by PH BLOOM — ignored traps baited with mice and sparrows that had worked well at other times. On the other hand, hard-to- catch raptors often can be trapped when they are
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PETERH. BLOOMWestern Foundation of Vertebrate Zoology, 439 Calle San Pablo, Camarillo, CA93012 U.S.A. WILLIAMS. CLARK2301 S. Whitehouse Crescent, Harlingen, TX 78550 U.S.A. JEFFW. K IDDWestern Foundation of Vertebrate Zoology, 439 Calle San Pablo, Camarillo, CA93012 U.S.A. INTRODUCTIONMany raptor studies, including those involving migra-tion, dispersal, home range use, anatomy, and toxicant ingestion, require that birds be captured for examina- tion, marking, or both. This chapter describes a variety of field-tested techniques for capturing birds of prey. Since the first edition of the Raptor Management Tech- niques Manual in 1987 (Giron Pendleton et al. 1987) almost no new, radically different raptor trap designs have been invented, but several have undergone design improvements and, importantly, several papers dealing with capture success and raptor trapping outside North America have been published.As Joseph J. Hickey remarked in the foreword toBirding with a Purpose (Hamerstrom 1984:vii), raptortrappers are generally different from the rest of the pop- ulace: fiYou™ve heard of wolf trappers, fox trappers, muskrat trappers, and the like. Raptor trappers are dif- ferent. Officially, they want to band birds to learn about their weight and moult, their later movements, theirlongevity, and all that. Underneath, they are unabashed admirers of the wildness, magnificent strength, and awesome flight of creatures at the top of the animal pyramid. I wouldn™t call them childlike; but they do have a youthful zest, and they will endure any hardship and go to any length to catch their birds.fl While passion and enthusiasm for raptor trappingare contributing factors, trapping success depends upon a number of other factors too. Some species such as Common Kestrel (Falco tinnunculus), Black-shoul-dered Kite (Elanus caeruleus), chanting-goshawks(Melierax spp.), and Red-shouldered Hawk (Buteo lin-eatus) are easy to capture, whereas others, includingmany eagles, kites, and condors, require more sophisti- cated techniques. Some raptors are more easily trapped on migration, whereas others are more easily trapped when nesting. The age of the bird also can be a factor. In general, juvenile raptors are easier to trap than adults, and hungry raptors always are more responsive to traps. Consistently successful trapping comes with experi- ence. Successful trappers not only can trap birds on migration, but also can trap specific individuals during the nesting season, and almost always without injuring them in any way or causing nest failures.Sometimes easy-to-catch raptors can be difficult to capture. WC noted that winged ants, emerging in droves after rains in Israel, were readily eaten by Steppe Buz- zards (B. buteo vulpinus), which then completelyignored traps baited with mice and sparrows that had worked well at other times. On the other hand, hard-to- catch raptors often can be trapped when they are espe- cially hungry. 193Capture Techniques12
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Trapping success often shifts seasonally. For exam- ple, Swainson™s Hawks ( B. swainsoni) are relativelyeasy to trap when breeding in North America, but are difficult to trap during migration, when they are nomadic. On the other hand, Sharp-shinned Hawks (Accipiter striatus) are readily captured along well-established migration corridors while migrating but are more difficult to catch during the breeding season. Knowing what trap to use, when to use it, and whatkind of lure to place in it requires familiarity with the target species™ecology and behavior. For example, Mer- lins (F. columbarius ) are easily captured with HouseSparrows (Passer domesticus) as lures in a smalldho-gaza trap, but Red-tailed Hawks (B. jamaicensis)are more often caught using the same lure in a bal-cha- tri. This is because Merlins are adapted to aerial pursuit of avian prey, whereas the Red-tailed Hawk is adapted to capturing mammalian prey on the ground. Fuller and Christenson (1976) and Hertog (1987) evaluated