Linzey - Vertebrate Biology - Chapter 11 pdf

Linzey: Vertebrate Biology 11. Movements Text © The McGraw−Hill Companies, 2003 CHAPTER 11 Movements ■ INTRODUCTION Vertebrates are mobile animals that move about to secure food, to locate suitable homes and nesting sites, to avoid unfavorable periods of the year, and to find mates. Some species move very little during their lifetimes, whereas others such as golden plovers (Pluvialis dominica) and elephant seals (Mirounga angustirostris) may cover over 20,000 km annually. Some movements are seasonal, or annual, whereas other movements occur only once in a lifetime. Orientation consists of two different phenomena: the control of an animal’s position and stability in space, and the control of an animal’s path through space (Wiltschko and Wiltschko, 1994). Movements undertaken by vertebrates can be categorized on the basis of where and when they occur—home range movements, dispersal, invasions, migration, homing, and emigra- tion. Alternatively, movements can be classified by the mechanisms by which the movement is achieved—vision, hearing, olfaction, navigation, or compass orientation. Our understanding of the way in which animals know how, when, and where to orient and navigate around their environment has grown considerably over the last few decades. ■ HOME RANGE Home range is highly variable and is often difficult to define. It is the area around the home of an individual that is covered by the animal in its normal activities of gathering food, mating, and caring for its young. Home ranges may be lin- ear, two-dimensional, or three-dimensional. Home range generally is correlated with the size of the animal. Small forms usually have relatively small home ranges, whereas larger species normally have larger home ranges. Among mammals of the same size, carnivorous species such as cougars (Felis concolor) generally have larger home ranges than herbivorous forms such as white-tailed deer (Odocoileus virginianus). A carnivore must expend considerably more energy and cover a much greater area in order to secure sufficient food. However, some small aerial species including bats, hummingbirds, and warblers cover great distances during their daily activities. Other factors affecting home range size include habitat, population density, sex, age, body size, and season of the year. In polygynous and some monogamous species, males generally have larger home ranges than females; in polyandrous birds, however, the female’s home range is larger (Blair, 1940d; Adams, 1959; Linzey, 1968). Very young and very old individuals of many species usually have the smallest home ranges. Animals living in marginal habitats generally need larger ranges than members of the same species living in bet- ter habitats. For example, Layne (1954) found that red squirrels (Tamiasciurus hudsonicus) living on the maintained portion of the Cornell University campus in central New York had an average home range of 2.0 to 2.5 hectare (ha), while red squirrels living in the more diverse and natural habitats of the nearby gorges had average home ranges of 0.12 to 0.16 ha. Population density also may play a significant role in determining the home range, with the average size of the home range generally decreasing as population density increases. Linzey (1968) recorded an average home range of 0.26 ha for male golden mice (Ochrotomys nuttalli) and 0.24 ha for females over a 3-year period in the Great Smoky Mountains National Park. During a portion of this study, the population decreased drastically in size. During this period, the male home range more than doubled (0.63 ha), but the female home range, possibly because of nesting responsibil- ities and caring for young, remained approximately constant (0.21 ha). The density of large trees and possibly population density were factors that affected koala (Phascolarctos cinereus) home ranges in Australia (males, 1.0 ha; females, 1.18 ha) (Mitchell, 1991b). Some animals that live in northern regions, such as white-tailed deer (Odocoileus virginianus), have a larger home range during the warmer months of the year but live in small restricted areas, termed yards, during the winter months. Few long-term home range studies exist. One such study of three-toed box turtles (Terrapene carolina triunguis) covered Linzey: Vertebrate Biology 11. Movements Text © The McGraw−Hill Companies, 2003 338 Chapter Eleven Exclusive boundary strip (white area) X X X XX X X X X X X X Capture sites Minimum area Inclusive boundary strip Three standard methods of calculating home range. FIGURE 11.1 a period of 25 years. It revealed permanent home ranges varying from 2.2 to 10.6 ha in size for turtles known to have inhabited the study area for all 25 years (Schwartz and Schwartz,1991). Home range figures are subject to a great deal of vari- ation; therefore, these figures must be used with a great deal of caution. Many methods can be used to calculate the home range of a species; thus, results are somewhat sub- jective. Figure 11.1 illustrates three methods of calculating home range using the same capture sites. The minimum area method, calculated by computing the area within the actual capture sites, results in the smallest measured range. The boundary strip methods utilize a boundary strip that extends half the distance to each of the nearest traps around it. This method recognizes that even though an animal entered a particular trap, it probably also utilized some of the adjacent areas. The inclusive boundary strip method connects the outer points of the boundary strips, includes the greatest amount of area, and results in the