53.7: Orientation and Migratory Behavior
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Animal migration
Adapted from Wikipedia, the free encyclopedia. Animal migration - Wikipedia
Mexican free-tailed bats on their long aerial migration
Animal migration is the relatively long-distance movement of individual animals, usually on a seasonal basis. It is the most common form of migration in ecology. It is found in all major animal groups, including birds , mammals, fish , reptiles, amphibians, insects , and crustaceans. [1] The trigger for the migration may be local climate, local availability of food, the season of the year or for mating reasons. [2]
To be counted as a true migration, and not just a local dispersal or irruption, the movement of the animals should be an annual or seasonal occurrence, such as Northern Hemisphere birds migrating south for the winter; wildebeest migrating annually for seasonal grazing; or a major habitat change as part of their life, such as young Atlantic salmon or sea lamprey leaving the river of their birth when they have reached a few inches in size. [3] [4]
A Christmas Island red crab on its migration
Migration can take very different forms in different species, and as such there is no simple accepted definition of migration. One of the most commonly used definitions, proposed by Kennedy [5] is
Migratory behavior is persistent and straightened out movement effected by the animal’s own locomotory exertions or by its active embarkation upon a vehicle. It depends on some temporary inhibition of station keeping responses but promotes their eventual disinhibition and recurrence. [5]
Migration encompasses four related concepts: persistent straight movement; relocation of an individual on a greater scale (both spatially and temporally) than its normal daily activities; seasonal to-and-fro movement of a population between two areas; and movement leading to the redistribution of individuals within a population. [1] Migration can be either obligate , meaning individuals must migrate, or facultative, meaning individuals can "choose" to migrate or not. Within a migratory species or even within a single population, often not all individuals migrate. Complete migration is when all individuals migrate, partial migration is when some individuals migrate while others do not, and differential migration is when the difference between migratory and non-migratory individuals is based on age or sex (for example). [1]
While most migratory movements occur on an annual cycle, some daily movements are also referred to as migration. Many aquatic animals make a diel vertical migration , travelling a few hundred meters up and down the water column, [6] while some jellyfish make daily horizontal migrations, traveling a few hundred meters across a lake. [7]
Irregular (non-cyclical) migrations such as irruptions can occur under pressure of famine, overpopulation of a locality, or some more obscure influence. [8]
Seasonal migration is the movement of various species from one habitat to another during the year. Resource availability changes depending on seasonal fluctuations, which influence migration patterns. Some species such as Pacific salmon migrate to reproduce; every year they swim upstream to mate and then return to the ocean. [9] Temperature is a driving factor of migration that is dependent on the time of year. Many species, especially birds, migrate to warmer locations during the winter to escape poor environmental conditions. [10]
Circadian migration is where birds utilize circadian rhythm (CR) to regulate migration in both the fall and the spring. In circadian migration clocks of both circadian (daily) and circannual (annual) patterns are utilized to determine the birds’ orientation in both time and space as they migrate from one destination to the next. This type of migration is advantageous in birds that during the winter remain close to the equator, and also allows the monitoring of the auditory and spatial memory of the birds’ brain to remember an optimal site of migration. These birds also have timing mechanisms that provide avians with the distance required to travel in order to reach their destination. [11] To regulate the migration patterns of these birds, the mammalian circadian clock is utilized. This clock allows birds to determine when the appropriate time is to migrate, which location will best help them regulate their metabolism, and whether land or water travel will be most advantageous. [12]
Tidal migration is the use of tides by organisms to move periodically from one habitat to another. This type of migration is often used in order to find food or mates. Tides can carry organisms horizontally and vertically for as little as a few nanometers to even thousands of kilometers. [13] The most common form of tidal migration is to and from Intertidal zone during daily tidal cycles. [13] These zones are often populated by many different species and are nutrient rich. Organisms like crabs, nematodes, small fish, corals, and other species cycle to these areas as the tides rise and fall typically about every twelve hours. The cycle movements are associated with foraging of marine and bird species. Typically, during low tide smaller or younger species will emerge to forage because they can survive in the shallower water and have less chance of being preyed upon. During high tide, larger species can be found due to the deeper water and nutrient upwelling from the tidal movements. Tidal migration is often facilitated by ocean currents . [14]
In specific groups
Flocks of birds assembling before migration southwards
Different kinds of animal migrate in different ways.
