Bird migration is the regular seasonal journey
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.
In contrast, birds that are non-migratory are said to be resident
or sedentary. Approximately 1800 of the world's
10,000 bird species are long-distance migrants.
Migration
routes of birds based on Newton, I. 2008.
The Migration
Ecology of Birds. Academic Press |
Many bird populations migrate long distances along a flyway.
The most common pattern involves flying north in the
spring to breed in the temperate or Arctic summer and returning
in the autumn to wintering grounds in warmer regions
to the south. (See Ruff, Philomachus puganx, on map above).
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.
See the Demoiselle Cranes fantastic journey across Himalaya
here.
(5 minutes video)
The primary motivation for migration appears to be food; for
example, some hummingbirds choose not to migrate if fed
through the winter. 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.
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Risks
during migration. 1.
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Populations of migratory birds are usually considered
to be limited by conditions in breeding or wintering areas,
but some might be limited by conditions encountered on
migration. This could occur at stopover sites where competition
for restricted food supplies can reduce subsequent survival
or breeding success, or during the flights themselves,
when
adverse weather can occasionally kill large numbers of
individuals. Competition for food could act in a density-dependent
manner and help to regulate populations, whereas weather
effects are more likely to act in a density-independent
manner.
When preparing for migration, birds must normally obtain
more food per day than usual, in order to accumulate the
body
reserves that fuel their flights. Birds often concentrate
in large numbers at particular stopover sites, where food
can
become scarce, thus affecting migratory performance. Rates
of weight gain, departure weights, and stopover durations
often correlate with food supplies at stopover sites,
sometimes influencing the subsequent survival and reproductive
success of individuals, which can in turn affect subsequent
breeding numbers.
Migrants in flight occasionally suffer substantial mortality
in storms, especially over water, sometimes involving
many
thousands of birds at a time. Other mass mortalities have
resulted from atypical ‘winter-like’ weather,
occurring soon after
the arrival of summer migrants in their breeding areas
or just before their departure in autumn. Again, many
thousands of
birds at a time have been killed in such incidents, causing
reductions of 30–90% in local breeding densities.
In some bird
species, migration-related events can at times have substantial
effects on the year-to-year changes in breeding population
levels. Nonetheless, the difficulties involved in investigating
migrating birds at different points on their migration
routes have
so far limited the number of studies on the influence
of events during migration periods on population levels.
From Journal of Ornithology,
Volume 147, Number 2 (2006), 146-166, DOI: 10.1007/s10336-006-0058-4
Review : Can conditions experienced during migration limit
the population levels of birds? by Ian Newton |
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Risks
during migration. 2.
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Malta and Cyprus are wellknown by birdlovers as virtual
death traps to millions of migrating birds every year
- and the
hunting that takes place is to a great extent illegal.
Cyprus and Malta are however far from the only countries
in the Mediterranean area with an extensive, and remarkably
regular practice of illegal hunting of migrating birds.
On the contrary, migrating birds are on principle hunted
all the way
from Portugal in the west to Lebanon and Syria in the
east. Of about 5 billion migrating birds passing through
the
Mediterranean area each year, 500 million are
shot or trapped. In other words: one migrating bird
in ten is killed by
hunters in the Mediterranean!
Seen in the perspective of how extensive landscape
changes, in particular intensive farming and forestry,
has affected the
birds of Europe, hunting has long been treated as a
minor problem. Nevertheless it has most likely had a
significant
importance both locally and, for some vulnerable species,
over a far wider area. A good example of this is the
Honey Buzzard, Pernis apivorus, which
has declined markedly in Scandinavia and which is shot
in large numbers
every year in the Mediterranean area. Another example
is the Ortolan Bunting,
Emberiza hortulana. This species is
also declining in Scandinavia, and we can only speculate
what effect hunting in France has had for some 50,000
birds
annually.
Today, a great number of the migrating birds killed
are consumed; but this has no longer any vital, if any
importance at
all, for the national economy. Instead it has become
a luxury consumption, when not regarded as preservation
of tradition
- or merely a leisure activity where the prey is simply
thrown away or (as in Malta) given to a taxidermist
for stuffing so
that they can subsequently end up on a hunter's bookshelf.
