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An Inexpensive Camera Setup for the Study of Egg Predation at Artificial Nests

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An Inexpensive Camera Setup for the Study of Egg Predation at Artificial Nests J. Field Ornithol., 58(3):372-382 AN INEXPENSIVE CAMERA SETUP FOR THE STUDY OF EGG PREDATION AT ARTIFICIAL NESTS JAROSLAVPICMAN Departmentof Biology Universityof Ottawa 30 Somerset E. Ottawa, Ontario KIN 6N5, Canada Abstract.--Nest predationis an important factor reducingreproductive success of many birds.However, few data are availableon the relativerole of different predators.This paper describesan automaticcamera setup that can be usedto studypredation on artificial nests. Becausethe setup is relatively inexpensive,it shouldallow fieldworkersto conductlarge- scaleinvestigations of nest predation and determineits importanceas a selectiveforce in the evolutionof avian reproductivestrategies. MONTAJEDE CAMARASFOTOGRJ, FICAS EN NIDOS ARTIFICIALES, PARA ESTUDIOS DE DEPREDACI•)N DE HUEVOS Sinopsis.--La depredaci6nen nidoses un factor de importanciaen la reducci6ndel •xito reproductivode muchasaves. Sin embargo,hay pocostrabajos que documentenel rol de diferentesdepredadores. Este trabajo describeel montajede una cfimaraautomfitica que puedeser utilizada para estudiarla depredaci6nen nidos artificiales.Debido a que el montaje cs de bajo costo,esto debe permitirle a los investigadores,11evar a cabo amplios estudiossobre el efectode depredadoresy susimplicaciones en la evoluci6nde estrategias reproductivasde aves. Predation is the most important causeof nestingmortality in many birds (e.g., Murphy 1983, Nilsson 1984, Pageet al. 1985, Ricklefs1969) and has played an important role in the evolutionof avian reproductive strategies(e.g., Crook 1964, Lack 1968). Very little work has beendone, however,to identifyindividual nest predators and determinetheir impact on prey.This is presumablybecause predation events are rarely witnessed and there has not been any inexpensivetechnique available that would allow fieldworkersto effectivelystudy this phenomenonon a larger scale. In 1985 I began a large scalestudy of intensity,type, and temporal and spatial patterns of predation on artificial nestsin different habitats. To record the predation at artificial nests, I designedan inexpensive automatic camera setup, describedhere. DESCRIPTION OF THE CAMERA SETUP To avoiddifficulties associated with the useof battery-operatedflashes and to keep the price of the setup minimal, I selectedan inexpensive camera,the KodakInstamatic X-15F (approximately$17 Cdn). Although the camera'soptics and smallerfilm format(126) resultin onlya moderate quality picture, the advantagesof this camera(flip flashesand low cost) justify its use. The setup consistsof four main components:(1) a nest supportwith trigger mechanism,(2) the Kodak Instamatic cameraX-15F attachedto the support, (3) a clock placed on the support near the nest, and (4) 372 Vol.5a, •o. • CameraSetup for Predation Studies [37 3 FIGURE1. The main componentsof the camerasetup; nest support with triggermechanism (a), camerawith support(b), clock(c), and coversprotecting camera, trigger and clock. The brake cable(d) is connectingthe triggermechanism on nestsupport and the camera shutterlever. Details of individual componentsare shownin Figures 2-4. protectivecovers (Fig. 1). In the following descriptionthe capital letters refer to parts shown on Figures 2-4. The nestsupport and the triggermechanism (Fig. 2).--To the top of a 120 cm long stake(40 x 16 ram; A) I attacheda basket(support for the artificial nest),which I madefrom vinyl-coatedfencing wire (G, H). The attachmentwas achievedby pushingthe two endsof the basketthrough the pre-drilledholes (the samediameter as the wires) in the stakeand bendingthe endsof the wires toward the stake(H). The bottomend of the stakeA is pointedso that it couldbe pushedinto the soil.The trigger mechanismconsists of three parts. An L-shapedwire (B) made of piano wire (diameter1.75 mm) with a large loop (diameter20 ram) at oneend for eggsupport, a small hook at the other end that holdspart C in place when the camerais set up, and a small loop (diameter2 mm) approxi- mately 30 mm from the hookend. The part B is attachedto the support stake A through the small loop with a screw (length 10 mm), which functionsas a hinge.Part C is a short(about 35 mm) straightwire (piano 374] J. Picman J.Field Ornithol. Summer 1987 FIGURE2. Nestsupport, parts of thetrigger mechanism and movement of triggerparts followingdepression of the trigger loop which supports an egg. wire, diameter0.75 mm) with a smallloop (diameter2 mm) at oneend. This part is attachedthrough its loop to the stakeA with a smallscrew (length10 mm), whichalso functions as a hinge,allowing it to rotate freelyaround the screw. The thirdpart is an approximately120 cm long bicyclebrake cable (D). The nestend of the cableis placedin a notch (110 mm long,6 mm wide,4 mm deep;E) madein the stakeA. To hold the cable,a 50 mm longmending plate (F) is attachedto the stake.The vol.58, No. • CameraSetup for Predation Studies [375 116 J • •Jl M FIGURE5. Details of the camerasupport and the attachmentof the brake cable to the camera shutter lever, the top view of the camera base (J) indicatingdimensions and positionof the notchfor the flip flash,and the detail of the cameraend of the brake cable(O) with the compressionspring (M) installed. 