Wild bird capture techniques

Check operative traps and nets at appropriate time intervals; birds should not Hand nets or poles can be used to direct the birds’ movements and catch any
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33Chapter 3Wild bird capture techniques For millennia, humans have relied on wild birds as a source of food, clothing, and social and religious manifestations of culture, art and sport. While their mobility, wariness of humans and diverse habitats often make live capture of wild birds a challenge, a multitude of trapping techniques and devices have been developed over the centuries. Most of the live capture techniques utilise bait, decoys, recorded calls or lures to attract birds to trapping sites, but a few active techniques in which the trapper actually pursues the bird have been developed and may be useful in some situations. Thus, there are few, if any, bird species which cannot be captured. Capture techniques specifically designed for wild birds such as waterfowl, shorebirds and other wetland species are of primary interest because current knowledge indicates these are the species that serve as the primary reservoirs of low pathogenic AI viruses. How- ever, practical techniques for capturing passerines, raptors and other bird groups vulnerable to the virus are also important. Extensive reviews of capture techniques for a wide range of bird groups can be found in Bub (1991), McClure (1984) and Schemnitz (2005). The health and well-being of the birds should be the primary concern during all phases of capture. The following principles should be adhered to ensure birds are captured cor- rectly, safely and with minimum disturbance: • Wild bird capture is an activity that is strictly controlled in most countries; those engaged in capture activities should always be aware of and comply with local and national laws regarding these activities and obtain all the required local, state, pro- vincial and federal permits well in advance.• Capture techniques and equipment which expose birds to foreseeable risk of injury should be avoided at all costs.• Those conducting capture efforts should take all necessary precautions to avoid dis- turbing nesting birds at breeding sites or enhancing vulnerability to nest site preda- tion following human intrusion.• Monitor weather forecasts prior to conducting capture efforts to ensure birds are not captured during extreme climatic conditions when they may be at increased risk of hypothermia or hyperthermia.• Always have a sufficient number of experienced personnel (at least four) available before undertaking any capture operation. • Check operative traps and nets at appropriate time intervals; birds should not remain in traps or nets any longer than is necessary. This is capture technique and weather dependent, and could be as short as every 15 minutes to twice a day. • Close or dismantle traps and nets that are inoperative and not checked regularly. manual5.indb 3319/03/2008 10:17:39

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Wild Birds and Avian Influenza: an introduction to applied field research and disease sampling techniques 34CORRAL TRAPS (ROUND-UPS)The two- to three-week period after breeding when waterfowl, grebes and coots simul- taneously moult all their flight feathers is an opportune time for capturing these species. During this flightless period, birds can often be “rounded up” by herding or driving them between barriers which funnel the birds into capture pens constructed near the moulting grounds. The basic drive trap design used by the Wildfowl & Wetlands Trust (WWT) consists of a capture pen or “corral” with two long barriers or “wings” extending some distance from the mouth of the corral (Figure 3.1). Birds may be on the water or on land when they are initially driven between the corral wings by the capture team, but if the wings extend out into the water they should eventually funnel the birds into a corral constructed on flat dry ground. Corral trap constructionSpecific features of the trap will depend on the size of the species to be captured. In the following instructions, a range of specifications for the corral pen(s) and wings are given both for smaller birds (ducks, grebes and coots) and larger waterfowl (geese and swans). • The corral pen and wings should be marked out with 1.5-2.0 m wooden posts or metal fence stakes firmly driven into the ground and spaced approximately 1 m apart; a round corral is usually best, but the shape may differ if conditions warrant. FIGURE 3.1Basic set-up of a corral trapCorral PenCorral Wing Herding Boat manual5.indb 3419/03/2008 10:17:40

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Wild bird capture techniques 35• The diameter of the corral is dependent on the number of birds to be caught and may vary from less than 2 m up to 30 m, or more (Figure 3.2). • Side pens may also be constructed to ensure that no single pen contains too many individual birds; this is particularly important for the welfare of birds during the cap- ture process. • The corral wings should be erected in straight lines over flat ground or water and should not snag on branches, brambles or other vegetation because this may damage the net and cause birds to become entangled. • The width of the wings at the entrance to the corral can be as narrow as 0.5-1.0 m for small numbers of ducks or up to 50 m when capturing large numbers of geese or swans.• Attach black nylon netting or other appropriate material to the corral and wing posts; use a material that will not injure birds when they run up against the corral pen or wing walls.• The nylon netting (or other wall material) should be stapled at the top, middle and bottom of wooden posts; metal stakes can be run through the top, middle and bot- tom of the netting.• When attaching the netting to the posts make sure the net is taut and the bottom 0.1 m of the net curves toward the inside of the corral to prevent birds escaping beneath the net during the ‘drive’.• The height of the corral should be 1.0 m for ducks and 1.5-2.0 m for geese and swans, but corral wings can be 1.0 m high for all three groups. FIGURE 3.2Corral trap penCREDIT: PAUL SLOTA manual5.indb 3519/03/2008 10:17:40

