Hi Everybody!!
Time for another update on the Hummingbird Migration and stop over at Kates Cabin. In real time on 9-8, is close to the peak week in this location. I have over 100 birds here now and the joint is jumping! They are waiting for the others, then they will all leave together. I have documentation of everyday and there are many surprises coming. Today's photostudy reflects Aug 14, when there were 10 birds (the earlybirds!). Some of you may want to know what is Bird Migration? I have shared excerpts from the Wikipedia Page below on Bird Migration. Birds travel more miles in their lifetime than most humans ever will. Many new efforts are at work recording the Migrations (even from Space). Enjoy!!
On Guard!
Trying to gain weight!
Link to G+ Album Gallery:
https://plus.google.com/u/0/photos/117645114459863049265/albums/6055560962934474913
https://en.wikipedia.org/wiki/Bird_migration
Bird migration
From Wikipedia, the free encyclopedia
Bird migration is the regular seasonal movement, often north and south along a flyway between breeding and wintering grounds, undertaken by many species of birds. Migration, which carries high costs in predation and mortality, including from hunting by humans, is driven primarily by availability of food. Migration occurs mainly in the Northern Hemisphere where birds are funnelled on to specific routes by natural barriers such as the Mediterranean Sea or the Caribbean Sea.
Historically, migration has been recorded as much as 3,000 years ago by Ancient Greek authors including Homer and Aristotle, and in theBook of Job, for species such as storks, turtle doves, and swallows. More recently, Johannes Leche began recording dates of arrivals of spring migrants in Finland in 1749, and scientific studies have used techniques including bird ringing and satellite tracking. Threats to migratory birds have grown with habitat destruction especially of stopover and wintering sites, as well as structures such as power lines and wind farms.
The arctic tern holds the long-distance migration record for birds, travelling between Arctic breeding grounds and the Antarctic each year. Some species of tubenoses (Procellariiformes) such as albatrosses circle the earth, flying over the southern oceans, while others such asManx shearwaters migrate 14,000 km (8,700 mi) between their northern breeding grounds and the southern ocean. Shorter migrations are common, including altitudinal migrations on mountains such as the Andes and Himalayas.
The timing of migration is controlled primarily by changes in day length. Migrating birds navigate using celestial cues from the sun and stars, the earth's magnetic field, and probably also mental maps. Migration has developed independently in different groups of birds and does not appear to require genetic change; some birds have acquired migratory behaviour since the last ice age.
General patterns[edit]
Migration is the regular seasonal movement, often north and south, undertaken by many species of birds. Bird movements include those made in response to changes in food availability, habitat, or weather. Sometimes, journeys are not termed "true migration" because they are irregular (nomadism, invasions, irruptions) or in only one direction (dispersal, movement of young away from natal area). Migration is marked by its annual seasonality.[8] Non-migratory birds are said to be resident or sedentary. Approximately 1800 of the world's 10,000 bird species are long-distance migrants.[9][10]
Many bird populations migrate long distances along a flyway. The most common pattern involves flying north in the spring to breed in the temperate orArctic summer and returning in the autumn to wintering grounds in warmer regions to the south. Of course, in the Southern Hemisphere the directions are reversed, but there is less land area in the far South to support long-distance migration.[11]
The primary motivation for migration appears to be food; for example, some hummingbirds choose not to migrate if fed through the winter.[12] Also, the longer days of the northern summer provide extended time for breeding birds to feed their young. This helps diurnal birds to produce larger clutches than related non-migratory species that remain in the tropics. As the days shorten in autumn, the birds return to warmer regions where the available food supply varies little with the season.[13]
These advantages offset the high stress, physical exertion costs, and other risks of the migration such as predation. Predation can be heightened during migration: Eleonora's falcon, which breeds on Mediterranean islands, has a very late breeding season, coordinated with the autumn passage of southbound passerine migrants, which it feeds to its young. A similar strategy is adopted by the greater noctule bat, which preys on nocturnal passerine migrants.[14][15][16] The higher concentrations of migrating birds at stopover sites make them prone to parasites and pathogens, which require a heightened immune response.[11]
Within a species not all populations may be migratory; this is known as "partial migration". Partial migration is very common in the southern continents; in Australia, 44% of non-passerine birds and 32% of passerine species are partially migratory.[17] In some species, the population at higher latitudes tends to be migratory and will often winter at lower latitude. The migrating birds bypass the latitudes where other populations may be sedentary, where suitable wintering habitats may already be occupied. This is an example of leap-frog migration.[18] Many fully migratory species show leap-frog migration (birds that nest at higher latitudes spend the winter at lower latitudes), and many show the alternative, chain migration, where populations 'slide' more evenly North and South without reversing order.[19]
Within a population, it is common for different ages and/or sexes to have different patterns of timing and distance. Female chaffinches in Eastern Fennoscandia migrate earlier in the autumn than males do.[20]
Most migrations begin with the birds starting off in a broad front. Often, this front narrows into one or more preferred routes termed flyways. These routes typically follow mountain ranges or coastlines, sometimes rivers, and may take advantage of updrafts and other wind patterns or avoid geographical barriers such as large stretches of open water. The specific routes may be genetically programmed or learned to varying degrees. The routes taken on forward and return migration are often different.[11] A common pattern in North America is clockwise migration, where birds flying North tend to be further West, and flying South tend to shift Eastwards.
