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67-493: The wildlife refuge was established for the protection of migratory birds in 1943. Its unique location is at the meeting of different climates and habitats: subtropical wetlands , Chihuahuan Desert , Gulf Coast , and Great Plains . Its riparian location has developed a reputation for diverse birding . Due to its location near the Mexico–United States border , the refuge was at risk of environmental damage during

134-478: A black bear , enter torpor and switch to multi-day cycles rather than rely on a circadian rhythm. However, it is seen that both captive and wild bears express similar circadian rhythms when entering torpor. Bears entering torpor in a simulated den with no light expressed normal but low functioning rhythms. The same was observed in wild bears denning in natural areas. The function of circadian rhythms in black, brown , and polar bears suggest that their system of torpor

201-498: A white stork was found in the German state of Mecklenburg with an arrow made from central African hardwood, which provided some of the earliest evidence of long-distance stork migration. This bird was referred to as a Pfeilstorch , German for "Arrow stork". Since then, around 25 Pfeilstörche have been documented. Migration is the regular seasonal movement, often north and south, undertaken by many species of birds. Migration

268-1284: A barrier, and detours avoiding such barriers are observed. For example, brent geese Branta bernicla bernicla migrating between the Taymyr Peninsula and the Wadden Sea travel via low-lying coastal feeding-areas on the White Sea and the Baltic Sea rather than directly across the Arctic Ocean and the Scandinavian mainland. Great snipes make non-stop flights of 4,000–7,000 km, lasting 60–90 h, during which they change their average cruising heights from 2,000 m (above sea level) at night to around 4,000 m during daytime. A similar situation occurs with waders (called shorebirds in North America). Many species, such as dunlin Calidris alpina and western sandpiper Calidris mauri , undertake long movements from their Arctic breeding grounds to warmer locations in

335-480: A body temperature 12 °C lower than normal. This reduction in metabolism allows it to conserve 30% of fat stores amassed from the previous day. Torpor can be a strategy of animals with unpredictable food supplies. For example, high-latitude living rodents use torpor seasonally when not reproducing. These rodents use torpor as means to survive winter and live to reproduce in the next reproduction cycle when food sources are plentiful, separating periods of torpor from

402-642: A chick on the Farne Islands in Northumberland off the British east coast, reached Melbourne , Australia in just three months from fledging, a sea journey of over 22,000 km (12,000 nmi), while another also from the Farne Islands with a light level geolocator tag 'G82' covered a staggering 96,000 km (52,000 nmi) in just 10 months from the end of one breeding season to

469-667: A heat-producing brown adipose tissue as a mechanism to accelerate rewarming. The mechanism of marsupial arousal is unknown, but appears not to rely on brown adipose tissue. The evolution of torpor likely accompanied the development of homeothermy . Animals capable of maintaining a body temperature above ambient temperature when other members of its species would not have a fitness advantage. Benefits of maintaining internal temperatures include increased foraging time and less susceptibility to extreme drops in temperature. This adaptation of increasing body temperature to forage has been observed in small nocturnal mammals when they first wake up in

536-487: A man's story about swallows being found in a chalk cliff collapse "while he was a schoolboy at Brighthelmstone", though the man denied being an eyewitness. However, he writes that "as to swallows being found in a torpid state during the winter in the Isle of Wight or any part of this country, I never heard any such account worth attending to", and that if early swallows "happen to find frost and snow they immediately withdraw for

603-414: A time—a circumstance this much more in favour of hiding than migration", since he doubts they would "return for a week or two to warmer latitudes". Only at the end of the eighteenth century was migration accepted as an explanation for the winter disappearance of birds from northern climes. Thomas Bewick 's A History of British Birds (Volume 1, 1797) mentions a report from "a very intelligent master of

670-468: A timing mechanism, instead moving in response to local weather conditions. Thus mountain and moorland breeders, such as wallcreeper Tichodroma muraria and white-throated dipper Cinclus cinclus , may move only altitudinally to escape the cold higher ground. Other species such as merlin Falco columbarius and Eurasian skylark Alauda arvensis move further, to the coast or towards the south. Species like

