Capturing Adult American Author(s): Gary Huschle, John E. Toepfer, Wayne L. Brininger, Jr. and David A. Azure Reviewed work(s): Source: Waterbirds: The International Journal of Waterbird Biology, Vol. 25, No. 4 (Dec., 2002), pp. 505-508 Published by: Waterbird Society Stable URL: http://www.jstor.org/stable/1522538 . Accessed: 12/03/2013 17:59

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This content downloaded on Tue, 12 Mar 2013 17:59:46 PM All use subject to JSTOR Terms and Conditions CapturingAdult American Bitterns

GARYHUSCHLE', JOHN E. TOEPFER2,WAYNE L. BRININGER,JR.3'5 AND DAVID A. AZURE4'6

'Agassiz National Wildlife Refuge, 22996 290th Street N.E., Middle River, MN 56737, USA Internet: [email protected]

2Society of Tympanuchus Cupido Pinnatus Ltd., Stone Ridge Suite 280, N14 W23777 Stone Ridge Drive Waukesha WI 53188, USA

3Department of Biological Sciences, Saint Cloud State University, St. Cloud, MN 56301, USA

4Department of Biology, University of North Dakota, P.O. Box 9019, Grand Forks, ND 58201, USA

5Present address: Rice Lake National Wildlife Refuge, Route 2 Box 67, McGregor, MN 55760, USA

6Present address: Kulm Wetland Management District, P.O. Box E, Kulm, ND 58456, USA

Abstract.-Capture techniques were developed to study the American ( lentiginosus). Mirror traps, mist nets, landing nets, night capture, funnel traps and net gun techniques were evaluated. Mirror traps and mist nets were used with a tape recording of the pumping call of the male bittern. Mist nets were also used to capture females at nest sites. Long-handled landing nets were used to capture molting and females on nests. Fun- nel traps were set at feeding sites. Mirror traps had a 50% success rate and were the most efficient means of captur- ing males. Mist nets were versatile with success rates of 40% on males and 50% on females. Landing net success was 76% on males and 70% on females but restricted to specific situations. Night capture was successful 33% of the time and only on molting birds. Net guns had limited success (6%) due to lack of skill and difficult to get close to birds. Funnel traps were not fully tested. Received1 February2002, accepted15June 2002. Key words.-American Bittern, Botauruslentiginosus, funnel trap, mirror trap, mist net, net gun, night capture, trapping. Waterbirds 25(4): 505-508, 2002

A study to examine the life history of the flection (Tanner and Bowers 1948; Gullion 1965). Mir- ror have also been used on waterfowl known for American Bittern (Botaurus was traps lentiginosus) aggressive behavior during the breeding season (Savard initiated at Agassiz National Wildlife Refuge 1985). Recordings of the territorial vocalization of male in northwestern Minnesota in 1994. We American Bitterns were used to bring adult male bit- wanted to American Bitterns for ra- terns to the traps and trails were used to orient them capture with the mirror. Mirror traps were constructed of 5 cm dio-marking to study home range, habitat x 10 cm mesh welded wire, 91 cm long, 40 cm wide by use, and breeding ground fidelity. American 61 cm high (Fig. 1). A single sliding door, measuring 25 Bitterns at National Wildlife cm x 40 cm, was released by a stiff 9-gauge wire connect- Agassiz Refuge ed to a treadle 35 cm inside the trap. A mirror, 30 cm x utilize grasslands, shallow marsh and deep 40 cm, was fastened to the opposite end of the trap. marsh habitats (Brininger 1996; Azure Mirror traps were deployed between dawn, and two to three hours after sunrise a 1998). This describes the use of mir- by approaching vocalizing paper male bittern to within 100 m in a shallow marsh setting. ror traps, mist nets, landing nets, night cap- Traps were set in water depths from zero to 15 cm. In ture, funnel traps and net gun techniques the first year, most traps were placed individually, but af- terwards were set in When set in developed to meet the field situations en- they pairs. pairs, traps were back to back in either existing trails or short trails countered and evaluates capture success made by stepping down vegetation for 3 m in length and from 1994 through 1998. 40 cm wide. When set individually, the back of the trap was placed against a clump of vegetation to discourage an approach from the rear. Vegetation was draped METHODS against the trap sides to prevent males from approach- ing from the side. A battery operated cassette tape play- er was to the of the and an Mirror Trap strapped top trap played endless loop cassette on which was recorded a sequence Mirror traps have been used to capture drumming of a male bittern vocalizing four times. The sequence Ruffed Grouse (Bonasa umbellus)because male grouse was repeated at one-minute intervals at the maximum return repeatedly to the same spot and traps could be volume that did not distort the sound. Traps were left placed where the would be oriented to see its re- unattended for up to four hours. Flagging tied to the