sever- al different trap types and quantified the effectiveness of different trapping techniques. Trapping success may be limited if raptors become fitrap-shy.fl Trap-shyness may be a serious problem if one needs to recapture specific individuals to replace transmitters or to study seasonal weight change or molt, etc. We believe that raptors become trap-shy as a result of negative or unrewarding experiences. Things that affect trap shyness, including trap shape, location, lure used, and proximity to people, should be considered prior to any attempt to recapture a trap-shy bird.In some situations where capturing many individu-als of several species is required, a combination of sev- eral strategically placed mist nets, bal-chatris and ver- bails, etc., with motion detector transmitters, can be extremely productive. Such set-ups typically require two to five people.Although being caught in a trap can stress a raptor, trapped birds rarely are injured physically. The most frequent causes of trap-related injury or death are preda- tion and weather. Raptors may succumb to temperature extremes or predation if allowed to struggle in traps for long periods. Used properly, the traps discussed in this chapter should rarely result in severe injury or death.While being handled, raptors may struggle, bite,grab, or vocalize depending upon the species and fiper- sonalitiesfl of the birds involved. Buteos and many owls, for example, struggle very little while being han- dled, and rarely vocalize, whereas accipiters, particular- ly Northern Goshawks (A. gentilis), struggle and vocal-ize most of the time, and readily attack. Most raptors arecapable of inflicting painful wounds with their beaksand talons, and large hawks and owls, eagles, and con- dors, can cause serious injury. In most species, particu- larly eagles, the talons are most dangerous. In general most species do not bite. Exceptions include vultures, California Condors (Gymnogyps californianus), fisheagles (Haliaeetus spp.), White-tailed Hawks ( B. albi-caudatus), and falcons.Researchers capturing and handling raptors musthave the proper permits, which vary among countries. In the U.S., these permits may include U.S. Geological Service bird-marking and salvage permits and endan- gered-species permits, as well as state permits. See Chapter 25 for details.CAPTURE TECHNIQUES AND THEIRAPPLICATIONThe first bible for avian trapping techniques was a smallbooklet titled Manual for Bird Banders by Lincoln andBaldwin (1929). Of about 35 traps and capture tech- niques described therein, only one, the Number 1 leg- hold trap, was used for the capture of birds of prey. Stewart et al. (1945) provided one of the earliest com- parisons of different raptor traps. Beebe (1964) focused on raptors trapped for use in falconry. McClure (1984) and Bub (1995) have written comprehensive overviews of most avian trapping techniques known worldwide. Today, raptor biologists have the option of using 20 dif- ferent basic trap designs and numerous variations, as well as trap monitors, which allow many traps to be monitored from a distance.Some countries prohibit the use of live lures in sci-entific research, and some researchers avoid live lures for personal reasons. Raptor researchers should ensure that the use of live lures is legal in the country they are trapping and should treat lures humanely and not sub- ject them to undue harm and stress. In the U.S. many, if not all, universities have Animal Care and Use Commit- tees that must approve research using live lures and in Canada at least, approval from an ethics sub-committee is now required (D. Bird, pers. obs.). Guidelines to theUse of Wild Birds in Research , a special publication ofThe Ornithological Council (Gaunt and Oring 1999), includes recommendations on wild-bird care in research.194CAPTURE TECHNIQUES
