ILAR Journal Online, Volume 31(2) 1989: Perspectives on Animal Use

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ILAR Journal V31(2) 1989
Perspectives on Animal Use

Why Field Biologists Mark Free-ranging Vertebrates for Scientific Study
Thomas A. Gavin and Carola A. Haas

Dr. Gavin is associate professor of wildlife management and Ms. Haas is a doctoral student in the Department of Natural Resources, Cornell University, Ithaca.

Introduction

Field biologists are scientists who study plants and animals under natural conditions. Their primary interest in a particular organism may be behavioral, ecological, physiological, genetic, or evolutionary. In other words, field biology is an approach for studying organisms by observing them in the environment where they live; field biologists probably represent most of the subdisciplines in biology that deal with live organisms at the level of the individual or above.

The kind of organism studied will influence the logistical problems biologists encounter in the field. Biologists who study sessile animals or plants simply return to their study plot, locate the individuals they have been observing through time by referring to a field map made during an earlier visit, and resume their collection of data. Of course, even barnacles and oak trees die someday, but this process is slow enough that the investigator can monitor these changes with relatively frequent visits to the study area (e.g., Connell, 1961).

Biologists who study wild, free-ranging vertebrates have two separate, but related, problems in this regard. First, those who study motile animals have the problem of relocating any individuals of the study species each time they go into the field. Natural food supplies, weather, predators, or other factors may have changed since the last encounter with the study species, so that no individuals may be present in the area where they were last studied. Second, if investigators need to monitor the same individuals through time, they must be sure they are observing the same individual from one time to the next. Even if an investigator finds an individual of the same size, color, and sex in exactly the same place where there was a similar animal the week or day before, a strong "gut" feeling that this is, in fact, the same individual will not be sufficient to pass the peer-review muster if such data are submitted for publication.

The only solution to this problem is to capture and mark animals so the investigator can recognize individuals in the field. That is, our ability to link past and future observations of the same individual to create a temporally continuous data set can only occur through techniques that make each individual readily identifiable.

To briefly review this large topic, we will list common techniques for marking animals and concentrate on how marking animals can provide information that would be difficult or impossible to obtain otherwise. Methods for capturing vertebrates, usually a necessary antecedent for marking, are described in detail elsewhere (e.g., Day et al., 1980). We will limit our review to terrestrial vertebrates (i.e., birds, mammals, reptiles, and amphibians), although the reader should be aware that fish, invertebrates, and plants also are marked routinely for scientific studies. Our treatment of this subject is undoubtedly biased in favor of birds and mammals, because our own research has focused on these groups.

Types of Marks and Marking Procedures

Studies are conducted in the field to document phenomena under natural conditions. A marking technique that has an adverse effect on the organism studied will yield results that are difficult to interpret or simply invalid. Therefore, it is important--for scientific as well as ethical reasons--to predict and avoid any adverse effects of marks on the health and activity of animals. An acceptable mark should meet the following criteria: it should affect neither survival nor behavior, minimize pain or stress, avoid misidentification due to loss or damage to the mark, and be easily applied and read (summarized in Ferner, 1979; Honegger, 1979). Marking techniques vary depending on the organism studied, the phenomenon studied, and to a certain extent the preference of the investigator. Several reviews of marking techniques exist and should be referred to for extensive lists and descriptions of techniques (Ferner, 1979; Honegger, 1979; Kenward, 1987; Stonehouse, 1978; and a series of symposium papers in Ecology, vol. 37, 1956).