376] J. Picman J.Field Ornithol. Summer 1987 brake line at the nest end of the cableis cut off and a small loop is made by twisting the steel wires together.The wire C is then placedthrough this loop.A screwW (length 15 mm) is screwedabout two thirds of the way into the stakeA abovethe top of the mendingplate F (Fig. 2). The function of this screw is to restrict the movement of wire C, therefore preventingit from escapingfrom the brake line loop. The movementof the trigger parts B, C, and D, following the depressionof the loop end of the part B in which the egg is placed,is shownin Figure 2. The camerasupport (Fig. 3) .--The camerasupport consists of two main components,a brake cableattachment and a camerasupport. The camera end of the brake cable is not altered with the exceptionof the addition of the compressionspring (M). The springis constantlyexerting pressure on the cylindricalend of the brake line, pulling it out of the cable(this end of the brake line setsoff the camera).This spring createsconstant downwardpressure on the trigger bar C (Fig. 2) at the nest end of the brake cable. I found it necessaryto glue a small (5 mm diameter and length) plasticcylinder to the shutterlever of the camera.This cylinder housesthe end of the brake line, therebypreventing it from slippingaway from the shutter lever when the trigger is depressed. The woodencamera base (J) is attachedwith two screws(length 40 mm) to the stake P (40 x 16 mm, but 20 cm longer than the supportA in Fig. 2, so that the picture is taken from slightly above). The joint betweenthe two parts (J and P) is further strengthenedby gluing these partstogether with Epoxyglue. The baseJ hasa notchfor the flip flash (seeFig. 5 for dimensionsand positionof this notch on the base). The camera, in an upside down position, is placed on a camera base and attached with several elastic bands. The camera end of the brake cable (O) is then placedin the notch 4 mm deep in the camerabase (Fig. 3) and positionedby tighteningthe wing nut (S) on bolt R (length 60 mm, diameter4 mm), which pressesthe washer (Q) againstthe brake cable. When the brake cable is in the right position,the metal cylinder at the end of the brake line must be pressingagainst the shutter lever of the camera. The clockattachment ('Fig. 4).--To recordthe time of the predation event,I useda battery-operatedclock (Brown AG; Type 4750/AB 3) to which I added an AM/PM indicator (X). This indicator is a thin (1 mm), light disk (Y) cut out of plasticgardening labels, with a small hole (diameterI mm) drilled in its centerand is turned by the passageof the hour hand. The length of the hour hand determinesthe positionand the size of the disk (i.e., the centerof the AM/PM indicator must be located abovethe end of the hour hand). If the hour hand is too long and does not leave enoughspace for the disk, it has to be shortenedslightly. To oneside of the disk I gluedfour dividers(cut out of the gardeninglabels) subdividingthe disk area into four equal fields(Z in Fig. 4). The height of these plastic dividers is determinedby the distanceof the hour and minute handsfrom the faceof the clock(i.e., the dividersshould be slightly higher than the distanceof the hour hand from the face of the clock,but Vol. 58, No. 3 CameraSetup for PredationStudies [377 --y FIGU•.E 4. The clock attachment and the detail of the AM/PM indicator. lower than the distanceof the minute hand from the clock).Two opposite 90ø fields are painted black and the other two white. The disk is then hinged through the hole in the center of the disk to the top part of the clockwith a small nail (diameter 1 mm, length 10 mm, but any excess length that would interfere with the mechanisminside the clockmust be cut off). The AM/PM indicatorhas to be positionedas closeas possible 378] J. Picman J.Field Ornithol. Summer 1987 to the face of the clockbut must be allowed to rotate freely around the nail. The nail is then glued in positionfrom inside the clockwith Instant Krazy Glue ©. Becauseonly the hour hand canrotate the disk,the indicator is rotated every 12 hours by 90ø and the position of the white and black fieldscan be usedto determineAM/PM from the picturesof predation events.The clockis positionedabout 30-40 cm asidefrom the nest. This placementis less likely to result in predatorsstanding in front of the clock. The clock T is attachedwith two elastic bands to the clock support baseU which is hingedthrough the stakeV to the nestsupport A. Hinging the clockattachment to the nestsupport allows collapsingthe clockto the nestsupport stake, making transportationof the setupless awkward. The screwW (length 20 mm), which is screwedabout two thirds of the way into the stakeA, fixes the supportingstake V in a selectedposition.
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