Nowadays hunting is a large scale activity as in Cyprus
where lime as well as mist nets are used, and as if
this isn't enough,
tape-recorders with endless tapes of bird song are used.
Sometimes whole plantations of shrubs are covered with
up to
nine meter high mist nets or are prepared with lime
sticks in the early evening. During the night the tape-recorder
plays the
song of, for instance, the Blackcap,
Sylvia atricapilla, and so attracts migrating
birds. In the morning the nets and sticks
are emptied, and the catch often consists of hundreds
or thousands of birds
Also, when it comes to hunting with fire-arms, there
has been a considerable change for the worse for the
birds during the
past few decades. While the hunters formerly used double-barrelled
shot-guns that needed reloading after two shots,
most of the hunters today have semi-automatic shot-guns
with several cartridges in the magazine. A passing bird
has little
chance of getting away, especially when lines of hunters
are posted along flight routes which the birds are obliged
to use.
Red-legged
Partridge,
Alectoris rufa
Photo:
Arturo Nikolai
From an Ad on Internet:
Spain will capture your heart while
enroute to the finest bird shooting in the world.
In keeping with the old world charm and character
of the jewel of Europe, xxxx will plan the
most exciting and authentic red-legged
partridge shooting experience
in existence.
You will have two full days of
shooting followed by a day of sightseeing and
then a third day of shooting. The expected bag
is 500 downed birds per day for a group of eight
to ten guns. |
Every year, roughly 20 million migrating birds are killed
in Cyprus. The majority of these birds are caught in mist
nets,
traps or with lime sticks. Mainly warblers (primarily
Blackcaps, Sylvia
atricapilla, Bee-eaters, Merops apiaster,
urtle Doves, Streptopelia turtur, Robins, Erithacus
rubecula, Nightingales, Luscinia megarhynchos,
Song Thrushes,
Turdus philomelos and sparrows, Passer ssp.
are caught. Thereafter the species not considered eatable
are discarded.
Blackcap
(Sylvia atricapilla)
Photo:
© www.arthurgrosset.com |
The remainder are sold as delicacies, and are said
to bring up to1 GBP/1 Euro) apiece. In shops and restaurants
they are
sold for more then 2 Euro). A complete dinner of small
birds often consists of more than a dozen birds.
An example of an illegal and devastatingly efficient form
of hunting is the so called baracca-hunt which is primarily
practised in Catalonia and Valencia in Spain. Artificial
shrubberies, often rectangular in shape, are created with
evergreen
trees. In these baraccas lime sticks are set out with
a tape-recorder playing an endless tape of most usually
Song Thrush
Turdus philomelos, song in the centre. During the
night the song is heard and passing migrants are attracted.
One single
baracca is said to trap up to 1,000 birds
a night.
Song
Thrush, Turdus
philomelos
Photo: © www.arthurgrosset.com
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Among the Song Thrushes other species such as Scops
Owls, Otus scops and Little Owls, Athene noctua,
also fall
victim to the traps. Hardly any hunter bothers to take
the time to clear these collateral catches from the
sticky lime; the
uneatable species are killed and discarded. This hunting
method is forbidden but nevertheless widely practised.
A complicating fact is that it has an unofficial support
among some politicians as it is regarded as a regional
Catalonian or
Valencian tradition, with which the central government
in Madrid (and even less the EU) have no business to
interfere.
Source: http://proaction.tripod.com/infoandlinks/id8.html
©
BirdLife Cyprus
BirdLife Cyprus has carried
out monitoring of illegal trapping right through
2011 and discovered that
2.8 million birds have been victims of this practice
during the year. It is the highest number of cases
reported since BirdLife Cyprus’ campaign
against the illegal killing of birds was launched
ten years ago.
This dramatic figure highlights the increasing
trend in bird trapping in the country, which threatens
to
reverse all the progresses achieved in the first
years of the new millennium.