Types of Marks

Temporary marks are used when the study is of short duration relative to the organism's life span, when permanent marks are likely to have an adverse effect on the organism, or when no suitable technique is available to mark the organism permanently. Small mammals and birds have been marked temporarily with low-activity radioisotopes that can be detected with scintillometers. Radiotelemetry, a technique whereby an animal can be located by the radio signal emitted from a transmitter it carries, has been used to identify and relocate individual birds (Figure 1), mammals, reptiles, and amphibians. Paint or dye is often applied to the skin, feathers, or fur of animals as a temporary marking technique (Figure 2), and colored elastic waistbands can be attached to frogs. Toe clipping, a permanent marking technique for mammals, may be temporary in those amphibians that tend to regenerate toes. A temporary mark may be applied in such a way that it will fall off at the end of the study (e.g. Clark and Gillingham, 1984; references in Karl and Clout, 1987), or it may have to be removed by the investigator.

Permanent marks are necessary for studies that span all or most of an organism's life. They are, therefore, almost always used to mark relatively short-lived animals, but are used commonly for long-lived animals as well. Leg bands, neck collars (Figure 1), or wing tags for birds; ear tags for mammals; toe clipping for lizards; and shell notching for turtles are common examples. Natural marks are permanently distinctive characters that an organism has naturally and are used to recognize animals when other techniques are impractical or unnecessary. For example, gorillas (Gorilla gorilla) (Schaller, 1963) and Bewick's swans (Cygnus bewickii) (Scott, 1978) were studied by recognizing distinctive facial features, and red-spotted newts (Notophthalmus viridescens) (Gill, 1978) were identified by each individual's unique pattern of spots on the dorsal surface. Usually, only small populations with minimal immigration can be studied using natural marks (but see Shine et al., 1988).

Potential Problems

Despite the best intentions, some adverse effects of marking procedures are likely. Capture and handling alone may involve substantial risks and stresses to wild animals. Gray wolves (Canis Iupus) sustained injuries to legs, feet, and teeth from four types of steel traps, although frequency of injuries varied with the type of trap (Kuehn et al., 1986). Trapping and handling of four species of small rodents resulted in weight loss that persisted for more than 24 hours after release; subsequent trapping resulted in continued weight loss (Korn, 1987). Meadow voles (Microtus pennsylvanicus) significantly reduced their activity for two days after being anesthetized and weighed (Hamley and Falls, 1975).

After an animal has been tagged and released, the mark itself may interfere with normal behavior. By attending to or attempting to remove the mark, an animal may reduce the amount of time it normally spends in other activities. Rough-legged hawks (Buteo lagopus) fitted with radio packages and vinyl wing-markers were observed to preen excessively for one to two days after release (Watson, 1985). Captive red grouse (Lagopus lagopus scoticus) carrying radio packages showed lower activity levels than unmarked birds, and marked females ate significantly less than did unmarked females (Boag, 1972). Toe clipping of large mammals (Henshaw, 1981) or affixing heavy radio packages to small mammals or birds (Hamley and Falls, 1975) may impair locomotion of marked individuals.

Especially when a mark affects the particular behavior to be studied, a more appropriate technique should be identified. Radiotransmitters, for example, are often used to determine levels and patterns of activity in the field. One study of meadow voles, however, showed reduced activity of voles that were carrying transmitters (Hamley and Falls, 1975). Clearly, it would be inappropriate to draw conclusions about activity levels of voles using only radiotelemetric data. Patagial-tagged mallards (Anas platyrhynchos) moved into more densely vegetated habitat than did unmarked birds (Szymczack and Ringelman, 1986), a response that would present difficulties if habitat selection were a focus of the study.

Some marks may cause injury or mortality at a time long after marking. Leg-banded vultures developed inflamed and irritated feet after excrement accumulated on the bands (Sweeney et al., 1985). Nasal saddles applied to ducks and geese are subject to icing during periods of extreme cold and high winds. Light icing seemed to have no effect on the behavior of mallards, but heavy icing resulted in mortality (Byers, 1987). Toe clipping significantly reduced the frequency of recapture of Fowler's toads (Bufo woodhouseifowleri), presumably because of increased mortality (Clarke, 1972). Discs attached by pins through turtles' shells had no adverse impact until the discs began to loosen after a year, allowing the turtles to become snagged (Graham, 1986). Red-headed woodpeckers (Picoides borealis) that were banded as nestlings with red leg bands were less likely to be sighted as fledglings than those banded with other colors, which suggests differential mortality (Hagan and Reed, 1988).