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Wild Birds and Avian Influenza: an introduction to applied field research and disease sampling techniques 36• Hessian (or any other fabric) should be tied to the bottom 0.5 -1.0 m of the corral to prevent birds catching their claws on the netting. • If the ground is wet or cold, clean straw should be spread on the ground in the corral to a depth of 3-15 cm.It should be noted that the details of corral construction described above apply to instances when the trap can be erected before the attempted drive. In some cases (e.g. on the tundra), it will often be impossible to predict where the final capture will occur and the corral will need to be constructed after the birds have been herded and surrounded. In such instances, less precise corral specifications are acceptable, from both a bird welfare and an effectiveness perspective. Herding birds into a corral trap Depending on the location of the capture efforts, birds can be driven between the corral wings and ‘funnelled’ into the corral either by rowing in small boats, wading through shal- low water or walking behind them. General instructions for ‘herding’ birds into the corral are described below: • The number of “herders” required will depend on the number of birds to be caught, the size of the corral enclosure and habitat. A minimum of four herders will be required. • The herders should form a line with the birds between themselves and the funnel shaped corral opening (Figure 3.3); in cases where the final capture site is uncertain, the herders should form a circle and drive birds towards a central point, then con- struct the corral near the herded birds and move them into it. FIGURE 3.3Technique for herding flightless waterfowl CREDIT: RUTH CROMIE manual5.indb 3619/03/2008 10:17:42