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Trap MonitorsThe use of motion-detector transmitters and scanningreceivers in raptor trapping has greatly advanced raptor trapping success and the ease with which traps are mon- itored. Any trap with moving parts, as well as traps that are moved when raptors strike them, can be monitored with these devices. This includes line trapping where as many as 20 bal-chatris, verbails, or Swedish goshawk traps, etc. are deployed over large areas (Bloom 1987). Trap monitors are available at Communications Spe- cialists, Inc. (www.com-spec.com). Prior to the use of trap monitors, each and everytrap had to be under continuous visual surveillance or checked at least hourly. This often meant that some birds were caught and escaped in the interim between checks, and that traps sprung by birds that were not caught were rendered non-functional for the remainder of that hour. Trap monitors also can reduce mortality as the sprung trap is visited immediately after having being triggered.Trap monitors work when a magnet attached to the transmitter is moved when the trap is sprung, initiating a signal that is detected by the receiver. Depending upon the terrain, traps can be monitored continually from a distance of 2Œ3 km or more. Two of us (PHB, JFK) that have used trap monitors since 1988 have found them useful in oak woodlands and grasslands of California when trapping resident Red-shouldered Hawks, Coop- er™s Hawks ( A. cooperii), Barn Owls (Tyto alba ); inagricultural areas in Argentina when trapping wintering flocks of Swainson™s Hawks; and in tropical forests in India when trapping Crested Serpent Eagles (Spilornischeela) and Crested Goshawks (A. trivirgatus ). In India,despite not having seen Crested Goshawks for almost a month, we caught six birds in two days after line trap- ping with trap monitors.Audio LuresThe use of tape-recorded playbacks of vocalizations can be used to bring raptors closer to field workers for iden- tification and surveying. Playbacks also can be used to attract owls to mist nets. This approach is now used to capture migrating Northern Saw-whet Owls (Aegoliusacadicus) and Flammulated Owls (Otus flammeolus) atmost migration banding stations where owls are trapped (e.g., Erdman and Brinker 1997, Evans 1997, Whalen and Watts 1999, Delong 2003). Playbacks also have been used with excellent suc-cess during the breeding season to trap Barn Owls,Western Screech Owls ( Megascops kennicottii), Long-eared Owls (Asio otus), Spotted Owls (Strix occidental- is), Great Horned Owls (Bubo virginianus ), Red-shoul-dered Hawks, Northern Goshawks, Cooper™s Hawks (PHB, JWK) and other species by drawing the birds into mist nets or other traps in the playback area. It is impor- tant to limit playback use during the breeding season as adult behavior and nest success may be influenced by excessive use of this technique.The Bal-chatriBecause this trap is one of the most successful devices used to date to catch raptors, considerable attention will be paid to it. The bal-chatri, which roughly translates to finoosed umbrellafl (Clark 1992), is a wire cage with monofilament nooses tied to the top, sides, or both, with a lure animal placed inside (Fig. 1; Berger and Mueller 1959). The size and shape of the trap depend upon the species being trapped. Typical lures include the house mouse (Mus musculus), black rat (Rattus rattus), gerbil(Gerbillus spp.), House Sparrow, Common Starling (Sturnus vulgaris ), and Common Pigeon (Columbalivia). In countries or remote areas where standard suchlures are not available, Red Junglefowl (domestic chickens, Gallus gallus) or ducks (Anas spp.) can beused. Several designs are in widespread use, including (1) quonset (Berger and Hamerstrom 1962, Ward and Martin 1968, Mersereau 1975), (2) cone (Kirsher 1958, Mersereau 1975), (3) octagonal (Erickson and Hoppe 1979), and (4) box with apron (Clark 1967). One mod- ification involves the use of a Plexiglass top for trap- ping screech owls (Smith and Walsh 1981). As with many traps involving live lures, trappersshould consider the placement of the trap carefully, as traps may be stepped on by farm animals, run over by cars, or moved by people. In some instances ants can kill the lure.Construction.Mesh and cage size are determinedby the species to be captured, and size of the bait ani- mal. The cage must be large enough for the bait animals to move (run or fly) within it, so that the raptor can detect them. The more space the bait animal has to move about, the more likely the raptor is to notice it quickly. For American Kestrels ( F. sparverius ) we recom-mend 0.6-cm hardware cloth rather than 1.3-cm cloth, as small-to moderately-sized house mice can escape through or become caught in the large mesh. For most other species up to the size of eagles 1.3-cm hardwareCAPTURE TECHNIQUES195