Observations of marked and unmarked individuals interacting in the wild have occasionally demonstrated impaired social behavior. Sandhill cranes (Grus canadensis) avoided conspecifics that were marked with vinyl flagging (summarized in Hoffman,1985). Female mule deer (Odocoileus hemionus) initially ran from young that were marked with radio collars, but accepted them later (Goldberg and Haas, 1978); similar observations have been made of white-tailed deer (O. virginianus) wearing white plastic collars (T. A. Gavin, unpublished observations, 1975). Birds for which body color is an important component of mate choice or dominance interactions may be influenced by the application of colored marks. Zebra finches (Poephila guttata) in an aviary were more likely to associate with conspecifics wearing red leg bands than green bands (Burley et al., 1982). Male red-cockaded woodpeckers (Dendrocopus borealis) wearing white bands were more likely to be mated than males without white bands (Hagan and Reed, 1988). These particular effects on the phenomenon of interest may be difficult to predict and must be addressed at some point during the course of any study.

Biological Studies That Use Marked Animals

Studies of Population Ecology

A reasonable question to ask is the following: If we could obtain any information we wanted on a population to understand its dynamics, of what would those data consist? The ideal data set would include the date when each animal was born, how many offspring each individual produced each year of its life, and when each individual died. With such complete demographic information, we would be able to calculate age-specific fecundity and age-specific mortality in an unbiased way. Unfortunately, we rarely have complete data for even one individual in the population, so we resort to relatively crude estimates of these parameters.

Typically, population ecologists investigate reproduction in mammals by examining reproductive tracts from a sample of females; this, in fact, may be the only feasible method to obtain these data for small, secretive mammals. Of course, collecting a large number of animals from a population obviates the study of natural mortality patterns (an area of population ecology to which we hoped to make a contribution with a study of Columbian white-tailed deer described below). Avian biologists can count the number of eggs in a female bird's nest or the number of young that fledge from the nest. However, both approaches provide only an instantaneous view of that particular female's potential reproductive history. Reproductive rates are calculated for the sample and then extrapolated to the population.

Data on reproduction are much more valuable if each female can be aged accurately, but even the most widely used aging techniques are prone to error that may be significant (Caughley, 1967). If aging is accurate, then age-specific fecundity can be estimated, as well as the proportion of the population found in each age class (i.e., age structure). If it can be assumed that the population from which the sample came had a stable age distribution, then the data on age-specific fecundity and population age structure can be used to estimate that population's rate of increase or decrease; obviously, this elusive parameter can be exceedingly valuable to any agency managing an economically important species or an endangered species.

Use of marked individuals benefits population studies of large or observable species or both in at least three ways. First, if individuals are marked when young, they can be aged accurately, and the value of these data increases as the animal gets older.

Second, the investigator can have a dynamic as opposed to only an instantaneous view of a phenomenon. For example, an adult female can be observed beginning near the time she gives birth, through the period of rearing and weaning her young, until her offspring either die or attain age of independence. This latter point is closer to what really counts to the biologist studying population dynamics, because the number of embryos carried by a mammalian female--or the number of eggs in a bird's nest--and the number of young surviving to adulthood are often quite different.

Third, the ability to quantify a female's reproductive output during every breeding season of her life not only reduces the error relative to other methods of estimating age-specific reproduction, but also reveals the pattern of annual successes and failures in reproduction, first as a female matures physically and socially, and then as she reaches senescence. By summing the number of offspring produced each breeding season, one can determine what evolutionary biologists call lifetime reproductive success. Lifetime reproductive success is of theoretical interest because differences among females' total lifetime reproductive success prompt a major question: Why are some females much more successful than others'? Although lifetime reproductive success is extremely difficult to obtain even with marked individuals (Howard, 1979), it is a worthy goal for any study that extends long enough to follow several year-classes from birth to death. The studies of red deer (Cervus elaphus) (Clutton-Brock et al., 1982), using collars and natural marks, and Florida scrub jays (Aphelocoma coerulescens) (Woolfenden and Fitzpatrick, 1984), using colored leg bands, are exemplary for the rare insights they have provided of lifetime reproductive success for two vertebrates in very different social and ecological contexts.
A Population Ecology Study of White-tailed Deer

