A. Overview

All laboratory and much field research involving wild birds requires that individuals be marked in some way for future identification. It is essential not only to the welfare of the birds but also to the integrity of the research results that the marking procedure not adversely affect the behavior, physiology, or survival of individuals. Because of the difficulty in providing appropriate controls for the marking method, systematic studies of possible

adverse effects of marking procedures are still few, and many of the cautions mentioned here are based on anecdotal observations. In general, investigators should not assume that marking procedures will have no adverse effects on their subjects and should make efforts to evaluate any such influences. Rather, it should be assumed that, if banding is done carefully with appropriately sized bands, harm to target birds will be minimized. Investigators should not allow unsupervised, inexperienced persons to handle birds until the persons have been properly trained to retrieve birds from nets or traps and to hold, handle, and release birds properly. Ultimately, this approach will yield benefits not only to the animal subjects but also to research quality. General references include (Marion and Shamis 1977; Stonehouse 1978; Schemnitz 1980, which includes a useful bibliography of bird-marking techniques; Calvo and Furness 1992). Techniques commonly used for raptors, but also useful for other species, are reviewed by Young and Kochert (1987).

For a marking procedure to be effective, it should meet as many of the following criteria as possible (Marion and Shamis 1977).

a. The bird should experience no immediate or long-term hindrance or irritation.

b. The marking should be quick and easy to apply.

c. The marking code (digits or colors) should be readily visible and distinguishable.

d. The markings should persist on the bird until research objectives have been fulfilled.

e. The bird should suffer no adverse effects on its behavior, longevity, or social life.

f. Careful records should be made of all aspects of the marking procedure. These should be maintained in an accessible and safe place.

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B. Metal Bands

Banding has been called the greatest advance in the study of birds in this century (Coulson 1993). Numbered metal (usually aluminum, but various alloys for special purposes) bands issued by the Bird Banding Laboratory (BBL) of the USGS or by CWS provide the most widely used method of individually marking birds. Animals must usually be recaptured in order for the band numbers to be read. It is imperative that bands of the correct size be used; bands too small for the species in question may cause serious injury to or even loss of the banded leg. Recommended band sizes for all species of North American birds can be found in the Bird Banding Manual (USFWS 1991) and in periodic memoranda to banders (MTAB) issued by BBL. Where appropriate band sizes are used, there are few indications that the application of metal bands produces adverse effects on the subjects (references cited in Marion and Shamis 1977). Species-specific problems are discussed in Marion and Shamis (1977), Henckel (1976), Salzert and Schelshorn (1979), Reed and Oring (1993), Gratto-Trevor (1994), and MTAB from BBL. Banders must know their subject well in order to minimize the likelihood of injury. Injuries may result from a bander's failure to anticipate future growth of young birds, to adequately consider size dimorphism when choosing band size or the risk of a large band slipping over the foot, or to recognize that determination of how many bands can be safely fitted on one leg is a species-specific issue. Two or more aluminum bands should not be applied to the same leg, as they may flange over and injure the leg.

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C. Colored Plastic and Celluloid Leg Bands

One or more colored leg bands are often applied to one or both legs of a bird. They provide a means of individually recognizing birds in the field without recapturing them. They are being used increasingly in studies of behavior and ecology, often involving large numbers of individuals. The use of color bands requires special permission from BBL. When used in combination with aluminum bands, plastic bands must be of the same size. When bands of the proper size are used, few adverse effects of color bands have been reported (cf. Nisbet 1991). However, some studies have shown that certain band colors, especially those that are similar to plumage or soft part colors involved in social signals, may affect mating attractiveness, dominance status, or aggression (e.g., Burley 1981, 1985, 1986a,b; Burley, et al. 1982; Johnson et al. 1993; Holder and Montgomerie 1993) in some species.

Depending upon the duration of the study, it may be important to consider that some colors of commercially available celluloid bands fade. After two years or so they may be unrecognizable (Anderson 1980; Hill 1992; Lindsey et al. 1995). UV-stable bands are available from several suppliers. Most colors of UV-stable plastic remain bright for several years unless covered with an obscuring substance such as dirt or algae. Blue bands fade relatively quickly. In recent years, students of long distance migrants, especially shorebirds, have employed plastic flags with unique colors representing different countries, e.g., green for U.S.A., and different positions being used to represent points of origin. The flags are larger and more conspicuous than bands, thus allowing sightings over longer distances. Given a philosophy that the manipulation of wild animals should be the minimum necessary for the study, flags should be used only when they provide a substantial advantage over normal color bands. The use of flags on newly hatched chicks is discouraged.

An inexpensive alternative to commercial color bands is described by Hill (1992). A technique for color banding nestling passerines is given by Harper and Neill (1990).

The use of constant numbers and relative positions of bands can help verify the correctness of reports of marked birds.