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cloth is best. When using quonset-shaped bal-chatris on large accipiters, buteos, large owls, and Harris™s Hawks (Parabuteo unicinctus), either 1.3-cm aviary cloth or2.5-cm chicken wire can be used, especially if the intent is to use a relatively large lure animal (e.g., Common Pigeon). Larger mesh makes the lure animal more visi- ble, particularly at great distances. In addition, the aviary cloth and chicken wire mesh are more flexible and more easily manipulated than hardware cloth, and are easier to work with. On the other hand, aviary- and chicken-wire traps are more easily dented or crushed than are hardware-cloth traps, and nooses cannot be attached as firmly to aviary cloth and chicken mesh as to hardware cloth. Plastic (modeling) cement applied to the area of attachment can alleviate much of this prob- lem.Asingle section of hardware cloth or several sec- tions in which the sides, bottom, and top are fastened together can be used to construct the cage. The different flaps or sections of the cage are most efficiently fas- tened with ring clips (Wiseman 1979) or with wire. The door for the lure animal should be on the bottom of the trap where it will not interfere with nooses.Camouflaging traps is important. Traps should be spray-painted before the nooses are attached. Good background colors are light green (live vegetation), tan (dead vegetation) and white (snow). Flat colors are preferable to glossy. A15-to 25-cm apron of hardware cloth with noos- es extending out from the cage increases the potential of capturing individuals that are shy of standing on the cage. This is particularly important for the capture of Burrowing Owls (Athene cunicularia).Some house mice used as lures will pull the noosesinside the bal-chatri, and will gnaw on them or, some- times, hang themselves. Amouse with a taste for monofilament can ruin hours of work and should be replaced. Placing short lengths of monofilament in the cage sometimes reduces chewing on nooses.Several knot-tying techniques have been described.Jenkins (1979) found that a running slipknot, which remains closed on the bird™s foot or toe once it has tight- ened, increased trapping success. Unfortunately, the use of such fione-timefl knots as part of the noose (the knot also can be used to anchor the noose to the cage) means that all nooses that are closed accidentally must be replaced or retied. We use the traditional technique of an overhand knot for the noose (Collister 1967) and a square knot for the anchor point. This employs simpler knots that can be tied quickly. Unfortunately it may allow more birds to escape than use of the running slip- knot. The North American Bird Banding Manual illus-trates another variation in which an overhand knot is used for the noose but a clinch knot is used at the anchor point (Environment Canada and U.S. Fish and Wildlife Service 1977).We agree with Jenkins (1979) that the best way to attach nooses to the wire mesh is diagonally across the junction of two wires. Vertical nooses are critical to trapping success. Most nooses can be made to stand ver- tically by several firm upward tugs on a thick pen tight- ened in the noose. The knot at the junction of the two wires should be rotated until the noose is in the most vertical position. Plastic cement also may be used to help maintain the erect posture of the noose. When using cement, be certain that it does not weaken the monofilament. See Figure 1 in Berger and Mueller (1959) for tips on attaching nooses so that they stand erect.The height and spacing of nooses also is important.For small raptors, we make nooses 4-cm tall, spaced at 3 cm. For medium to large raptors we make nooses 5Œ6.5-cm tall, spaced at 5 cm. Adjacent rows of nooses 196CAPTURE TECHNIQUESFigure 1.Bal-chatris can be made in a variety of shapes. The box-shaped bal-chatri works well on accipiters, buteos, and owls, where- as the cone-shaped trap works best on kestrels and Burrowing Owls (Athene cunicularia).