From 1974-1979, T.A.G. studied an isolated, unhunted population of deer on the Columbian White-tailed Deer National Wildlife Refuge in southwestern Washington (Gavin et al., 1984). The refuge was established to protect the largest remaining population of Columbian whitetails, an endangered subspecies (0. v. leucurus). (There are 38 subspecies of white-tailed deer; only two are endangered). Little was known about the population ecology of this group, so we began a study of reproduction, natural mortality, movements, and social organization. Refuge personnel also wanted to know the size of the population and how best to manage the habitat for the deer. Although refuge personnel and the federal agency (U.S. Fish and Wildlife Service) responsible for managing the deer needed certain practical information, we were also interested in contributing to knowledge of how populations of large mammals function in the wild.

To obtain information on the topics listed above, we needed individuals to be identifiable. Although these deer were relatively easy to observe because of their habituation to humans and the open, flat terrain, they bore no natural marks for reliable identification. We chose a white plastic collar bearing a large black number as a suitable mark for older animals: these numbers could be read up to 300 meters away with a spotting scope. Fawns were captured when a few days old, and each one was marked with a numbered ear tag to which a small piece of colored flagging was attached. Using a variety of capture techniques over a 2-year period, we marked 100 fawns, yearlings, and adults of both sexes (Figure 3).

Each time we observed a marked deer, we plotted the time, date, and animal's location on a map of the refuge, as well as the sex and age of other deer accompanying the marked animal. Over time, maps of each individual's home range were generated. Knowledge of the social group to which each marked animal belonged soon became apparent, as these were quite stable throughout most of the year. After fawns were born in June, the number of fawns associated with a marked female was used as a measure of that female's reproductive success that year. Because fawns generally associate with their dam for about one year, regular observations of a marked female without a fawn were an indication that she had not bred, or that her fawn(s) had died since we last observed them together.

We searched daily for any marked or unmarked deer that had died to quantify temporal and spatial patterns of natural mortality by sex and age and to determine causes of death in the population. Obviously, cause of death was easier to determine if we found the carcass quickly. Marked deer were particularly valuable in this effort. If we did not observe number 17 for several days, for example, we searched her known home range intensively for the carcass or a broken collar. The apparent physical condition of a marked deer when last seen alive could sometimes be used to supplement posthumous conjectures of the circumstances leading to its death. Our knowledge of fawn mortality was enhanced because we could focus our search for these relatively small carcasses within the dam's home range when a marked female was no longer observed with one of her fawns. As the study progressed and deer that had been marked as fawns or yearlings died, we were able to verify our aging technique (i.e., sectioning of teeth to count cementum annuli) by examining the deposition pattern of annuli of known-aged individuals.

A common method of estimating the size of any wild population is to capture, mark, and release a sample of individuals at time, t₁. At a later time (t₂), the investigator recaptures a random sample of individuals from the same population, and tallies the number recaptured that were marked at t₁. Although there are a large number of procedural and statistical modifications of this basic technique and several important assumptions (Seber, 1973), the fundamental relationship is that the ratio of the number of individuals captured and marked to the total population size (N) at t₁is equal to the ratio of marked individuals recaptured to the total number of individuals (marked and unmarked) caught at t₂. This simple equation is then solved for N to obtain an estimate of population size.

