Linzey - Vertebrate Biology - Chapter 14 pps

Limitations inherent in field and laboratory investigations of animal populations make it even more critical that researchers choose most carefully the techniques to be used.. For some p

C H A P T E R 1 4

Techniques for Ecological and Behavioral Studies

Discovery and problem solving in all fields of science employ

techniques of gathering, coordinating, organizing, and

evalu-ating information as it relates to a specific subject In a

scien-tific approach to any problem, the researcher must first ask a

question or identify a problem based on observations of objects

or events Then, a hypothesis or potential answer to the

ques-tion being asked is proposed, and the investigator predicts what

the consequences might be if the hypothesis is valid The

inves-tigator then devises ways to test the hypothesis by making

observations, developing models, or performing experiments

Hypotheses must be testable; those that are not testable are

inadmissible in science Observations and/or tests should be

repeated as often as necessary to determine whether results will

be consistent and as predicted Hypotheses that are found upon

testing to be contradicted by the evidence must be modified or

abandoned The investigator must then report objectively on

the results and on conclusions drawn from them, presenting

both the data and the investigator’s intepretation of the

infor-mation as it relates to the hypothesis This mode of action is

known as the scientific method Critical evaluation of the

tech-niques—or methodology—used in any scientific investigation

is extremely important Thus, scientists constantly must be

con-cerned with the selection and application of the best techniques

for use in each of these steps A deficiency in any of these steps

will hinder the interpretation of the results

Limitations inherent in field and laboratory investigations

of animal populations make it even more critical that researchers

choose most carefully the techniques to be used The mobility,

secretiveness, and constant fluctuation in numbers of practically

all wild animals make precise data difficult to secure For these

reasons, census work often requires a major portion of the time

in many field investigations The secretive nature of most wild

animals makes the determination of the influence of pathology,

disease, and related factors especially difficult to examine for any

species of animal in nature

Because the objective of any investigation is to gather and

evaluate accurate data, the investigator must always bear in

mind that the techniques used should yield data that are objec-tive and reliable If the investigator’s approach to the problem

is not scientifically sound—if the techniques are inadequate or flawed—the results will be of little value Critical appraisal of the investigational techniques should be made at the begin-ning, not at the termination, of the research project The difficulties mentioned above highlight the need for careful planning and equally careful collection of data on the part of fish and wildlife investigators Inexperienced investi-gators often propose to collect data that, due to field condi-tions or the characteristics of the animal being investigated, are impossible to secure Thus, detailed planning, including critical scrutiny of all the proposed techniques to be employed,

is necessary to ensure that insurmountable problems are not encountered in the proposed study Long-term studies are needed to learn these limitations and to collect the necessary information; yet this is rarely accomplished, since most

stud-ies are short-term (and are financed as short-term projects).

Many studies do not require the capture of individual ani-mals Techniques employing simple observation, aerial pho-tography, aerial censusing, transect counts, actual counting of individuals such as fishes and hawks that pass a certain point

on their migratory journeys, and identification of signs such as tracks and scats can provide valuable data For some purposes, animals such as amphibians, reptiles, and mammals killed by vehicles (DOR=dead on road) can yield useful data Many behavioral studies can be done in the animal’s natural habitat Other studies, however, do require direct contact between animal and investigator Such studies include those dealing with the collection of anatomical data such as weight, length, con-dition of molt, or the like; or those dealing with age determi-nation, sex ratios, genetic analyses, home ranges, and parasites

A wide variety of techniques are used for capturing verte-brates Humane capture techniques should always be employed They should not injure or increase the mortality

(a) The cannon net is an effective way of taking gamebirds, unharmed,

for scientific purposes The birds are prebaited at the site; the net is then

carefully folded and camouflaged in front of the “cannons.” (b) When

properly deployed, the net is highly effective The birds are snow geese

(Chen hyperborea).

FIGURE 14.1

(a)

(b)

of the animals, and they should not cause more than

mini-mal disruption to the animini-mals’ normini-mal behavior patterns

Dip-netting, seining, the use of trap- and gill-nets, and

the use of immobilizing chemicals and electroshocking are

among the capture methods utilized by fish biologists Most

amphibians can be captured either by hand or with the use

of a net Some terrestrial reptiles also can be taken by hand,

although nets, nooses, and tongs frequently are used for some

species Aquatic turtles may be secured through the use of

turtle traps, commercial fish trap-nets, and trawls

Nestling birds can be removed from the nest by hand for

weighing, sexing, and tagging Fine-mesh mist nets are often

used to capture small flying birds, which become entangled in

the mesh and can be removed uninjured for study Live traps

placed on the ground and baited with seeds are used

success-fully for some granivorous species The projection, or cannon,

net trap is widely used for turkeys and waterfowl (Fig 14.1)