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are staggered. When the trap is complete, we examine it for spaces and add more nooses as needed. Nooses become brittle with age, particularly when traps are rolled in dust or mud or are exposed to long hours in the sun. Depending upon the amount of use that a trap sus- tains, we replace all nooses one to five times annually. Bal-chatris are relatively light traps that must beweighted to prevent birds from taking off with them. For traps under constant surveillance we recommend either a 0.7-or 1-kg barbell weight attached to the trap via a 1-m length of nylon cord. Many researchers attach the weight directly to the floor or sides of the bal-chatri, rather than by a nylon cord with a fishock-absorbingfl spring. Aproblem with the first approach is that there is no opportunity to place a spring between the trap and weight and, as a result, both the weight and noose attachments break more readily. Also, we believe that weights attached to the trap make the trap more con- spicuous than a weight on a 1-m line, and that this reduces the likelihood of birds striking the trap. Lighter weights can be dragged short distances by the bird, but are less stressful on the nooses and on the bird™s toes than are heavier, stationary weights. The only drawback with having the weight separately rather than directly attached to the trap is that the vehicle must be going slower for the drop. When traps are checked hourly, we recommend either tying the trap to a stationary object or using a heavy weight so that the trap is less likely to be dragged off. Aspring or other fishock absorberfl must be used in situations where the trap is tied to a stationary object. The shock absorber has two functions. First, it reduces the stress on the nooses, which may snap if tugged sufficiently, and second, it reduces the risk to raptors, which may hemorrhage and die if allowed to struggle against a stationary object for more than 10 minutes (pers. obs.). Barn Owls in particular are prone to the latter. The spring should be securely attached on a nylon cord between the trap and the weight to prevent the bird from escaping with a bal-chatri.Application.The bal-chatri is an extremely effec- tive, versatile, and portable trap. It can be used during all seasons, and has a success rate of up to 85% for most species that are attracted to it. Most North American raptor species have been captured on bal-chatris. In Guatemala, Thorstrom (1996) captured 12 species, including hawks, hawk-eagles, falcons, and owls, with this technique, some of them in trees. In India, Kenya, South Africa, and Israel, PHB, WSC, or both, have used bal-chatris to catch a wide variety of species of kites, accipiters, buzzards, harriers, small to large eagles, fal- cons and owls. One of the more difficult species to catch with bal-chatris is the Black Kite (Milvusmigrans).There are two principal applications. The first is road trapping, in which traps are placed on the roadside from a vehicle in the immediate vicinity of perched rap- tors. The second is line trapping, in which 10Œ15 bal-chatris are placed out before the target bird(s) arrive in known use areas. Line trapping is particularly effec- tive on owls and woodland raptors. In both procedures, traps usually are placed to capture perched raptors. Fly- ing accipiters are the occasional exceptions. Road trap- ping is best attempted from roads with minimal vehicle use, as cars and trucks tend to frighten the birds. That said, it is indeed possible to catch birds along busy high- ways. Trapping involves driving on country roads while scanning for raptors perched near roads, often on power poles or utility lines. Once a raptor is identified, a weighted bal-chatri is placed on the shoulder of the road. Time spent dropping the trap from the vehicle should be minimal; on the other hand, merely throwing the bal-chatri from a moving vehicle is construed by some as cruel to the lure prey inside. To improve trap- ping success and avoid injury to the bird and the lure prey: (1) the vehicle should not be stopped when drop- ping the trap, as this frequently frightens the bird, (2) the door of the vehicle should be closed quietly, (3) the weight and trap should be placed as far from the edge of the road as possible to ensure that the captured hawk or owl does not drag the trap onto the road, and (4) the trap should be placed from the side of the vehicle away from the perched bird, and on roadside opposite to it such that the bird cannot see the trap being set. If it is necessary to stop, do not step out of the vehicle. In all trapping it is best to disassociate yourself from the trap as much as possible. In most instances this can be achieved by not letting the bird see you with