In this study--unlike those with small mammals--the deer did not actually have to be recaptured at t2; we only needed to conduct transect counts and record the number of marked and unmarked deer observed during a count to generate an estimate of N. Two troublesome assumptions of this method are that (1) during the experiment there is no loss of marks used to identify the marked segment of the population and (2) marked and unmarked individuals leave the population through death or emigration at the same rate. However, because searches were intensive in this study, we knew with virtual certainty whether a marked deer had died or lost its collar, and our observations of marked deer led to the conclusion that these deer never left the "ecological island" encompassed by the refuge. This knowledge was used to modify the analysis of the mark-release-recapture data accordingly to provide the most accurate estimate possible.

And finally, refuge personnel needed to know which method of keeping vegetation short and actively growing provided high quality grazing areas for these deer. By observing deer while they were feeding, we concluded that deer preferred fields that had been grazed by cattle rather than fields that had been cut for hay. This answer did not require the use of marked animals, but our observations of marked deer indicated that only deer with home ranges adjacent to or including these fields used them for feeding. This realization led to the decision to have numerous small feeding areas throughout the refuge rather than a few large feeding areas centrally located.

The refuge population of Columbian white-tailed deer has continued to grow since 1979. We would like to believe this is due, at least in part, to management recommendations resulting from this study of marked individuals. Certainly, the habitat management scheme described above has been of tangible benefit. The patterns of high male mortality during winter and generally low fawn production that were revealed by studying marked animals allowed us to establish what is "normal" in this population. Refuge personnel are aware of these background patterns, and they are, therefore, less likely to initiate an unnecessary or harmful management practice that might perturb the steady-state balance in this unhunted population.

Studies of Behavior

Reproductive success of males as well as females (already discussed) is extremely relevant to sociobiologists and evolutionary biologists. Whether adults are strictly monogamous or highly polygamous, maintain short- or long-term pair bonds if any at all, prefer or avoid mating with close relatives, and use particular behavioral mechanisms to effect these outcomes also are subjects of research. Data on these topics always become more valuable if the same individuals can be monitored over a greater number of breeding seasons. Again, the use of reliable artificial or natural marks is paramount.

Although observations of the behavior between marked males and females are suggestive of each male's reproductive success, there are serious difficulties in correctly assigning paternity to a particular male.

Copulations between males and females are difficult to observe under most field conditions, and one can never be certain that an observed mating resulted in the siring of young by that male. Of much recent interest is the determination of paternity, which does not always agree with what is expected based on pair-bonding behavior between a male and a female (Westneat 1987a,b). In the phenomenon called multiple paternity, which has been documented in each of the vertebrate groups, more than one male successfully sires young born in the same clutch or litter (Gavin and Bollinger, 1985; Gibson and Falls, 1975; Hanken and Sherman, 1981; Tilley and Hausman, 1976). Genetic techniques, such as gel electrophoresis or DNA fingerprinting, can be used to assign paternity in these studies. We believe it is the incongruity between the apparent mating system, which is revealed by observations, and the effective mating system, which is revealed by genetic analyses, that is most interesting. Observations of marked individuals are being enhanced rather than replaced by genetic analyses of tissue samples.

Many other aspects of behavior are revealed best by observing marked individuals, especially when knowledge of the variation among individuals is important. It is this variation among individuals that provides the raw material for evolution through natural selection. The ontogeny of song development in male birds is an active area of research. Tracing the development and change of song dialects in particular males within and among years should be a necessary part of this research program (e.g., Payne et al., 1988), especially given the probable importance of communication in maintaining territories and attracting mates. Consistent individual-specific differences among animals in capturing prey, escaping from predators, and interacting with dominant or subordinate members of their social group would not be apparent without a means of identifying individuals.

Much can be learned through study of unmarked animals, but the range of questions that can be addressed is limited. There is no need to mark individuals, for example, to observe animals marking with scent, singing, or engaging in aggressive encounters. However, to determine if a behavior is concentrated at territorial boundaries or directed at members of the same sex or age, members of the population must be marked. Territorial boundaries can then be delimited and patterns of behavior defined.