It consists of a large, light net that is carried over the baited

birds by mortar projectiles or rockets Funnel-entrance traps

are used commonly for waterfowl Hawks can be trapped by

using traps baited with live prey Some carrion-eating species

have been immobilized by consuming drug-laden meat

Many small-mammal researchers employ traps These

should be live traps suitable for the species, although snap

traps were extensively used in the past Traps may be placed

on the surface of the ground or in tunnels, or they may be

affixed to the branches of trees

Shrews are taken most effectively in pitfall traps in which

a series of containers (cans, plastic cups, etc.) are buried with

their tops flush with the ground and loosely covered by a

piece of wood or some other object Due to the shrews’ high

metabolism, this method of collection will yield live shrews

only if the cans are checked several times each day If the cans

cannot be checked frequently, they can be partially filled with

a preservative liquid/fixative to kill and preserve animals for

future study All cans should be removed and the holes filled

at the conclusion of the study Small-mammal distribution

studies can be augmented by examining discarded bottles

along roadsides Shrews are the most abundant small

mam-mals found in bottles (Morris and Harper, 1965; Glegg,

1966; Pagels and French, 1987) Examination of owl pellets

also can yield valuable distributional and population data on

shrews, voles, and other small mammals

Bats usually are captured with mist nets positioned at

cave entrances or along watercourse flyways Nets must be

monitored continually, and bats removed as soon as possible

in order to prevent injury

Although mammals as large as bears can be trapped

suc-cessfully with snares and culvert traps, most large mammals

are shot with a tranquilizer-containing dart Fairly accurate

estimation of weights of animals in the field must be made

for proper dosages to be administered

Drift fences and traps are used for studies on a wide range

of terrestrial vertebrates, including amphibians, reptiles, and

mammals This method requires the erection of one or more

fences with openings at periodic intervals The object is to direct

the movement of an animal into a trap at one of the openings

To study the movements and behavior of animals in the wild, there must be a means of identifying specific individuals In some cases, this can be accomplished by noting unique indi-vidual characteristics such as distinctive coloration, scars, deformities, injuries, or some aberrant behavior For exam-ple, Schaller (1963) found that the noses of mountain goril-las appeared distinctive and served as the best single character for recognizing individuals

In most cases, however, it is not possible to distinguish individuals visually Therefore, some appropriate method of marking or tagging each individual animal must be devised

In deciding on a particular technique, consideration must be given as to whether the study in question is short-term or long-term and how many animals will be involved The method selected should not injure the animal, alter the animal’s behavior or locomotion, or cause increased susceptibility to predation Many identifying techniques have been devised including marking, tagging, photography, use of radio trans-mitters, and satellite tracking

A biologist tags a hawksbill turtle (Eretmochelys imbricata) in an effort to

gather more information on the species’ movements and habitat needs The threats facing this species include habitat destruction and commer-cial demand for stuffed juveniles and products made out of its shell.

FIGURE 14.2

Marking

Marking usually refers to changing a part of the animal’s

body so that it can be discerned readily from all other

mem-bers of the population Moyle and Cech (1996) summarized

fish marking methods as follows: “Marks may consist of clipped

fin rays, liquid nitrogen ‘cold brands,’ pigmented epidermis

from high-pressure spray painting, or fluorescent rings on

bones or scales (visible under ultraviolet light) from

incor-poration of tetracycline or 2, 4-bis(N,

N′-dicarboxymethyl-aminomethyl) fluorescein (DCAF) in the diet.” Juvenile

salmonids have been marked chemically by feeding them

dissolved strontium, a biologically rare element, which is

then incorportated into their scales (Snyder et al., 1992)

Amphibians usually are marked by toe clipping—that is,

excising the terminal phalanx of one or more toes in a

spe-cific pattern They also may be marked by branding and by

the use of dyes and phosphorescent powders Larval (tadpole)

stages may be semipermanently marked by injecting an

acrylic polymer dye into the fin A detailed discussion of

marking and tagging techniques suitable for amphibians may

be found in Heyer et al (1994)