Many, if not most, birds migrate in flocks. For larger birds, flying in flocks reduces the energy cost. Geese in a V-formation may conserve 12–20% of the energy they would need to fly alone.[21][22] Red Knots Calidris canutus and Dunlins Calidris alpina were found in radar studies to fly 5 km per hour faster in flocks than when they were flying alone.[11]
Birds fly at varying altitudes during migration. An expedition to Mt. Everest found skeletons of northern pintail and black-tailed godwit at 5000 m (16,400 ft) on the Khumbu Glacier.[23] bar-headed geese have been recorded by GPS flying at up to 6,540 metres while crossing the Himalayas, at the same time engaging in the highest rates of climb to altitude for any bird. Anecdotal reports of them flying much higher have yet to be corroborated with any direct evidence.[24] Seabirds fly low over water but gain altitude when crossing land, and the reverse pattern is seen in landbirds.[25][26] However most bird migration is in the range of 150 m (500 ft) to 600 m (2000 ft). Bird strike aviation records from the United States show most collisions occur below 600 m (2000 ft) and almost none above 1800 m (6000 ft).[27]
Bird migration is not limited to birds that can fly. Most species of penguin migrate by swimming. These routes can cover over 1000 km. Blue GrouseDendragapus obscurus perform altitudinal migration mostly by walking. Emus in Australia have been observed to undertake long-distance movements on foot during droughts.[11]
Nocturnal migration in smaller insectivorous birds[edit]
Many of the smaller insectivorous birds including the warblers, hummingbirds and flycatchers migrate large distances, usually at night. They land in the morning and may feed for a few days before resuming their migration. The birds are referred to as passage migrants in the regions where they occur for short durations between the origin and destination.[42]
Nocturnal migrants minimize predation, avoid overheating, and can feed during the day.[1] One cost of nocturnal migration is the loss of sleep. Migrants may be able to alter their quality of sleep to compensate for the loss.[43]
[edit]
Main article: Animal navigation
Navigation is based on a variety of senses. Many birds have been shown to use a sun compass. Using the sun for direction involves the need for making compensation based on the time. Navigation has also been shown to be based on a combination of other abilities including the ability to detect magnetic fields (magnetoception), use visual landmarks as well as olfactory cues.[57]
Long distance migrants are believed to disperse as young birds and form attachments to potential breeding sites and to favourite wintering sites. Once the site attachment is made they show high site-fidelity, visiting the same wintering sites year after year.[58]
The ability of birds to navigate during migrations cannot be fully explained by endogenous programming, even with the help of responses to environmental cues. The ability to successfully perform long-distance migrations can probably only be fully explained with an accounting for the cognitive ability of the birds to recognize habitats and form mental maps. Satellite tracking of day migrating raptors such as Ospreys and Honey Buzzards has shown that older individuals are better at making corrections for wind drift.[59]
Migratory birds may use two electromagnetic tools to find their destinations: one that is entirely innate and another that relies on experience. A young bird on its first migration flies in the correct direction according to the Earth's magnetic field, but does not know how far the journey will be. It does this through a radical pair mechanism whereby chemical reactions in special photo pigments sensitive to long wavelengthsare affected by the field. Although this only works during daylight hours, it does not use the position of the sun in any way. At this stage the bird is in the position of a boy scout with a compass but no map, until it grows accustomed to the journey and can put its other capabilities to use. With experience they learn various landmarks and this "mapping" is done by magnetites in the trigeminal system, which tell the bird how strong the field is. Because birds migrate between northern and southern regions, the magnetic field strengths at different latitudes let it interpret the radical pair mechanism more accurately and let it know when it has reached its destination.[60] There is a neural connection between the eye and "Cluster N", the part of the forebrain that is active during migrational orientation, suggesting that birds may actually be able to see the magnetic field of the earth.[61][62]
Threats and conservation[edit]
Main article: Bird migration perils
Human activities have threatened many migratory bird species. The distances involved in bird migration mean that they often cross political boundaries of countries and conservation measures require international cooperation. Several international treaties have been signed to protect migratory species including the Migratory Bird Treaty Act of 1918 of the US.[95] and the African-Eurasian Migratory Waterbird Agreement[96]
The concentration of birds during migration can put species at risk. Some spectacular migrants have already gone extinct; during the passenger pigeon's (Ectopistes migratorius) migration the enormous flocks were a mile (1.6 km) wide, darkening the sky and 300 miles (480 km) long, taking several days to pass.[97]
Other significant areas include stop-over sites between the wintering and breeding territories.[98] A capture-recapture study of passerine migrants with high fidelity for breeding and wintering sites did not show similar strict association with stop-over sites.[99]
Hunting along migration routes threatens some bird species. The populations of Siberian cranes that wintered in India declined due to hunting along the route, particularly in Afghanistan and Central Asia. Birds were last seen in their favourite wintering grounds in Keoladeo National Park in 2002.[100] Structures such as power lines, wind farms and offshore oil-rigs have also been known to affect migratory birds.[101] Other migration hazards include pollution, storms, wildfires, and habitat destruction along migration routes, denying migrants food at stopover points.[102] For example, in the East Asian–Australasian Flyway, up to 65% of key intertidal habitat at the Yellow Sea migration bottleneck has been destroyed since 1950s [103][104]
...this is brendasue signing off from Rainbow Creek. See you next time!
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