Download Appendix S1. Characteristics of ungulate carcasses.

Appendix S1. Characteristics of ungulate carcasses.
We detected 1333 carcasses through our monitoring techniques. We identified the species of
most carcasses from the skull or hair. We conducted necropsies on as many carcasses as
logistical constraints would permit. In total, we necropsied 895 ungulates that died during winter
and 310 that died during spring or summer. We did not distinguish the two species of deer (mule
and white-tailed) on which wolves fed, although few white-tailed deer are present within our
study area. For many of the smaller carcasses detected during spring and summer (n = 67), we
were unable to identify the species from the skull or hair. These carcasses were identified by
analysis of mitochondrial DNA from tissue and/or bone fragments (Wildlife Genetics
International, Nelson, BC, Canada). In total, we determined the species for 1312 of 1333
carcasses detected through our monitoring techniques.
For small ungulates detected during spring and summer (e.g., adult deer and neonate
ungulates between 0 and 3 months of age), we assumed wolves had killed the prey unless
specific evidence suggested otherwise (e.g., when a carcass had been cached by a cougar). For
all other ungulate carcasses, we judged whether wolves had killed or scavenged the prey on the
basis of field sign, such as presence of blood, disturbance of vegetation, extent of disarticulation,
or evidence of cougar predation (e.g., presence of cougar tracks).
We judged the age class of each ungulate on the basis of size and tooth eruption patterns.
Because the birthing period for elk spans from mid-May to mid-June (Barber-Meyer, Mech &
White 2008), ungulates that would properly be described as calves (i.e., < 12 months) during
spring and summer include both very young animals (i.e., a few weeks old) and animals that are
just a few weeks shy of being 12 months. Therefore, we classified each ungulate as a neonate
calf (0-3 months), calf (4-14 months), yearling (15-26 months), or adult (≥ 27 months). For adult
prey, we determined sex through characteristics related to the horns or antlers (in Feldhamer,
Thompson & Chapman 2003). We determined sex for 759 of 799 adult ungulate carcasses that
we detected through our monitoring techniques. Of these 799 adult ungulates, we necropsied
747. If the mandible of an adult was present, its age at time of death was determined by counting
cementum annuli of teeth (Matson’s Laboratory, Milltown, MT, USA). We obtained yearspecific ages from 670 of 747 adult ungulates that we necropsied.
We assessed the nutritional condition of wolf-killed elk by determining the fat content of
marrow samples collected from the femur. We dried marrow samples (4-8 cm3) at 65º C and
calculated the percent marrow fat as the dry mass of the sample divided by the wet mass,
multiplied by 100 (Neiland 1970). We conducted this analysis on adult elk whose sex could be
identified and for which a femur could be found (i.e., 510 of 626 adult elk we necropsied).
During spring and summer, we also assessed how the nutritional condition of wolf-killed adult
elk was influenced by Julian day. For this assessment, we also included adult elk of unknown
sex (n = 3). Our assessment of nutritional condition in the spring and summer included 84
marrow samples.
To estimate the biomass of each carcass, we used body growth curves for elk and deer,
which represented 95·4% of the carcasses that wolves killed or scavenged (see Results), that
were specific to sex, age (in years), and season (Murphy et al. 1998). For context, a five-year
old male elk was predicted to have a live weight of 303 kg in early winter, 264 kg in late winter,
289 kg in mid-May, 316 kg in mid-June, and 342 kg in mid-July. Additionally, a newborn elk
was predicted to have a live weight of 27 kg in mid-June, 52 kg in mid-July, 130 kg in early
winter, 103 kg in late winter, and 123 kg in mid-May. For deer, a five-year old male was
predicted to have a live weight of 100 kg in early winter, 88 kg in late winter, 86 kg in mid-May,
89 kg in mid-June, and 92 kg in mid-July. For bison we used estimates of biomass that were sex
and age specific (0-6 months [20 kg], 6-12 months [167 kg], and each year thereafter; Meagher
1986; YNP, unpublished data). A five-year old bison, for example, was assigned a live weight
of 408 kg for a female and 725 kg for a male. Of note, the few bison (0-6 months) that we
detected were very small, neonate bison (i.e., < a few weeks old). For other species, which
occurred only rarely (see Results), we estimated biomass from previously published estimates
that were specific to the species, sex, and age class (i.e., calf or adult; in Feldhamer et al. 2003),
and, for moose, also to season (in Matson 1997).
On rare occasions (n = 18), we discovered a carcass where a pack had either lost biomass
due to scavenging by another pack, or acquired biomass by scavenging a carcass originally
acquired by another pack. In these instances, we estimated the portion of edible biomass to
which each pack had access. These estimates were based on visually observing how much each
pack had fed on the carcass, and were limited to these categories: 5, 25, 50, 75, or 95%. Also on
rare occasions (n = 8), we determined a pack had scavenged from a cougar-killed prey. In these
instances, we often could not estimate the amount of edible biomass available to wolves through
visual observations. In these cases, we assigned the biomass acquired by wolves based upon the
average time that cougars feed on a carcass before they are displaced by wolves (T.K. Ruth,
unpublished data).
References
Barber-Meyer, S.M., Mech, L.D. & White, P.J. (2008) Elk calf survival and mortality following
wolf restoration to Yellowstone National Park. Wildlife Monographs, 169, 1-30.
Feldhamer, G.A., Thompson, B.C. & Chapman, J.A. (eds) (2003) Wild mammals of North
America: second edition. John Hopkins University Press, Baltimore, Maryland.
Matson, D.J. (1997) Use of ungulates by Yellowstone grizzly bears Ursus arctos. Biological
Conservation, 81, 161-177.
Meagher, M.M. (1986) Bison bison. Mammalian Species, 266, 1-8.
Murphy, K.M., Felzien, G.S., Hornocker, M.G. & Ruth, T.K. (1998) Encounter competition
between bears and cougars: some ecological implications. Ursus, 10, 55-60.
Neiland, K.A. (1970) Weight of dried marrow as indicator of fat in caribou femurs. Journal of
Wildlife Management, 34, 904-907.