Deferred Maturity

by Dave Hanks

Young song birds hatch, fledge, and are ready for migration. The young birds usually resemble the female parent. However, by the following spring the males acquire their adult breeding plumage and assume parenthood. Their development is relative simple and quick. However, most raptors and gulls go through several stages before reaching sexual maturity. Large birds like eagles or buzzards have 4 to 5 stages of development. Hawks usually have two stages to go through over a two year period to reach maturity.

Buteos are large hawks with broad wings. The FERRUGINOUS HAWK (pictured) is the largest American Buteo. Only the Bald Eagle, Golden Eagle, and female Snowy Owl weigh more than this hawk. Ferruginous Hawks go through three stages after the nestling stage: juvenile, sub-adult, and finally adult – three years from hatching to adulthood. This species has been known to live for 20 years (determined by re-catching banded birds), although the majority die within a 5 year period –which allows a five year old bird two opportunities to nest.

Ferruginous Hawk’s first year mortality is estimated at around 66% and adult mortality at about 25% per year thereafter. This ground nesting bird is preyed upon by Coyotes, Golden eagles, and Great horned Owls. Jackrabbits rank high on this species food list. When prey sources are at a low, many hatchlings will die of starvation. Illegal shooting of adult birds has also caused a problem to this not-so-common species.

This magnificent hawk has been used as a falconry bird in its native range.

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A young Ferruginous in the sub-adult phase

 

Types of Migration

by Dave Hanks

When one thinks of migration, one usually thinks that animals go south in the autumn and go north in springtime. That is what is called COMPLETE MIGRATION, but it is an over simplification. Amount of daylight, weather conditions, or food supplies; are factors that influence the time or type of movement. Some species like Robins, Red-Tailed Hawks, and Towhees are PARTIAL MIGRATORS. Many of these species migrate but a portion stay around all year long – especially if food sources are adequate or to protect a territory and nesting site. Young birds are more apt to make the long trip because of a low social rank. Adult individuals force them to vacate the area.

DISPERSAL is the result of newly fledged birds moving to find space where they can establish their own territory. It is believed that this type of movement is the origin of complete south/north migratory patterns. Another type of migration is called DIFFERENTIAL. This type is influenced by existing conditions. Where nest cavities are in short supply, the American Kestrel may not move away from his established nest box. Water birds may move to the closest area that has open water. ALTITUDINAL MIGRATION is from High Mountain (where weather conditions mimic the more northern latitudes) down to lower elevations to spend the winter. Pine Grosbeaks and Juncos fit this type. Juncos that are abundant around bird feeders in winter are absent in summer.

IRRUPTIVE MIGRATION is very irregular. This is not necessarily a north/south trajectory, but often a lateral movement for better feeding conditions, and is not made every year. Years of severe weather can be a stimulus. A shortage of conifer cones makes Crossbills move to more productive forest areas. Abundance of small rodents (voles, mice, gophers, etc) affects predator movements. Owls especially are birds that are subject to these conditions.

Like all things in life, what appears simple on the surface is usually much more complicated.

A Great Gray Owl: An irruptive species

A Great Gray Owl: An irruptive species

Flight Speed and Altitude

Migrants do not usually fly at their top speed, but fly more leisurely to conserve energy. That way they can maintain their flight for greater distances. Cloud cover can influence altitudes flown. Most, like airplanes, will fly above the haze. Flights over an ocean are usually done at lower altitudes, and songbirds seldom get above 5000 feet. However, the larger birds can get as high as 6000 to 8000 feet. When mountain ranges are in the path, birds can fly very high – high enough to get over the range, although most find it easier to take flight paths that miss obstacles.

Sandhill Crane can cruise along without flap-flying, once they have reached sufficient height and air speed. They can glide long distances. Tundra Swan can fly 250 miles at a stretch at 45 miles per hour. The Canada Goose can exceed that by 50 miles at the same speed. The fact that they can do 60 miles an hour closer to the ground, shows how energy and endurance is preserved once flying altitude is obtained.

The Canada Goose is very familiar to us all, as it is the most widespread goose in North America. It can be found in all kinds of water and is a familiar presence (and nuisance) on many golf courses. Their honking leaves a deep impression, as they fly overhead in their classic V formation during spring and fall migrations. Newly hatched young look like ducks, but in a week or two become a fuzzy gray. In nine to ten weeks they grow flight feathers and look like small versions of the adult birds. The webbed feet of this species will leave definite evidence as to their presence when one sees their tracks.

This is a very popular waterfowl for hunters, and their haunting calls add greatly to the autumn mystic.

Canada Geese: Long distance, top speed migrators

Black, White, and Rose: Subtle Beauty in the Bushes

To me, the ROSE-BREASTED GROSBEAK is absolutely one of the most attractive of the bird world. The way the three colors, of this species, are combined makes a very pleasing effect. Unfortunately, it is an eastern species that is not usually seen in the western USA. Its western counterpart (Black-Headed Grosbeak) nests in our yard, but it would be keen if we could have access to both.

This Robin-sized bird has a large seed-eating beak, but throughout most of the year, over half of their diet is made up of insects. Their song also resembles the American Robin’s, but more subdued and mellow.

The males arrive before the females on their breeding grounds – in mid May and they leave in early August. When courting, the male sings while in pursuit of the female. He will also crouch, spread and droop his wings while his tail is erect and fanned. He will also sing when not flying, while retracting his head and waving it from side to side. The male will do most of the brooding and he often sings while sitting on the nest. One’s imagination can visualize lullabies being sung to the young. Now what female could resist these multiple actions?