Lizards and snakes may be marked by toe clipping, by

excising specific scales in a prearranged manner, or by using

a latex-based house paint Marking methods for reptiles have

been reviewed by Dunham et al (1988) Individual turtles

can be identified by having an identifying mark painted on

their shells or by notching specific marginal scutes Birds

may be marked by dyeing their feathers

Mammals may be marked by toe clipping, fur clipping,

ear notching, tattooing, branding, dyeing, painting, or

bleaching In the case of toe clipping, smoked paper affixed

to plywood or cardboard can be placed throughout the study

area so that whenever a marked animal crosses the surface,

it will leave its own distinctive identifying imprint

Commercial dyes have been employed in various ways

to identify mammals In some species, the dye is applied to

the captured animal prior to its release In other studies, a

marking device may be placed in the animal’s normal habitat

(designed in such a way that the animal triggers the device

in its typical pattern of activity) Once triggered, the device

discharges a quantity of the dye onto the animal’s body The

use of a dye in this manner will provide visual identification

until the animal undergoes its next molt Fluorescent

pow-ders have also been used successfully

Tagging

Tagging requires the attachment of a metal, plastic, or cloth

device to the body of an animal to allow for future

identifi-cation (Fig 14.2) Any tagging device must anticipate the

growth of the animal and must not impede its movements

or other normal behavior

Tagging of fishes can be done by externally and internally

attached disks, microtags, dart tags, plates, streamers, and

small, implantable metal rods detectable in a magnetic field

(Moyle and Cech, 1996) Electronic tags that record depth,

water temperature, and light intensity weigh as little as 16 g

and can store more than 500,000 data samples (Metcalfe and

Arnold, 1997) Data on plaice (Pleuronectes platessa) have been

recorded continuously by electronic tags for over 200 days Amphibian studies have used tags and radioactive iso-topes for identifying individual animals The use of isoiso-topes allows the continuous monitoring of an individual without recapture Passive integrated transponder (PIT) tags are small, glass-encapsulated diodes (0.1 g) and do not require batteries (Camper and Dixon, 1988) When activated by a detector, they transmit a unique code back to the receiver PIT tags must be implanted in the animal (thus, infection is

a major consideration), and current transponder systems have

a very short range Ingested radio transmitters also have been successful in yielding short-term data on amphibians such as

the common frog (Rana temporaria) and the common toad (Bufo bufo) (Oldham and Swan, 1992) as well as on snakes.

Several unique methods of tracking turtles have been employed Stickel’s (1950) attachment of a spool of thread

to the carapace of a box turtle yielded valuable data on the movements of this species The attachment of helium-filled weather balloons to marine turtles allowed tracking of their movements for short periods of time

For years, ornithologists have been studying migration in birds, as well as many other aspects of avian biology, by using aluminum, stainless, or monel alloy leg bands (Figs 14.3a, b and 14.4) These tags are numbered and contain the address

of an agency to which the finder should mail them In the United States, the agency is the U.S Fish and Wildlife Ser-vice Bands come in a variety of sizes, and future growth in the diameter of the leg must be carefully anticipated prior to attachment of the band These bands have provided valuable data on the migratory habits of many species of birds, but a bird must either be recaptured or found dead in order to be

positively identified A toll-free telephone number

(1-800-327-BAND) is now available to report any bird band

identi-fied or recovered in North America This recording service,

developed in cooperation with the National Biological

Sur-vey, the U.S Fish and Wildlife Service, and the Canadian

Wildlife Service, can be called from anywhere in the United

States, Canada, and most parts of the Caribbean

Colored leg bands, neck bands, or plastic streamers are

used in behavioral or home range studies so that individual

birds can be identified without recapture (Fig 14.5) Patagial

tags and feather grafts also have been used as field

identifi-cation tags (Fig 14.6)

Researchers studying western European populations of

the white stork (Ciconia ciconia) implanted electronic PIT

tags (30 mm long, 3 mm in diameter, 0.8 g mass) beneath the

stork’s skin (Michard et al., 1995) The tag, which permits

automatic individual identification, is long-lasting because it

does not require a battery Body condition also can be

assessed, as the birds weigh themselves on scales coupled with

tag-identification systems at feeding sites The tags are read

by an antenna-recorder from a distance of approximately 1 m

Mammals may be tagged in a variety of ways Studies

involving bats utilize lightweight aluminum bands similar to

those used for birds These bands are numbered and are

affixed to the forearms of the bats In some studies, inch-long

luminous cyalume rods have been attached to the backs of

bats for easier tracking at night Metal or plastic ear tags

FIGURE 14.3

(a)

(b)

(a) Banding a woodcock (Philohela minor) Future growth of the leg

must be anticipated when selecting the proper size band (b) Bands of

various sizes, made of soft, lightweight metal, are provided by the U.S.

Fish and Wildlife Service for bird banding to determine the migratory

movements of various species.

