Mindblowing Planet Earth

Tuesday, 17 September 2019

The Red-tailed Hawk Facts

Order Falconiformes, Family Accipitridae. The family Accipitridae includes most birds of prey except falcons, owls, and American vultures. Buteo hawks are moderately large soaring hawks that inhabit open or semi-open areas. They are the most common daytime avian predators on ground-dwelling vertebrates, particularly rodents and other small mammals.

They range in size from the broad-winged hawk (41 cm bill tip to tail tip) to the ferruginous hawk (58 cm). Hawks egest pellets that contain undigestible parts of their prey, such as hair and feathers, that can be useful in identifying the types of prey eaten (bones usually are digested completely).

Where Does Red-tailed Hawk Live?

The red-tailed hawk “Buteo jamaicensis” is the most common Buteo species in the United States. Breeding populations are distributed throughout most wooded and semi-wooded regions of the United States and Canada south of the tundra, although some populations are found in deserts and prairie habitats. Six subspecies are recognized. Nesting primarily in woodlands, red-tails feed in open country on a wide variety of small-to-medium-sized prey.

Body Size

Males of this medium-sized buteo (46 cm) weigh about 1 kg, and females are approximately 20 percent heavier than the males. Otherwise, the sexes look alike.

Habitat

Red-tails are found in habitats ranging from woodlands, wetlands, pastures, and prairies to deserts. They appear to prefer a mixed landscape containing old fields, wetlands, and pastures for foraging interspersed with groves of woodlands and bluffs and streamside trees for perching and nesting. Red-tails build their nests close to the tops of trees in low-density forests and often in trees that are on a slope.

In areas where trees are scarce, nests are built on other structures, occasionally in cactus, on rock pinnacles or ledges, or man-made structures. In winter, night roosts usually are in thick conifers if available and in other types of trees otherwise.

What Does Red-Tailed Hawk Eat?

The Red-tails hunt mainly from an elevated perch, often near woodland edges. Small mammals, including mice, shrews, voles, rabbits, and squirrels, are important prey, particularly during winter. Red-tails also eat a wide variety of foods depending on availability, including birds, lizards, snakes, and large insects.

In general, red-tails are opportunistic and will feed on whatever species are most abundant Winter food choices vary with snow cover; when small mammals such as voles become unavailable (under the snow), red-tails may concentrate on larger prey, such as pheasants.

Juvenile Red-tailed Hawk

Juveniles molt into adult plumage in a gradual process from the spring (age about 14 months) to summer or early fall.

Migration.

The more northerly red-tailed hawk populations are migratory while the more southerly is year-round residents.

Red-tailed Hawk Life Cycle

Red-tails lay one clutch per year consisting of one to three eggs, although a replacement clutch is possible if the initial clutch is lost early in the breeding season. Their nests are large and built of twigs. Both sexes incubate, but the male provides food for the female during incubation and the entire family following hatching. The parents continue to feed their young after fledging while they are learning to hunt.

Red-tailed Hawk Lifespan

The average life span of a wild red hawk is around 20 to 25 years.

Re-tailed Hawk Behavior

Red-tailed hawks are territorial throughout the year, including winter. Trees or other sites for nesting and perching are important requirements for breeding territories and can determine which habitats are used in an area.

Home range size can vary from a few hundred hectares to over 1,500 hectares, depending on the habitat. The size of red-tail territories and the location of boundaries between territories varied little from year to year, even though individual birds or pairs died and were replaced.

Population density.

Population densities normally do not exceed 0.03 pairs per hectare, and habitually are lower than 0.005 pairs per hectare. Populations in southern areas such as Florida can increase substantially in the winter with the influx of migrants from the more northerly populations.

Population dynamics.

Beginning at 2 years of age, most red-tailed hawks attempt to breed, although the proportion of breeding can vary by population and environmental conditions. Average clutch size varies regionally, tending to increase from east to west and from south to north. The density of their main prey, the snowshoe hare, over the years.

The mean clutch size for the red-tail population, however, appeared to vary with prey density, from 1.7 to 2.6 eggs/nest. Over the course of the study, about 50 percent of observed nestling losses occurred within 3 to 4 weeks after hatching due to starvation.

Most of the variance in yearly mortality of nestlings could be attributed to the amount of food supplied and the frequency of rain. Large raptors such as horned owls also can be important sources of mortality for red-tail nestlings in some areas.