This post was
written by: BirdLife Europe, http://www.birdlife.org/community/author/birdlife-europe/
downloaded May 18th, 2012
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Risks
during migration. 3.
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Migratory
birds flying above the col d'Iraty,
French Basque country.
© Franco Zecchin / Picturetank ZEF0184420
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France is the country of hunting (2 times more
hunters than in the UK), and the southwest is its
paradise. From the 25th
of October until the 15th of November, from Bordeaux
to Toulouse, a large part of the adult male population
is all over
the Pyrenees mountains, hunting the "palombe
bleue", the king of birds. The migratory wood
pigeon (ring dove) flies
above the mountains during its annual migration
from the north to the south of Europe. On the ground,
thousands of
hunters are waiting. As many as 1,8 million of these
birds are killed each year in the southwest of France,
by more
than 100.000 hunters
Source: http://franco.zecchin.book.picturetank.com/___/series/e2848ef0fb853ebc7292071ca6888da8/a/Hunting_Frenzy.html |
Bird-lovers and nature-lovers of France pay about 15.000
Euros, or US $ 25.000, for hiring a hill like the one
on the
picture above, from Sept 15th ot Nov. 15th. They put up
their binoculars and cameras, and count the birds passing
the Pyrenean Mountains, and they keep the hunters away
from this place at least. But as shown on the picture,
there
have been built hiding-places for the hunters all the
way up to the top. During 1980 there were killed about
5.700.000 doves in the French part of the Pyreneans. Huntes
also have to pay as much for the rights to sit on a hill,
and thay tells how popular this sport really is among
the hunters.
For 13 hill-ridges the communities or other propertyowners
receive about 300.000 US $ a year, which makes it
very difficult for them to stop this 'sport'.
Cranes
in flight,
another popular target while crossing the Pyreneans
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The shelters on the ridges may range from a few up to
20 on larger ridges. In each shelter their are room for
1 to 8
hunters. Several thousand cranes also pass this area during
the autumn, and are easy targets for the hunters, but
doubfully no value to the hunters when the cranes are
shot.
Source: The book "Vårens
Budbärare Tranan" (swedish) by Britt Traneving. |
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. 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.
Migrating
waders in Roebuck Bay, Western Australia
Limosa lapponica and Thalasseus bergii,
http://en.wikipedia.org/wiki/File:Waders_in_flight_Roebuck_Bay.jpg
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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. 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.
Black-tailed
Godwit, Limosa limosa, Belgium
Photo: Hans Hillewaert |
Birds fly at varying altitudes during migration. An expedition
to Mt. Everest found skeletons of Pintail and Black-tailed
Godwit
at 5000 m on the Khumbu Glacier. 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. Seabirds fly
low over water but gain altitude when crossing land, and the
reverse pattern is seen in landbirds. However most bird
migration is in the range of 150 m to 600 m.
See the Demoiselle Cranes fantastic journey across Himalaya
here.
(5 minutes video)
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 Grouse, Dendragapus obscurus, perform
altitudinal migration mostly by walking. Emus in Australia
have been observed to undertake long-distance movements on foot
during droughts.
Source: http://en.wikipedia.org/wiki/Bird_migration
Migration
of the Bar-tailed Godwit Limosa lapponica
Map: United States Geological Survey,
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Migration
of the Bar-tailed Godwit Limosa lapponica.Bar-tailed
Godwits have recently (March 2007) been shown to
undertake the longest non-stop flight of any bird. Using satellite
tracking, birds in New Zealand were tagged and tracked
all the way to the Yellow Sea in China. According to Dr. Clive
Minton (Australasian Wader Studies Group) "The distance
between these two locations is 9,575 km, but the actual track
flown by the bird was 11,026 km. This is the longest known
non-stop flight of any bird. The flight took approximately nine
days. At least three other Bar-tailed Godwits also appear to
have reached the Yellow Sea after non-stop flights from New
Zealand."
One
specific female of the flock, nicknamed "E7", (see
story below) flew onward from China to Alaska and stayed
there for
the breeding season. Then on 29 August 2007 she departed on
a non-stop flight from the Avinof Peninsula in western Alaska
to the Piako River near Thames New Zealand, setting a new known
flight record of 11,680 kilometres. Stray birds from
Europe and Asia occasionally appear on both North American coasts.