505

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small piece of black tape on vegetation directly above the nest to aid in placing the landing net over the nest. 40 cm 91 cm Night Capture To recapture radio-marked birds at night, hand Mirror held, 100,000 candlepower spotlights were used while 40 x 30 on the airboat. When walking spotlights were attached cm to a helmet and powered by a battery placed in a plastic 1 food cooler mounted on a similar to that used 61 cm backpack by Drewien et al. (1967). Birds that flushed prematurely Wiremesh from the approach of the airboat were picked up in the size beam in an attempt to confuse them and force them to 5x 10cm land. Most capture attempts were made by two people, Treadle Vertical approaching the bittern's approximate location on Sliding door mesh size 2.5 x 5 cm foot. A net was used to 40 x 25 cm 35 cm landing capture birds once they were located visually.

Figure1. Mirrortrap used to captureadult male Ameri- Net Gun can Bittern.A recordingof a male bitternvocalizing on a continuousloop cassettewas playedin a cassettetape Two styles of net gun were tested. One gun was man- playerplaced on top of the trapto attractmale bittern to ufactured by Coda Enterprises, Mesa, Arizona and shot the set. A trailin frontof the door wasused to orientthe a square net with 3.3 m sides. The other gun, made by male bittern with the mirror.Drawing by Ell-KayFoss, Northern Prairie Science Center, Jamestown, North Da- Wildlife Technician,Red Lake Wildlife Management kota (Mechlin and Shaiffer 1980), shot a triangular net Area,Minnesota Department of NaturalResources. with three-m sides. Most net gun attempts were made on birds feeding in roadside ditches. Some attempts were made from the airboat at birds that did not flush imme- diately. Another technique involved a person crawling top of the door aided in determiningdoor closure.Use toward a vocalizing male bittern while carrying the net of binocularsincreased the distancerequired to check gun and a tape recorder and intermittently playing the trapsto avoidflushing uncaptured birds prematurely. recording of a vocalizing male bittern. The person and the bittern would approach each other and when the MistNets distance closed to less than ten m, the person would rise and shoot the net at the flushing bittern. Vocalizingmale bitternswere approachedto within 100 m bywading out from the shore or via airboatto set Funnel Traps mist nets. Three mist nets, 12 m long witha mesh size of 125 mm, were set in a "U"-shapeconfiguration with the Funnel traps (Toepfer et al. 1988; Schroeder and open side of the "U"toward the bittern.Nets werehung Braun 1991) were made of 2.5 cm x 5 cm mesh welded on two three-mtelescoping lengths of galvanizedcon- wire with two drift fences of poultry wire approximately duit (one 1.27cm diameterinside of a 1.90 cm diameter 10 m long. The drift fences were placed in a "V"-shape conduit) at each end of the net. The net top was about along the edge of ditches where birds were consistently 3.5 m high and the net bottomwas at vegetationlevel. A feeding. The open ends of the drift fence "V" were cassettetape playerwith the same recordingpreviously placed near the edge of the water. The funnel trap was describedwas placed approximatelytwo m in front of set at the pointed end of the "V"in vegetation about five the net. Aftersetting the net, observersmoved approxi- m from the water. Observers visited the trap frequently mately 100 m to the side. Malebitterns usually made a and when a bittern was between the poultry wire leads, low level flight to within20 m of the net or flew directly it was gradually disturbed so it would walk into the trap into the net. Observersapproached from behind the without flushing. When not being tended, the trap was bitternand flush the bird towardthe nets. lifted so could escape under it. To capturefemales returning to feed nestlings,four mist nets were set in a squaresurrounding the nest. Af- ter setting the nets, observersmoved back 100 m and RESULTS waitedfor the female to land and to have had time to walk under the nets into the square. Observersap- Mirror proachedthe nets on an airboator on foot from oppo- Trap site sides, flushingthe female into the nets. Mirror traps had a 50% success rate (Ta- LandingNets ble 1) for capturing adult male American Bitterns and were most efficient because Long-handledfish landingnets were used to capture flightlessor poor flying bitternsduring the wing molt they did not require continuous observation. that were encountered in the marshwith the airboat. Success was improved by moving traps closer The net hoop was80 cm in diameterwith a telescoping handle that extended to 2.8 m. Net mesh was 50 mm. to the bittern if they failed to approach the The landing net was also used to capture females on trap. Two or three moves were sometimes nests. Nests were markedon a prior visit by placing a made before capturing the male or the at-

