Range: North America , Canada , Mexico. Color: Brown , White. Size: Medium. View all. By investing in our future, you advance our mission to cultivate widespread enjoyment and understanding of all things green. Return to site. Open today: am - pm. If you respond and have not already registered, you will receive periodic updates and communications from Golden Gate National Parks Conservancy. Unpacking the phenology of Bay Area raptors. The autumn raptor migration at the Golden Gate runs August through December.
The spring migration is late February through May. So how is it that my neighborhood Bay Area Redtails are nesting in April? How exactly does the hawk breeding season fit between May and August? This is all about the science of phenology. Phenology is the study of the dates and timing of ecological events. Phenology is grounded in human curiosity and survival. Imagine for a second living thousands of years ago at the edge of San Francisco Bay in the winter.
She who accurately knew the dates when Snow Geese returned to the Bay was a critical provider for her people. One of the earliest forms of scientist, phenologists recorded dates of events, tracking change from year to year, so it is no surprise that our intuitions today still try to make sense of dates in the lives of other species. Beginning in , the annual date was written down, and it is still noted today—a year ecological record!
For a student of global change, such as climate change, that record is pure gold today. What, you wonder, does this have to do with the hawk nesting and migration near the Golden Gate?
We too are tracking the timing of raptor migrations past the Golden Gate each year. For each of the nineteen species of hawk, eagle, falcon, osprey, vulture, and harrier, we study the migratory peak dates annually, but also the first and final migration dates where possible. Not only does each species of bird have a different migration or non-migration strategy, but sometimes within a species, there are multiple migration strategies. Redtails are one of those. If you have a bird field guide, pull it out and flip to the Red-tailed Hawk page.
Look at the range map. What do you see? Adults are brownish above, with white mottling, and whitish to cream colored below. Many, but not all individuals, have partial belly bands comprised of dark brown streaks. Juveniles, which tend to have paler heads than adults, have narrower wings and longer, light-brown—not rufous—tails with narrow dark-brown bands. The belly bands of juveniles often are more conspicuous than those of adults.
Males and females overlap considerably in size. Redtails tend to flap less, and to be more deliberate in their maneuvers while soaring than other buteos. Red-tailed Hawks are opportunistic predators, scavengers, and piratical raptors that feed on most medium-sized mammals, birds, and reptiles. Most hunting is done from perches, although individuals also hunt while hovering, especially in regions with few trees. Many redtails supplement captured prey by scavenging on recently killed carcasses, including roadkills.
In winter, the species frequently robs smaller raptors, including Rough-legged Hawks and Northern Harriers, of their prey. Some individuals appear to specialize in such piratical tactics. Redtails, even sedentary birds who have maintained close contact with their mate from the previous breeding season, begin courting in late winter.
Courtship, which typically involves circle soaring in tandem at great heights, sky-dancing i. Copulation lasts from 5 to 15 secs. Redtails—especially sedentary individuals—frequently are monogamous, and sometimes mate for life. Red-tailed Hawks build relatively large stick nests that sometimes measure 30 inches across. Nests, which are built by both members of the pair, typically are placed in the crowns of tall trees in woodlots and tree-rows, and, less frequently, in large contiguous forests.
Nest-sites usually afford a commanding view of the surrounding landscape. The nest, which takes about a week to build, often is refurbished with greenery.
Although many pairs reuse nests from previous years, others build one or more alternative nests in a single season. Females lay eggs, which are incubated by both parents, and which take from 4 to 5 weeks to hatch. Young redtails, which fledge days after hatching, remain close to the nest and are fed by their parents for an additional 2 to 4 weeks. Some juveniles remain somewhat attached to their parents for as long as 10 weeks after fledging. Although a few yearlings breed successfully, most individuals do not breed until they are almost two years old.
Unlike several other large raptors, the Red-tailed Hawk was never singled out as a pest species in Pennsylvania. As a result the redtail was considered a rare breeder in and around Hawk Mountain as recently as the late s. Evidence suggests that this threat has declined in recent years. Red-tailed Hawks did not undergo large-scale reproductive failures or population declines during the DDT era earlier this century.
Current threats to the species include sporadic shooting and harassment at nest sites, and collisions with automobiles and trucks. Red-tailed Hawks have largely replaced Red-shouldered Hawks throughout much of eastern North America as forest fragmentation has created patchwork habitats favorable to the former.
Overall, the species appears to be increasing its breeding and wintering populations throughout Pennsylvania and much of eastern North America. Red-tails tend to be resident at low latitudes and migratory at higher latitudes, especially in regions of prolonged snow cover.
There is little evidence that redtails were substantially affected by the widespread use of organochlorines during the middle of the 20th Century. In the 20th Century, their range expanded due to increased availability of suitable habitat due to human activities, and reduced human persecution. Redtails favor open areas with patches of trees. When such areas are either further deforested or are allowed to grow into unbroken forest the number of redtails in the area is likely to decline.
Automobile collisions, nest interference, and, to a lesser extent, shooting are threats to this species. Within- and among-year effects of cold fronts on migrating raptors at Hawk Mountain, Pennsylvania, The Auk Hawks in flight. Houghton Mifflin Company, Boston, Massachusetts. Red-tailed hawks are monogamous and may mate for life. They make stick nests high above the ground, in which the female lays one to five eggs each year. Both sexes incubate the eggs for four to five weeks, and feed the young from the time they hatch until they leave the nest about six weeks later.
According to the scientific literature, Red-tailed Hawks usually incubate their eggs for about days, but the hawks at this site tend to incubate a little bit longer. The eggs hatched on April 22, April 24, and April Start by changing your feeders, switching to ones that have a large cover or canopy overhead.
You also can try caged bird feeders that will put the birds out of grasp.
0コメント