-Owl (WESO)

    • Can change shape and postures dramatically to blend in with surroundings

    • Will hunt birds if rodents are in short supply

    • Heavily preyed upon by GHOW; a tape of a WESO will often bring in a GHOW

    • They don't actually screech -- they make a very soft "who" sound

  • Burrowing Owls (BUOW)

    • Long legs; usually perched on the ground or on fenceposts

    • Nest in burrows; usually lay 6-8 eggs but can lay up to 12

    • Use ground squirrel or prairie dog burrows

    • Often will try to nest in construction sites during the early stages of a project

    • Predation by cats is a big problem

    • Males stand outside on watch, so their color is often bleached out

    • They like a clear view, so too much grass is a problem (if cows are taken off a field they populate, they may leave)

    • Eat lots of insects and rodent

  • Northern Saw-whet Owl (NSWO)

    • Very large head compared to size of body

    • Very small

    • Nocturnal

  • Northern Pygmy-Owl (NOPO)

    • Hardly any facial disk and a long tail -- hunts during the day, for birds

    • Very fast, and extremely good camouflage

    • Will bathe

    • Often mobbed by songbirds

    • Status of the population is difficult to know

    • Has eye spots on the back of head, similar to AMKE, which may confuse potential preditors.

Raptor Handling and Housing

  • Falconry has been around for centuries

  • Mongolian shepherds have used eagles for falconry for hunting wolves that predate on sheep (note: Alida said wolves, but in other articles on the web I found, it said that they use them to hunt foxes for fur.)

  • Japanese and Arabs have strong falconry cultures

  • Probably cem to Europe during the crusades

  • Birds were usually released in the spring to breed

  • Frederick II wrote a treatise on raptors and falconry

  • Transport

    • Hooding can calm the bird

  • Bracelets go on legs; grommets provide hole

  • Block perches are often used for falcons

  • Hunger streaks or stress marks on feathers will be breakage later

  • Mouth color

    • RTHA: red/pink

    • NOHA: purple

    • Choanal slit allows air to enter from the nares

    • Frounce is a disease of the mouth and throat, often found in stressed birds that have been injured but continuing to live in the wild

  • Bumblefoot is an inflammation of the feet that is almost always a problem of captivity (pressure on feet causes sores)

  • Hack boxes are used to release young birds

  • Any bird's success in adapting to a disability depends to a large extent on that individual bird. For example, some birds may adapt to a missing leg while others do not.

  • Housing

    • Redwood lath is springy; the bird can hit it and bounce back without serious damage; should be placed vertically so the bird won't grab and perch (which will cause them to break feathers)

    • Use wire fencing on the outside, 4 inches away from the lath.

    • Doors always need to have backups (double doors)

    • Power can be helpful (heat lamps can calm WTKI)

    • Perches across corners

    • Pea gravel on floor; 2 foot layer is best (allows for good drainage, easy cleaning, and is a bit yielding)

    • Birds are most comfortable when perched at or above eye level, but do not do stair-steps up to a high perch for a disabled bird that will injure itself falling.

    • Local temperature, wind, and snow must be taken into consideration

    • Weathering areas must be in a covered area for predator control by law

    • Raptors do not drink a great deal but do need water available (food in captivity does not contain as much water as in the wild). PEFA love to bathe, other falcons may also.

  • Birds act and react differenctly when they are closely observed. Try to observe from a distance first

  • Perches

    • Falcons that are cliff dwellers are usually given a block perch (large falcons)

    • GHOW usually have tough feet and like natural branch perches

    • Sometimes it's good for a perch to have some give for injured birds that may make a clumsy landing

    • GOEA get flat perches

    • Minimum height of a perch is the length of the tail; the diameter must be large enough to accomodate the feet

    • Monsanto astroturf, "daisy doormat", is the best covering -- other varieties may be too sharp which can produce paper cuts

  • For easily injured birds, a cardboard box with pine shavings may be the best housing.

  • Some terms:

    • Hawks -- can mean buteos+accipiters, or all diurnal raptors, or all "true hawks" which are accipiters only

    • Crepuscular means active at dusk and dawn

    • Altricial: helpless in the nest; raptors and passerines are altricial. Imprinting is not a big problem in altricial birds

    • Prcocial: babies are able to move about and feed on their own (quail, pheasants, ducks); these birds MUST imprint on their parent immediately because they need to stay close to them for safety

    • Age terms:

      • Haggard: a bird in full adult plumage

      • Passage: an immature bird in first-year plumage (dispersing)

      • Brancher: pre-fledging but mobile; starting to leave the nest

      • Eyas: a downy youngster in the nest

    • Malar stripe: in falcons, a sort of moustache

    • Patagium: RTHA

    • Saying that a bird mutes means that the bird defecates

    • Eyrie is a nest usually on a cliff (falcons, eagles)

    • Four letter codes for one-word birds is usually just the first four letters (MERL); if two words, first two letters of each word (PEFA); if three, first letter of first two words plus two letters of third word (RTHA).