largest home range estimate. The exclusive boundary strip method allows the investigator to utilize his or her judgment about unsuit- able areas of habitat when drawing the perimeters of the home range. This home range value will be between the minimum area estimate and the inclusive boundary strip estimate. Though it is possible to gain an approximate idea of the size of the home range of a species, such statistics should not be accepted as absolute. Table 11.1 lists typical home ranges for selected vertebrates. Under normal conditions, many animals have permanent ranges and spend their entire lifetimes within these areas. Most frogs, salamanders, lizards, turtles, snakes, moles, shrews, woodchucks, chipmunks, deer mice, and many others establish permanent home ranges. For example, after dis- persing from their parental (natal) area, many lizards will remain in the same area throughout their lives. The home range generally will center around a favorable basking site or perch (Fig. 11.2). Migratory species such as sea turtles, many birds, elk, and caribou have seasonal home ranges. Their summer home ranges usually include the locations where they reproduce and care for their young, and their winter range is in a different area in order to allow them to survive adverse seasonal or climatic conditions. Most home ranges are usually amorphous or amoeboid in shape. Some may be bounded by natural landmarks such as a river, whereas others are bounded by human-made struc- tures such as roads or railroad tracks. Home ranges and even “core areas” (areas of high-intensity use) of several members of the same species often overlap. For example, giant pandas have ranges between 3.9 and 6.2 km 2 that may overlap extensively (Catton, 1990). Most pandas, especially females, tend to concentrate their activity within core areas of 0.3 to 0.4 km 2 . Overlapping areas usually are not used at the same time; this helps to avoid conflict. However, in western North Car- olina, neighboring black bears often use areas of overlap for the same activities (e.g., feeding, denning) and at the same time (Horner and Powell, 1990). In Alabama, adult home ranges of long-nosed (nine-banded) armadillos (Dasypus novemcinctus) overlapped extensively, and there was no indi- cation of territorial or aggressive interactions (Breece and Dusi, 1985). Adults often were seen feeding within 3 m of each other, and on one occasion, three adults were seen leaving one den. Home ranges often are marked by means of glandular secretions (pheromones), urine, or excrement. Ungulates, such as deer, use secretions from tarsal and metatarsal glands on their lower legs and orbital glands on their head to mark their home ranges. Tenrecs (Echinops telfairi) put saliva on the object to be marked and transfer their body odor by alternately scratching themselves with a foot and then rubbing the foot in the saliva. Galagos (Galago sp.) urinate on the palms of their hands and rub the urine into the soles of their feet. When climbing about, they leave obvious scent marks that also are visible as dark spots. Some mammals in which the anal glands are well developed, such as martens (Martes) and hyenas, use pheromones from anal glands to mark their home range. Gray squirrels (Sciurus carolinensis), fox squirrels (S. niger), and red squirrels (Tamiasciurus hudsonicus) use cheek-rubbing to deposit scent from glands in the oral–labial region (Benson, 1980; Koprowski, 1993). Rabbits use their pheromone-containing chin glands, urine, and feces for marking. Small mounds of fecal pellets indicate that an area is occupied. Linzey: Vertebrate Biology 11. Movements Text © The McGraw−Hill Companies, 2003 Movements 339 A chuckwalla (Sauromalus obesus) basking in the warm Arizona desert sun. FIGURE 11.2 TABLE 11.1 Home Ranges of Selected Vertebrates Species Home Range Locality Reference Red salamander 6.1–41.2 m 2 California Stebbins, 1954 Spadefoot toad 30.5 m 2 East North America Pearson, 1955 Eastern box turtle 101–113 m 2 Maryland Stickel, 1950 2.2–10.6 ha 2 Missouri Schwartz and Schwartz, 1991 Desert tortoise 4–41 ha 2 SW U.S. Woodbury and Hardy, 1948 White-throated monitor lizard 5–16 km 2 S. Africa Phillips, 1995 Red kangaroo 4.3–6.3 km 2 Australia Dawson, 1995 Short-tailed shrew 0.41 ha Michigan Blair, 1940a Meadow vole 0.08–0.21 ha Michigan Blair, 1940b Deermouse 0.21 ha Michigan Blair, 1940c Meadow jumping mouse 0.37 ha Michigan Blair, 1940d Varying hare 7.5–10.1 ha Montana Adams, 1959 5.9 ha Alaska O’Farrell, 1965 Red squirrel 1.3–1.5 ha Saskatchewan Davis, 1969 Armadillo 7.6–10.8 ha Florida Galbreath, 1983 3.5 ha Texas Clark, 1951 3.5 ha Alabama Breece and Dusi, 1985 Fisher 16.3–30.9 km 2 Maine Arthur et al., 1989 1,500–1,971 ha New Hampshire Kelly, 1977 Least weasel 1–15 ha England King, 1975 Cheetah 24–483 km 2 Tanzania Caro, 1996 Asian lion 77–129 km 2 India Chellam, 1996 Jaguar 3.2–39 km 2 Central America Rabinowitz, 1996 Mountain lion 196–453 km 2 Idaho Seidensticker et al., 1973 The “home” is within the home range and serves as a refuge from enemies and competitors. It may be in the form of an underground burrow, a cave, a tree cavity, a rotting log, an arboreal nest, or a brush pile. It may be the nest of a bird, the temporary “form” (nest) of a rabbit, or the more permanent burrow of a gopher tortoise (Gopherus) or woodchuck (Marmota). It may serve a single animal (cougar, Felis concolor), a pair of adults and their offspring (beaver, Castor canadensis), or a colony of animals (flying squirrels, Glau- comys; golden mice, Ochrotomys). Some species such as har- vest mice (Reithrodontomys) have been shown to have