In summary, study of the social behavior of any animal is synonymous with intensive observation. Wilson (1975) concluded that for studies of primates, a minimum of 1,000 hours of observation were needed to develop a "sound idea of the nature of individual relationships." This assumes that individuals are recognizable, without which no amount of time would suffice to understand how, when, and why individuals behave the way they do toward one another.

Survey of Recent Literature

A survey of recent studies of free-ranging vertebrates allowed us to examine how often marked animals are used by field biologists. We reviewed papers published in 1987 and 1988 in four journals: Auk (a journal of ornithology), Journal of Mammalogy, Journal of Herpetology, and Herpetologica. Each of these journals addresses a variety of questions and techniques involved in the study of a particular vertebrate group. (Reptiles and amphibians typically are grouped in the category "herptiles," and we continue that treatment here.) Including only those articles and brief notes that reported research on wild, free-ranging populations, we recorded whether each study used marked or unmarked individuals. Because a high proportion of research on herptiles is conducted in the laboratory, we reviewed two herpetological journals to obtain-a larger sample of papers on free-ranging herptiles. Of the 59 studies of free-ranging herptiles, 33 (56 percent) used marked animals. The 110 studies of birds included 56 (51 percent) with marked individuals. Research on mammals used marked animals in 70 out of 95 studies (74 percent).

The 264 studies were grouped in 10 categories (Table 1). Three of these categories--population dynamics, movements, and reproductive behavior--included predominantly studies that used marked animals. As discussed in the previous section, these types of studies, which rely on an ability to recognize individuals at two or more points in time, are often impossible to conduct on unmarked populations.

Most of the seven remaining categories contained approximately equal numbers of studies using marked and unmarked animals. Studies for which data can be collected from each organism at a single point in time, such as some of the studies of energetics and physiology, are less likely to use marked animals.

Although the numbers of studies in these categories are small, it is interesting to note those instances in which marked animals are used more often in one vertebrate group than in others. Estimates of mammal and herptile population sizes are often obtained using a mark-recapture technique. Bird populations, however, are most commonly enumerated by counts of singing males or of flocks and roosting aggregations. Birds, therefore, are less commonly marked to obtain population estimates. Because birds are usually more conspicuous to human observers than are mammals, information on their distribution and spacing can also be collected by direct observation rather than retrapping of marked individuals.

Conclusions

We are convinced that the quality of field studies of free-ranging vertebrates may be enhanced by using marked animals. Investigators studying a wide range of ecological and behavioral phenomena routinely mark the organisms they study. We have highlighted current biological questions most likely to benefit from this approach rather than debate the relative value of studies that do not require the use of marked animals versus those that do. And we have been somewhat selective in choosing the biological questions to address. For example, we have not discussed the importance of marked animals in understanding the movements of migratory species (e.g., ducks and geese), which may cross state or national borders.

Field biologists who have marked animals know that this activity requires a significant amount of labor, time, and money and that they risk perturbing the system or phenomenon under study. Therefore, common sense dictates that the potential return should exceed the probable cost of this risk before a marking program is initiated. Furthermore, guidelines published for each vertebrate group by the respective professional societies are now available and should be consulted before marking begins in order to learn the proper methods of capturing, handling, marking, sampling blood and tissue, and performing euthanasia.

Finally, the perfect mark does not exist. When we can remotely apply unique, readable marks to animals without capture and without affecting their behavior or survival, field biology will benefit greatly. Although the technology for field marking has advanced considerably in just a few decades, the search for safe, reliable marks that can be applied easily is worthy of further investigation.

Acknowledgments

We wish to thank T. Peare for reviewing recent literature on this topic and J. P. Hayes for suggesting additional references. M. E. Richmond provided helpful comments, and L. Oltz typed portions of the manuscript.

References

Boag, D. A. 1972. Effect of radio packages on behavior of captive red grouse. J. Wildl. Manage. 36:511-518.