737-560: A vessel" who, "between the islands of Menorca and Majorca , saw great numbers of Swallows flying northward", and states the situation in Britain as follows: Swallows frequently roost at night, after they begin to congregate, by the sides of rivers and pools, from which circumstance it has been erroneously supposed that they retire into the water. Bewick then describes an experiment that succeeded in keeping swallows alive in Britain for several years, where they remained warm and dry through

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804-627: Is a much more complex phenomenon that may include both endogenous programs as well as learning. The primary physiological cue for migration is the changes in the day length. These changes are related to hormonal changes in the birds. In the period before migration, many birds display higher activity or Zugunruhe ( German : migratory restlessness ), first described by Johann Friedrich Naumann in 1795, as well as physiological changes such as increased fat deposition. The occurrence of Zugunruhe even in cage-raised birds with no environmental cues (e.g. shortening of day and falling temperature) has pointed to

871-483: Is alterable with selective breeding. Many migration routes of long-distance migratory birds are circuitous due to evolutionary history: the breeding range of Northern wheatears Oenanthe oenanthe has expanded to cover the entire Northern Hemisphere, but the species still migrates up to 14,500 km to reach ancestral wintering grounds in sub-Saharan Africa rather than establish new wintering grounds closer to breeding areas. A migration route often does not follow

938-576: Is an example of leap-frog migration . 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 the order. Within a population, it is common for different ages and/or sexes to have different patterns of timing and distance. Female chaffinches Fringilla coelebs in Eastern Fennoscandia migrate earlier in

1005-695: 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. Red knots Calidris canutus and dunlins Calidris alpina were found in radar studies to fly 5 km/h (2.5 kn) faster in flocks than when they were flying alone. Birds fly at varying altitudes during migration. An expedition to Mt. Everest found skeletons of northern pintail Anas acuta and black-tailed godwit Limosa limosa at 5,000 m (16,000 ft) on

1072-665: Is evidence that this enables the migrants to obtain more of their preferred foods such as fruits. Altitudinal migration is common on mountains worldwide, such as in the Himalayas and the Andes . Dusky grouse in Colorado migrate less than a kilometer away from their summer grounds to winter sites which may be higher or lower by about 400 m in altitude than the summer sites. Many bird species in arid regions across southern Australia are nomadic; they follow water and food supply around

1139-559: Is evolutionarily advanced. Torpor has been shown to be a strategy of small migrant birds to preserve their body energy stores . Hummingbirds, resting at night during migration, were observed to enter torpor which helped to conserve fat stores during migration or cold nights at high altitude. This strategy of using torpor to preserve energy stores, such as fat, has also been observed in wintering chickadees. Black-capped chickadees , living in temperate forests of North America, do not migrate south during winter. The chickadee can maintain

1206-508: 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. 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

1273-499: Is marked by its annual seasonality and movement between breeding and non-breeding areas. Nonmigratory bird movements include those made in response to environmental changes including 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). Non-migratory birds are said to be resident or sedentary. Approximately 1,800 of

1340-477: The Bay of Fundy and Delaware Bay . Some bar-tailed godwits Limosa lapponica baueri have the longest known non-stop flight of any migrant, flying 11,000 km from Alaska to their New Zealand non-breeding areas. Prior to migration, 55 percent of their bodyweight is stored as fat to fuel this uninterrupted journey. Seabird migration is similar in pattern to those of the waders and waterfowl. Some, such as

1407-711: The Bosphorus at migration times. More common species, such as the European honey buzzard Pernis apivorus , can be counted in hundreds of thousands in autumn. Other barriers, such as mountain ranges, can cause funnelling, particularly of large diurnal migrants, as in the Central American migratory bottleneck. The Batumi bottleneck in the Caucasus is one of the heaviest migratory funnels on earth, created when hundreds of thousands of soaring birds avoid flying over

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1474-531: The Khumbu Glacier . Bar-headed geese Anser indicus have been recorded by GPS flying at up to 6,540 m (21,460 ft) 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. Seabirds fly low over water but gain altitude when crossing land, and