This is a lower Central American species that migrates across the Gulf of Mexico to the eastern states and Canada. We have expended much effort and miles seeking this charismatic bird. We have had very brief sightings of it in Minnesota, north-eastern British Columbia, plus strays in Montana’s Centennial valley, Alberta’s Jasper Park, and Idaho’s Silver Creek Nature Preserve. All these experiences were brief and discouraging. It had to be in Texas, the state with the most birds in the union, where we finally got lucky! Here we spent two days with some newly arrived males. They were eating some seeds that had been spread, by some thoughtful person, on a large, horizontal tree branch.

a Rose-Breasted Grosbeak checks the area below from a branch before descending

Checking the area before descending

Nighttime Migration

Many species of birds migrate at night. You may have been observing a sizable number of a particular species one day, only to wonder the next day where they all went to. The birds obviously migrated during the night. Tanagers, orioles, thrushes, thrashers, buntings, warblers, and wrens are some of the special birds you may like to watch that use the nighttime sky in their movements.

Most fly at altitudes from 1500 to 5000 feet, but there are records of some that have cleared mountains as high as 20,000 feet. Star patterns and constellations are used for navigation purposes – especially the North Star. Birds will also take advantage of a weather front to help push them along their way. The moon, however, is not used. Its brightness may even interfere with navigation – as will the lights of a large city.

To be aware of migratory movements, pay attention to weather forecasts (such as a northern moving front in the spring or a southern moving one in the fall). On a moonlit night, birds can be detected flying across the moon’s face.

The bird pictured, TOWNSEND’S WARBLER, is a small yellow bird that is strikingly arrayed in black, white, and olive-green. It is one of the most interestingly colored birds in western North America. It nests in coniferous forests from Alaska to Oregon and winters in Central America. It feeds mainly on insects, but on wintering grounds it will consume honeydew, a sugary liquid excreted by insects.

This is the only warbler to have such a distinctive face patch. We don’t see this bird very often, but it’s a treat when we get lucky enough to do so!

A Townsend’s Warbler, a night traveler, clings to the side trunk of a tree

Townsend’s Warbler, a night traveler

South Padre Island: A Spring Bird Bonanza

Flight requires a bird to have a faster metabolism, a faster heart beat, and a higher body temperature. Therefore, more energy is needed in the form of food. Meat eating raptors do not eat as often as others, but the seed and insect eaters feast all through the day. The old saying: “to eat like a bird” is extremely misleading, as birds spend every waking hour in obtaining food. If humans ate like birds, they would consume a significant percent of their body weight every day.

Migrating birds must increase their weight by half in order to have the energy that is required to make the trip. Migration is also very hazardous. So, why don’t they just stay where you would find them nine months of the year? Migrating north has advantages that offset the dangers to a species. More moderate temperatures are conducive to reproduction, so many more eggs are laid, and the longer daylight gives more time to find the necessary food. Birds flying over land can stop, rest, and feed – not so when crossing large water bodies.

SOUTH PADRE ISLAND is about two miles away from the southern tip of Texas. It is often the first land seen and exhausted birds, that have just crossed the Gulf of Mexico; gratefully drop into the trees and bushes to feed and recuperate. A small group of trees and shrubs (by the Island’s Convention center) that is not as big as our yard here in Idaho, is just teeming with species. Photographers from all over the USA, Canada, England, and even South Africa; also flock to this place and line up around the area shoulder to shoulder to get pictures. Every time a bird shows itself, you can hear cameras click- click-clicking in a sudden frenzy.

We photographed two species of orioles, two species of tanagers, ten different warblers, a grosbeak, as well as various other species. The PAINTED BUNTING (Pictured) was a special attraction for everyone. It is a small, seed eating bird, 4 ½ inches long, which looks like a first grader had colored it with four brightly colored crayons.

After four very productive days at this special spot, a strong wind came up from the south. It “huffed and puffed” and blew all the birds north.

A Painted Bunting in his coat of many colors

A Painted Bunting in his coat of many colors

LONG-BILLED CURLEW: Bird of Isolated, Moist Meadows

I hear her agitated, desperate call over my head! We have been driving along a back country road of Cassia County in the outer spots of cattle country. The road is parallel to pastureland. Looking overhead, I see the object of all the excitement. It’s a large bird with ample wing span. Unknowingly, we have violated her nesting territory. This bird’s name resembles its call – “curlee, curlee..” It is loud and somewhat musical. The bird can become wildly excited when something is close to the nest.

The Long-Billed Curlew is large, about 23 inches long, and has a cinnamon-brown body above with a streaked, buff-colored underside. Both sexes are large, but the female is the larger. But besides their large size, it is the long, down-curved beak that is most noticeable. It’s an adaptation useful to probe for beetles, grasshoppers, crickets, and other invertebrate organisms lurking in meadowlands and marshes.

They nest on the ground in a hollow that is close to rocks or bushes. Four eggs are laid which take a month to incubate. The chicks are precocial and the mother stays with them for two to three weeks. At that time she abandons them, and the male finishes the rearing of their offspring. Despite her departure, she will again pair up with the same male the next year.

In winter, they migrate to coastal and lake beaches. At this time they will flock and fly in formation. When we have been in California during January/February, we have seen this bird along the Pacific Ocean coast line going about the daily chore of catching shrimp and crabs.

For those of us that love birds, Numenius americanus is a treat to behold.

Hunting prey in a meadow, south of Burns, Oregon

Hunting prey in a meadow, south of Burns, Oregon