the trap. Many birds appear initially suspicious of the figift-wrappedfl food and will not come down to the trap, and will hesitate for a long time and, eventually, leave the area, even when these procedures are followed. Sometimes, birds repeatedly fly down to traps but do not touch it or do not become entangled, and eventually lose interest. Placing a second trap in a new site frequently results in renewed interest and success.Line trapping differs from road trapping in that 10Œ15 bal-chatris are placed (1) in a specific territory in an effort to catch a targeted bird or pair of birds or (2) in appropriate habitat across several square kilometers to trap as many birds as possible. As with road trapping, CAPTURE TECHNIQUES197
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traps should not be placed directly in sight of a bird, butinstead near known or suspected hunting and resting perches (e.g., perches near nests where the male or female may spend time while not on the nest). The entire trap line is checked hourly or is monitored via trap monitors. As traps are checked and birds removed, they are reset (i.e., closed nooses are reopened), and captured birds are retained until the entire series of traps is checked.Line trapping has three advantages over road trap-ping, including (1) high trapping rates, (2) more appro- priate habitat selection for trap placement, and (3) more effective trapping of troublesome or trap-shy individu- als through placement of several camouflaged traps. Three disadvantages are that (1) predators occasionally kill birds caught on the trap, (2) birds have more time to free themselves compared with road trapping, and (3) trapping is not as selective in that individuals of non- target species may be caught. The first two disadvan- tages above can be reduced by using trap monitors that signal the trapper immediately when the trap has been moved or sprung.When line trapping, there is time to conceal the bal-chatris and tack them to the ground to prevent flipping. Trappers should push surrounding leaves or grass around the trap and place leaves or grass between the nooses on the top, making sure that nothing becomes entangled in the nooses. If you use enough grass or leaves to make the traps difficult to re-locate, the hawk or owl will find them for you. If a bird is trap-shy of bal-chatris, use two to three traps at each perch.Proper lure animals are important. Pigeons, star-lings, and House Sparrows are best for attracting accip- iters. Occasionally a house mouse or gerbil can be used. Most falcons do not respond to lures in bal-chatris. One exception is the American Kestrel, which is easily caught on bal-chatris baited with either house mice or House Sparrows. Prairie Falcons (F. mexicanus ) andAplomado Falcons (F. femoralis ) are easily caught onbal-chatris baited with house mice, gerbils, and House Sparrows or combinations thereof. Peregrine Falcons (F. peregrinus ) and Gyrfalcons (F. rusticolus )(B. Anderson, pers. comm.) are rarely if ever caught on bal- chatris.In our opinion, the best bait animals for capturingbuteos are paired combinations of domestic house mice and gerbils, house mice and House Sparrows, or wild and domestic mice. B. Millsap (pers. comm.) has had excellent success trapping Cooper™s Hawks using a ger- bil-House Sparrow combination. Common Pigeons canbe used to lure Cooper™s Hawks, Northern Goshawks, Harris™s Hawks, and large buteos. Most wild rodents, including Microtus , Peromyscus , and Neotomaspp., arepoor attractants because they tend to remain motionless. Northern Harriers (Circus cyaneus ) and White-tailed Kites (E. leucurus) have been caught on bal-chatris withhouse mice, gerbils and House Sparrows. Medium to large owls are most easily caught on house mice and gerbils. Great Horned Owls can be lured with Common Pigeons. Although Strigidae, which seem to hunt much more by sight than by sound to Tytonidae, readily attack animals in bal-chatris with or without dry leaves in the trap, the latter rarely strike a bal-chatri unless they can hear the sound of the lure animal rustling the leaves.Although pigeons, starlings, House Sparrows, ger-bils, and house mice are the fistandardfl lures, other species can be used in emergencies (e.g., chipmunks, squirrels, and rabbits). Most native vertebrates are pro- tected by various state and federal laws however, and must not be used without appropriate permits.The Bartos TrapArelatively new kind of raptor trap, which blends the concepts of the bow net and the box trap, is the Bartos trap (Bartos et al. 1989). Although this trap has not been used widely to date, it has been used to capture Collared Sparrowhawks (A. cirrhocephalus ) and Moreporks(Ninox novaeseelandiae) in Australia. The trap, which shows