  • Preparing a bird for release

    • There is sometimes strong sentiment against rehab. Birds must be properly prepared, otherwise they are unsuccessful

    • Adult birds already know how to hunt; a starving passage bird brought in during the winter may not know how to hunt

    • Preparation for flight: different flight styles indicate different approaches

      • RTHA good with creance flight training

      • Falcons are not good with creance nor flight cage; need to be falconry trained. Bird must be comfortable flying to you even if others are around. PEFA and MERL MUS be falconry trained. Kestrels could be cage trained if there's a large enough cage.

      • Accipiters use short, fast bursts of speed rather than sustained flight, and are fairly active in captivity. SSHA can be cage trained; COHA can be cage trained or creanced

      • Harriers need to be cage trained; cannot creance delicate feet

  • Options for young and baby birds

    • Nest replacement is best

    • Hacking is next best; build a box that resembles a nest; the birds go into the box when they can thermoregulate and self-feed; must be aware of the specific windows of opportunity

    • Surrogate parents may be an option; sometimes even other species will surrogate or can mix young of different species (better to be raised with other birdes so they know they're birds). Don't want to associate humans with food, so food bowls are placed in cages even before they begin eating from them.

    • Farmers are good with hack boxes and daily feeding.

    • When birds begin to move around, remove the front of the box (before dawn if diurnal, before dusk if nocturnal). Birds will return to the box for food until they can hunt for themselves. In diurnal species, the males usually leave first. Once the cover is off, it stays off.

    • Hack boxes don't need to be particularly high (PG&E spools sometimes work)

    • Most will stay with adults 3-4 weeks, though it varies, for food. AMKE will stay less than a week (insects are easier). Larger birds are dependent longer.

    • GHOW will stay with adults 3-4 months. They may spend a week on the ground, begging, fed by parents. Will usually successfully scare off predators during this time. Then they regroup in trees and learn to hunt with the adults; they will return for food for 4-6 months.

  • Creance flying

    • Use nylon rope (has some give)

    • Do not tie to something solid! Various size tires are good.

    • GOEA can be creanced but can be very unpredictable

  • Hack platforms can be used to evaluate a questionable bird; the bird will return for food until it can hunt on its own. If it keeps returning, can be re-trapped and taken into care.

  • Banding: Fish and Game is often reluctant to do this because it is a lot of work tracking for rehab centers that release birds that are unlikely to survive (in working with AMKE, out of 600 bands, only got about 20 returns).

  • Digestive tract

    • Organs are streamlined for flight; weight is in center of body

    • Owls swallow prey whole

    • Air flow

      • Nares: nasal openings that take air in, located in the cere

      • Cere: fleshy area around the beak

      • Choanal slit: opening in the roof of the mouth that allows air flow to continue

      • Trachea: opening is at the base of the tongue

    • Esophagus

    • Crop often pronounced in grain eating birds, but not as prominent in raptors; in GHOW, it's almost just a straight-thru tube

    • Proventriculus - the acid stomach -- this is where the chemical breakdown occurs

    • Ventriculus - the gizzard or mechanical stomach; replaces teeth

      • Grit used in the ventriculus is called "rangle"

      • Falcons are prone to pick up bits of rangle

    • Pellet formation happens in the gizzard and is passed back thru the mouth ("casting a pellet')

      • Since owls swallow food whole, the pellets usually have bones intact. Since hawks tear at their food, bones are not intact.

      • Falcon castings are tiny; they love to pluck and they don't ingest much bone or feather

      • When they cast depends on how much food is eaten and how plentiful the food is. If food is plentiful for owls,m their pellets are not as dense or compacted.

      • Diurnal raptors often will not hunt in the morning until they cast; they will often go thru casting motions even if they have nothing to cast.

  • Feathers

    • Tail feathers are attached to the pygostyle (the bottom vertebrate are fused into a sort of platform). The pygostyle is extra strong and wide in falcons.

    • There are 12 tail feathers numbered 1-6 on each side, from the inside out; the two feathers in the center are the "deck feathers"

    • Molting happens in pairs

    • Wings

      • Primaries are attached to metacarpals (analogous to fingers); they are very mobile in many species. The primaries are counted from the inside out, beginning at the carpal (wrist) joint. In most species there are 10 primaries and these also molt in pairs.

      • Secondaries are attached to the ulna (forearm). In raptors, the ulna is larger than the radius. These feathers are counted from the outside in, and there are 11-25 per wing. Large soaring birds have more secondaries than small power fliers.

      • Primaries provide power; secondaries provide lift.

      • Tertiaries are attached to the humerus; these provide lift and fill gap next to body

      • Alula - 3-4 on each side; like a thumb; used to smooth air over the wing and prevent stalling

    • Uropygial gland is on the upper side of base of tail; when the bird preens, it gets oil from this gland and distributes it along each feather. The uropygial gland is very prominent on GHOW; it is small on a RTHA (if it's large, it indicates a problem)

    • Feathers grow out of follicles like hair; a new feather pushes out the old.

    • Feather structure from large to small: shaft, barbs, barbules, barbicels or hooklets

    • When a bird preens, it "rezips" the barbicels

    • Imping means to join a new end on a feather that is broken

    • Bent feathers can sometimes be straightened wth heat

    • Bone growth is the immediate need in a baby, but after that, features are most important.