Linzey - Vertebrate Biology - Chapter 11 pdf

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

C H A P T E R 1 1

Movements

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

oth-ers such as golden plovoth-ers (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

mal’s position and stability in space, and the control of an

ani-mal’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

move-ments, 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 is highly variable and is often difficult to define

It is the area around the home of an individual that is

cov-ered 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

con-siderably 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 dis-tances 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 gener-ally 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

squir-rels (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

Exclusive boundary strip (white area)

X X

X

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

vary-ing 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 perma-nent ranges and spend their entire lifetimes within these areas Most frogs, salamanders, lizards, turtles, snakes, moles, shrews, woodchucks, chipmunks, deer mice, and many oth-ers 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 km2that may overlap exten-sively (Catton, 1990) Most pandas, especially females, tend

to concentrate their activity within core areas of 0.3 to 0.4

km2 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

rub-bing 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

hud-sonicus) 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

A chuckwalla (Sauromalus obesus) basking in the warm Arizona

desert sun.

FIGURE 11.2

TABLE 11.1

Home Ranges of Selected Vertebrates

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

perma-nent burrow of a gopher tortoise (Gopherus) or woodchuck

(Marmota) It may serve a single animal (cougar, Felis

con-color), 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

per-cent 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

tun-nels constructed by a colony currently comprising 87 animals

was more than 3.0 km long and occupied an area greater

than 100,000 m2—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,

4 3

2

1 13 12 April 17, 1962

Yellowhead territories Redwing territories

May 6, 1962

7 6

3 2

1

13 12

11 10 9 8

11 10

Redwing territories

Yellowhead interspecific aggression

Interspecific territoriality between red-winged blackbirds (Agelaius phoeniceus) and yellow-headed blackbirds (Xanthocephalus xantho-cephalus) 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

popula-tions and population dynamics As a result of territorial

behavior, some individuals are forced into suboptimal

habi-tat, 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

ter-ritory 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 mam-mals, 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

sala-manders (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 feed-ing 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)

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

chal-lenge 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 call-ing again After remaincall-ing 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); how-ever, 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 small-est 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 exam-ple, 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 mam-mals use scents, urine, and excrement to mark the boundaries

of their territories (Smith, 1990)

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 terri-tories for the first time

In many species of vertebrates, dispersal is density-dependent There is a tendency to move only if the population

9066

9087

9063a

9068

180 °

150

° W

165° E 60

° S

9089a Cape Colbeck

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

par-ents 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

chip-munks, tend to have an innate predisposition to travel away

from their place of birth regardless of the density of the

pop-ulation 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

juve-niles 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

sug-gests 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

dis-perse 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

mat-ing 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

rel-ative 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 genet-ically 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 dis-persal prior to this time The lampreys reached Lake Huron

in the 1930s and Lake Superior by the mid-1950s This inva-sion 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

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

predis-position 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

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

cen-tury 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

dis-persal/invasion, as does the northward and eastward

expan-sion 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

north-eastern 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

The periodic movement of a population or a part of a pop-ulation 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 pro-duce 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 star-lings (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)

FIGURE 11.11

Elk (Cervus elaphus) spend the summer months in high mountain

mead-ows and descend into lower valleys during the winter months This alti-tudinal 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

nutri-tious 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

thou-sand meters in elevation, whereas closely related subspecies

and species such as the boreal slate-colored junco (Junco

hye-malis hyehye-malis) 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, partic-ularly 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

Atlantic 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

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

Guy ana

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

sev-eral 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

migra-tion corridors leading southwest from their nesting sites in Costa Rica (Morreale et al., 1996) (Fig 11.14) Travel dis-tances up to 2,700 km have been recorded

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)

0 1,000 2,000

kilometers

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

tur-tles’ 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

annu-ally 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

per-cent (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