FIGURE 14.4

The neck collars on these parent Canada geese (Branta canadensisi)

make it possible to keep track of eggs and young up to the migratory stage, yielding information on daily and seasonal habitat preferences.

Colored patagial tags have been used to study the breeding behavior

of mourning doves (Zenaidura macroura).

FIGURE 14.5

have been used on mammals of all sizes In some cases, col-ored plastic streamers have been attached to the tags so that visual identification can be made at a distance Neck collars are used on larger mammals Unfortunately, all tags are

Feather graft of an immature wing feather onto the head of a great

black-backed gull (Larus marinus) Best results are obtained when the

graft is made on immature birds The grafted feather is permanent and

molts with other body feathers, thereby serving as a permanent field

identification “tag.”

FIGURE 14.6

subject to loss; Siniff and Ralls (1991), for example, reported

an estimated annual tag loss rate of 26 percent in California

sea otters (Enhydra lutris).

Spool-and-line tracking has been employed in several

mammal studies This technique utilizes a spool of thread

attached to the animal’s body The spool continuously releases

thread as the animal moves, thus providing a fairly accurate

representation of the animal’s travels For example, Hawkins

and Macdonald (1992) used spools attached to webbed

col-lars to investigate the movements of badgers (Meles meles).

One disadvantage of this method is that it yields only 1 or 2

nights of potentially high-quality data per capture

Dyes have been incorporated in food in order to stain

the feces In small-mammal studies, dropping boards are

placed throughout the study area in order to facilitate the

recovery of dyed fecal pellets This is a temporary technique

that depends on the rate of passage of the food material

through the animal’s alimentary canal

Radioactive isotopes in the form of wires and pellets

have been inserted under the skin of various species of

mam-mals This method of tagging permits continuous location of

the animal with minimal disturbance Radioactive materials

injected into animals will render their feces identifiable

The use of genetic tagging has revealed individual local

and migratory movements and yielded estimations of

abun-dance in humpback whales (Megaptera novaeangliae) (Palsboll

et al., 1997) Genetic tagging consists of collecting skin

sam-ples, removing the DNA, and determining the sex and

geno-type at six Mendelian-inherited microsatellite loci for each

sample More than 2,300 unique genotypes were identified

Genetic tracking has also allowed the tracking of an

indi-vidual whale from fishery to market (Cipriano and Palumbi, 1999) This technique, as well as similar genetic tools, will allow new management efforts to focus on the individual, rather than the species, and to distinguish individual “legal” whales (those of a particular sex and size which can be legally harvested) from all others

Tagging frequently requires specific federal and/or state permits, as well as approval from university and institutional animal care and/or ethics committees in many instances, par-ticularly when dealing with species whose travels cross inter-national boundaries, such as most birds Researchers must be qualified in identification and handling of particular species,

as well as in the tagging/marking techniques to be employed

Photography

Photography is useful for making a permanent record of the location and/or behavior of a marked or tagged animal

Approximately 80 percent of the manatees (Trichechus man-atus) in the Homosassa and Crystal rivers in Florida are

dis-tinctively scarred, primarily from boat strikes These scar patterns have been used to identify individual manatees Pho-tographs were taken at regular intervals (twice a week, weekly, biweekly), both from the water’s surface and from beneath the surface, and were incorporated into an identification cat-alogue (Powell and Rathbun, 1984; Rathbun et al., 1990)

Resightings of humpback whales (Megaptera novaeangliae)

returning to their summer feeding grounds have been veri-fied photographically Photoidentification of cetaceans is a worldwide ongoing endeavor with regional catalogues and specific repositories of all photographed whales

Photography also has been used in some studies so that

an unsuspecting animal triggers a mechanism and takes its own picture This not only provides a record of the animal’s presence but may also identify food brought to the nest and the frequency and length of absence from the nest A clock

or timing device can be positioned so that it is included in the photograph and records the time the photograph was taken Small video systems and data loggers that were mounted

on the heads of four adult Weddell seals (Leptonychotes wed-dellii) at McMurdo Sound in Antarctica have revealed some

aspects of the secret lives of diving animals (Davis et al., 1999) (Fig 14.7) The video system recorded images of the seal’s head and the environment immediately in front of the animal Filming was accomplished in near-infrared light emitted from the camera like a flashlight The light, which was invisible to the seal’s eye and its prey, should not have altered either one’s behavior The data logger recorded time, depth, water speed, and compass bearing once per second Flipper stroke frequency and ambient sound were recorded continuously on the audio channels Several unknown tactics used by the seals to extract prey from their refuges in the ice were revealed

Radio Transmitters

One of the earliest reports on the use of radio telemetry to locate free-ranging animals was their use on woodchucks

(Marmota monax) by LeMunyan (1959) The use of radio

transmitters has met with considerable success since that

A Weddell seal (Leptonychotes weddellii) surfaces in McMurdo Sound,

Antarctica, with a 40-pound cod in its mouth and a video camera

strapped to its head Filming was accomplished in near-infrared light

emitted from the camera The video camera and data logger revealed

heretofore unknown behavior and tactics used by the seals to secure

their food beneath the ice.