a metabolic rate ranging from 7 percent to as much as 24 percent lower when in their nest than when they are active (Kaye, 1960). Radio transmitters attached to subterranean naked mole rats (Heterocephalus glaber) revealed that the network of tunnels constructed by a colony currently comprising 87 animals was more than 3.0 km long and occupied an area greater than 100,000 m 2 —about the size of 20 football fields (Sher- man et al., 1992) (Fig. 11.3). Much of the tunneling to dig their vast network of tunnels is a cooperative effort to find food. One animal gnaws at soil, while others, in turn, trans- port it to a surface opening, where it is ejected by a larger colony mate. Some vertebrates actively defend a portion of their home range. The defended area is known as the territory and con- tains the home or nest site. In general, an individual or a group of animals is considered to be territorial when it has exclusive use of an area or resource with respect to other members of its species and defends it in some way (either actively through aggression or passively through advertise- ment). Habitat quality, particularly the availability of food, can influence territorial behavior and territory size. Thus, Linzey: Vertebrate Biology 11. Movements Text © The McGraw−Hill Companies, 2003 340 Chapter Eleven 7 6 5 4 3 2 1 13 12 April 17, 1962 Yellowhead territories Redwing territories May 6, 1962 7 6 5 4 3 2 1 13 12 11 10 9 8 11 10 9 8 Redwing territories Yellowhead interspecific aggression Interspecific territoriality between red-winged blackbirds (Agelaius phoeniceus) and yellow-headed blackbirds (Xanthocephalus xanthocephalus). Redwings that have established territories in the center of the marsh are evicted by the later-arriving yellowheads. Arrows indicate areas with intensive interspecific aggression. FIGURE 11.4 Naked mole rats (Heterocephalus glaber) live in a cooperative eusocial society. These subterranean mammals dig vast networks of tunnels—in some instances, more than 3.0 km long—to locate food. FIGURE 11.3 optimal size may vary from year to year and from locality to locality (Smith, 1990). The territory may be fixed in space, or it may be mobile as in bison (Bison bison), barren ground caribou (Rangifer tarandus), and swamp rabbits (Sylvilagus aquaticus), where a male may defend an area around an estrous female. Some male cichlid fishes occupy the same territory for as long as 18 months (Hert, 1992). Drifting territoriality has been reported in a red fox (Vulpes vulpes) population in England (Doncaster and Macdonald, 1991). Troops of howler mon- keys (Alouatta spp.) have little or no area of exclusive use, but they do defend the place where they happen to be at a given time. During the breeding season, male northern fur seals (Callorhinus ursinus) come onto land, choose and defend a breeding area against other bulls, and then collect a harem within this area. Territoriality is one of the most important behavioral traits affecting the spatial organization of animal populations and population dynamics. As a result of territorial behavior, some individuals are forced into suboptimal habitat, which reduces the relative fitness of these individuals (Smith, 1990) (Fig. 11.4). Territorial behavior may prevent overpopulation and overexploitation of the available habitat by ensuring a certain amount of living space or hiding places for an individual or a group of animals (Alcock, 1975; Smith, 1990). Territories may be defended by a single individual (Fig. 11.5), by a pair of adults, or by larger groups such as a flock of birds, a pack of wolves, or a troop of baboons or gorillas (Smith, 1990). Although defense is usually by the male, both male and female may share in defending the territory. In some cases, such as the American alligator, the female is the sole defender. The defended territory is usually much smaller than the home range, although in a few species the territory and the home range may be equivalent. As the size of the territory increases, the cost of defending the territory increases (Smith, 1990). Many fishes, lizards, crocodilians, birds, and mammals, as well as some salamanders, will actively defend an area immediately around their nests and/or homes, particularly during the breeding season and, if they provide parental care, during the time they are caring for their young. Many colo- nial birds nest just out of range of pecking distance of their neighbors (Fig. 11.6). Both male and female red-backed salamanders (Plethodon cinereus) mark their substrates and fecal pellets with pheromones (Jaeger and Gergits, 1979; Jaeger et al., 1986; Horne and Jaeger, 1988) and defend these feeding territories ( Jaeger et al., 1982; Horne, 1988; Mathis, 1989, 1990a). Territoriality may affect the mating success of males, because territorial quality has been found to be posi- tively correlated with body size in Plethodon cinereus (Mathis, 1990b, 1991a, b). Linzey: Vertebrate Biology 11. Movements Text © The McGraw−Hill Companies, 2003 Movements 341 The striking wing pattern of the willet (Catoptrophorus semipalmatus) is important in advertising its territory and in defense. FIGURE 11.5 Gannet (Morus bassanus) nesting colony. Note the precise spacing of nests so that each bird is just beyond the pecking distance of its neighbors. FIGURE 11.6 Some anurans defend their territories, which may include feeding sites, calling sites, shelter, and oviposition sites. During the breeding season, for example, male bullfrogs (Rana catesbeiana) defend an area surrounding their calling site from other males. A resident frog floats high in the water with its head raised