1541-515: The black guillemot Cepphus grylle and some gulls , are quite sedentary; others, such as most terns and auks breeding in the temperate northern hemisphere, move varying distances south in the northern winter. The Arctic tern Sterna paradisaea has the longest-distance migration of any bird, and sees more daylight than any other, moving from its Arctic breeding grounds to the Antarctic non-breeding areas. One Arctic tern, ringed (banded) as

1608-798: The dark-eyed junco migrates from subarctic and arctic climates to the contiguous United States and the American goldfinch from taiga to wintering grounds extending from the American South northwestward to Western Oregon . Some ducks, such as the garganey Anas querquedula , move completely or partially into the tropics. The European pied flycatcher Ficedula hypoleuca follows this migratory trend, breeding in Asia and Europe and wintering in Africa. Migration routes and wintering grounds are both genetically and traditionally determined depending on

1675-483: The stork in the heavens knows its seasons, and the turtle dove , the swift and the crane keep the time of their arrival." In the Pacific, traditional land-finding techniques used by Micronesians and Polynesians suggest that bird migration was observed and interpreted for more than 3,000 years. In Samoan tradition, for example, Tagaloa sent his daughter Sina to Earth in the form of a bird, Tuli, to find dry land,

1742-531: The 'tubenose' order Procellariiformes , are great wanderers, and the albatrosses of the southern oceans may circle the globe as they ride the " Roaring Forties " outside the breeding season. The tubenoses spread widely over large areas of open ocean, but congregate when food becomes available. Many are among the longest-distance migrants; sooty shearwaters Puffinus griseus nesting on the Falkland Islands migrate 14,000 km (7,600 nmi) between

1809-785: The Andes and Himalayas . The timing of migration seems to be controlled primarily by changes in day length. Migrating birds navigate using celestial cues from the Sun and stars, the Earth's magnetic field, and mental maps. Writings of ancient Greeks recognized the seasonal comings and goings of birds. Aristotle wrote that birds transmuted into other birds or species like fish and animals, which explained their disappearance and reappearance. Aristotle thought many birds disappeared during cold weather because they were torpid , undetected in unseen environments like tree hollows or burrowing down in mud found at

1876-853: The Black Sea surface and across high mountains. Birds of prey such as honey buzzards which migrate using thermals lose only 10 to 20% of their weight during migration, which may explain why they forage less during migration than do smaller birds of prey with more active flight such as falcons, hawks and harriers. From observing the migration of eleven soaring bird species over the Strait of Gibraltar, species which did not advance their autumn migration dates were those with declining breeding populations in Europe. Many long-distance migrants appear to be genetically programmed to respond to changing day length. Species that move short distances, however, may not need such

1943-640: The Southern Hemisphere) to overwinter; In contrast, among (pelagic) seabirds, species of the Southern Hemisphere are more likely to migrate. This is because there is a large area of ocean in the Southern Hemisphere, and more islands suitable for seabirds to nest. The control of migration, its timing and response are genetically controlled and appear to be a primitive trait that is present even in non-migratory species of birds. The ability to navigate and orient themselves during migration

2010-518: The United States. More than 300 species of butterflies have been observed at the refuge, with as many as 65 having been seen on a single day. References Bird migration Bird migration is a seasonal movement of birds between breeding and wintering grounds that occurs twice a year. It is typically from north to south or from south to north. Migration is inherently risky, due to predation and mortality. The Arctic tern holds

2077-452: The active part of their day, such animals maintain normal body temperature and activity levels, but their metabolic rate and body temperature drop during a portion of the day (usually night) to conserve energy. Some animals seasonally go into long periods of inactivity, with reduced body temperature and metabolism, made up of multiple bouts of torpor. This is known as hibernation if it occurs during winter or aestivation if it occurs during

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2144-405: 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. The higher concentrations of migrating birds at stopover sites make them prone to parasites and pathogens, which require a heightened immune response. Within a species not all populations may be migratory; this

2211-778: The autumn than males do and the European tits of genera Parus and Cyanistes only migrate their first year. 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

2278-628: The bottom of ponds, then reemerging months later. Still, Aristotle recorded that cranes traveled from the steppes of Scythia to marshes at the headwaters of the Nile , an observation repeated by Pliny the Elder in his Historia Naturalis . Two books of the Bible may address avian migration. The Book of Job notes migrations with the inquiry: "Is it by your insight that the hawk hovers, spreads its wings southward?" The Book of Jeremiah comments: "Even