FIGURE 14.7

time, as transmitters continue to be miniaturized and

receiv-ing equipment continues to be improved In many ways, the

use of radio transmitters has revolutionized the study of

ani-mal movements They have been used in studies involving all

of the vertebrate groups

The use of radio telemetry in field studies of vertebrates

provides the ability to locate the transmitter regularly, both

day and night, to check on the location and condition of the

carrier Radio telemetry is valuable in studying predation,

individual behavior patterns, and home ranges Several

telemetry techniques have been designed specifically for

detecting mortality in free-ranging animals For example,

transmitters may contain temperature sensors that detect the

drop in body temperature upon the death of the animal

Transmitters may be strapped to the body, attached by

means of a collar placed around the neck (Fig 14.8), wired

to the carapace of turtles, or implanted intraperitoneally or

subcutaneously (Ralls et al., 1989; Werner, 1991; Rowe and

Moll, 1991; and others) For example, surgically implanted

temperature-sensitive radio transmitters revealed daily

vari-ations in the body temperatures of free-ranging garter snakes

(Thamnophis elegans vagrans) in eastern Washington

(Peter-son, 1987) (Fig 14.9) Collars may be designed to

deterio-rate after a certain length of time, or in long-term studies,

the animal may need to be recaptured and refitted with a

new collar Intraperitoneal radio transmitter implants were

found to have no effect on reproductive performance

(copu-lation, embryonic and fetal development, and lactation) in

river otters (Reid et al., 1986)

Transmitters have been glued to the bony shells of some

species of turtles, but the oily, flexible skin that covers the

thin, loosely fused, bony plates in a leatherback sea turtle’s

carapace resists adhesives In an experimental technique, the

bone is pierced with half-inch-long screws made of a

syn-thetic polymer that slowly dissolves (Raloff, 1998) A nylon

suture is threaded through each screw and serves to firmly attach the transmitter As the screws dissolve, they are replaced by bone that continues to anchor the sutures until they weaken and release the transmitter

Male elk (Cervus elaphus) with a radio transmitter, permitting movement

and behavioral studies of animals of known age and sex, even though they may be located several miles away.

FIGURE 14.8

Time of day

50

40

30

20

10

0

-10

Oscillating pattern

Plateau pattern

No 20 4-5 August 1979

No 30 6-7 April 1980

Smooth pattern

No 135 2-5 September 1979

Daily Variation In Snake Temperatures

Tb

Tb

Tb

Surgically implanted temperature-sensitive radio transmitters have been used to reveal daily variations in the body temperatures of free-ranging

vertebrates including garter snakes (Thamnophis elegans vagrans) in

eastern Washington The daily body temperature patterns shown here

are classified as (a) plateau pattern, (b) smooth pattern, and (c)

oscillat-ing pattern Sunrise (↑) and sunset (↓) are indicated on the time axis.

Source: Data from Peterson in Ecology, 68(1)1987.