considerable potential for capturing small to medium-sized forest raptors lured with small birds, can be suspended at almost any height, in a building, or in a tree near a nest, and does not require attendance, is col- lapsible for easy transport.Bow NetsSeveral variations of this trap have been used to trap many species, including owls, eagles, falcons, harriers, buteos, and accipiters. The trap consists of two semicir- cular bows of light metal with gill netting strung loose- ly between them (Fig. 2). Hinges and springs connect the two semicircles at their bases, the lower one of which is fixed to the ground. When setting the trap, the upper bow is pulled over the lower stationary bow and latched into position. Alure animal, usually a bird, is placed in the center of radius of the trap. When a raptor grabs and holds the lure bird, the trap is triggered, either by a person in a blind pulling a trigger line (Meredith 1943, Mattox and Graham 1968, Clark 1970, Field198CAPTURE TECHNIQUES
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lure raptors during the breeding season (Redpath andWyllie 1994), is another successful box trap, and Ken- ward and Marcstrom (1983) provide detailed descrip- tions of similar compartment traps that may be more useful than the Swedish goshawk in trapping in certain situations. Application.Meng (1971) provides an excellentdescription of the materials used in the construction of the Swedish goshawk trap. The Swedish goshawk trap has been used to capture most large hawks (and Great Horned Owls) in North America, as well as Great Black Hawks (Buteogallus urubitinga) and Ornate Hawk-Eagles (Spizaetus ornatus) in Guatemala (Thorstrom1996). This trap is particularly useful for falcons because they tend to walk around the trap and do not enter the compartment from above (Meredith 1943). Lure animals typically include Common Pigeons or Common Starlings. Two or more lures should be placed in each trap to increase their movement and visibility, and the trap should be placed in a highly visible loca- tion. Although trapping with this method is relatively slow, most birds that enter the trap are caught and do not escape. The best attribute of the trap is that it only needs to be checked every three hours or so and can be moni- tored using trap monitors.Trapping during the nesting season involves the placement of two or three traps between 50 and 200 m from the nest. Trapping during migration entails the placement of 5 to 10 traps spaced 0.5 to 1.0 km apart along pole or fence lines in valleys where birds perch to hunt or, less desirably, on ridges where many birds are moving.One of us (WC) used from 5 to 10 box traps to cap-ture migrating raptors on return migration in Eilat, Israel. In one season, 45 of 653 captured raptors were caught in them, including 41 Steppe Buzzards, 2 Eurasian Sparrowhawks (A. nisus), a Levant Spar-rowhawk (A. brevipes ), and a Black Kite. The next sea- son, using fewer traps, 10 of 445 raptors were caught, including 7 Steppe Buzzards, 2 Levant Sparrowhawks, and a Eurasian Sparrowhawk. The traps were baited with domestic house mice, House Sparrows, or both.Cannon and Rocket NetsCannon and rocket nets are used to capture vultures, eagles, and condors. They are similar, relatively expen- sive traps, but are very effective and can be used to cap- ture many individuals at a single firing. The technique consists of three to four cannons or rockets that propel a large net over the birds (Mundy and Choate 1973). Animal carcasses are used as bait.Application.Because they involve explosives, can-non and rocket nets are more dangerous than other traps. The cannon net is less dangerous than the rocket net, and we limit our discussion to it, although much of what follows also applies to rocket nets. Because of the difficulties involved in building this trap, we recom- mend purchasing it from a manufacturer (e.g., Wildlife Materials Inc., www.wild lifematerials.com). One of the safest and simplest designs is described in Mundy and Choate (1973) (J. Ogden and N. Snyder, pers. comm.). Other designs are in Dill and Thornsberry (1950), Grieb and Sheldon (1956), Marquardt (1960a,b), Thompson and DeLong (1967), and Arnold and Coon (1972). Nets and mesh vary in size depending upon the target species. A15.2 × 15.2-m net of 10.2 × 20.3-cm mesh is good for trapping eagles. Smaller mesh causes the net to remain airborne too long, allowing birds to escape. Because 10.2 × 20.3-cm mesh is not standard, it must be created by cutting the 10.2 × 10.2-cm mesh to create larger holes. Permits, which must be acquired before 200CAPTURE TECHNIQUESFigure 3.A Northern Goshawk (Accipiter gentilis) lands on the trig-ger stick of a Swedish goshawk trap containing Common Pigeons (Columba livia) as bait.