Similar species

1. The ferruginous hawk (Buteo regalis), one of the larger buteos (58 cm), inhabits the dry open country of the western United States.

2. The red-shouldered hawk (Buteo lineatus) is slightly smaller (53 cm) and feeds on snakes, frogs, crayfish, mice, and some small birds. Its range is east of the Rocky Mountains and in California, with moist mixed woodlands preferred.

3. Swainson's hawk (Buteo swainsoni) is restricted to the open plains of the western United States. Although it is as large (53 cm) as the red-tail, it preys mostly on insects.

4. The broad-winged hawk (Buteo platypterus) is one of the smaller buteos (41 cm) and preys on mice, frogs, snakes, and insects. It prefers woodlands and is found almost exclusively east of the Mississippi River.

5. Harris' hawk (Parabuteo unicinctus) is similar in size (53 cm) to the red-tailed hawk but is restricted to the semiarid wood and brushlands of the southwest. This bird nests in saguaro, mesquite, and yucca and preys on rodents, lizards, and small birds.

6. The rough-legged hawk (Buteo lagopus) is one of the larger buteos (56 cm). It winters throughout most of the United States in open country but breeds only in the high arctic of North America.

7. The zone-tailed hawk (Buteo albonotatus) is slightly smaller (51 cm) than most buteos and feeds on rodents, lizards, fish, frogs, and small birds. It can be found in mesa and mountain country within its limited range between the southwest United States and Mexico.

8. The short-tailed hawk (Buteo brachyurus) is the smallest buteo (39 cm) and can only be found in the southern tip of Florida in mixed woodland and grassland habitats.

Read More – The Lesser Goldfinch (Spinus psaltria) / The Himalayan Cutia / The fire-tailed myzornis / Pando – The One Tree Forest / Great Blue Heron

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Thursday, 12 September 2019

American Robin Facts

The American robin (Turdus migratorius) occurs throughout most of the continental United States and Canada. This is a migratory songbird of the true thrush genus and Turdidae, the wider thrush family Muscicapidae. American robins are common garden birds overmuch of North America and their distinctive foraging behavior is well known. During the breeding season and winters in the southern half of the United States and in Mexico and Central America.

The breeding range of the robin has expanded in recent times with the increasing area covered by lawns and other open habitats. American Robin body size is approximately 23 to 28 cm long, with weight of average 77g. However, female robin is about 59 to 91g. This is commonly a friendly songbird, very much comfortable around people. Sometimes even get close to dogs while playing in yard, also fast and strong in flight. Male Robins are more aggressive then females and like to spend maximum time in interactions with fertilizable mates.

American Robin Bird

The sexes are similar in size and appearance. Their size varies slightly geographically. The smallest robins are found in the eastern United States and along the Pacific coast, and the largest ones occur in the Rocky Mountains, northern Great Plains, and northern deserts. The size of robins tends to increase with latitude in eastern North America but does not in western North America. Fledglings attain adult size at approximately 6 weeks of age.

Male Robin head differs from black to grey, with white eye arcs and white supercilia. But the throat is white with black streaks, and under tail coverts and belly are white. The bird has a brown back and a reddish-orange breast, changing from a rich red maroon to peachy orange. The bill is mostly yellow with a patchily dark tip, the dusky area becoming more widespread in winter, and the legs and feet are brownish.

Habitats

Access to fresh water, protected nesting sites, and productive foraging areas are important requirements for breeding robins. Breeding habitats include moist forests, swamps, open woodlands, orchards, parks, and lawns. Robins forage on the ground in open areas, along habitat edges, or the edges of streams.

Moreover, they also forage above ground in shrubs and within the lower branches of trees. The main threat to Juvenile robins and eggs are preyed upon by snakes, squirrels, other birds, i.e., blue jays, Steller’s Jay, scrub jays, grackles, American crows, and common ravens.

American Robin Nest

The robins mostly nest in wooded areas are usually near some type of opening such as the forest edge or a treefall gap. During the nonbreeding season, they prefer moist woods or fruit-bearing trees and shrubs. In the fall season, flocks of migratory robins are often found along forest edges or clearings where fruits are most plentiful.

