*3.3. Insect Scavenging Experiments*

Although in most cases the covered carcasses started to decay later than uncovered carcasses (*n* = 5 in each treatment), the difference between median dates of decay initiation of covered versus uncovered carcasses (6.27 vs. 4.27; ns) was not significant. Both the inflection point (8.41 vs. 5.41; *p* = 0.015) and day of flattening out of the decay curve (11.11 vs. 6.41; *p* = 0.0079) occurred significantly later for covered carcasses (Table 2, Figure 3), implying that covering slowed invertebrate consumption/decomposition.

**Table 2.** Values obtained by fitting a four-parameter Weibull model by non-linear regression to the consecutive weigh of the roe deer carcasses deployed to simulate lynx kills (NC: not covered; C: covered). In parentheses, it is reported the initial weight of the not covered/covered carcasses/carcass parts. Day of start of decay = minimum value of the second order derivate, inflection point = minimum value of the first order derivate and day of flattening out of the decay curve = maximum value of the second order derivate.


**Figure 3.** Daily weight variation (kg) and fitted Weibull curves describing the decay process of (**a**) five covered, and (**b**) five uncovered paired roe deer carcass or parts placed in a metal cage to exclude vertebrate scavengers during summer in South-Eastern Norway. The line in black in (**a**,**b**) are whole carcasses; the other lines are parts.

## **4. Discussion**

This study provides clear evidence that the simple act of covering a kill with vegetation or snow delays scavenger arrival and the rate of meat loss. The lynx-killed roe deer that were uncovered were three times more likely to have been found by scavengers than the kills that were covered. Covering the video-monitored experimental carcasses delayed their discovery by avian scavengers by 4–5 days. Covering the carcass parts delayed the rate of consumption by invertebrates by more than five days, although this result should be taken with caution due to the limited sample size for the insect experiment. This implies that covering a carcass constitutes a very effective cache protection measure [13,31] for a large felid preying on ungulates in forested habitats. Our results are consistent with a similar study on mountain lion caching behavior in Arizona, which showed that simulated caching reduced wastage during dry and hot periods [21].

Although most of the lynx-killed roe deer carcasses were from the winter, and only ca. 10% were from the summer, it is likely that caching behavior is similar in the two seasons. In the summer, there is no snow to cover kills with, so lynx can only use vegetation, and there is more competition with invertebrate scavengers, making covering more important (see experiment). However, in the summer there are also more leaves on trees and bushes making visual detection by avian scavengers harder. In the summer, the olfactory cues due to insect and microorganism activity might also increase the probability of a carcass being discovered. These aspects are not likely to affect the overall relative utility of covering kills vs. leaving them uncovered.

Although other authors have described this tendency of large felids to cover their cached kills with vegetation e.g., [5,13,21], this is the first study to actually test the anti-scavenger efficacy of this measure in the field, using both observational data from documented lynx kills and experimental approaches. Combined, these studies are revealing insights into the subtle ways that predator behavior responds to the potential for food loss from both vertebrate and invertebrate scavengers [11].

The results from the video-monitoring suggest that covering was efficient for deterring avian, but not mammal, scavengers. This indicates that the effect is mainly through visual occlusion, rather than by reducing the olfactory signal of the kills. The effect on invertebrate activity is probably through a process of physically obstructing invertebrate access to the kill, although the covering may also shade the kill and reduce decomposition speed by reducing the temperature. In a similar study conducted in the Bavarian forest in summer, roe deer carcasses simulating lynx kills (covered by vegetation) were completely consumed within 10 days, mostly by invertebrates [13].

Although the main focus of our study was to test the efficacy of caching, it is interesting to note that considerable periods of time, measured in days, went by before scavengers detected the kills. In contrast, studies on cheetahs in savannah ecosystems have shown that scavengers find kills within hours of death [20]. The effect is that many cheetah kills are either lost to kleptoparasites or are so rapidly consumed by scavengers that cheetahs are not able to consume more than one meal per kill. The lynxes in our study area, by comparison, were usually able to completely consume most of the meat on their kills over several days. This allows them to continue being roe deer specialists even when roe deer occur at low density [31], because even though there may be considerable search time expended in finding a prey, once killed it can provide food for many days. In turn, this can help explain why lynx presence has such a clear impact on low-density roe deer populations [32,33]. This efficient use of prey also implies that the energy budget of lynx should be considerably buffered against changes in prey density. The results also provide insight into the ways in which studying predator–prey dynamics needs to consider wider ecosystem processes.

At the time of our study, the area lacked the large scavengers such as wolverine (*Gulo gulo*), brown bear (*Ursus arctos*), wolf (*Canis lupus*) and wild boar (*Sus scrofa*), which could potentially drive a lynx off its kill and appropriate the kill in a single act. However, a study conducted in Sweden found no evidence of kleptoparasitism by wolves on roe deer killed by lynx [34]. The largest scavengers we documented were humans who regularly removed lynx kills [35], not an uncommon practice on a global scale [36]. It is hard to know how the absence of these natural members of the mammalian scavenger guild influences the generality of our results. A study conducted in Slovenia and Croatia found that brown bears were able to discover 32% of lynx prey remains, and 15% of all biomass of large prey killed by lynx was lost to bears [37]. Since this study was conducted, wolves and wild boar have colonized the landscape, opening for future comparative studies. However, the situation does reflect the current reality for lynx throughout much of its present day distribution in Europe [38,39], and the literature does tend to place greatest emphasis on the role of avian scavengers [16,40] for which our results indicate that the anti-scavenging behavior had the greatest effect.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/1424-2818/12/9/350/s1, Table S1: Data from 79 lynx-killed roe deer inspected after the kill was made (South-Eastern Norway, 1995–2008). Table S2: Data from 26 experimentally-deployed whole roe deer carcasses (obtained as roadkill, South-Eastern Norway 2002–2003), used as simulated lynx kills for seven days using time-lapse video equipment. Table S3: Data from two whole roe deer and eight roe deer body parts (placed in iron mesh cages (size 1 × 1 × 0.5 m, mesh diameter 2.5 cm) in forest habitat during summer (South-Eastern Norway, 2003) to explore the rate of weight loss by invertebrate scavenging and decomposition.

**Author Contributions:** Conceptualization, J.D.C.L. and I.J.M.T.; methodology, J.D.C.L., C.M., J.O. and I.J.M.T.; formal analysis, C.M., J.O. and I.J.M.T.; writing—original draft preparation, J.D.C.L., C.M., J.O. and I.J.M.T.; writing—review and editing, C.M., J.D.C.L., J.O. and I.J.M.T.; funding acquisition, J.D.C.L., J.O. and I.J.M.T. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study is part of the SCANDLYNX project, and is funded by the Norwegian Environment Agency, the Research Council of Norway (two individual travel scholarships to IJM Teurlings and projects 134242, 165814, 183176, 212919, 251112), the county governor's office of Viken county, the Norwegian University for Science and Technology, and the Schure-Beijerinck-Popping Fund.

**Acknowledgments:** We would like to thank Ivar Herfindal for his statistical advice, Alan Bryan, Jan van Mil and all the other people who helped with the fieldwork.

**Conflicts of Interest:** The authors declare no conflict of interest.
