Transcript eScholarShare - Drake University

The Effectiveness of Innovative Wildlife Harvest
Tools II: Decoy Colors and Waterfowl Hunter Success
Scott K. Anliker, Luke C. Campillo, and Muir D. Eaton
Drake University, College of Arts and Sciences, Department of Biology
INTRODUCTION
RESULTS AND DISCUSSION
• 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)
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.
A
• Unrelated research has demonstrated that all birds see ultraviolet
wavelengths (Fig. 1; Cuthill et al. 2000), which humans do not see.
• 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).
• 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).
% Reflectance
• Our study: 1. From an avian visual perspective, do these new UVpaint 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?
80
B
60
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).
40
20
0
300
Relative Sensitivity
• 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.
400
500
600
700
Wavelength (nm)
adfadsfa
% Reflectance
45
C
• 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).
30
15
0
300
400
500
600
700
adlkfjlk;adjf (nm)
Wavelength
Wavelength (nm)
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 nonUV decoys, and 20 real ducks from museum specimens (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.
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.
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
UV vs. Real Non-UV vs. Real UV vs. Non-UV
• 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).
• 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.
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
1.2
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.
1
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.
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 265:351-358
4. Wilson, R.E. et al. 2008. Orn. Neotrop. 19:307-314
ACKNOWLEDGMENTS
We 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.
# / hunter hour
• 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.
Head
0.8
0.6
0.4
0.2
0
Ducks harvested
Shots taken
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.