American Robin Diet

The robins forage by hopping along the ground in search of ground-dwelling invertebrates and by searching for fruit and foliage-dwelling insects in shrubs and low tree branches. In the months preceding and during the breeding season, robins feed mainly on invertebrates and on some fruits.

However, during the remainder of the year, their diet consists primarily of fruits. Robins eat a wide variety of both plant and animal. The Robins don’t like to eat many seeds, so don’t try to entice with whole peanuts, mixed bird seeds, Nyjer seeds.

What Do American Robins Eat?

It is commonly eaten fruits include plums, dogwood, sumac, hackberries, blackberries, cherries, greenbriers, raspberries, and juniper. The common invertebrates include beetles, caterpillars, moths, grasshoppers, spiders, millipedes, and earthworms.

The seasonal changes in the proportion of plants and invertebrates consumed by robins in three different sections of the United States. The average occurrence of fruits of various plant families in the stomachs of robins by month for these sections. The occurrence of fruits of various plant families in more specific areas of the United States.

There are no differences between the sexes in the proportion of types of invertebrates and fruits eaten. Very young robins (up to at least 35 days of age) feed almost entirely on insects and other invertebrates. However, older juveniles tend to eat a higher proportion of fruit and easy-to-capture prey than adults.

American Robins often show food preferences: a population in central New York seemed to prefer northern arrowwood and spicebush fruits over most other plants. Moreover, in Illinois, a group ate predominantly frost grapes and Virginia creeper in the late summer and fall.

During seasons when fruits dominate the diet, robins may need to consume quantities more than their body weight to meet their metabolic needs each day. Robins, as well as other fruit-eating birds, exhibit a low digestive efficiency for fruits. It is estimated that the metabolizable energy coefficient, the proportion of food energy that is assimilated for robins eating a mixed fruit diet to be only 55 percent.

Perhaps of the low retention time of the digested matter in the gut. The short retention time might be an adaptation to eating fruit because large quantities of the fruit must be processed to obtain an adequate protein intake. In contrast, when eating insects, robins, as well as other bird species, exhibit a higher digestive efficiency of approximately 70 percent.

Moreover, the energy content of insects tends to be higher than that of most fruits, particularly on a wet weight basis. Thus, during the spring when robins are consuming insects, they should consume a smaller amount relative to their body weight than when eating fruits.

Molt

Post juvenile and post-breeding molts occur from late July to October. During this molt, robins are consuming largely fruits and other plant materials, which contain limited proteins. This may contribute to larger fruit consumption rates at this time. During the pre-breeding molt, robins are feeding primarily on insects and other invertebrates.

Migration of American Robin

Most robins nesting in the northern United States and Canada winter in the Gulf Coast States and the Carolinas. Wintering robins are most abundant between 30- and 35-degrees N latitude. Robin flocks migrate during the day, most northern robins leave their breeding grounds from September to November and return between February and April.

American Robin Song / Call

American Robin has the sweet familiar sound of spring, a string of clear whistles with a brief pause, often repeated syllables, like cheer up, cheerily, cheer up, cheerily. The male bird sings when he is in the mood to attract females. The song varies with time of the day habitually sings from a high perch in a tree. This bird sings before and after the storms, used different calls to communicate specific information to others. The Robin also alarm in a different call, when a ground predator reaches, or their nest is being directly threatened.

Breeding activities and social organization.

The onset of the breeding season is later at higher latitudes approximately 3 days for each additional degree in the east and altitudes. But mating and egg-laying generally occur in April or May. Males arrive on the breeding grounds before females to establish territories.

The female’s pair with established males, usually for the duration of the breeding season. The female primarily builds the nest out of mud, dried grass, weedy stems, and other materials constructing it on horizontal limbs, tree-branch crotches, within shrubs, or on any one of several man-made structures with horizontal surfaces.

Eggs of American Robin

First clutches usually contain 3 to 4 eggs; later clutches tend to contain fewer eggs. The female does all the incubating, which continues for 10 to 14 days following the laying of the second egg.

American Robin Nestlings

Both males and females feed the nestlings. Following fledging, the brood often divides, with the male and female each feeding half of the fledglings for another 2 weeks. Females may start another brood before the current one is independent, leaving the male to feed all the fledglings. After reaching individuality, juveniles often form foraging flocks in areas of high food availability.