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D. Dyes and Ultraviolet Markers

Dyes applied to the plumage are used extensively on birds, especially colonial water-birds and waders. Water-proof, felt-tip markers are useful for short-term markers, as are tattoo inks, wax cattle-marking sticks, and non-lead paint. Picric Acid, Rhodamine B and Malachite Green are among many frequently used dyes. Picric acid (picronitric acid; trinitrophenol; nitroxanthic acid: carbazotic acid; phenoltrinitrate) can be a significant explosion hazard. During extended storage, it may lose water and become unstable. Never open nor touch a bottle of dry or contaminated picric acid; an explosion could result from the friction produced. Crystallized picric acid is a severe explosion risk, is especially reactive with metals or metallic salts, and is also toxic by skin absorption and inhalation. For all these reasons, the use of picric acid is strongly discouraged. Methods of dye use are discussed in Kennard (1961), Taber and Cowan (1969) and Day et al. (1980). Recommendations for fixatives to improve retention of the dyes on feathers can be found in Belant and Seamans (1993). Caution must be exercised in applying the dye, especially when contour feathers are extensively colored. The alcohol or detergent base may remove oil from the bird's feathers, and wetting can lead to heat loss. Care should be taken to ensure that dyed birds are thoroughly dry prior to release. A method for color-marking incubating birds by applying dye to their eggs (Paton and Pank 1986; Cavanagh et al. 1992) can result in high rates of egg mortality and should be used only with appropriate cautions (Belant and Seamans 1993).Dyed birds are sometimes treated differently by conspecifics, and may be subject to greater risk from predators (Frankel and Baskett 1963). Investigators should make systematic attempts to evaluate such possible effects because they may influence not only the welfare of the subjects but the research results as well. Paint of any kind should be used only sparingly on feathers because of its impact on feather structure and function.

Aerial and ground spraying techniques, developed to mass-mark birds in roosting or nesting colonies, employ various colors of fluorescent particles (suspended in a liquid adhesive) that are sprayed from agricultural spray systems (Jaeger et al. 1986; Otis et al. 1986). The marker is visible under long-wave UV light when a bird is examined in hand and is retained for several months or until molt. No adverse effects have been noted, and behavioral changes are not likely because the marker is not visible in daylight. As with any spray application, the nature of the habitat and the composition of the spray formulation should be examined for potential environmental concerns. Fluorescent dyes are also useful for locating and tracking cryptically colored birds (Steketee and Robinson 1996). Applications of mass-marking agents should be coordinated with BBL.

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E. Neck Collars

Plastic neck bands or collars have been used extensively for marking waterfowl. Aldrich and Steenis (1955) concluded that properly applied neck bands are effective markers with few adverse effects on geese. In general, neck collars seem to be superior to nasal discs for tagging waterfowl (Sherwood 1966; Raveling 1976: but cf. Helm 1955; Lensink 1968; Ankney 1975; Hawkins and Simpson 1985; Abraham et al. 1983; Macinnes and Dunn 1988;

Ely 1990). As with all marking techniques, responses differ among species, and investigators should systematically evaluate any possible influences of the marker.

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F. Nasal Discs and Saddles

These are numbered and/or colored plastic discs or plates applied to each side of the bird's bill, fastened together through the nasal opening by various methods (Bartonek and Dane 1964; Sugden and Poston 1968; Doty and Greenwood 1974; Alison 1975). They have been applied primarily to waterfowl. Various undesirable results have been reported, including high rates of marker loss, often with injury to the nares (Sherwood 1966), higher mortality rates attributed to entanglement with submerged vegetation (Sugden and Poston 1968), mortality due to ice accumulation (Byers 1987), and reduced success in obtaining mates (Koob 1981). The data suggest that nasal discs are better suited for larger species of birds that do not dive. Caution is advised in their use, and where practical other marking methods should be substituted.

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G. Patagial (Wing) Markers and Leg Tags

Wing tags have been applied to many species of birds. The main advantages are that the tags are highly visible, may be coded for individual recognition, and are retained by birds for relatively long periods of time. They are often useful to the success of studies of social behavior, migration, and natal and winter site fidelity. Descriptions of tag types and evaluations of their effectiveness may be found in Hester (1963), Anderson (1968), Hewitt and Austin-Smith (1966), Southern (1971), Stiehl (1983), Curtis et al. (1983), Sweeney et al. (1985), and Cummings (1987). Some reports indicate that most birds accept patagial tags readily, and adverse effects seem to be minimal (e.g., Maddock and Geering 1994). On the other hand, Kinkel (1989) reported that the survivorship and reproductive behavior and abilities of ring-billed gulls were adversely affected for up to four years after tagging. The effects disappeared when the tags were replaced with colored bands. Tags sometimes result in some callousing of the wing, and feathers in the area of the tag may not be replaced at the time of molt. Investigators should be alert to the possibility of negative behavioral effects (H. Blokpoel, pers. comm., W.H. Drury, pers. comm.) and increased predation (D. Lank, pers. comm.).