In birds
Main article: Bird migration
Approximately 1,800 of the world's 10,000 bird species migrate long distances each year in response to the seasons. [15] Many of these migrations are north-south, with species feeding and breeding in high northern latitudes in the summer, and moving some hundreds of kilometres south for the winter. [16] Some species extend this strategy to migrate annually between the Northern and Southern Hemispheres. The Arctic tern is famous for its migration; it flies from its Arctic breeding grounds to the Antarctic and back again each year, a distance of at least 19,000 km (12,000 mi), giving it two summers every year. [17]
In fish
Main article: Fish migration
Many species of salmon migrate up rivers to spawn
Most fish species are relatively limited in their movements, remaining in a single geographical area and making short migrations for wintering, to spawn, or to feed. A few hundred species migrate long distances, in some cases of thousands of kilometres. About 120 species of fish, including several species of salmon , migrate between saltwater and freshwater (they are 'diadromous'). [18] [19]
Forage fish such as herring and capelin migrate around substantial parts of the North Atlantic ocean. The capelin for example spawn around the southern and western coasts of Iceland; their larvae drift clockwise around Iceland, while the fish swim northwards towards Jan Mayen island to feed, and return to Iceland parallel with Greenland's east coast. [20]
In the ' sardine run ', billions of Southern African pilchard Sardinops sagax spawn in the cool waters of the Agulhas Bank and move northward along the east coast of South Africa between May and July. [21]
In insects
Main articles: Insect migration and Lepidoptera migration
An aggregation of migratory Pantala flavescens dragonflies, known as globe skimmers, in Coorg , India
Some winged insects such as locusts and certain butterflies and dragonflies with strong flight migrate long distances. Among the dragonflies, species of Libellula and Sympetrum are known for mass migration, while Pantala flavescens , known as the globe skimmer or wandering glider dragonfly, makes the longest ocean crossing of any insect, between India and Africa. [22] Exceptionally, swarms of the desert locust, Schistocerca gregaria , flew westwards across the Atlantic Ocean for 4500 km during October 1988, using air currents in the Inter-Tropical Convergence Zone . [23]
In some migratory butterflies , such as the monarch butterfly and the painted lady , no individual completes the whole migration. Instead the butterflies mate and reproduce on the journey, and successive generations travel the next stage of the migration. [24]
In mammals
Wildebeest on the Serengeti 'great migration'
Further information: List of mammals that perform mass migrations
Some mammals exhibit extraordinary migrations, with caribou having one of the longest known terrestrial migrations on the planet, reaching as much as 4868 km/year in North America. However, over the course of a year, gray wolves move the most. One gray wolf, in particular, covered a total cumulative annual distance (TCAD) of 7247 km. [25]
Mass migration occurs in mammals such as the Serengeti 'great migration' , an annual circular pattern of movement with some 1.7 million wildebeest and hundreds of thousands of other large game animals including gazelles and zebra . [26] [27] A literature survey in 2009 found more than 20 species which engage, or used to engage, in mass migrations. [28] Of these migrations, those of the springbok , black wildebeest , blesbok , scimitar-horned oryx , and kulan have ceased. [29] Long-distance migrations occur in some bats, notably the mass migration of the Mexican free-tailed bat between Oregon and southern Mexico. [30] Migration is important in cetaceans , including whales, dolphins and porpoises. [31]
In other animals
Some reptiles, especially the sea turtles , and amphibians migrate. [32] Some crustaceans migrate, most spectacularly the Christmas Island red crab which moves en masse each year by the million. [33]
Animal migration tracking
Adapted from Wikipedia, the free encyclopedia. Animal migration tracking - Wikipedia
Radio-collared wolf in Yellowstone National Park
Employee of US Fish and Wildlife Service tracking a mountain lion tagged with a radio collar
Animal migration tracking is used in wildlife biology , conservation biology , ecology , and wildlife management to study animals' behavior in the wild. One of the first techniques was bird banding , placing passive ID tags on birds legs, to identify the bird in a future catch-and-release. Radio tracking involves attaching a small radio transmitter to the animal and following the signal with a RDF receiver . Sophisticated modern techniques use satellites to track tagged animals, and GPS tags which keep a log of the animal's location. One of the many goals of animal migration research has been to determine where the animals are going; however, researchers also want to know why they are going "there". Researchers not only look at the animals' migration but also what is between the migration endpoints to determine if a species is moving to new locations based on food density, a change in water temperature, or other stimulus, and the animal's ability to adapt to these changes. Migration tracking is a vital tool in efforts to control the impact of human civilization on populations of wild animals, and prevent or mitigate the ongoing extinction of endangered species .