2345-678: The breeding colony and the North Atlantic Ocean off Norway . Some Manx shearwaters Puffinus puffinus do this same journey in reverse. As they are long-lived birds, they may cover enormous distances during their lives; one record-breaking Manx shearwater is calculated to have flown 8 million kilometres (4.5 million nautical miles) during its over-50-year lifespan. Some large broad-winged birds rely on thermal columns of rising hot air to enable them to soar. These include many birds of prey such as vultures , eagles , and buzzards , but also storks . These birds migrate in

2412-488: The chaffinch are much less migratory in Britain than those of continental Europe, mostly not moving more than 5 km in their lives. Short-distance passerine migrants have two evolutionary origins. Those that have long-distance migrants in the same family, such as the common chiffchaff Phylloscopus collybita , are species of southern hemisphere origins that have progressively shortened their return migration to stay in

2479-442: The common spiny mouse it spends more time in a torpid state. A drop in temperature from torpor has been shown to reduce the ability of parasites to reproduce. In temperate zones, the reproductive rates of ectoparasites on bats decrease when the bats enter torpor. In regions where bats don't undergo torpor, the parasites maintain a consistent reproductive rate throughout the year. In 2013, SpaceWorks Engineering began researching

2546-455: The composition of a migrating flock, and can sometimes encode the sex of a migrating individual, and to avoid collision in the air. Nocturnal migration can be monitored using weather radar data, allowing ornithologists to estimate the number of birds migrating on a given night, and the direction of the migration. Future research includes the automatic detection and identification of nocturnally calling migrant birds. Nocturnal migrants land in

2613-763: The construction of the Trump wall . The administration exempted the construction in the refuge, but built on the border of it, leading to possible interference due to noise. 397 bird species have been documented within the park's borders. Many of those are migratory species on their way to and from Central and South America. A few species to be found there are black-bellied whistling-duck , fulvous whistling-duck , mottled duck , blue-winged teal , green-winged teal , cinnamon teal , least grebe , anhinga , tricolored heron , white ibis , lesser yellowlegs , long-billed dowitcher , and least tern . Osprey , broad-winged hawk , northern harrier , and peregrine falcon are among

2680-498: The country in an irregular pattern, unrelated to season but related to rainfall. Several years may pass between visits to an area by a particular species. Sometimes circumstances such as a good breeding season followed by a food source failure the following year lead to irruptions in which large numbers of a species move far beyond the normal range. Bohemian waxwings Bombycilla garrulus well show this unpredictable variation in annual numbers, with five major arrivals in Britain during

2747-499: The daytime. Migratory species in these groups have great difficulty crossing large bodies of water, since thermals only form over land, and these birds cannot maintain active flight for long distances. Mediterranean and other seas present a major obstacle to soaring birds, which must cross at the narrowest points. Massive numbers of large raptors and storks pass through areas such as the Strait of Messina , Gibraltar , Falsterbo , and

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2814-469: The evening. Although homeothermy lends advantages such as increased activity levels, small mammals and birds maintaining an internal body temperature spend up to 100 times more energy in low ambient temperatures compared to ectotherms. To cope with this challenge, these animals maintain a much lower body temperature, staying just over ambient temperature rather than at normal operating temperature. This reduction in body temperature and metabolic rate allows

2881-412: The far south to support long-distance migration. The primary motivation for migration appears to be food; for example, some hummingbirds choose not to migrate if fed through the winter. In addition, 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

2948-425: The last 500 years. Torpor enables animals to reduce energy requirements allowing them to better survive harsh conditions. Interspecific competition occurs when two species require the same resource for energy production. Torpor increases fitness in the case of inter-specific competition with the nocturnal common spiny mouse . When the golden spiny mouse experiences reduced food availability by diet overlap with

3015-418: The local temperature to time their spring migration departure. Notably, departure responses to temperature varied between individuals but were individually repeatable (when tracked over multiple years). This suggests that individual use of temperature is a cue that allows for population-level adaptation to climate change . In other words, in a warming world, many migratory birds are predicted to depart earlier in