This content downloaded on Tue, 12 Mar 2013 17:59:46 PM All use subject to JSTOR Terms and Conditions CAPTURINGAMERICAN BITTERNS 507

Table 1. Trapping results for American Bitterns 1994- Most bittern females that were incubat- 1998. ing stayed on the nest and were captured Number 70% of the time. After the eggs hatched, suc- Method of attempts % success cess decreased as nestlings grew older and moved away from the nest. Mirror trap 127 50 Mist net-males 15 40 Mist net-nests 24 50 Night Capture Landing net-molt 29 76 Landing net-nests 23 70 Night capture attempts on birds that Night capture 15 33 were molting were successful, but attempts Net gun 47 6 to birds not in the molt were Funnel 7 29 capture wing traps unsuccessful and lowered the success rate to 33%. Birds whose flight was not impaired by tempt terminated. No mortality occurred molting became increasingly wary and flush- while birds were in traps. Scraping or other ing distance increased from less than ten m injury was infrequent and minor. After the to over 50 m with subsequent approaches. first year, one to three males were recaptured Only one female in partial molt stopped fly- each year with mirror traps. Recapturing ing when shined with the spotlight. birds during the same breeding season was avoided but it did occur on several occasions. Net Gun

Mist Nets The three birds captured were shot at from an airboat while they were still on the Mist nets were successful in 40% of the at- ground. On three other occasions, birds tempts to capture males (Table 1) and was were hit with the net but escaped before they the most versatile technique because of its could be secured. One captured bird was eu- success in shallow and deep marsh situations. thanized due to a broken wing inflicted by a Unsuccessful attempts were due to bitterns net weight. flushing prior to complete set up, not ap- close to the net, proaching enough flying past Funnel Traps the net, walking under the net before flush- ing, escaping the net before we could reach Funnel traps were only used during 1997 the bird, or not responding to the tape re- and 1998. Both of the birds captured were fe- cording. This technique was also successful in males. It was an opportunistic method that had recapturing males from prior years. to be used immediately when a bird consis- Capture attempts on females at nest sites tently feeding in the same spot was located. were 50% successful. DISCUSSION Landing Nets Mirror traps were the most efficient The success rate of 76% (Table 1) for method for capturing adult males. They pro- capture attempts of molting birds does not vided the opportunity to make multiple include birds flushed that exhibited a strong catches per morning because they did not re- flight and were not pursued. Most molting quire continuous observation and several bitterns were encountered in large areas of sets could be made. Mirror traps were peri- Cattail (Typha sp.) away from shorelines odically checked as long as males were re- while conducting other activities with the air- sponding to the tape, which was usually boat or on trips made expressly for this pur- around midday. Male bitterns also vocalize in pose. After a capture attempt, additional the evening and a few mirror trap sets were searching in the area was often successful in made during evening hours. Since 1998, sev- locating additional bitterns. eral birds have been captured during the