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detonators (blasting caps) can be purchased, should beapplied for one year in advance of the proposed trap- ping effort. Cannon nets have been used to capture manyspecies including waterfowl, seabirds, shorebirds, passerines, cranes, and grouse (Dill and Thornsberry 1950, Thompson and DeLong 1967, Arnold and Coon 1972). More recently, raptors, including Black Vultures (Coragyps atratus) and Turkey Vultures ( Cathartesaura), Andean Condors ( Vultur gryphus ), CaliforniaCondors, Bald Eagles, White-bellied Sea Eagles ( H.leucogaster) (Hertog 1987) and Golden Eagles havebeen captured using these traps. The cannon net is one of the best traps available for gregarious species where several individuals accumulate simultaneously. Cannon nets also allow the trapper to capture birds selectively. Non-target species pose little problem when trapping with this method because non-target species feeding at them often attract target species. To achieve maximum success with eagles, vultures, and condors, lure carcasses should be staked down to render them immoveable. Ideally, the site should be baited at least one week prior to capture attempts, and should be baited continually until the project is finished. Where large nocturnal scavengers such as bears or wild dogs are present, the carcass may need to be removed at the end of each day or be replenished more frequently. Observations should be made from a nearby blind or from about 0.8 km away. Typical bait animals include virtually any medium to large carcass. Fresh rather than rotten carcasses seem to be more attractive to raptors. Stillborn calves are frequently available from dairies. Between 1982 and 1987, 10 California Condorswere captured with cannon nets using the carcasses of stillborn calves as bait (PHB, unpubl. data). Most con- dors were recaptured using the cannon net at both the same and different locations. During the same period, 43 Golden Eagles were captured, four of which were recaptured. The trap was 100% effective in that none of the targeted condors or eagles escaped capture. On sev- eral occasions two to four Golden Eagles were captured with one firing, and Golden Eagles and condors were captured together in the same firing. No injuries or mor- talities occurred to either species. In Israel, trappers caught 35 Black Kites with one firing of a cannon net. In Israel, an air-powered cannon net captured European Honey Buzzards (Pernis apivorus) when they came todrink at a small pond (WC).Although selective and efficient, cannon nets are labor-intensive. Initial installation and site preparation requires about four hours. Each firing or preparation forfiring takes about one hour. Four people are needed to stretch and fold the net after each firing. Test-firings are needed to determine whether cannons are wired and angled correctly, and to be certain that the net deploys properly. Selecting a good trap site is important as consider-able effort goes into its preparation. Awell-camou- flaged blind of suitable size should be placed in cover 30Œ60 m from the trap. Clumps of grass, branches, or both should be placed around each cannon, and the net should be covered lightly with grass.Cannon and rocket nets set fires easily if dry fuel isavailable. If wildfires are a strong possibility or the habitat consists of dry vegetation, ridge tops rather than valleys should be used. Regardless of where the trap is set, cut all dry grass from within 5 m of the cannons, and strip this area to near bare earth. Grass within the net landing area, but further than 5 m from the cannons, should be cut to 2 cm. Green grass need not be cut.Once the trap is ready and desirable raptors arecoming to the trap, the blind should be entered about an hour before sunrise. Silence in the blind is important, as eagles, vultures, and condors are highly suspicious and frequently watch for hours before finally settling in to feed. The slightest noise or movement can alert them to the presence of the trappers.The detonator button on the firing box can bepushed when desired raptors are in position, preferably with their heads down feeding on the carcass. Be certain that no birds are standing where the four projectiles will land, and that no birds are airborne. Once the net has landed and birds secured, they can be taken from under the net and processed. Birds under the net must be sep- arated from each other to avoid having them bite and claw each other. When many raptors are captured with a single firing, each bird should be placed in a restrain- ing device or covered with a light blanket while still under the net.Cast Lures and Hand NetsThis technique has been used effectively on Great Grey Owls (S. nebulosa) and Spotted Owls, but should besuccessful on other approachable Strix spp. The cast lure and hand net consists of a stuffed lure or live rodent attached to a nylon line that is pulled across the terrain, or simply a live rodent placed at the foot of the trapper. When the owl comes into the lure, a fish-landing net is quickly flipped over the bird.CAPTURE TECHNIQUES201
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