3082-561: The long-distance migration record for birds, travelling between Arctic breeding grounds and the Antarctic each year. Some species of tubenoses , such as albatrosses , circle the Earth, flying over the southern oceans, while others such as Manx shearwaters migrate 14,000 km (8,700 mi) between their northern breeding grounds and the southern ocean. Shorter migrations are common, while longer ones are not. The shorter migrations include altitudinal migrations on mountains, including

3149-517: The loss. The typical image of migration is of northern land birds, such as swallows (Hirundinidae) and birds of prey, making long flights to the tropics. However, many Holarctic wildfowl and finch (Fringillidae) species winters in the North Temperate Zone , in regions with milder winters than their summer breeding grounds. For example, the pink-footed goose migrates from Iceland to Britain and neighbouring countries, whilst

3216-454: The migratory birds of prey found in the refuge. Hook-billed kite and gray hawk , seen occasionally in the refuge, attract birders from around the world. More than 35 species of New World warblers have been seen, including the golden-winged warbler , magnolia warbler , Northern parula , tropical parula , American redstart , palm warbler , and yellow-breasted chat . Santa Ana is home to almost half of all butterfly species found in

3283-427: The morning and may feed for a few days before resuming their migration. These birds are referred to as passage migrants in the regions where they occur for a short period between the origin and destination. Nocturnal migrants minimize depredation, avoid overheating, and can feed during the day. One cost of nocturnal migration is the loss of sleep. Migrants may be able to alter their quality of sleep to compensate for

3350-502: The most direct line between breeding and wintering grounds. Rather, it could follow a hooked or arched line, with detours around geographical barriers or towards suitable stopover habitat. For most land birds, such barriers could consist of large water bodies or high mountain ranges, a lack of stopover or feeding sites, or a lack of thermal columns (important for broad-winged birds). Conversely, in water-birds , large areas of land without wetlands offering suitable feeding sites may present

3417-458: The nineteenth century, but 18 between the years 1937 and 2000. Red crossbills Loxia curvirostra too are irruptive, with widespread invasions across England noted in 1251, 1593, 1757, and 1791. Bird migration is primarily, but not entirely, a Northern Hemisphere phenomenon. This is because continental landmasses of the northern hemisphere are almost entirely temperate and subject to winter food shortages driving bird populations south (including

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3484-456: The northern hemisphere. Species that have no long-distance migratory relatives, such as the waxwings Bombycilla , are effectively moving in response to winter weather and the loss of their usual winter food, rather than enhanced breeding opportunities. In the tropics there is little variation in the length of day throughout the year, and it is always warm enough for a food supply, but altitudinal migration occurs in some tropical birds. There

3551-559: The prolonged survival of animals capable of entering torpid states. In 2020, scientists reported evidence of the torpor in Lystrosaurus living ~250 Mya in Antarctica – the oldest evidence of a hibernation-like state in a vertebrate animal. Slowing metabolic rate to conserve energy in times of insufficient resources is the primarily noted purpose of torpor. This conclusion is largely based on laboratory studies where torpor

3618-540: The reproduction period. The eastern long-eared bat uses torpor during winter and is able to arouse and forage during warm periods. Some animals use torpor during their reproductive cycle, as seen in unpredictable habitats. They experience the cost of a prolonged reproduction period but the payoff is survival to be able to reproduce at all. It is suggested that this daily torpor use may have allowed survival through mass extinction events . Heterotherms make up only four out of 61 mammals confirmed to have gone extinct over

3685-902: The reverse pattern is seen in land birds. However most bird migration is in the range of 150 to 600 m (490–2,000 ft). Bird strike Aviation records from the United States show most collisions occur below 600 m (2,000 ft) and almost none above 1,800 m (5,900 ft). Bird migration is not limited to birds that can fly. Most species of penguin (Spheniscidae) migrate by swimming. These routes can cover over 1,000 km (550 nmi). Dusky grouse Dendragapus obscurus perform altitudinal migration mostly by walking. Emus Dromaius novaehollandiae in Australia have been observed to undertake long-distance movements on foot during droughts. During nocturnal migration ("nocmig" ), many birds give nocturnal flight calls, which are short, contact-type calls. These likely serve to maintain