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Wild bird capture techniques 37• Using coordinated movements, the herders should then drive the birds as a group toward the corral opening (or central point). • Birds should be herded at a steady pace so that they do not panic and scatter in all directions or charge at speed into the corral causing the walls of the pen to col- lapse.• Hand nets or poles can be used to direct the birds’ movements and catch any birds which try to escape through the line (although it is better to let a single bird escape rather than break the line and risk losing the entire flock); waving a hand-net will persuade a bird to move away, while pointing the net to the right or to the left, may persuade birds to move in the desired direction. • Once all birds have entered the corral, the mouth of the corral should be carefully closed (making sure no birds are caught in the door) and the designated bird extractor should position him/herself inside the pen and in front of the exit. BAITED TRAPSDrive traps for waterfowl can only be used near moulting areas when birds undergo their annual wing moult, so other capture techniques must be employed outside the flightless moulting period. Baited traps are an effective technique for capturing a wide array of wild birds, including waterfowl and many ground-feeding terrestrial species. However, because hunting often occurs where waterfowl and other game birds aggregate, it is advisable to locate bait traps within “sanctuaries” (when practical) to avoid attracting birds to areas where high levels of lead shot may be ingested. Many of the baited trap designs utilise self-contained wire cages or enclosures sup- ported by posts that are baited with appropriate food stuffs for the target species. For most waterfowl, typical baits include wheat, corn kernels, whole rice or other grains. These traps may go by several different names (e.g., cloverleaf traps, drift traps), but two designs particularly useful for waterfowl are baited funnel traps and baited dive-in traps. Funnel trapA baited funnel trap can be deployed or constructed on land or in water shallow enough for foraging by dabbling ducks, coots and waders, usually <25-30 cm, although the design will function in deeper water provided those handling the birds can reach the trap site in waders or a boat. The basic funnel trap design consists of a wire cage or enclosure with one or more funnel shaped entrances which the birds can enter, but have difficulty exiting (Figure 3.4). Fine mesh netting can be placed over enclosure traps to prevent birds escaping over the wire fence when handlers approach. Funnel trap construction• An appropriate trapping site should be selected (preferably a site already frequented by the target species) and bait type (catered for the targeted species) spread over the site for several days before the trap is constructed. • The funnel trap enclosure should be marked out with 1.5-2.0 m posts firmly driven into the ground or shallow wetland substrate; many different trap sizes and shapes with one to many entrances have been designed (Figures 3.5, 3.6 and 3.7). manual5.indb 3719/03/2008 10:17:45 PAGE - 6 ============ Wild Birds and Avian Influenza: an introduction to applied field research and disease sampling techniques 38• The size of the enclosure or trap should be appropriate for the number and size of the target species.• The funnel entrance(s) should be just wide enough to allow birds to pass through the opening, or push through the opening if the material is slightly flexible; the larger the entrance the greater the likelihood of birds escaping. • Put the wire enclosure fencing around the post border; use fencing with a lattice pat- tern that will not allow birds to get stuck while trying to escape. • Attach the wire fencing to the posts with plastic or soft wire ties, making sure the fence extends all the way down to the ground or substrate; cut and adjust the tie ends so they cannot cut or scratch birds. • If possible, attach the wire fence to the posts prior to placement at the site as this may facilitate construction of the trap; for some smaller diameter traps, posts may not be necessary at all.• The nylon netting (or other cover material) should be attached with ties to the top of the wire fencing; if needed a wooden “tent” pole can be placed in the middle of the enclosure to hold up the net cover. • Create a doorway in the enclosure at the opposite end of the trap from the funnel entrance that allows birds to enter a capture box or net for easy removal from the trap.• Bait heavily inside the trap but lightly around the funnel entrance to entice birds into the enclosure. FIGURE 3.4Basic set-up of a baited funnel trap2.5-4.0 m Capture Box Metal FencePostRampMesh NetCover Wire Fence FunnelEntranceBaitmanual5.indb 3819/03/2008 10:17:45 PAGE - 8 ============ Wild Birds and Avian Influenza: an introduction to applied field research and disease sampling techniques 40and drive birds through the open doorway into a holding box or net. In smaller traps, birds can be removed by a handler outside the enclosure with a hand-held keep net. Birds can be removed individually and processed at the capture site or transferred to a travel container and transported to a nearby processing site. Dive-in trapsAs the name implies, baited dive-in traps are effective for capturing aquatic diving birds, primarily diving ducks. Dive-in traps can be constructed in relatively shallow water (<1.25 m) habitats that are frequented by diving birds and accessible to handlers in small boats or wearing chest waders. The basic dive-in trap design is similar to the funnel trap enclosure; however, in the case of dive-in traps, the wire fence is raised (0.3-0.5 m) slightly off the wetland bottom allowing the birds to dive under and into the enclosure (Figure 3.8). Dive-in traps are only effective in wetland habitats, but may be used in permanent water bodies of adequate depth or tidally influenced wetlands. Some familiarity with tide levels will be necessary when deploying traps in tidal wetlands. Dive-in traps may be con- structed during low tides when the trap site may be completely exposed, but will need to be checked whenever the tide rises to inundate the site and birds move in to feed. Because diving ducks have some difficulty taking off directly from the water, fine mesh netting placed over traps may not be necessary. If netting is used to cover the trap, it should be removed from unattended traps to avoid drowning birds at high tides. FIGURE 3.7Self-contained wire funnel trap for shorebirds CREDIT: SCOTT NEWMAN manual5.indb 4019/03/2008 10:17:52 PAGE - 9 ============ Wild bird capture techniques 41Dive-in trap constructionMany of the issues involved in the construction of dive-in traps are similar to those for funnel traps:• An appropriate trapping site should be selected (preferably a site already visited by the target species) and bait spread over the site for several days before the trap is constructed.• The dive-in trap enclosure should be marked out with 1.5-2.0 m posts firmly driven into wetland substrate; circular dive-in traps are most common (Figure 3.9), but other shapes may be optimal in certain circumstances. • As for funnel traps, the diameter of the enclosure should be appropriate for the number and size of the target species to be captured. • Put the wire fencing in place around the fence post border; be sure to use wire fenc- ing with a lattice size that will not allow birds to get stuck while trying to escape. • Attach the wire fencing to the posts with plastic or soft wire ties, raising the fence approximately 0.3-0.5 m off the substrate all the way around the enclosure; cut and adjust the tie ends so they cannot cut or scratch birds. • If possible, attach the wire fence to the posts prior to placement at the site as this may facilitate construction of the trap.FIGURE 3.8Basic set-up of a baited dive-in trap2.5-3.0 mWireFenceMetal FencePost0.3-0.5 mBaitmanual5.indb 4119/03/2008 10:17:54 PAGE - 10 ============ Wild Birds and Avian Influenza: an introduction to applied field research and disease sampling techniques 42• Nylon netting (or other cover material) may or may not be needed to prevent birds escaping over the top of the enclosure; if netting is needed it should be attached with ties to the top of the wire fencing and supported in the middle with a “tent” pole. • Bait heavily inside the trap but lightly around the funnel entrance to entice birds into the enclosure. Dive-in traps are generally baited in the late evening and checked first thing in the morning, although tidal fluctuations will affect schedules for traps in tidal zones. Birds should be removed by reaching over the enclosure fence with a hand-held net and dipping the birds out of the trap. Holding boxes floated on buoys can be used to transport birds to the shoreline. CANNON NETSBirds that congregate in large numbers at roosting or feeding sites can be captured with large mesh nets attached to projectiles that are propelled over the roosting or feeding flocks by explosive charges (Figure 3.10). However, as might be expected with high veloc- ity projectiles launched near dense bird congregations, there is a significant risk of injury or mortality to wild birds and humans if this technique is used by inexperienced opera- tors. Because cannon-netting requires a high level of technical expertise, it should not be attempted without assistance from experienced personnel. Details of cannon-netting procedures are best obtained from experienced practitioners and specific training manuals (e.g. Appleton, undated), however, some general guidelines in the use and application of the technique are provided. Cannon nets have been used to capture many species of waterfowl, wading birds such as herons and egrets, upland game birds, gulls and shorebirds. Some scouting is usually FIGURE 3.9Dive-in trap set up in a tidal wetland CREDIT: DARRELL WHITWORTH manual5.indb 4219/03/2008 10:17:55 PAGE - 11 ============ Wild bird capture techniques 43necessary to identify suitable capture sites where predictable roosting or feeding flocks con- gregate in open and dry upland or very shallow (a few centimetres deep at most) wetland habitats. Bait and decoys can also be used to attract waterfowl and other target species to suitable capture sites. FIGURE 3.11Basic set-up at a cannon-netting siteFIGURE 3.10Launching the cannon-netCannonLauncherIgnition WireCaptureNetBlindBaitCREDIT: ALYN WALSH manual5.indb 4319/03/2008 10:17:59 143 KB – 18 Pages