Technologies
A monarch butterfly shortly after tagging at the Cape May Bird Observatory Cape May Bird Observatory is one of the organizations that has a monarch identification tagging program. Plastic stickers are placed on the wing of the insect with identification information. Tracking information is used to study the migration patterns of monarchs, including how far and where they fly.
In the fall of 1803, American Naturalist John James Audubon wondered whether migrating birds returned to the same place each year. So he tied a string around the leg of a bird before it flew south. The following spring, Audubon saw the bird had indeed come back.
Scientists today still attach tags, such as metal bands, to track movement of animals. Metal bands require the re-capture of animals for the scientists to gather data; the data is thus limited to the animal's release and destination points.
Recent technologies have helped solve this problem. Some electronic tags give off repeating signals that are picked up by radio devices or satellites while other electronic tags could include archival tags (or data loggers). Scientists can track the locations and movement of the tagged animals without recapturing them using this RFID technology or satellites. These electronic tags can provide a great deal of data. Modern technologies are also smaller, minimizing the negative impact of the tag on the animal. [1]
Radio tracking
The right one of these two brush-tailed rock-wallabies is wearing a radio tracking collar.
Tracking an animal by radio telemetry involves two devices. Telemetry , in general, involves the use of a transmitter that is attached to an animal and sends out a signal in the form of radio waves , just as a radio station does. [2] A scientist might place the transmitter around an animal's ankle , neck , wing , carapace , or dorsal fin . Alternatively, they may surgically implant it as internal radio transmitters have the advantage of remaining intact and functioning longer than traditional attachments, being protected from environmental variables and wear. [3] The transmitter typically uses a frequency in the VHF band as antennas in this band are conveniently small. To conserve battery power the transmitter usually transmits brief pulses, perhaps one per second. A specialized radio receiver called a radio direction finding (RDF) receiver picks up the signal. The receiver is usually in a truck , an ATV , or an airplane . [2] The receiver has a directional antenna (usually a simple Yagi antenna ) which receives most strongly from a single direction, and some means of indicating the strength of the received signal, either by a meter or by the loudness of the pulses in earphones. The antenna is rotated until the received radio signal is strongest; then the antenna is pointing toward the animal. To keep track of the signal, the scientist follows the animal using the receiver. This approach of using radio tracking can be used to track the animal manually but is also used when animals are equipped with other payloads. The receiver is used to home in on the animal to get the payload back.