to display its yellow throat, and it calls frequently. Initial defensive behavior consists of a vocal challenge followed by an advance toward the intruder. This is followed by another vocal challenge and an advance of a few feet, and so on until the intruder leaves. If the intruder does not leave, the two frogs push and wrestle each other and grasp each other’s pectoral regions, each attempting to throw the other on its back. As soon as one frog is forced onto its back, contact is broken and the winner begins calling again. After remaining submerged for several seconds, the loser usually swims away some distance under water before surfacing. Little owls (Athene noctua) of Germany are a non- migrating, all-year territorial species (Finck, 1990); however, distinct seasonal changes in territory size and in intraspecific aggressiveness of males have been observed. Territories were largest during the courtship season (March and April) and averaged 28.1 ha. They reached their smallest size (average 1.6 ha) during July and August, when the fledglings were still being fed in the parents’ territory. As the young began to disperse in September, territories again began to increase in size. Little, if any, evidence of territoriality has been reported among turtles and snakes. A study of male snapping turtles in Ontario revealed they do not occupy a fixed, exclusive, defended area (Galbraith et al., 1987). They do, however, occupy relatively stable home ranges that overlap and whose spacing may in part be determined by aggressive interactions. Even in burrow-dwelling species such as desert tortoises (Gopherus agassizi) that rarely share summer holes, there is no evidence for the existence of defended territories. In most species, territorial boundaries are marked in the same manner as the boundaries of the home range. For example, some salamanders, such as the red-backed salamander (Plethodon cinereus), produce fecal pellets that serve as pheromonal territorial markers (Jaeger and Gergis, 1979; Jaeger et al., 1986; Horne and Jaeger, 1988). Birds commonly use song and characteristic display behavior, whereas mammals use scents, urine, and excrement to mark the boundaries of their territories (Smith, 1990). ■ DISPERSAL/INVASION Dispersal refers to the movement an animal makes from its point of origin (birthplace) to the place where it reproduces. This type of movement generally occurs just prior to sexual maturity and takes place in all vertebrate groups. Dispersal is significant for a number of reasons. It tends to promote outbreeding in the population; it permits range extension; it may contribute to the reinvasion of formerly occupied areas; and it tends to reduce intraspecific competition. Many of the gradual invasions made by vertebrate species into newly developed or previously occupied territories are the result of dispersal of the young and their selection of breeding territories for the first time. In many species of vertebrates, dispersal is density- dependent. There is a tendency to move only if the population Linzey: Vertebrate Biology 11. Movements Text © The McGraw−Hill Companies, 2003 342 Chapter Eleven 9069 9066 9087 9063a 9068 180° 150° W 165° E 60° S 9089a Cape Colbeck Cape Adare Cape Washington Ross Sea Cape Washington Ross Sea Routes of emperor penguin juveniles (Aptenodytes fosteri) obtained from satellite transmitters. From December 15–19, 1994 and 1995, the birds were captured and released near the ice edge of Cape Wash- ington. Within a few hours of release, the birds entered the water. Posi- tions were monitored from January 4, 1995, to March 6, 1996. During this time, all birds had reached positions far enough north to be in the Westwind Drift. Although researchers had expected signals to continue during June, the lack of signal suggests that the birds remained in water north of the pack ice. FIGURE 11.8 in a given area is high or if aggression is shown by the parents. This is the case with many amphibians, reptiles, and birds and is also true of mammals such as beavers (Castor canadensis), bears (Ursus), and many species of mice. Other species, such as spruce grouse, deer mice, voles, and chipmunks, tend to have an innate predisposition to travel away from their place of birth regardless of the density of the population. After reaching a certain age, members of these species tend to wander away in search of unoccupied areas (Fig. 11.7). Five juvenile emperor penguins (Aptenodytes forsteri) were fitted with satellite transmitters and tracked for several weeks after leaving their place of birth at Cape Washington in Antarctica (Fig. 11.8) (Kooyman et al., 1996). The juveniles traveled beyond the Ross Sea, with one individual being recorded 2,845 km from Cape Washington when last located. The fact that juveniles engage in such extensive travels suggests that adequate protection against human disturbance is not being provided during all phases of the life cycle of this species. Of most concern is the impact of commercial fish- ing around the Antarctic continent. Among mammals that live in groups, males usually disperse about the time they reach breeding age. Sometimes it is voluntary, but other times they are pushed out of the group by dominant, older males who prevent adolescents from mating with the group’s available females. In other groups, both males and females leave their birthplace. In a few species, such as the African hunting dog (Lycaon pictus) and chim- panzees (Pan troglodytes), only the females leave the security of their home group and disperse. The dynamics of groups favoring female dispersal may be driven, in part, by the