FIGURE 14.9

BIO-NOTE 14.1

Teaching Birds to Migrate

Trumpeter swans (Cygnus buccinator) are white with a

black beak, weigh up to 13.5 kg, have a 2.5-m wing span,

and can stand 1.8 m tall with neck outstretched They

vanished from the Chesapeake Bay nearly 200 years ago

Scientists working with the Defenders of Wildlife, a

Washington, D.C.–based conservation organization, and

the U.S Fish and Wildlife Service are now trying to

restore America’s largest waterfowl to the mid-Atlantic

region by reteaching the birds to migrate by using a bright

yellow ultralight plane with an overarching white wing

The goal of this project is to reestablish a migration route

between upstate New York and Maryland’s Eastern Shore

Migration is important because birds that do not fly south

for the winter are more likely to exhaust their food supply,

become a nuisance to people, get sick, or freeze to death

Trumpeter swans learn to migrate from their parents, but

if the older birds in a flock are killed by hunters, the

young do not know where to migrate and the knowledge

is forever lost

In December 1997, three trumpeter swans followed

the ultralight plane from the Airlie Environmental Center

in Warrenton, Virginia, to open tidewater marshes near

Cambridge in Dorchester County, Maryland, a distance of

166 km (Fig 14.10) All three swans returned halfway from

their winter site near Cambridge to Airlie in Spring 1998,

not deviating by more than 5 miles from the pre-selected

route they had been shown in December 1997 One

returned to within 10 miles of Airlie; another was injured

and was trucked back The third was also trucked back

from Cambridge after backtracking there None of these

three females returned to their winter site near Cambridge

in 1998–99 They remained at Airlie

A second project, begun in December 1998, involved transporting 13 trumpeter swans from where they were trained at a traditional breeding ground at a New York Department of Environmental Conservation site near Buf-falo, to the Wildfowl Trust of North America on Chesa-peake Bay near Grasonville, Maryland Instead of flying them the entire 320-mile route, they were trucked between stops with the birds being flown as high as possible at each stop In Spring 1999, this flock, while showing migration intention behavior, did not explore more than

10 miles from their wintering quarters Thus, having failed

to return to New York on their own, they were trucked back

in May to the New York Department of Conservation’s Oak Orchard Wildlife Management Area a few miles from where they were trained during Fall 1998 On January 22, 2000, one of the experimental trumpeter swans arrived in Clays-burg, Pennsylvania, roughly 210 miles due south from the summer site and approximately 100 miles west of the migra-tion route Since the male bird arrived shortly after a storm, researchers feel that it may have been blown off course

In 1993, a motorized ultralight led a Canada goose migration from Ontario, Canada, to the Airlie Center, a trip

depicted in the 1996 movie Fly Away Home In October

1995, an ultralight aircraft led eight sandhill cranes on an 11-day, 1,204-km trip from Idaho to the Bosque del Apache National Wildlife Refuge in New Mexico In October 1997,

an ultralight painted to look like a whooping crane guided two of the endangered white birds and six sandhill cranes on

a 9-day flight from Idaho to New Mexico

Lewis, 1996 Rininger, 2000

Satellite Tracking

Satellite tracking is one of the latest tools in the repertoire

of wildlife biologists It allows for monitoring of an indi-vidual by providing an update with every pass of the satel-lite It has been used successfully on a variety of species, including sea turtles, penguins, whales, elephant seals, ele-phants, caribou, bears, musk-oxen, and manatees (Mate, 1989; Reynolds, 1989; Rathbun et al., 1990; Holden, 1992; Stewart and DeLong, 1995; Reid, 1997) One of the first successful tracking experiments of a bird using satellite telemetry was reported by Jouventin and Weimerskirch

(1990), who showed that wandering albatrosses (Diomedea exulans) remain active at night, fly at speeds of up to 80

km/hr, and range over distances of up to 900 km per day Albatrosses covered from 3,600 to 15,000 km in a single foraging trip during the time their mates had taken over the duties of incubation

Satellite tracking is best used in situations where con-ventional tracking techniques are not useful, such as animals that range widely or are in habitats where they cannot be followed Compared with conventional radio-tracking, satel-lite tracking is less accurate and more expensive

Radio contact with migrating whooping cranes (Grus

americana) was maintained by means of leg-band radio

trans-mitters, antennas attached to aircraft struts, and radio

receivers carried in the aircraft (Kuyt, 1992) Radio signals,

which could be picked up from distances up to 155 km,

allowed researchers to follow the cranes Visual contact was

maintained for up to 50 percent of the migration, enabling

air crews to obtain data on flight behavior

In studies of marine species, specific problems arise

because of diving and because of the effect of high electrolyte

concentrations on the radio signals A floating transmitter

tethered to a swivel strapped to the tail stock was devised and

successfully used in studies of manatees (Rathbun et al.,1987)

Baits containing acoustic transmitters have been consumed

by deepsea fishes In conjunction with an automatic

track-ing system and cameras on the sea floor, this technique has

allowed the tracking of the speed and direction of travel in

deepsea scavenging fishes (Priede et al., 1991)

A summary of standard radio-tracking techniques was

presented by Mech (1983) Specific data for amphibians were

reviewed in Heyer et al (1994); data for mammals were

reviewed in Wilson et al (1996)

FIGURE 14.10

Trumpeter swans (Cygnus buccinator) following an ultralight aircraft,

a method designed to teach birds the ancient migratory route of

their ancestors

Geographic Information Systems (GIS) technology is the

computerized recording of data for a region, using geographic

coordinates as the primary indexing system The kinds of data

that can be stored include presence or absence of a species,

abundance of that species where it is present, ecosystem type,

soil type, geology and physiography, land protection status,

and many other variables For example, most home range

stud-ies have focused only on the horizontal component of the

land-scape (planimetric area), where the slope of the terrain is

assumed to be zero Topography adds an important element

to landscape because the slope of the terrain often fluctuates

throughout the home range, and because changes in

topogra-phy can increase the surface area A GIS that incorporates

topography can account for topographic changes and yield

more accurate estimates of home range size (Stone et al., 1997)

