Animal migration

On their journey they cross wildebeest ( Connochaetes taurinus ) a river in southeastern Africa

Contemporary depiction of the hunt for migrating North American migrating pigeons ( Ectopistes migratorius ), which was re- enacted until it was extinct . Sometimes huge swarms of many millions of individuals formed.

For Migrating include those aspects animal's behavior to be associated with the movement within their territory or habitat of her and the change distribution area are:

• Migration , the time-coordinated, directed, mostly periodic mass movement of all or many individuals of a species or population ( English migratory species )
• Stripes or strokes , the migration of individual specimens of a species or population

The two phenomena cannot be precisely delimited from one another, since mass movements can also consist of individual movements that are not obviously connected.

Basics

The routes of animal migrations can remain stable over longer periods of time, i.e. remain limited to very specific regions, and also shift relatively quickly to other regions, and are then to be understood as a special form of expansion . There are animal migrations for species of different animal phyla and in many time gradations (from daily to once in a lifetime to the development of new habitats over many generations). Most of the migrations are active, but displacements also occur as partially or completely passive changes of location, for example through air or water currents, transport by other animals and humans. In the case of marine life forms in particular , little is known about which migratory movements underlie the regional appearance of a species.

Capture

Migrating cranes over Marburg

Animal migrations are examined by zoogeography or geozoology as part of behavioral biology , chorology  deals with the areas of distribution - the areas traveled through - and chronobiology deals with the temporal coordination of animal migrations .

So far, about 4,000 vertebrate species were as real hikers ( true migrants classified), perform the return hike, of which 1,000 species of fish. In total - as a rough estimate - there are between 5000 and 10000 migratory species.

The bird migration is relatively well understood, migrations of mammals usually only for large mammals, the migration of fish but only for economically important species for fishing. Little is known about bats , Asian antelopes , small whales , fish species from tropical rivers and insects.

In aquatic animals - including microorganisms - there is also a vertical migration within the body of water in addition to geographic migration .

causes

Even if the willingness to migrate is presumably often genetically determined, two main causes can be named as concrete impulses:

• Firstly, an insufficient supply of food, mostly combined with or due to unfavorable weather conditions. The migration is an example.
• Second, reproduction . For example, animals that are otherwise widely dispersed often move to certain places during the mating season . This increases your chances of finding a partner.

Animal migrations have often been described in great detail and are well known, but their exact triggers, whether they are migratory instincts or a specific reaction to environmental conditions, and the mechanisms of orientation ( e.g. the magnetic sense of migratory birds) have often not yet been adequately researched. What is certain is that when a migration begins , several factors usually play a role: length of day , temperatures, moulting in birds , condition of the fat deposits and others.

In addition, the connection with any effects of climate change is also the goal of current research.

Migrating species

Marine vertical walks

→ Main article : vertical migration

Animal plankton organisms of the world's oceans, for example luminous shrimp , are often found in a water depth of several hundred meters during the day in order to better hide themselves from predators, while in the dark of the night they feed on the plant plankton in the uppermost water layer. Accordingly, the plankton-eating fish stay in different water depths, as do their predators (mostly also fish).

Especially in the high latitudes there are vertical hikes in a seasonal rhythm. The juveniles of many species of copepods sink in autumn, when the food supply consisting of plant plankton becomes scarcer with increasing darkness, from the sea surface to a depth of up to 3000 meters. There they go into a kind of dormant state , only to rise to the surface again in the following spring.

Puller

Zieher stay in different regions during different seasons or under certain climatic conditions ( rainy season / dry season and the like) and sometimes cover enormous distances.

• Migratory birds
  • the arctic tern , whose breeding areas are circumpolarly mostly north of 45 ° N, but which overwinters on the South African coasts as far as the pack ice zone of the Antarctic. It covers 30,000 kilometers a year.
• Migratory butterflies , such as the admiral and painted lady in Europe, the monarch butterfly in North America
• Herbivores in search of grazing areas
  • The migrations of the North American bison are legendary
  • Every year tens of thousands of wildebeest , gazelles , zebras and buffalo migrate in the Serengeti in search of fresh grass
  • Reindeer are typical hikers: the Alaskan caribou migrate in about 30 herds with an average of about 30,000 animals up to 80 km per day and 6,000 km annually; the Canadian caribou migrates to Newfoundland seasonal than 2000 km in one direction in the closest association to protect themselves from the sandflies to protect, on the way back but isolated over a huge stretch of land distributed to the - for the individual animal most deadly attack - with warble flies to escape.
• Predators in search of prey, which often follow its migrations as well as delimit their territories.
• Maritime creatures:
  • Fish migration : salmon and other salmonids from the North Atlantic and Pacific; River eels thatmigratefrom the salt water of the Sargasso Sea to the upper river basins of the Atlantic
  • Hawksbill sea turtles
  • most of the whales and dolphins . The record among mammals is held by the gray whales in the Pacific , which migrate annually from the Bering Sea to the coast of Mexico and back, covering around 20,000 kilometers.