A VelcroÆ leg tag developed for marking gull chicks (Wiltsteed and Fetterolf 1986) may not be suitable for all species because of differences in growth rates that require frequent adjustment of the tag (Cavanagh and Griffin 1993).

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H. Radio Transmitters

During the past three decades, the attachment of small radio transmitters to free-living birds has become a routine means of enabling investigators to monitor the location and movements of tagged individuals. Transmitters are applied most frequently to large (> 100 g) species, but the development of units weighing 2 g or less has made their application feasible even for small (< 50 g) birds. It is axiomatic that the application of an additional mass to a bird's body will have some effect on its energetics and aerodynamics. That effect presumably increases in proportion to the percent body mass of the transmitter and will be influenced by its placement on the bird's body. The effects are evident even in such medium-sized, strong flyers as homing pigeons (Gessaman and Nagy 1988). For large birds, for which transmitters often amount to less than 1% of body mass, these effects are negligible. With small birds, transmitters are often 5-10% of lean body mass. Transmitters weighing more than 10% of body mass should not be applied to birds released into the field, and where possible transmitters should not exceed 5% (Caccamise and Hedin 1985). As many birds, including some small passerines, accumulate migratory fat deposits that may equal up to 50% of body mass, for specific, short-term (i.e., the bird will be recovered within a short time and the excess weight removed) purposes this weight guideline could be relaxed. The use of such excess weight requires specific justification. Application of radio transmitters can have significant adverse effects on survival, reproductive success, energetics and behavior (Boag 1972; Ramakka 1972; Boag et al. 1973; Greenwood and Sargeant 1973; Gilmer et al. 1974; McCrary 1981; Nesbitt et al. 1982; Morris et al. 1981;

Hooge 1991 and many references cited therein; Foster et al.1992; Gammonley and Kelley 1994: Ward & Flint 1995; Robb, 1997). Therefore, the use of transmitters should be undertaken with caution and is most appropriate for studies in which the data can be obtained in no other manner or in which data acquisition will be significantly improved. Excellent discussions of methods used in radio tracking studies can be found in Amianer and Macdonald (1980), Cochran (1980), and Kenward (1987).

A wide variety of attachment methods is currently in use, including body harnesses, attachment to the skin of the back with adhesives and/or sutures, neck collars, attachment to rectrices, attachment to the leg, and abdominal or subcutaneous implants. Assuming that transmitters of appropriate size are used, most negative effects of radio transmitters on birds result from the attachment method. Robb (1997) found that mallards fitted with transmitters on Dwyer harnesses survived longer, but behaved differently from other members of the population, including those with collar-mounted transmitters. Investigators desiring to employ telemetry should consult the sources relevant to their species for methods of affixing transmitters. In general, observation of individuals in captivity should be employed in evaluating the efficacy of attachment methods. Many species react negatively to harnesses that in some way go around the wings. Wherever possible, alternative methods of attachment should be employed (e.g., tail-mounting on larger species, suturing and subcutaneous anchors for large species, gluing and alternative harness designs for smaller shorebirds and passerines). Mounting radio transmitters on neck collars has been found to be inappropriate for at least one waterfowl species (Sorenson 1989). Special attention must be given to attachment in species that live in dense vegetation and those that roost or nest in cavities. Consideration should be given to the risk of birds being injured if transmitters become entangled in vegetation (Karl and Clout 1987). The removal of transmitters at the end of the experiment is not mandated, and indeed may not be possible, but investigators should consider whether an attachment that will "self-remove" at the end of the useful life of the transmitter will fit the experimental design. "Self-removal" should be rapid, as a loosely attached, flapping transmitter can be both an impediment to locomotion and an attractant for predators.

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I. Electronic Tags

Small chips, each containing an individual digital code, have been developed for injection under the skin (Bio Medic Data Systems, Maywood, NJ). The code can be detected by a scanner that is passed over the animal's body. Although developed for laboratory animals, these chips have been used on wild storks (Michard et al. 1995) and on burrowing petrels (Mauck et al. 1995). The chips and scanners are expensive, but they offer the enormous advantage that, if the tagged animal can be induced to enter the field of a scanner (e.g., at feeding or nesting sites), various data can be automatically recorded and assigned to specific individuals, thus completely eliminating the need for additional handling. Gluing the chips to feathers permits their recovery at the completion of the experiment, thereby decreasing cost (Mauck et al. 1995).

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J. Responsibility of Bander

The primary responsibility for ethical marking lies with the master permit holder under whose auspices the marking takes place. Similarly, the primary ownership of resighting data lies with the master permit holder. At the same time, the master permit holder has a responsibility to inform persons reporting resightings of the nature of the research involved and the status of the birds whose location was reported, should such information be requested.
 

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