We would like to thank Bushnell® for their generous donation of six trail cameras at a steeply discounted rate; Clint Epps PhD and Matt Shinderman PhD for their invaluable advice and support; Steve George from Oregon Department of Fish and Wildlife for wildlife take permitting; Hardy Hanson and the City of Bend for providing deer carcasses; Brett Michalski and his donation of personal cameras for initial part of study; High Desert Museum for allowing us to store deer carcasses in deep freeze during summer months; Jeff Cooney PhD for deer carcass donation; Amy Baggett , Nicole Lafey, and Dani Yeager for data collection during initial study.

1. Blázquez, Miguel, J.A. Sánchez-Zapata, F. Botella, M. Carrete, and S. Eguía. 2009. Spatio-temporal segregation of facultative avian scavengers at ungulate carcasses. Acta Oecologica 35: 645–650.

2. Cortes-Avizanda, A., M. Carrete, and J.A. Donazar. 2010. Managing supplementary feeding for avian scavengers: guidelines for optimal design using ecological criteria. Biological Conservation 143: 1707–1715.

3. Goodale, E., G. Beauchamp, R.D. Magrath, J.C. Nieh, and G.D. Ruxton. 2010. Interspecific information transfer influences animal community structure. Trends in Ecology & Evolution 25: 354–361.

4. Seppänen, J.T., J.T. Forsman. 2007. Interspecific social learning: novel preference can be acquired from a competing specie. Current Biology 17: 1248-1252.

5. Sánchez‐Zapataa, J.A., S. Eguíab, M.Blázquez, M. Moleónc, and F. Botellaa. 2009. Unexpected role of ungulate carcasses in the diet of Golden Eagles (Aquila chrysaetos) in Mediterranean mountains. Bird Study 57: 352-360.

JON D. NELSON1*, MATTHEW ORR PHD2, AND EMILY C. WEIDNER3

1OREGON DEPT. OF TRANSPORTATION; 2OREGON STATE UNIVERSITY-CASCADES; 3DEPT. OF FISHERIES AND WILDLIFE, OREGON STATE UNIVERSITY

Heterospecific information transfer within a guild of avian scavengers in Central Oregon

Heterospecific competition for carrion may influence community structure; organisms generally use heterospecifics to avoid predators or to find food (Seppänen et al. 2007).

Dominant species are predicted to exploit subordinate, social species to gain access to resources (Goodale et al. 2010).

Carcasses attract diverse guilds of scavenging species, which offers an opportunity to evaluate the above predictions (Cortes-Avizanda et al. 2010).

HYPOTHESESIn this study, we tested the following hypotheses concerning transfer of information between heterospecifics: H1: Raptors use ravens (Corvus corax) to locate carrion. H2: Raptors benefit ravens by tearing open a carcass and providing

access to meat. H3: Ravens intentionally recruit raptors to open carcasses for them.

Initial analyses suggest the following: H1: While there is a correlation between raptor arrival time and raven

arrival time we did not analyze how other variables might influence the relationship.

H2: There were significant shifts in raven feeding locations after a carcass was opened by raptors. Based on a limited number of carcasses (n=11), chi-square analysis suggests ravens may benefit from the presence of raptors at closed carcasses. Additionally, on baits where carcasses were experimentally opened, ravens were less likely to spend time feeding on extremities of the carcass.

H3: Lag raptor arrival times did not differ between open and closed carcasses , which signifies that ravens may not actively recruit raptors to carrion resources.

ADDITIONAL OBSERVATIONS Eagles were ubiquitous on carcasses from September to April with

majority of utilization occurring in the cold seasons. Carrion is likely underrepresented in dietary analyses of golden eagles and it is possible that carrion, in certain areas, plays an important role in overwinter survival of eagles (Blázquez et al. 2009 & Sánchez‐Zapataa et al. 2009). Further research is needed in order to quantify the importance of carrion in the diets of bald and golden eagles.

BAITS Initial trial baits were five steer heads, where we found raptors arrived shortly after ravens. We then tested H1 - 3 using road-killed mule deer (Odocoileus

hemionus hemionus). Carcasses were placed >150 yards from roads and were separated

spatially by >5 miles and/or temporally by >14 days (Figure 1). Motion-activated Bushnell Trophy Cam® was placed approximately 15

feet from each carcass. Cameras took three photographs per detection with 15 second intervals between subsequent activations.

Some carcasses were experimentally opened to remove the possible incentive to recruit raptors.

PHOTO ANALYSIS For H2, 50 raven feeding locations (head, anus, or muscle/viscera) were

recorded before and after raptor arrival, scan-sampling once per minute.STATISTICS H1: Linear regression for raven vs. raptor arrival times correlation. H2: Chi-square analysis for raven feeding location (anus & head vs.

muscle) before and after raptor arrival. H3: T-test to compare raptor arrival times after ravens at open versus

closed carcasses.

METHODS

INTRODUCTION DISCUSSION

STUDY AREA

ACKNOWLEDGEMENTS

SELECTED REFERENCES

RESULTS

Bait Bait – open/closed ᵡ2 DOF p-value

2 open 7.4 1 0.006425 open 0 1 0.987629 open 0.157 1 0.691631 open 2.819 1 0.093234 open 0.003 1 0.9593J closed 71.9 1 < .00011 closed 46 1 < .000124 closed 61.7 1 < .000119 closed 28.4 1 < .000130 closed 16.7 1 < .000135 closed 12.9 1 0.0003

Figure 1. Each point represents a bait location. There were 45 baits total: 8 cow heads and 37 deer carcasses.

Table 1. Chi-square comparison of feeding location on closed and open carcasses.

Figure 5. Lag time of raptor arrival after raven arrival.

Jan-Apr May-Jun Jul-Aug Sep-Oct Nov-Dec (6) (9) (6) (8) (15)

Figure 2.Seasonal carcass utilization, x-axis represents season with numbers in parentheses denoting number of baits

• Carcass utilization by ravens and raptors tended to overlap and differed from seasonal use by Turkey Vultures (Cathartes aura) (Figure 2).

• In 22 of 24 carcasses (cow or deer), the first raptor arrived at a carcass after ravens, as shown by points above line. Approximately 48% of the variation in raptor arrival time at deer carcasses was explained by raven arrival time (R2 adj. = 0.48; df = 1,17; F = 15.8; P < 0.001) (Figures 3 & 4).

• At four out of five experimentally opened carcasses ravens did not change feeding location before and after raptor arrival. In contrast, at all six closed carcasses ravens changed feeding location (extremities to muscle/viscera) after raptors arrived (Table 1)

• Time required for first raptor to arrive after first raven did not differ between experimentally pre-opened deer carcasses (19.7 + 16.3 hr; median 22.2 hr) and intact deer carcasses (103.7 + 268.4 hr; median 23.5 hr; T = -0.48, df = 16, P = 0.63) (Figure 5).

*Abbreviations for Figures 3 & 4: GOEA – Golden Eagle (Aquila chrysaetos); BAEA – Bald Eagle (Haliaeetus leucocephalus); RTHA – Red-tailed Hawk (Buteo jamaicensis).

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Figure 2. Seasonal distribution for ravens, raptors, and Turkey Vultures.

Figure 3.* Scatterplot of raptor arrival times vs. raven arrival times ; outlier included (932.26, 933.41).

Figure 4.* Scatterplot of raptor arrival times vs. raven arrival times , with one-to-one line; outlier eliminated.

*hour data log transformed to show lag time range with outlier present