3752-446: The role of circannual endogenous programs in controlling bird migrations. Caged birds display a preferential flight direction that corresponds with the migratory direction they would take in nature, changing their preferential direction at roughly the same time their wild conspecifics change course. Satellite tracking of 48 individual Asian houbaras ( Chlamydotis macqueenii ) across multiple migrations showed that this species uses

3819-428: The same hemisphere, but others such as semipalmated sandpiper C. pusilla travel longer distances to the tropics in the Southern Hemisphere. For some species of waders, migration success depends on the availability of certain key food resources at stopover points along the migration route. This gives the migrants an opportunity to refuel for the next leg of the voyage. Some examples of important stopover locations are

3886-475: The social system of the species. In long-lived, social species such as white storks (Ciconia ciconia), flocks are often led by the oldest members and young storks learn the route on their first journey. In short-lived species that migrate alone, such as the Eurasian blackcap Sylvia atricapilla or the yellow-billed cuckoo Coccyzus americanus , first-year migrants follow a genetically determined route that

3953-718: The start of the next, travelling not just the length of the Atlantic Ocean and the width of the Indian Ocean, but also half way across the South Pacific to the boundary between the Ross and Amundsen Seas before returning back west along the Antarctic coast and back up the Atlantic. Many tubenosed birds breed in the southern hemisphere and migrate north in the southern winter. The most pelagic species, mainly in

4020-420: The summer. Daily torpor, on the other hand, is not seasonally dependent and can be an important part of energy conservation at any time of year. Torpor is a well-controlled thermoregulatory process and not, as previously thought, the result of switching off thermoregulation. Marsupial torpor differs from non-marsupial mammalian ( eutherian ) torpor in the characteristics of arousal. Eutherian arousal relies on

4087-409: The time a hibernator spends at low body temperature, lasting days to weeks, or it can refer to a period of low body temperature and metabolism lasting less than 24 hours, as in "daily torpor". Animals that undergo daily torpor include birds (even tiny hummingbirds , notably Cypselomorphae ) and some mammals, including many marsupial species, rodent species (such as mice ), and bats . During

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4154-416: The tropics. As the days shorten in autumn, the birds return to warmer regions where the available food supply varies little with the season. These advantages offset the high stress, physical exertion costs, and other risks of migration. Predation can be heightened during migration: Eleonora's falcon Falco eleonorae , which breeds on Mediterranean islands, has a very late breeding season, coordinated with

4221-459: The winters. He concludes: These experiments have since been amply confirmed by ... M. Natterer , of Vienna ... and the result clearly proves, what is in fact now admitted on all hands, that Swallows do not in any material instance differ from other birds in their nature and propensities [for life in the air]; but that they leave us when this country can no longer furnish them with a supply of their proper and natural food ... In 1822,

4288-443: The word tuli referring specifically to land-finding waders, often to the Pacific golden plover. Aristotle, however, suggested that swallows and other birds hibernated. This belief persisted as late as 1878 when Elliott Coues listed the titles of no fewer than 182 papers dealing with the hibernation of swallows. Even the "highly observant" Gilbert White , in his posthumously published 1789 The Natural History of Selborne , quoted

4355-409: The world's 10,000 bird species are long-distance migrants. 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. Of course, in the southern hemisphere, the directions are reversed, but there is less land area in

4422-474: The year for their summer or winter destination. In polygynous species with considerable sexual dimorphism , males tend to return earlier to the breeding sites than their females. This is termed protandry. Torpid Torpor is a state of decreased physiological activity in an animal, usually marked by a reduced body temperature and metabolic rate . Torpor enables animals to survive periods of reduced food availability. The term "torpor" can refer to

4489-455: Was observed to follow food deprivation. There is evidence for other adaptive functions of torpor where animals are observed in natural contexts: Animals that can enter torpor rely on biological rhythms such as circadian and circannual rhythms to continue natural functions. Different animals will manage their circadian rhythm differently, and in some species it's seen to completely stop (such as in European hamsters ). Other organisms, such as

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