Early in the breeding season, robins often roost communally. Males can continue to use these roosts throughout the breeding season. Whereas female birds stop once they begin incubating eggs. As fall approaches and their diet turns more toward fruits, robins in many areas begin to roost communally again and may join other species, such as common grackles and European starlings, in large roosts.

American Robin Nesting Habits

During the breeding season, male robins establish breeding territories, which the female helps to defend against other robins. Nonetheless, the territories of different pairs often overlap where neither pair can establish dominance. Most foraging during the breeding season is confined to the territory, but adults sometimes leave to forage in more productive areas that are shared with other individuals.

In some prime nesting areas (e.g., dense coniferous forest), where robin densities are high, territories are small, and the birds might often forage elsewhere. Adult robins often return to the same territory in succeeding years. During the nonbreeding roosting period, robins are likely to return to the same foraging sites for many weeks and to join roosts within one to three kilometers of these foraging areas.

Nesting population density varies with habitat quality. Densely forested areas that provide well-protected nest sites have been found to support high densities of nesting robins. Therefore, the relatively small territories found in these areas might not be used as much for foraging as those containing open areas.

In the nonbreeding season, robins often join single-or mixed-species roosts that can include tens of thousands of birds. Wintering robins are most common in pine or oak-pine communities of the southeastern and southcentral United States and decrease in abundance in drier, less forested areas westward.

Robins first attempt to breed the year after they hatch and will raise multiple broods in a season. Predation is often a major source of mortality for both eggs and nestlings. Approximately half of the adult birds survive from year to year. The average longevity of a robin that survives to its first January is from 1.3 to 1.4 years.

Similar Species

The wood thrush (Hylocichlamustelina), which is smaller than the robin (18 cm), co-occurs with the robin in some woodland habitats but is only present in the eastern United States. This species nests primarily in the interiors of mature forests and have been decreasing in abundance over the past decade as forested habitats in North America become increasingly fragmented. This species is also primarily a summer resident, wintering in Florida and the neotropics.

The hermit thrush (Catharusguttatus) is found in coniferous and mixed woodlands at northerly latitudes or high elevations and winters primarily in the southern half of the United States. This species is also significantly smaller (15 cm) than the robin.

Swainson's thrush (Catharusustulatus) is present in the western and northeastern United States during the summer months, wintering in the neotropics. It is also smaller than the robin (16 cm).

The varied thrush (Ixoreus naevius) occurs in moist coniferous forests of the Pacific Northwest. This bird is similar in size (21 cm) to the robin.

Moreover, the thrushes are common, medium-sized birds that eat worms, insects, and fruit. They live in a variety of habitats, including woodlands, swamps, suburbs, and parks. Most thrushes build nests of mud and vegetation on the ground or in the crotches of trees or shrubs; bluebirds’ nest in holes in trees and posts or in nest boxes.

This group forages primarily on the ground and in low vegetation by probing and gleaning. Some thrushes are neotropical migrants while others reside year-round in North America. Thrushes range in size from the eastern and western bluebirds (18 cm from bill tip to tail tip) to the American robin (23cm to 25 cm). Male and female plumages are similar in most thrushes, although in some species, such as the bluebirds, the males are more brightly colored.

Read More – The Lesser Goldfinch (Spinus psaltria) / The Himalayan Cutia / The fire-tailed myzornis / Pando – The One Tree Forest / Great Blue Heron

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Wednesday, 11 September 2019

Great Blue Heron Facts

Herons, egrets, and bitterns are medium to large wading birds with long necks and spear-like bills. Nearly all species feed primarily on aquatic animal life e.g., fish, frogs, crayfish, insects. The common along the margins of most freshwater and saltwater bodies and wetlands. Their long legs, necks, and bills are adapted for wading in shallow water and stabbing prey.

Most species build their nests in trees near their foraging habitat, and many nests colonially. Members of this group range in size from the least bittern 28-36 cm bill tip to tail tip to the great blue heron 106-132 cm tall. The sexes are similar in size and appearance.

The great blue heron (Ardeaherodias) is the largest member of the group in North America and feeds primarily on aquatic animals. It is widely distributed in both saltwater and freshwater environments. There are following subspecies in the United States and Canada:

h. wardi (Kansas and Oklahoma across the Mississippi River to Florida).
h. herodias (remainder of the North and Central American range).
h. fannini (Pacific coast of North America from Alaska to Washington).
h. occidentalis (extreme south of Florida)
h. occidentalis (the great white heron) is an all-white color morph that was formerly considered a separate species.