Burley, N., G. Krantzberg, and P. Radman. 1982. Influence of colour-banding on the conspecific preferences of zebra finches. Anim. Behav. 30:444-445.

Byers, S. M. 1987. Extent and severity of nasal saddle icing on mallards. J. Field Ornithol. 58:499-504.

Caughley, G. 1967. Parameters for seasonally breeding populations. Ecology 48:834-839.

Clark, D. L., and J. C. Gillingham. 1984. A method for nocturnally locating lizards. Herpetol. Rev. 15:23-25.

Clarke, R. D. 1972. The effect of toe clipping on survival in Fowler's toad (Bufo woodhouseifowleri). Copeia 1972:182-185.

Clutton-Brock, T. H., F. E. Guinness, and S. D. AIbon. 1982. Red Deer: Behavior and Ecology of Two Sexes. Chicago: University of Chicago Press.

Connell, J. H. 1961. The influence of interspecific competition and other factors on the distribution of the barnacle Chthamalus stellatus. Ecology 42:710-723.

Day, G. I., S. D. Schemnitz, and R. D. Taber. 1980. Capturing and marking wild animals. Pp. 61-88 in Wildlife Management Techniques Manual, S. D. Schemnitz, ed. Washington, D.C.: Wildlife Society.

Ferner, J. W. 1979. A review of marking techniques for amphibians and reptiles. Herpetological Circulars No. 9. Oxford: Society for the Study of Amphibians and Reptiles.

Gavin, T. A., and E. K. Bollinger. 1985. Multiple paternity in a territorial passerine: The bobolink. Auk 102:550-555.

Gavin, T. A., L. H. Suring, P. A. Vohs, Jr., and E. C. Meslow. 1984. Population characteristics, spatial organization, and natural mortality in the Columbian white-tailed deer. Wildl. Monogr. 91.

Gibson, A. R., and J. B. Falls. 1975. Evidence for multiple insemination in the common garter snake, Thamnophis sirtalis. Can. J. Zool. 53:1362-1368.

Gill, D. E. 1978. The metapopulation dynamics of the red-spotted newt, Notophthalmus viridescens (Rafinesque). Ecol. Monogr. 48:145-166.

Goldberg, J. S., and Z. W. Haas. 1978. Interactions between mule deer dams and their radio-collared and unmarked fawns. J. Wildl. Manage. 42:422-425.

Graham, T. E. 1986. A warning against the use of Petersen disc tags in turtle studies. Herpetol. Rev. 17:42-43.

Hagan, J. M., and J. M. Reed. 1988. Red color bands reduce fledging success in red-cockaded woodpeckers. Auk 105:498-503.

Hamley, J. M., and J. B. Falls. 1975. Reduced activity in transmitter-carrying voles. Can. J. Zool. 53:1476.

Hanken, J., and P. W. Sherman. 1981. Multiple paternity in Belding's ground squirrel litters. Science 212:351-353.

Henshaw, R. E. 1981. Toe-clipping coyotes for individual identification: A critique. J. Wildl. Manage. 45:1005-1007.

Hoffman, R. H. 1985. An evaluation of banding sandhill cranes with colored leg bands. North Am. Bird Bander 10:46-49.

Honegger, R. E. 1979. Marking amphibians and reptiles for future identification. Int. Zoo Yearb. 19:14-22.

Howard, R. D. 1979. Estimating reproductive success in natural populations. Am. Nat. 114:221-231.

Karl, B. J., and M. N. Clout. 1987. An improved radio transmitter harness with a weak link to prevent snagging. J. Field Ornithol. 58:73-77.

Kenward, R. 1987. Wildlife Radio Tagging: Equipment, Field Techniques, and Data Analysis. New York: Academic Press.

Korn, H. 1987. Effects of live-trapping and toe-clipping on body weight of European and African rodent species. Oecologia 75:597-600.