relative ages of dominant fathers and maturing daughters. In these groups, females that reach maturity while older-gen- eration males still are breeding run a high risk of mating with their fathers or other close relatives. In these cases, it is genetically advantageous for them to leave in order to avoid inbreeding among closely related individuals. The invasion of the Great Lakes by the sea lamprey (Petromyzon marinus) was made possible by the completion, in 1829, of the Welland Canal, which bypassed Niagara Falls. Niagara Falls had served as a natural barrier to aquatic dispersal prior to this time. The lampreys reached Lake Huron in the 1930s and Lake Superior by the mid-1950s. This invasion of lampreys drastically reduced populations of lake trout, lake whitefish, and burbot in most of the Great Lakes. Con- trol measures, including the release of sterile males and the use of a lampricide specific for ammocoete larvae, have allowed the prey species to partially recover and reach an equilibrium with the lampreys. The rapid spread of the English sparrow (Passer domes- ticus) ( Johnston and Selander, 1964) and starling (Sturnus Proportion of mice 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0–50 51–100 101–150 151–200 201–250 251–300 Natal dispersal distance (m) Male Female Natal dispersal distances for 22 male and 9 female juvenile white- footed mice (Peromyscus leucopus). This species has an innate predisposition to disperse regardless of the density of the population. Source: Data from Keane, “Dispersal in White-footed Mice,“ Association for Study of Animal Behavior, 1990. FIGURE 11.7 Linzey: Vertebrate Biology 11. Movements Text © The McGraw−Hill Companies, 2003 Movements 343 1966 1964 1970 1994 1979 1965 1961 1958 1960 1951 1993 1956 Post-breeding dispersal 1970 1943 1937 1954 The cattle egret (Bubulcus ibis) is a native of Africa. It feeds on the insects disturbed by grazing ungulates. This species apparently crossed the South Atlantic Ocean from Africa under its own power and became established in northeastern South America by the late nineteenth century. It dispersed rapidly and is now one of the most widespread and abundant herons in the New World. FIGURE 11.9 vulgaris) (see Fig. 3.35) serve as excellent examples of dispersal/invasion, as does the northward and eastward expansion of the coyote (Canis latrans) (see Fig. 3.37). The gradual northward expansion of the range of the gray fox (Urocyon cinereoargenteus), opossum (Didelphis virginiana), and armadillo (Dasypus novemcinctus) are less dramatic examples. All of these movements have resulted in the expansion of the range of the individual species. The cattle egret (Bubulcus ibis) (Fig. 11.9) is a native of Africa. It crossed the South Atlantic under its own power and was first recorded in Dutch Guiana (now Suriname) in 1877 (Line, 1995). By the late nineteenth century, it had become established on the northeastern coast of South America and, since that time, has dispersed rapidly to become one of the most abundant herons in the Americas. The distance from the bulge of West Africa to the northeastern coast of South America is approximately 2,870 km. Taking into consideration the prevailing trade winds, it is estimated that the trip would have required about 40 hours. Even today, cattle egrets are routinely sighted at sea between Africa and South America. ■ MIGRATION The periodic movement of a population or a part of a population of animals away from a region and their subsequent return to that same region is termed migration. Migration is a transfer of the home range to a distant region. Many animals travel either at regular times during the year or at a particular time during their lives. Some travel to avoid cold or hot weather, some to find a steady food supply, and others to move to breeding sites or to special places to produce their young. The length of the trip varies from species to species, with many traveling in large groups, whereas others travel alone. Migratory movements—which may be daily, seasonal, or irregular in occurrence—may cover short distances or many thousands of kilometers. They may occur annually, as is the case in many birds and mammals, or they may require a lifetime to complete, as is true of some salmon and freshwater eels. Daily movements commonly occur among fishes that move upward and downward in the water column. Such movements are generally in response to sim- ilar movements of zooplankton, although some upward and downward movements are associated with predator avoid- ance. Hammerhead sharks (Sphyrna spp.) in the Gulf of California engage in nightly round trips to feeding sites using magnetic undersea peaks as navigational centers (Klimley, 1995). Crows (Corvus brachyrhynchos) and starlings (Sturnus vulgaris) move from roosts to feeding areas and back each day. Some vertebrates inhabit areas that have suitable living conditions during only part of the year. During the colder winter months, these species must either hibernate or migrate. Thus, migration permits a species to leave an area with unfavorable conditions during a period of the year, for one with more favorable conditions, even though this move is only temporary. Microgeographic (Short-Distance) Migration Some species migrate only short distances. This local, or microgeographic, migration is typical of some ambystom- atid salamanders that migrate from their subterranean hiber- nacula to their breeding pond (Fig. 11.10). They remain active and above ground for several weeks before returning to their underground existence. Many anurans move to breeding ponds in the spring. Norway rats (Rattus norvegi- cus), house mice (Mus musculus), and some snakes may move from fields into barns during the winter and then return to the fields in the spring. Mule deer (Odocoileus hemionus) in the western mountains move from their summer ranges on north-facing slopes to wintering grounds on south-facing slopes (Taber and Dasmann, 1958). Linzey: Vertebrate Biology 11. Movements Text © The McGraw−Hill Companies, 2003 344 Chapter Eleven FIGURE 11.11 Elk (Cervus elaphus) spend the summer months in high mountain meadows and descend into lower valleys during the winter months. This altitudinal migration may lower insect harassment, reduce the risk of predation, and enable the elk to take advantage of a more nutritious food supply. FIGURE 11.10 Some ambystomid salamanders, such as (clockwise from top) the mar- bled salamander (Ambystoma opacum), tiger salamander (A. tigrium), Jefferson’s salamander (A. jeffersonianum), and spotted salamander (A. maculatum). Altitudinal Migration Some species that live in mountainous regions move between higher and lower elevations in a kind of altitudinal migration. For example, many elk (Cervus elaphus) in the western United States spend the summer months in high mountain meadows and descend into lower valleys during the winter months (Fig. 11.11). These movements may be to reduce insect harassment (e.g., black flies, mosquitos), to seek more abundant or nutritious forage, and/or to lower the risk of predation. Carolina dark-eyed juncos (Junco hyemalis carolinensis) and the Carolina chickadee (Parus carolinensis) in the southern Appalachians of North Carolina, Tennessee, and Virginia migrate several thousand meters in elevation, whereas closely related subspecies and species such as the boreal slate-colored junco (Junco hyemalis hyemalis) and the black-capped chickadee (Parus atri- capillus) migrate hundreds, sometimes thousands, of kilometers twice a year between their breeding and wintering areas. Alti- tudinal migrators face considerably fewer hazards and expend much less energy than long-distance migrators; thus, the sur- vival value of this behavior is great. Macrogeographic (Long-Distance) Migration The best known migrators are the macrogeographic,or long-distance, migrators such as ducks, geese, swans, cranes, vireos, warblers, flycatchers, swallows, and thrushes. These species feed primarily on aquatic vegetation and/or flying insects, neither of which is available during the winter months in northern regions. Three hundred and thirty-two of the 650 (51%) North American migratory bird species spend from 6 to 9 months of the year in the tropics of the Americas, where they live under environmental conditions very different from those of their breeding grounds. Many of these migratory birds, especially waterfowl and shorebirds, use four major flyways in North America. From east to west, these are the Atlantic flyway, the Mississippi flyway, the Cen- tral flyway, and the Pacific flyway (Fig. 11.12). These four migration flyways were originally proposed by U.S. Fish and Wildlife Service biologist Frederick Lin- coln (1935), and many federal and state wildlife refuges have been established along the four routes. Although the concept of flyways is useful, especially for waterfowl and shorebird movements during fall migrations, it is an overly simple depiction of migration patterns of most other birds, particularly passerines. Studies by Bellrose (1968) and Richardson (1974, 1976) suggest that most species migrate over broad geographic fronts, particularly in spring, and do not follow narrow migratory corridors. Furthermore, not all birds migrate north and south; some fly east and west. For example, Pacific populations of harlequin ducks (Histrionicus histrionicus) overwinter in the western coastal waters from northern California to Alaska (Turbak, 1997). In the spring, they fly eastward to nest along mountain streams in Alaska, Washington, Oregon, Mon- tana, Idaho, Wyoming, Alberta, British Columbia, the Yukon, and the Northwest Territories. A few even cross the Continental Divide to nest. Harlequin society is matriarchal, with adult females returning salmonlike to their natal streams to reproduce. The Pacific population of harlequins is the only duck population in the world that divides its time between sea and mountains. A small eastern population breeds in maritime Canada and winters on the New England coast. The migratory journeys of some species are astounding because of their length and/or duration. Adult Pacific salmon Linzey: Vertebrate Biology 11. Movements Text © The McGraw−Hill Companies, 2003 Movements 345 Atlantic flyway Pacific flyway Central flyway Mississippi flyway Important wintering areas Important breeding areas The four major flyways used by migratory birds in North America: the Atlantic, Mississippi, Central, and Pacific flyways. Source: Data from Miller, Resource Conservation and Management, 1990, Wadsworth Publishing. FIGURE 11.12 Gulf of Mexico Mexico 30° N 0° 90° W 60° W 30° W Nicaragua Colombia Venezuela French Guiana Caribbean Sea Pacific Ocean Atlantic Ocean Ascension Island Aves Island Hutchinson Island Tortuguero South America Suriname Feeding grounds of Tortuguero turtles Overlapping feeding grounds of Tortuguero and Aves Island turtles Feeding grounds of Aves Island turtles Feeding grounds of Ascension Island turtles Guyana FIGURE 11.13 The Atlantic green turtle (Chelonia mydas) (inset) nests on Ascension Island in the South Atlantic Ocean but lives most of its life in the warm shallow waters off the coast of Brazil. The foraging grounds in the Caribbean and West Central Atlantic Ocean