One Arctic
Tern,
Sterna paradisaea, ringed (banded)
as a chick on the Farne Islands off the British east coast,
reached Melbourne, Australia in just three months from fledging,
a sea journey of over 22,000 km |
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The
Story about the E7 flight
The famous female Bar-tailed Godwit, E7
Illustration
of Earth showing the 29,000 km round-trip flight path
from New Zealand
of the Bar-tailed Godwait dubbed "E7."
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A female Bar-tailed Godwit, a large, streamlined shorebird,
has touched down in New Zealand following an epic,
29,000 km long series of flights tracked by satellite, including
the longest non-stop flight recorded for a land bird.
The U.S. Geological Survey's Alaska Science Center tracked
the odyssey of the bird as part of an ongoing collaborative
effort with colleagues in California and New Zealand. The scientists
were hoping to better understand potential
transmission of avian influenza by migratory birds.
The bird, dubbed "E7" after the tag on its upper
leg, was captured along with 15 other godwits in New Zealand
in early
February 2007. There each bird was fitted with a small, battery-powered
satellite transmitter. USGS scientists hoped
the transmitters' batteries would last long enough to track
the birds' northward migration to Alaska.
On March 17, E7 departed Miranda on the North Island of New
Zealand and flew non-stop to Yalu Jiang, China,
completing the 11.000-km-long flight in about eight days. There
she settled in for a 5-week-long layover before departing
for the breeding grounds.
On the evening of May 1, she headed east out over the Sea of
Japan and the North Pacific, eventually turning northeast
towards Alaska, crossing the end of the Alaska Peninsula en
route to her eventual nesting area on the Yukon-Kuskokwim
River Delta in western Alaska. This flight was also accomplished
non-stop, covering some 7.250 km in five days.
E7 was then tracked to the coast of the Yukon Delta where she
joined other godwits preparing for their return flight to
New Zealand.
On the early morning of August 29, she took off southeast back
across the Alaska Peninsula, went out over the vast North
Pacific and headed towards the Hawaiian Islands. When less than
a day's flight from the main Hawaiian Islands, she
turned southwest, crossing the Hawaiian Archipelago over open
ocean 200 km west of Kauai, heading towards Fiji.
She crossed the dateline about 480km north-northeast of Fiji,
and then appeared to fly directly over or slightly west of
Fiji, continuing south towards New Zealand.
In the early afternoon of September 7th she passed just offshore
of North Cape, New Zealand, and then turned back
southeast, making landfall in the late evening at the mouth
of a small river, eight miles east of where she had been captured
seven months earlier.
The last leg of E7's journey is the most extraordinary, entailing
a non-stop flight of more than eight days and a distance of
11.500 km, the equivalent of making a roundtrip flight between
New York and San Francisco, and then flying back again
to San Francisco without ever touching down.
Since they are land birds, godwits like E7 can't stop to eat
or drink while flying over open-ocean. The constant flight speeds
at which E7 was tracked by satellite indicate that she did not
stop on land.
Godwits do not become adults until their 3rd or 4th year and
many live beyond 20 years of age. If 29,000 km is an
average annual flight distance, then an adult godwit would fly
some 460,000 km in a lifetime, or about 11,5 times around
the globe..
The study that recorded E7's epic flight is a collaborative
effort led jointly by USGS and Point Reyes Conservation
Science, with cooperators from Massey University and Miranda
Shorebird Centre, New Zealand, and The Global
Flyway Network. The project is funded by the David and Lucile
Packard Foundation, the USGS, Alaska Science
Center, and the U.S. Fish and Wildlife Service.
For more information, or to track E7, the Bar-tailed Godwit,
visit the Shorebird Research Web site.
Contact
Information:
U.S. Department of the Interior, U.S. Geological Survey
Office of Communication
119 National Center
Reston, VA 20192 Mike Gauldin
Phone: 703-648-4447
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