Improved trapping methods for Loggerhead Shrikes

Improvedtrappingmethodsfor LoggerheadShrikes Alan Kridelbaugh

heLoggerhead Shrike (Lanius ludovicianus) char-

acteristicallyfeeds on large insectsand small mammals(Bent 1950),and bal-chatritrapshave occasionally been used to trap them (Berger and Mueller 1959,Clark 1968,Ward and Martin 1968).I found balchatri traps relatively ineffectivefor capturingshrikes and useda modification of the trap describedby Lohrer (19741.

I used a single-cellwire box trap (20x20x20cm) with 1.2 cm mesh,a drop door on one side, a treadle rather than a singletrip bar, a removablebait compartment, and no floor (Fig. 1). Single-cellsquare traps were more effective than 2-cell rectangulartraps because shrikesspent less time seekingentrance along sides without doors.The tendencyof shrikesto land beside their prey and peck at it, rather than land on top of it, accountsfor greatersuccessof trapswith side doors. Traps with treadlesworked best becausesomebirds hoppedover trip bars; I never had a shrike negotiate a treadle without gettingcaught.I prefer traps without floorsbecausebait is more easilyplacedin them and no cleaning is required. The separate bait compartment preventedshrikesfrom killing the mouse. Kaufman (1973)has shown that shrikes,when given a choice,prefer mice (Mus musculus)of natural color. Lohrer (1974) reported trapping successwith white mice. I successfullyattractedshrikesinto traps using various colored mice, but the best year-aroundbait was a 5-8 g agouti-coloredmouse. In summer, when shrikesfed primarily on insects,someindividualsdid

ler (1959)during a 2-year period had a successrate of 58.7%while trappingAmericanKestrels(Falcosparverius)with bal-chatritraps. The sex ratio of trapped shrikeswas skewed slightly toward males (54%). This skewednessdoes not seem to reflect a difference in responseof the sexes to the trap, but rather a seasonalbias in trappingeffort.Most of my trappingwas done when femaleswere incubating (males do not help with incubationor brooding). At this time males increasedtheir foragingin order to meet food demandsof females and nesfiingsand thuswere more exposedto trapping.

The improvementsto Lohrer'smethodare: (1) no floor (2) treadle vs. trip bar, (3) separatebait compartment, and (4) impaled insectsas bait. I am gratefulto William H. Elder for guidancethroughout this study,to Jim Rathert,MissouriDepartmentof Conservation,who supplied the photograph,and to Sandy Clark for editing.This paper is a contribution from the MissouriCooperativeWildlife ResearchUnit. Financial supportwas providedby the Schoolof Forestry, Fisheriesand Wildlife, University of MissouriColumbia; Edward K. Love Foundation; and Northeast-

ern Bird-Banding Association..•

not respond well to mice as bait. These birds were

caughtwith a largebeetletetheredinsidethe trap with a small-gauge wire pushedthroughits abdomen.Tethered insectsmay also be useful for trapping other birds, such as Mockingbirds,that may be difficult to trap in a net (Lohrer,pers.comm.).

Using the trap described,I trapped 60 Loggerhead Shrikesin centralMissouriduring1980and 1981(Kridelbaugh1982).I calculatedtrappingsuccess by dividing numberof birds caughtby numberof timesthe trap was set. As I made no attemptto excludetimeswhen I believed the bird failed to see the bait or when some

other disturbance(e.g.,a pa•singcar) interferedwith trapping,I mayhave under-estimated, but my trapping success for the 2-yearperiod was 73% -- a high successrate for any trap. For example,Bergerand MuelPage 50

Figure I

North American Bird Bander

Vol. 7, No. 2

LITERATURE

CITED

Kridelbaugh, A.L. 1982.An ecologicalstudyof Logger-

Bent,A.C. 1950.Life historiesof North Americanwagtails, shrikes, vireos, and their allies. U.S. Natl. Mus. Bull. 197.

Berger,D.D., and H.C. Mueller. 1959. The bal-chatri: a trap for birdsof prey. Bird-Banding 30:18-26.

Clark,W.S.1968.Modificationof the bal-chatritrap for shrikes. EBBA News 30:147-149.

Kaufman,D.W. 1973. Shrike prey selection:color or conspicuousness. Auk 90:204-206.

head Shrikes in central Missouri. M.S. thesis, Univ. Missouri, Columbia, MO.

Lohrer,F.E. 1974.Sometechniques usedin a field study of Loggerhead Shrikes.Bird-Banding 45:361-362. Ward, P.F., and D.P. Martin. 1969.An improvedcage trap for birdsof prey. Bird-Banding39:310-313. Schoolof Forestry,Fisheriesand Wildlife,Universityof Missouri, Columbia, MO 65211.

To catcha woodpecker Tom Mutchler

Take I one-ce]ledPottertrap Attachit -- I used1/2"staples-- to a 1/2-1"thickboard twicethe lengthof the bottomof the Pottertrap. Straightenthe release bar and attach to the board. Fastena suetbag of brightlycoloredmesh,i.e. onionor turkey bag, to what is normally the back of the trap (now,the top),suspended fromthe centerof the trapso the suet cannotbe reachedfrom the outside.(A) Attach, to the bottom of the gate, a pull string long enough to reach the point of operation, passingit throughstapleor eyeletguides.(B) Attach board, with the gate side down, to a window side,tree, or whereverthe woodpeckers frequent. This is a selectivetrap. If the bird is banded, one can let it dine. If it is not banded, simply pull the string quickly.It is excellentfor trappingsuet-eating birds. Our traps are mountedbeside a window. We can see the traps from another window. The trap string is pulled througha partially openedwindow. The traps canbe emptiedthroughthe window and resetby hand.

Banding results,first 4 days of operation:9 Downy Woodpeckers,5 Red-breastedNuthatches,and 3 Hairy Woodpeckers -- eventhoughwe had othersuetbagsin the open. RD 1 Box 212X, Monticello, NY 12701

Apr.-- Jun.1982

NorthAmerican BirdBander

Page 51