Kuehn, D. W., T. K. Fuller, L. D. Mech, W. J. Paul, S. H. Fritts, and W. E. Berg. 1986. Trap-related injuries to gray wolves in Minnesota. J. Wildl. Manage. 50:90-91.

Payne, R. B., L. L. Payne, and S. M. Doehlert. 1988. Biological and cultural success of song memes in indigo buntings. Ecology 69:104-117.

Schaller, G. B. 1963. The Mountain Gorilla. Chicago: University of Chicago Press.

Scott. O. K. 1978. Identification of individual Bewick's swans by bill patterns. Pp. 160-168 in Animal Marking: Recognition of Animals in Research, B. Stonehouse, ed. Baltimore: University Park Press.

Seber, G. A. F. 1973. The Estimation of Animal Abundance and Related Parameters. London: Charles Griffen.

Shine, C., N. Shine, R. Shine, and D. Slip. 1988. Use of subcaudal scale anomalies as an aid in recognizing individual snakes. Herpetol. Rev. 19:79-80.

Stonehouse, B., ed. 1978. Animal Marking: Recognition of Animals in Research. Baltimore: University Park Press.

Sweeney, T. M., J. D. Fraser, and J. S. Coleman. 1985. Further evaluation of marking techniques for black and turkey vultures. J. Field Ornithol. 56:251.

Szymczack, M. R., and J. R. Ringelman. 1986. Differential habitat use of patagial-tagged female mallards. J. Field Ornithol. 57:230-232.

Tilley, S. G., and J. S. Hausman. 1976. Allozymic variation and occurrence of multiple inseminations in populations of the salamander Demognathus ochrophaeus. Copeia 1976:734-741.

Watson, J. W. 1985. Trapping, marking and radio-monitoring rough-legged hawks. North Am. Bird Bander 10:9-10.

Westneat, D. F. 1987a. Extra-pair copulations in a predominantly monogamous bird: Observations of behaviour. Anim. Behav. 35:865-876.

Westneat, D. F. 1987b. Extra-pair fertilizations in a predominantly monogamous bird: Genetic evidence. Anim. Behav. 35:877-886.

Wilson, E. O. 1975. Sociobiology: The New Synthesis. Cambridge: Belknap Press.

Woolfenden, G. E., and J. W. Fitzpatrick. 1984. The Florida Scrub Jay: Demography of a Cooperative-Breeding Bird. Princeton: Princeton University Press.

TABLE 1 Summary of Recently Published Field Studies of Vertebrates^awith Respect to Whether Animals were Marked (M) or Unmarked (U)

	Herps		Birds		Mammals		Total
Type of study	M	U	M	U	M	U	M	U
Social behavior	2	3	7	9	4	1	13	13
Population dynamics	8	0	3	1	5	0	16	1
Population estimates	2	0	0	3	4	2	6	5
Movements	7	0	5	1	9	0	21	1
Natural history	8	9	16	21	17	13	41	43
Reproductive behavior	2	1	15	4	7	2	24	7
Distribution/spacing	0	2	2	3	6	1	8	6
Energetics/physiology	1	5	2	4	4	0	7	9
Other behavioral studies	1	1	2	1	3	4	6	6
Other ecological studies	2	5	4	7	11	2	17	14
Total	33	26	56	54	70	25	159	105

^aAll papers in the following journals were summarized for 1987 and 1988: Journal of Mammalogy, Auk, Journal of Herpetology, and Herpetologica.

Figure 1 Canada goose (Branta canadensis) fitted with neck collar for visual identificatin and with backpack transmitter for location by radio telemetry. Photo courtesy Mark Lindberg.

Figure 2 Common tern (Sterna hirundo hirundo) with color-marked breast. Photo courtesy Kim Claypoole.

Figure 3 Adult female Columbian white-tailed deer (O.v. leucurus) wearing a plastic collar and ear tag. The collar number (17) is faded because the doe had worn the collar for about seven years. Ear tags were of particular value in this study for identifying deer found dead who had lost their collars. Photo by Thomas A. Gavin.