RESULTS AND DISCUSSION

Harvest Data• The total number of ducks harvested were 105 and 78, and the total number of shots taken were 403 and 265 using UV decoys and non-UV decoys, respectively.

• However, there were no significant differences in number of ducks harvested per hunter hour (p=0.34) nor shots taken per hunter hour (p=0.49) given the combined data across all three years (Fig. 4).

• While other decoy technologies substantially impact wildlife harvest rates (Ackerman et al 2006), our data do not show significant increases in harvest rates of waterfowl.

Color Comparisons• Reflectance data of decoy colors shows obvious differences between UV-paint and non-UV paint, with the former reflecting more ultraviolet light, and obvious differences between both paints and real duck plumage (Fig. 2).

• Visual modeling of color discrimination indicates that both UV and non-UV decoy colors are equally different to a waterfowl visual system compared to real duck plumage colors (Table 1).

• Given that analyses of color discrimination from the perspective of waterfowl visual capabilities indicate that UV and non-UV decoy colors are essentially visually identical to ducks, this provides a potential reasonable explanation for the lack of significant differences in hunter harvest data.

The Effectiveness of Innovative Wildlife Harvest Tools II: Decoy Colors and Waterfowl Hunter Success

INTRODUCTION

• For centuries, decoys have been used to harvest wildlife, and recent technological advances have resulted in more effective waterfowl hunting decoys, such as spinning-wing decoys (Ackerman et al. 2006)

• Unrelated research has demonstrated that all birds see ultraviolet wavelengths (Fig. 1; Cuthill et al. 2000), which humans do not see.

• Recognition of visual differences between birds and humans has led to development of waterfowl decoy paint colors that aim to resemble duck feather colors as birds would see them, through the inclusion of UV-reflectance (see Fig. 2).

• Our study: 1. From an avian visual perspective, do these new UV-paint colors more closely resemble real duck plumage colors compared to traditional, non-UV paints? 2. Does use of decoys with UV-paint colors result in higher harvest rates of waterfowl?

Scott K. Anliker, Luke C. Campillo, and Muir D. EatonDrake University, College of Arts and Sciences, Department of Biology

Figure 1. Spectral sensitivity functions for the different single cone cells found in the retina of waterfowl (top) and humans (bottom). Note the VS cone of birds is sensitive to UV wavelengths (300-400nm), while human vision is restricted to wavelengths above 400nm (adapted from Cuthill et al. 2000).

METHODS

Color Comparisons• Reflectance data of drake Mallards (Anas platyrhynchos) was collected from the head, neck ring, speculum border, speculum, tertial, flank, rump, and outer tail regions on 24 UV decoys, 24 non-UV decoys, and 20 real ducks from museum specimens (Fig. 2).

• We calculated the linear distance between two colors in avian perceptual color space (ΔS) using the Vorobyev-Osorio (1998) color discrimination model. Model parameters include spectral sensitivity functions for single cone cells (Fig. 1), noise-to-signal ratios of single cone cells given their relative abundances, and reflectance data of colors to be compared. For detailed calculations, see Wilson et al. 2008.

• By definition threshold for color discrimination is ΔS=1jnd (just noticeable difference), where two colors are barely distinguishable under ideal viewing conditions. ΔS from 1 to 3 represent color differences that are difficult to distinguish, and ΔS>3 represent easily distinguishable colors (Table 1).

Harvest Data•Volunteer hunters were solicited to participate in data collection to assess the effectiveness of UV decoys. All hunting day trials took place at the Chichaqua Bottoms Greenbelt Controlled Waterfowl Hunting area, Polk Co., IA (Fig. 3). This area consists of 13 permanent hunting blinds in fixed locations on an approximately 120- acre hunting marsh.

• On a given hunting day, volunteer hunting groups were given either four dozen UV decoys or four dozen non-UV decoys, and these were used for hunting from sunrise to 1pm at one of the 13 permanent hunting blinds.

• Hunters recorded shots taken, hours hunted, and ducks harvested. All duck species were included in total ducks harvested. We calculated shots per duck hunter hour and ducks harvested per duck hunter hour for each hunting trial. Data was pooled from 106 total hunting trials across the 2008, 2009, and 2010 Iowa waterfowl hunting seasons for decoy treatment comparisons (Fig. 4).

• Using a student’s t-test, we tested for differences between UV and non-UV decoy ducks harvested, ducks harvested per hunter hour, shots taken, and shots taken per hunter hour.

Figure 2. Example decoys used in field trials (A), and reflectance data from the white tail (B) and grey body (C) colors. Note that the two decoys are visually identical to humans (A), although, one is painted with UV-colors while the other is painted with traditional non-UV colors. Comparing reflectance data of the UV-paints, non-UV paints, and real duck plumage reveals the differences in UV reflectance for both the white tail colors (B) and the grey body colors (C). Given Figure 1, these differences in UV reflectance should result in different colors seen by the ducks (see Table 1). Diamonds represent non-UV decoys, X’s UV decoys, and triangles real mallard plumage.

LITERATURE CITED:1. Ackerman, J.T. et al. 2006. J. of Wildlife Management. 70:799-804 2. Cuthill, I.C. et al. 2000. Advan. Study Behav. 29:159-215.3. Vorobyev, M. and D. Osorio. 1998. Proc. R. Soc. Lond. B 265:351-3584. Wilson, R.E. et al. 2008. Orn. Neotrop. 19:307-314

ACKNOWLEDGMENTSWe thank Doug Sheeley for permission to collect data on the controlled hunting marsh at Chichaqua Bottoms Greenbelt, and for use of facilities for storage of equipment; all volunteer hunters that participated in data collection; Flambeau Outdoors, Inc. for an equipment grant to support this research, and Drake University for financial support.

Figure 3. Photos from Chichaqua Bottoms Greenbelt study site. Top shows typical placement of decoys for a given trial day. Bottom shows typical permanent blind used for hunting trials.

Figure 4. Hunter success, as measured through average ducks harvested per hunter hour and shots taken per hunter hour. Data compiled for 2008, 2009, and 2010 hunting seasons, with error bars representing 95% CI. Black bars represent UV decoy use; white bars represent non-UV decoy use.

A

0

20

40

60

80

300 400 500 600 700

0

15

30

45

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Wavelength (nm)

Wavelength (nm)

% R

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Ref

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C

B

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0.4

0.6

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1

1.2

Ducks harvested Shots taken

# / h

un

ter

ho

ur

Wavelength (nm)

  UV vs. Real Non-UV vs. Real UV vs. Non-UV

Head 9.46 9.21 0.52

Neck ring 3.59 3.43 0.66

Speculum Edge 3.37 1.96 2.00

Speculum 4.89 4.51 0.48

Tertials 1.42 1.83 0.78

Flanks 4.48 3.48 1.54

Rump 2.87 3.58 1.33

Outer tail 3.56 2.34 1.83

Table 1. Color discrimination (ΔS) values using the Vorobyev-Osorio (1998) model comparing colors from UV decoys, non-UV decoys, and real duck plumage. From an avian visual perspective, ΔS=1 represents threshold for color discrimination, ΔS from 1 to 3 represent difficult to distinguish color differences, and ΔS>3 represent easily distinguishable colors

Rel

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• Waterfowl visual modeling also indicates that UV and non-UV decoy colors are either not distinguishable as different, or are very difficult to distinguish as different, from each other (Table 1).