Another form of radio tracking that can be utilized, especially in the case of small bird migration, is the use of geolocators or "geologgers". [4] This technology utilizes a light sensor that tracks the light-level data during regular intervals in order to determine a location based on the length of the day and the time of solar noon. [4] While there are benefits and challenges with using this method of tracking, it is one of the only practical means of tracking small birds over long distances during migration. [4] [5]
Passive integrated transponders (PIT) are another method of telemetry used to track the movements of a species [4] Passive integrated transponders, or "PIT tags", are electronic tags that allow researchers to collect data from a specimen without the need to recapture and handle the animal. [6] Data is captured and monitored via electronic interrogation antennae, which records the time and location of the individual. [6] Pit tags are a humane method of tracking that has little risk of infection or mortality due to the limited contact necessary to monitor the specimens. They are also cost-efficient in that they can be used repeatedly should the need arise to remove the tag from the animal. [7]
Satellite tracking
A saltwater crocodile with GPS-based satellite transmitter for migration tracking
Receivers can be placed in Earth - orbiting satellites such as ARGOS . Networks, or groups, of satellites are used to track animals. Each satellite in a network picks up electronic signals from a transmitter on an animal. Together, the signals from all satellites determine the precise location of the animal. The satellites also track the animal's path as it moves. Satellite-received transmitters fitted to animals can also provide information about the animals' physiological characteristics (e.g. temperature and habitat use.) [8] [9] Satellite tracking is especially useful because the scientists do not have to follow after the animal nor do they have to recover the tag to get the data on where the animal is going or has gone. Satellite networks have tracked the migration and territorial movements of caribou , sea turtles , [10] whales , great white sharks , seals , elephants , bald eagles , ospreys and vultures . [8] Additionally Pop-up satellite archival tags are used on marine mammals and various species of fish. There are two main systems, the above-mentioned Argos and the GPS . [11] Thanks to these systems, conservationists can find the key sites for migratory species. [11] Another form of satellite tracking would be the use of acoustic telemetry . This involves the use of electronic tags that emit sound in order for the researchers to track and monitor an animal within three dimensions, which is helpful in instances when large quantities of a species are being tracked at a time. [12]
Stable isotopes
Sea turtle eggs being laid by the mother. Unhatched eggs can be used in stable isotope analysis.
Stable isotopes are one of the intrinsic markers used for studying migration of animals. [13] One of the benefits of intrinsic markers in general, including stable isotope analysis, is that it does not require an organism to be capture and tagged and then recaptured at a later time. Each capture of an organism provides information on where it has been based on diet. The three types of intrinsic markers that can be used as tools for animal migration studies are: (1) contaminants, parasites and pathogens , (2) trace elements, and (3) stable isotopes. Certain geographic regions have specific stable isotope ratios that affect the chemistry of organisms foraging in those locations, this creates "isoscapes" that scientists can use to understand where the organism has been eating. A couple prerequisites must be met in order to use stable isotope analysis successfully: (1) the animal must have at least one light isotope of interest in specific tissues that can be sampled (this condition is almost always met since these light isotopes are building blocks of most animal tissues), and (2) the organism needs to migrate between isotopically different regions and these isotopes must be retained in the tissue in order for the differences to be measured. [13]
Stable isotope analysis has a lot of benefits and has been used in terrestrial and aquatic organisms. For example, stable isotope analysis has been confirmed to work in determining foraging locations of nesting loggerhead sea turtles . [14] Satellite telemetry was used to confirm that the location derived from the analysis were accurate to where these turtles actually traveled. This is important because it allows for greater sample sizes to be used in migration studies, since satellite telemetry is expensive and tissue , blood , and egg samples can be taken from the female turtles laying eggs. [14]
Importance
Electronic tags are giving scientists a complete, accurate picture of migration patterns . For example, when scientists used radio transmitters to track one herd of caribou , they learned two important things. First, they learned that the herd moves much more than previously thought. Second, they learned that each year the herd returns to about the same place to give birth . This information would have been difficult or impossible to obtain with "low tech" tags.
Tracking migrations is an important tool to better understand and protect species . For example, Florida manatees are an endangered species , and therefore they need protection. Radio tracking showed that Florida manatees may travel as far as Rhode Island when they migrate. This information suggests that the manatees may need protection along much of the Atlantic Coast of the United States. Previously, protection efforts focused mainly in the Florida area.
In the wake of the BP oil spill , efforts in tracking animals has increased in the Gulf. Most researchers who use electronic tags have only a few options: pop-up satellite tags, archival tags, or satellite tags. Historically these tags were generally expensive and could cost several thousands of dollars per tag. However, with current advancements in technology prices are now allowing researchers to tag more animals. With this increase in the number of species and individuals that can be tagged it is important to record and acknowledge the potential negative effects these devices might have. [15] [16]
References - Animal migration
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References - Animal migration tracking
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