are used by green turtles that nest at three of the four surveyed rookeries (the foraging grounds of the Florida colony are unknown). Source: Data from A. B. Meylan, et al., “A Genetic Test of the Natal Homing Versus Social Facilitation Models for Green Turtle Migration” in Science, 248(4956):724–727, May 11, 1990. (Oncorhynchus) of the North Pacific breed in freshwater streams or lakes, and the young migrate to the sea within the first 2 years of their lives. After 2 to 4 years at sea (during which time the salmon mature), they then travel back to the river system in which they were born. They swim upstream to the head- waters of rivers such as the Columbia and Yukon, where they will spawn and die. Some of these fish will have covered several thousand kilometers during their migratory travels. One population of the Atlantic green turtle (Chelonia mydas) (Fig. 11.13) nests on Ascension Island in the South Atlantic Ocean (Bowen et al., 1989). After depositing their eggs, females return to the warm shallow waters off the coast of Brazil, a distance of over 1,600 km. After feeding on marine vegetation for several years, they return to the same beach to lay another clutch of eggs. Recent studies analyzing mitochondrial DNA (mtDNA) from eggs and hatchlings at four green turtle breeding sites in the Atlantic and Caribbean—Florida, Costa Rica, Venezuela, and Ascension Island—have revealed slight differences in their genetic sequences; this may complicate efforts to preserve this endangered species, because each subgroup could be unique and irreplaceable (Bowen et al., 1989; Meylan et al., 1990). This finding lends credence to the natal homing theory, proposed in the 1960s, which holds that, while turtles hatched in different regions may share common feeding grounds away from home, the animals part company at breeding time, each swimming hundreds or thousands of kilometers to breed and nest at their own (natal) birthplace. Female leatherback turtles (Dermochelys coriacea) appear to travel along migration corridors leading southwest from their nesting sites in Costa Rica (Morreale et al., 1996) (Fig. 11.14). Travel distances up to 2,700 km have been recorded. Linzey: Vertebrate Biology 11. Movements Text © The McGraw−Hill Companies, 2003 346 Chapter Eleven Galápagos Chile Peru Brazil Colombia Caribbean Pacific Ocean Chile Peru Brazil Colombia Caribbean Chile Peru Brazil Colombia Caribbean 100 10°N 1992 10°S 0 90 Longitude (°W) Latitude 80 70 100 90 80 70 100 0 1,000 2,000 kilometers 90 80 70 1994 1995 FIGURE 11.14 Migratory movements of eight leatherback turtles (Dermochelys coriacea) monitored by satellite transmitter after nesting near Playa Grande, Costa Rica. The Cocos Ridge runs beneath the first 1,500 km of the migration corridor, extending out to the Galapagos Islands. Four turtles were tracked as they passed the Galapagos and continued beyond the ridge into deeper Pacific waters. Between 1978 and 1988, scientists collected more than 22,000 eggs of Kemp’s ridley sea turtles (Lepidochelys kempii) from the species’ only known nesting colony at Rancho Nuevo, a Mexican beach 160 km south of Brownsville, Texas. The young were released at Padre Island, Texas, in hopes that the turtles would imprint on the Texas site and return when they reached maturity in 10 to 15 years (Kaiser, 1996). Two turtles returned and nested in 1996. In addition, in May, 1996, a Kemp’s ridley turtle, originally tagged in the Chesa- peake Bay near the mouth of the Potomac River in 1989, was found on the beach at Rancho Nuevo. This is the first known Kemp’s ridley from the Atlantic Ocean to return to the turtles’ ancestral nesting ground. The golden plover (Pluvialis dominica) breeds in the Arc- tic and winters in southeastern South America. It is estimated that these birds cover a distance of 25,000 to 29,000 km annually. The Alaskan population of the wheatear (Oenanthe oenanthe), which winters in southeastern Africa, can make annual journeys of about 30,000 km (Kiepenheuer, 1984). The champion migrator, however, is the Arctic tern (Sterna paradisaea), whose annual round-trip journey from its Arctic breeding grounds near the North Pole to its winter quarters in Antarctica may cover up to 50,000 km per year (Berthold, 1998) (Fig. 11.15). Only three Southern Hemisphere birds—Wilson’s petrel, the sooty shearwater, and the great shearwater— migrate north in large numbers to spend their winters in the Northern Hemisphere, in contrast to the hundreds that go south during our winter. Wilson’s petrel (Oceanites oceanicus), for example, breeds in the Antarctic and may be found as far north as Labrador, a distance of approximately 11,250 km. Many neotropical migrants, such as warblers, thrushes, bobolinks, tanagers, orioles, and hummingbirds, fly nonstop some 1,000 km over the Gulf of Mexico from the Gulf Coast of North America to Central America, a journey requiring about 20 hours. Blackpoll warblers (Dendroica striata) use a trans-Atlantic route in the fall, but an over- land route in the spring (Fig. 11.16). On their southward journey, some use the islands of Bermuda as a resting stop, whereas others fly nonstop from New England to South America, a journey requiring approximately 100 hours of continuous flight time. Many migrants carry at least a 40 percent fat load, which serves as their source of energy for this strenuous journey (Alerstam, 1990). The ruby-throated hummingbird (Archilochus colubris) breeds from the Gulf of St. Lawrence and Saskatchewan to the Gulf of Mexico. It normally weighs no more than 2.5 g, but increases its weight with at least 2 g of fat before migrating over