Body Size

Males average slightly heavier in weight than females. Northern continental herons are somewhat smaller than those found in the south determined a relationship between age and body weight for nestling great blue herons where BW equals body weight in grams and A equals age in days.

Great Blue Heron Habitat

Great blue herons inhabit a variety of freshwater and marine areas, including freshwater lakes and rivers, brackish marshes, lagoons, mangroves, and coastal wetlands, particularly where small fish are plentiful in shallow areas. They are often seen on tidal flats and sandbars and occasionally forage in wet meadows, pastures, and other terrestrial habitats.

Great Blue Heron Nest

Great blue herons tend to nest in dense colonies or heronries. The location of the heronry is generally close to foraging grounds, and tall trees are preferred over shorter trees or bushes for nest sites. They also may nest on the ground, on rock ledges, or on sea cliffs.

Great Blue Heron Food Habits

Fish are the preferred prey, but great blues also eat amphibians, reptiles, crustaceans, insects, birds, and mammals. When fishing, they mainly use two foraging techniques: standing still and waiting for fish to swim within striking distance of 2-3 Great Blue Heron slow wading to catch more sedentary prey (such as flounder and sculpin). To fish, they require shallow waters (up to 0.5 m) with a firm substrate.

Fish up to about 20 cm in length were dominant in the diet of herons foraging in southwestern Lake Erie, and 95 percent of fish consumed by great blues in a Wisconsin population was less than 25 cm in length. Great blues sometimes forage in wet meadows and pastures in pursuit of lizards, small mammals, and large insects.

In northern areas, small mammals such as meadow voles may be an important part of the diet early in the breeding season, possibly because some aquatic foraging areas may still be partially frozen when the herons arrive. Consumption of larger prey (fish, frogs, rodents) is often followed by drinks of water; terrestrial prey such as voles are usually dunked in water before they are swallowed.

Adult herons tend to deliver the same type and size of food to their nestlings that they consume themselves, but they deliver it well digested for young nestlings and less well digested as the nestlings grow. Adults tend to feed solitary, although they may feed in single or mixed species flocks where there are large concentrations of prey, fledglings are frequently seen foraging together.

Molt.

Adults undergo a complete molt in the late summer and fall and a partial molt of the contour feathers in the late winter and early spring. Young herons attain full adult plumage in the summer/fall molt at the end of their second year.

Great Blue Heron Migration

In the northern part of its range, most great blues are migratory, some moving to the southern Atlantic and the Gulf States to overwintering with the resident populations of herons, others continuing to Cuba and Central and South America. Most migrating herons leave their breeding grounds by October or November and return between February and April.

Breeding Activities and Social Organization

The male great blue heron selects the site for the breeding territory, and nests generally consist of a stick platform over 1 m in diameter. Great blues often use a nest for more than 1 year, expanding it with each use. Mean clutch sizes range from three to five in general, clutch size tends to increase with latitude.

Only one brood is raised per year; however, if a clutch is destroyed, great blues may lay a replacement clutch, usually with fewer eggs than the initial clutch. Both parents incubate and feed the young. During the breeding season, great blues are monogamous and colonial, with from a few to hundreds of pairs nesting in the same area or heronry. Colonies may be 2-4 Great Blue Heron & include other species, such as great egrets or double-crested cormorants.

Great Blue Heron Range

Breeding colonies are generally close to foraging grounds the distance between heronries and possible feeding areas in Minnesota lakes to range from 0 to 4.2 km, averaging 1.8 km. Another study found that most heroines along the North Carolina coast were located near inlets with large concentrations of fish, an average of 7 to 8 km away.

Fifteen to 20 km is the farthest great blue herons regularly travel between foraging areas and colonies. In the northern portion of their range, great blue herons often build nests in tall trees over dry land, whereas in the southern part of their range, they usually nest in swamp trees, including mangroves.

Each breeding pair defends a small territory around the nest, the size of which depends on local habitat and the birds' stage of reproduction. Herons in some areas also defend feeding territories. In other areas, great blues appear to be opportunistic foragers, lacking strict fidelity to feeding sites. A study shows that herons often returned to the same general areas, but different individuals often used the same areas at different times.