GIS systems are well adapted to using data from remote

sensing sources Detailed data on the actual vegetation of a

geographical area are difficult to obtain from traditional

veg-etation maps, which often show the potential climax

vegeta-tion thought to characterize a region rather than the

vegetation actually present With improved satellite imagery

and analysis, detailed data on the vegetation that actually

exists can be determined on a grid scale and entered into the

indexing system Ideally, a GIS system permits data on a

par-ticular feature to be stored for all the geographic units included

in the indexing system With modern GIS systems, it should

be possible to develop much more comprehensive databases

than previously available for researchers and conservationists

The word “census” is defined as a count, which usually includes

details as to sex and age A true census is a count of all

indi-viduals present in a given area Because such counts of wild

ani-mals are rarely possible, estimates usually are made based on

some sampling procedure Sampling estimates are derived

from counts made on sample plots or a portion of a popula-tion These estimates have variability, but still permit inferences

about the population An index is a count of some object that

is related in some numerical way to the animal, such as tracks, feces, call counts, or nests For example, Richard and Karen Barnes developed the first standardized method for gauging elephant populations by counting dung piles along previously identified routes and inserting the results into a mathematical formula that considers rates of defecation and dung decay (Tangley, 1997) Similar methods have been developed for jackrabbit indexing (Blackburn, 1968)

For population estimates to be valid, all members of a population must have an equal probability of being counted,

or the relative probabilities of counting different categories

of individuals (e.g., sex and age classes) must be known Ani-mals must not group by sex or age; they must mix randomly; and they must not develop “trap-shyness” or “trap-happiness”

if grid live-trapping is being employed (see Chapter 11) In addition, during the period when data are collected, either mortality and recruitment must be negligible, or the esti-mates must be corrected for these effects

Data may be gathered by visual observation or by evi-dences of an animal’s presence (tracks, calls, etc.) For

instance, haypiles of pikas (Ochotona) may be found in late

summer and fall and can be used as an index The average distance between the haypiles of adjacent pikas is approxi-mately 30 m (Smith, 1982) Another method of gathering

data is by the use of a transect Transects are

predeter-mined routes that are covered in an effort to estimate a pop-ulation All animals that are sighted or heard are recorded Transect data from different seasons and years provide rel-ative estimates of population size

Many territorial species can be observed easily within their territories and counted for a specific area The result usually is expressed as animals per hectare However, nonterritorial indi-viduals in these species often are hard to count Animals that congregate in groups or flocks (e.g., coveys of quail, flocks of turkeys and other birds, herds of antelope and bison) are rel-atively easy to count either on the ground or by means of aer-ial photographs In those species of frogs and birds that call or sing, the vocal members of the population can be counted The National Audubon Society’s annual Christmas Bird Count provides an index of species’ abundance nationwide The North American Breeding Bird Survey has provided valu-able data on the sizes of breeding bird populations since 1965, especially those of neotropical migrants Such databases are revealing steady population declines of breeding birds for many species in North America (see Chapters 15 and 16) Statistical estimates of population size based on sample plots, indices, rates of capture, changes in sex or age ratios, recaptures, or home range data can be calculated by many dif-ferent methods (Mosby, 1963) The Lincoln Index (also known as the Petersen–Jackson Method because it was first used on wild populations of plaice by Petersen [1896]), for example, is based on the recapture of marked individuals

where the population (N) is related to the number marked

(b)

(c)

V P

V P

If caught in December

If caught in January

(Assumed)

1 2

1 2 3

First year Second year

FIGURE 14.11

and released (M) in the same way as the total caught at a

sub-sequent time (n) is related to the number of marked

indi-viduals captured (m).

Censusing methods, along with capture and marking

techniques, have been discussed for game birds and mammals

by Mosby (1963), for terrestrial vertebrates by Davis (1982),

for amphibians by Heyer et al (1994), and for mammals by

Wilson et al (1996)

Many fishes, amphibians, and reptiles grow throughout their

lives This indeterminate growth is most rapid in younger

individuals, and it may speed up when food and

environ-mental conditions are favorable and slow down when

condi-tions are more stressful, such as during periods of cold,

drought, and food shortage

Birds and mammals generally experience a steady

increase in size until they reach maturity, after which growth

slows and essentially ceases for the remainder of their lives

This is known as determinate growth.