This content downloaded on Tue, 12 Mar 2013 17:59:46 PM All use subject to JSTOR Terms and Conditions 508 WATERBIRDS evening. Water depth was not recorded for forehand and required getting close to the each trap set but we believe that mirror traps bird. Even with our limited use of this tech- were most successful when placed in five to nique we encountered one bird injury. Inju- ten cm of water with heavy vegetation along ries to birds have been reported by other each side of the trail. In deeper water, prob- researchers using this method (Mechlin and lems were encountered in keeping the trap Shaiffer 1980). solidly elevated to allow entry. Mirror traps We have not fully explored the applica- were successful only during the breeding tion of funnel traps. They provided opportu- season. Males were captured from 1 May to nities to capture females prior to incubation, 18 June but the peak activity occurred dur- which has been a shortcoming of other ing late May.The large mesh wire was instru- methods employed. mental to the success of the traps and for One of con- minimizing injury. pair traps ACKNOWLEDGMENTS structed of 1.2 cm x 2.5 cm mesh failed to catch bitterns. We believe these any traps The authors are grateful to the staff at Agassiz Na- were too closed in for the bitterns to feel tional Wildlife Refuge for logistical support that kept us comfortable in the field. U.S. Fish and Wildlife Service, Division of entering. Birds and Division of The of the mist nets allowed us Migratory Refuges partially fund- versatility ed the project. Saint Cloud State University and Univer- to capture males in deep water, males that sity of North Dakota respectively supported Wayne would not enter a mirror and females at Brininger and Dave Azure while obtaining Master trap as of this work. of nest sites. The mesh size of the nets allowed Degrees part Society Tympanuchus Cupido Pinnatus Ltd. contributed funding and support. several birds to escape without becoming en- We modified one net out tangled. by cutting LITERATURECITED every other string to double the mesh size, and the birds that were in it entan- captured Azure, D. A. 1998. Aspects of American Bittern ecology gled in the netting better than the other in Northwest Minnesota. Unpublished M.S. Thesis, nets. Success with mist nets was limited to University of North Dakota, Grand Forks. W. 1996. The of the calm mornings for two reasons. Brininger, L., Jr. ecology American presumably Bittern in Northwest Minnesota. Unpublished M.S. Wind movement of the nets may have alert- Thesis, Saint Cloud State University, St. Cloud, MN. ed the bitterns to the nets presence or the Drewien, R. C., H. M. Reeves, P. F. Springer and T. L. Kuck. 1967. unit for waterfowl bitterns may not have heard the Back-pack capturing recording and upland game by night capture.Journal of Wild- due to the distance at which the nets were set life Management 31: 778-783. from the bittern. Gullion, G. W. 1965. Improvements in methods for trap- We did not detect abandonment of ping and marking ruffed grouse.Journal of Wildlife any Management 29:109-116. territories due to the playing of the vocaliza- Mechlin, L. M. and C. W. Shaiffer. 1980. Net-firing gun tion call in male territories even on birds for capturing breeding waterfowl. Journal of Wild- that were difficult to and had life Management 44: 895-896. capture traps L. 1985. Use of a mirror to ter- set near them on several Savard,J.-P. trap capture consecutive days. ritorial waterfowl. Journal of Field Ornithology 56: After radio-marking and releasing males near 177-178. the site were located teleme- Schroeder, M. A. and C. E. Braun. 1991. Walk-in traps capture they by for chickens on leks. of in capturing prairie Journal try the immediate vicinity of the capture Field Ornithology 62:378-385. site on subsequent days and many were also Tanner, W. D. and G. L. Bowers. 1948. A method for male ruffed of Wildlife vocalizing. We did not record nest aban- trapping grouse. Journal any Management 12: 330-331. donment due to capturing and radio-mark- Toepfer,J. E.,J. A. Newell andJ. Monarch. 1988. A meth- ing the females. od for trapping prairie grouse hens on display 21-31 in Prairie chickens on the Net guns may be a good technique for re- grounds. Pages Sheyenne National Grasslands (A. P. Bjugstad, Ed.). searchers skilled in its use. This technique United States Department of Agriculture, Forest Ser- was time consuming, required practice be- vice General Technical Report RM-159.

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