Population density. Because great blues nest colonially, local population density (i.e., colony density, colony size, and the number of colonies) varies with the availability of suitable nesting habitat as well as foraging habitat. On islands in coastal Maine, Gibbs and others found a significant correlation between colony size and the area of tidal and intertidal wetlands within 20 km of the colonies, which was the longest distance herons in the study colonies traveled on foraging trips.

In western Oregon, the size of heronries was found to range from 32 to 161 active nests; the area enclosed by peripheral nest trees within the colonies ranged from 0.08 to 1.21 ha. Population dynamics. Most nestling loss is a result of starvation, although some losses to predation do occur. In a study of 243 nests in a coastal California colony, 65 percent of the chicks fledged, 20 percent starved, 7 percent were taken by predators, and 7 percent were lost to other causes. Estimates of the number of young fledged each year by breeding pairs range from 0.85 to 3.1.

Based on banding studies, about two-thirds of the fledglings do not survive more than 1 year, although they may survive better in protected wildlife refuges. Values for later years indicate that about one-third to one-fifth of the 2-year-old and older birds are lost each year.

Similar Species

The great egret (Casmerodiusalbus) is almost the same size (96 cm length) as the great blue heron and is found over a limited range in the breeding season, including areas in the central and eastern United States and the east and west coasts. It winters in coastal areas of the United States and in 2-5 Great Blue Heron and Mexico and farther south. The great egret's habitat preferences are like those of the great blue heron.

The snowy egret (Egretta thula), one of the medium-sized herons (51 to 69 cm), shuffles its feet to stir up benthic aquatic prey. It is found mostly in freshwater and saltwater marshes but also sometimes follows cattle and other livestock as does the cattle egret. It breeds in parts of the western, southeastern, and east coasts of the United States and winters along both coasts of the southern United States and farther south.

The cattle egret (Bubulcusibis) is seen in agricultural pastures and fields, where it follows livestock to pick up insects disturbed by grazing. An Old-World species, it was introduced into South America and reached Florida in the 1950s. It reached California by the 1960s and has been continuing to expand its range.

The green-backed heron (Butorides striatus), one of the smaller herons (41 to 56 cm), breeds over most of the United States except for the northwest and southern Midwest. It has a winter range like that of the snowy egret and seems to prefer water bodies with woodland cover.

The tricolored heron (Egretta tricolor) (formerly known as the Louisiana heron) is common in salt marshes and mangrove swamps of the east and gulf coasts, but it is rare inland.

The little blue heron (Egretta caerulea) is common in freshwater ponds, lakes, and marshes and coastal saltwater wetlands of the Gulf Coast States. Juveniles are easily confused with juvenile snowy egrets. This species hunts by walking slowly in shallow waters, and its diet typically includes fish, amphibians, crayfish, and insects.

The black-crowned night heron (Nycticorax nycticorax), characterized by a heavy body, short thick neck, and short legs (64 cm), is a common heron of freshwater swamps and tidal marshes, roosting by day in trees. It typically feeds by night, predominantly on aquatic species, fish, amphibians, and insects. This heron is extremely widespread, occurring in North and South America, Eurasia, and Africa. It breeds over much of the United States and parts of central Canada and winters along both coasts of the United States and farther south.

The yellow-crowned night heron (Nyctanassa violacea) (61 cm) is similar to the black-crowned but is more restricted in its range to the southeastern United States. It roosts in trees in wet woods, swamps, and low coastal shrubs.

The American bittern (Botauruslentiginosus), another of the medium-sized herons (58 to 70 cm), is a relatively common but elusive inhabitant of freshwater and brackish marshes and reedy lakes. It is a solitary feeder, 2-6 Great Blue Heron & consuming fish, crayfish, reptiles, amphibians, insects, and even small mammals. Its breeding range includes most of Canada and the United States, although much of the southern United States is inhabited only during the winter.

The least bittern (Ixobrychusexilis), the smallest of the North American herons (33 cm), also is an elusive inhabitant of reedy areas. Its breeding range is restricted largely to the eastern half of the United States.

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Read More – The Lesser Goldfinch (Spinus psaltria) / The Himalayan Cutia / The fire-tailed myzornis / Pando – The One Tree Forest

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