Various methods of determining the age of vertebrates

have been developed Animals that are captured shortly after

hatching or birth and that are marked and recaptured at

peri-odic intervals provide the most accurate means of

determin-ing age under natural conditions In some cases, direct

observation of an animal’s life stage, physical features, and

size can give an approximation of its age Life cycles of most

amphibians, for example, involve two, and sometimes three,

distinct stages (larval or tadpole, and adult) Few long-term

age-determination studies have been reported In one

long-term reptilian study, three-toed box turtles (Terrapene carolina

triunguis) studied for 25 years had estimated ages ranging

from 27 to 59 years of age at the conclusion of the study

(Schwartz and Schwartz, 1991)

Most young birds have several distinct juvenile and

subadult plumages as they mature (natal down, juvenal

plumage, first winter plumage, nuptial plumage; see

Chap-ter 12 for detailed discussion of molts and plumages) Some

birds, such as bald eagles, may not attain their full adult

plumage until they are 3, 4, or even 5 years old The pelage

of many young mammals also differs from the adult pelage

and is known as the juvenal pelage When molting occurs,

this pelage usually is replaced by the postjuvenal pelage and

then by the adult pelage.

More precise age-determination techniques vary among

the vertebrates and involve features of the integumentary,

skeletal, and even the nervous system Some techniques are

useful in field investigations with live animals, whereas

oth-ers can only be used on dead specimens For example,

tem-perate zone fishes can be aged by examining the annuli on

scales (Fig 14.11a), bones, and ear-stones (otoliths) (Fig

14.11b), and in cross sections of fin rays, fin spines, and

ver-tebral centra Many fish deposit otolith growth increments

with a 24-hour periodicity (Pannella, 1971; Prince et al., 1991;

Kingsmill, 1993) In some species, such as Atlantic salmon

(Salmo salar), the scales may contain spawning marks

Exam-ination of such scales can provide information about when the fish first went to sea, its age when it first spawned, how many times it has spawned, and its age at capture Because growth accelerates in the sea, annuli are more widely spaced Annuli also are evident on the scutes of some turtles Most juvenile turtles add single growth rings each year, whereas rings are added less frequently as adults (Galbraith and Brooks, 1989) (Fig 14.11c) Moll and Legler (1971) reported that

(a) A typical ctenoid scale, showing groups of concentric rings that can

be classified into annuli and interpreted as seasonal growth marks.

Source: Calliet, Love, and Ebeling, Fishes: A Field and Lab Manual,

1986, Wadsworth Publishing (b) A fish otolith showing annuli A year

class and/or birth date can be assigned, using the time of year the fish

was collected (c) Growth lines (annuli) on the vertebral (V) and the pleural (P) shields of the terrapin (Malaclemmys) (left) and the box turtle (Terrapene) (right) In Malaclemys, embryonic shield areas are near the center of the shields; in Terrapene, they are eccentrically located, and

growth proceeds primarily anteriorly and laterally.

Source: (a) Calliet, Love, and Ebeling, Fishes: A Field and Lab Manual,

1986, Wadsworth Publishing (c) Zangerl, “The Turtle Shell” in C Gans, Biology of the Reptiles, 1969.

multiple growth lines were added each year in a population of

neotropical sliders (Pseudemys scripta) in Panama Annual bone

rings in the phalanges and femurs of lizards have been used to

age such species as tuataras (Sphenodon) (Castenet et al., 1988).

Klinger and Musick (1992) injected tetracycline into juvenile

loggerhead turtles (Caretta caretta) in the Chesapeake Bay area

and found annular deposition in bone layers

The condition of teeth is useful for establishing the age

of mammals Both the deciduous and permanent dentitions usually erupt in a definite sequence and at definite times in different species Patterns of wear, particularly of the per-manent dentition, provide a fairly accurate means of deter-mining age, particularly in large herbivores (Fig 14.12) In addition, roots of teeth in some mammals form annual

(e)

(g)

(i)

(f)

(h)

Progressive wear on the molars is used to determine the age of white-tailed deer (Odocoileus virginianus): (a) 1 year, 7 months; (b) 2.5 years; (c) 3.5 years; (d) 4.5 years; (e) 5.5 years; (f ) 6.5 years; (g) 7.5 years; (h) 8.5–9.5 years; (i) 10.5 or older.

Sources: Halls (ed.) in White-tailed Deer Ecology and Management, 1984, Stackpole Books, and Cockrum, Mammalogy, 1962, Ronald Press.

FIGURE 14.12