Inland migrants

Inland migrants stay within a (often larger) region. Their migrations are rather short distances and short periods of time, characterized by factors of food intake and reproduction, and often only typical for certain populations. Sometimes, however, the hikes extend over several months and follow the cycle of the seasons with great regularity.

• Antelopes of the African steppe make long migrations across several national borders in order to get essential salt, which they lick up in dried up salt lakes. Similar behavior is known from certain elephant and zebra populations , South American macaws and numerous other animal species.
• Wild horses and wild asses , wild camels and dromedaries travel up to 40 km per day through steppes and prairies
• Stroke birds seek breeding areas within a region
• Migratory butterfly:
  • On Rhodes almost all butterflies of the species Euplagia quadripunctaria gather in a small area in summer . After mating, they spread over the island again and lay their eggs.
• Small planktonic crustaceans “pull” vertically every day . At night they stay in the nutrient-rich surface water, during the day they sink into deeper layers. There they find less food, but they are better protected from predators.

Partial puller

There are also partial migrants in which only a part of the population migrates, especially birds (see partial migrants ).

Long-term hikers

Some of the pullers are long-term hikers who never or rarely stay longer in one region.

• Petrels that spend most of their life on the high seas
• Tuna , marlin , deep sea sharks , sailfish , swordfish , the Atlantic Highly Migratory Species (HMS) , which cannot be assigned to any specific distribution area within the Atlantic
• Snow leopards have a territory to which they are loyal, but they roam around it incessantly without having permanent sleeping places and are therefore very difficult to track down. Other big cats ( tigers , jaguars ) show similar behavior

Migration and species protection

The Convention for the Conservation of Migratory Species of Wildlife ( Bonn Convention ) of 1983 is the first to develop joint protection for “the entire population or a geographically defined subpopulation of any species or any lower taxon of wild animals, a significant proportion of which is cyclical and predictably crosses one or more national jurisdictions ”.

literature

• Peter Berthold : Bird migration - a current overview . Scientific Book Society, Darmstadt 2000, ISBN 353413656X .
• Vitus B. Dröscher , Gerd Werner, Janice Brownlees-Kaysen: Animal migrations. What's what? Volume 77. Tessloff Verlag, 1985, ISBN 3788604174 .
• Sidney A. Gauthreaux (Editor): Animal Migration, Orientation, and Navigation . Academic Press, 1997, ISBN 0-122777506 .
• Bernd Heinrich: The home instinct. The secret of animal migration. Matthes & Seitz, Berlin 2017.
• KM Kostyal: The great miracle of animal migration , National Geographic Germany, Hamburg 2010 ISBN 978-3-86690-192-6 .
• Carlo Mari: On the trail of water. The fascinating animal migration in the African steppe . Frederking & Thaler Verlag, 2000, ISBN 3894054247 .
• Talbot H. Waterman: The Inner Compass. Sensory performance of wandering animals . Spectrum of Science, 1990; ISBN 3-922508-98-7 .

Web links

• World register of migratory animal species , www.groms.de - records over 4,300 migratory vertebrate species with a minimum migration distance of 100 km
• The Western Hemisphere Migratory Species Initiative. On: www.fws.gov (English)

Individual evidence

1. ↑ ^{a b} Klaus Riede (University of Bonn): Detailed German short version for the BMU (Federal Ministry for the Environment, Nature Conservation and Nuclear Safety) on the final report “World Register of Migratory Species ” - ( Global Register of Migratory Species ) PDF document
2. ^ ^{A b} Sigrid Schiel, Barbara Niehoff: Das Pelagial . In: Gotthilf Hempel, Irmtraut Hempel, Siegrid Schiel (eds.): Fascination Marine Research . HM Hauschild, Bremen 2006, ISBN 3-89757-310-5 , p. 27-29 .
3. ↑ Holger Auel, Wilhelm Hagen: A virtual journey through the oceans - energy flows, food paths and adaptation paths . In: Gotthilf Hempel, Irmtraut Hempel, Siegrid Schiel (eds.): Fascination Marine Research . HM Hauschild, Bremen 2006, ISBN 3-89757-310-5 , p. 31-39 .
4. ^ The Magnuson-Stevens Act , at 16 USC 1802 (14). Quoted from Final Consolidated Atlantic Highly Migratory Species Fishery Management Plan . Office of Sustainable Fisheries, July 2006. Chap. I, pp. 1–1 ( PDF ( Memento of May 10, 2009 in the Internet Archive ))
5. ↑ Article I §1a. Convention on the Conservation of Migratory Species of Wild Animals (CMS) . Depositary's Original, German version, www.cms.int, 2003. Convention Text , directory of PDF files.