the sea (Alerstam, 1990). The rufous hummingbird (Selasphorus rufus) of western North America breeds from northern Cal- BIO-NOTE 11.1 A Lengthy Turtle Trek An estimated 10,000 juvenile loggerhead turtles (Caretta caretta) feed and develop off the coast of Baja California annually. The nearest known nesting sites, however, lie in Japan and Australia, some 10,000 km away. Mitochondrial DNA samples from Baja turtles, and from another group caught by North Pacific fishermen, revealed that 95 percent (of both groups) carried the same distinctive genetic sequences as the baby turtles in Japan, while the remain- der matched the DNA markers of the Australian turtles. If additional data support these findings, the 10,000-km trek to Baja—a distance spanning more than one-third of the globe—would rank among the longest docu- mented marine vertebrate migrations. Bowen, 1995 [...]... growing at a rate of 15 percent annually (Cochran, 1996) Virginia agricultural Linzey: Vertebrate Biology 348 11 Movements Text © The McGraw−Hill Companies, 2003 Chapter Eleven BIO-NOTE 11. 2 BIO-NOTE 11. 3 How Hummingbirds Store the Energy to Migrate The Migratory Diet Hummingbirds, which are among the smallest endothermic vertebrates, have a high metabolic rate Flying hummingbirds must fuel their high.. .Linzey: Vertebrate Biology 11 Movements Text © The McGraw−Hill Companies, 2003 Movements FIGURE 11. 15 347 FIGURE 11. 16 Halifax ? Cape Cod ? ? 40° United States ? ? Wallops Island 35° Bermuda Breeding area Wintering area Autumn migration Spring migration 30° (a) 0° 60° 25° 60° Miami Cuba 20° Puerto Rico Ice limit in November Equator Antigua Central America 120° Heard Island 40° Mainly 60° 1st-years... suggested that birds possibly could sense low-intensity alternating-current electromagnetic fields and that they also could sense natural fluctuations in the Earth’s magnetic field Permanently magnetic iron oxide (probably magnetite, Fe3O4) has been found concentrated in Linzey: Vertebrate Biology 350 11 Movements Text © The McGraw−Hill Companies, 2003 Chapter Eleven the head and neck muscles of both... (Witherington and Bjorndal, 1991) Once they reach water, they must orient into the waves, FIGURE 11. 17 A leatherback sea turtle (Dermochelys coriacea) instinctively makes its way to the sea upon hatching It seeks out bright, open horizons and orients toward violet and blue-green wavelengths Linzey: Vertebrate Biology 11 Movements Text © The McGraw−Hill Companies, 2003 Movements swimming toward approaching... temperature, salinity, and chemicals; sun orientation; orientation to polarized light; and orientation to geomagnetic and geoelectric fields Salmon hatch in Linzey: Vertebrate Biology 354 11 Movements Text © The McGraw−Hill Companies, 2003 Chapter Eleven FIGURE 11. 21 Homing Migration Mechanisms for determining the home course Genetically encoded directional information Compass mechanisms Flight direction The... Bermuda Biological Conservation 42:133–145 Weidensaul, S 1999 Living on the Wind: Across the Hemisphere with Migratory Birds New York: North Point Press Linzey: Vertebrate Biology 356 11 Movements Text © The McGraw−Hill Companies, 2003 Chapter Eleven Vertebrate Internet Visit the zoology website at http://www.mhhe.com to find live internet links for each of the references listed below 1 FishFAQ2 This... stars), and polarized light—as major aids in navigation (Wiltschko et al., 1996) Starlings and white-throated sparrows apparently use the star pattern in the sky (Kramer, 1957, 1959; Sauer, 1958) (Fig 11. 18) Golden-crowned (Zonotrichia coronata) and white-crowned sparrows (Z leucophrys) as well as white- 351 throated sparrows caged outdoors show a strong orientation toward the north in the spring and... orientational mechanisms (Alerstam, 1990) The navigational system undergoes a change during the first few months of a pigeon’s life FIGURE 11. 22 Canada geese (Branta canadensis) silhouetted against the moon as they migrate south to spend the winter Linzey: Vertebrate Biology 11 Movements Text © The McGraw−Hill Companies, 2003 Movements Initially, birds must rely on mechanisms such as visual cues to determine... (Myotis sodalis), n=700; meadow vole (Microtus pennsylvanicus), n=460; and black bear (Ursus americanus), n =112 Source: Data from Robinson and Falls, 1965; MacArthur, 1981; Hassel, 1960; in J Bovet “Mammals” in Animal Homing, F Papi (editor), 1992, Chapman and Hall, New York Linzey: Vertebrate Biology 11 Movements Text © The McGraw−Hill Companies, 2003 Movements from their San Jose, California, wintering... and intermediate-age terns migrate mainly westward off the Antarctic coast before continuing north in the Atlantic There are indications that first-years in particular migrate around the South Pole to summer on the Humboldt Current ifornia, Oregon, Idaho, and Washington northwestward through British Columbia to the southeastern Alaskan coast, and it winters in Mexico Thus, this 9-cm-long bird may migrate . 10,000-km trek to Baja—a distance spanning more than one-third of the globe—would rank among the longest docu- mented marine vertebrate migrations. Bowen, 1995 Linzey: Vertebrate Biology 11. Movements. species of vertebrates, dispersal is density- dependent. There is a tendency to move only if the population Linzey: Vertebrate Biology 11. Movements Text © The McGraw−Hill Companies, 2003 342 Chapter. ranges on north-facing slopes to wintering grounds on south-facing slopes (Taber and Dasmann, 1958). Linzey: Vertebrate Biology 11. Movements Text © The McGraw−Hill Companies, 2003 344 Chapter Eleven FIGURE

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