Estimating Calf Elk Summer Survival Through Aerial and Ground-Based Classifications
Map of hunting district 292 study site outlined in red and yellow
Ron Howell University of Montana, Project TRAIN 2004 Undergraduate Research Fellow
Calf elk recruitment, as indexed by spring classification flights, has progressively declined across western Montana, including upon our study site in the Garnet Range, over the past 3 decades. We compare summer calf elk survival estimates generated from regular ground-based and aerial classifications to survival estimates generated from a radio-marked calf elk sample. Both aerial and ground techniques demonstrate variability; however, ground techniques were highly variable. Both techniques tended to underestimate survival compared to survival from the radio-marked sample. We make several recommendations to wildlife managers charged with estimating summer elk calf survival.
Aerial photo of cow elk pushing calf elk
- Calf elk recruitment has progressively declined in west-central Montana over the past 3 decades, causing concern for wildlife managers.
- Calf: 100 Cow ratios measured through spring green-up fixed-wing aircraft surveys show declines from 47 to 18 calves per 100 cows since 1988 on our study site, Montana Department of Fish, Wildlife & Parks (FWP) Hunting District 292-00, in the Garnet Mountains (Fig 1).
- I participated in a study that is radio-marking newborn elk to determine if decreasing recruitment is primarily a function of inadequate nutrition, increased predation, or a low proportion of mature bulls.
- From summer 2002 to 2004, this study has systematically conducted regular calf: cow classifications from fixed-wing aircraft to compare to calf survival estimates from radio-marked sample.
- I collected regular ground-based classifications in the summer of 2004 to compare to both aerial classifications and calf elk survival estimates.
- My primary objective is to provide information to wildlife managers about how summer ground-based classifications relate to aerial classifications and calf elk survival.
- Ground-based classifications showed a high degree of variability throughout the summer while aerial classifications were moderately variable.
- In all but 3 instances, ground and aerial classifications underestimated calf elk survival relative to survival estimates generated from radio-marked sample.
- Ground-based classification survival estimates tended to be closer to survival estimates from radio-marked sample when a large total number of elk were observed.
- Ground-based classifications may be used to estimate survival when habitat allows for regular observation of large numbers of elk.
- Wildlife managers should adjust for negative survival bias associated with ground-based classifications; also, numerous observations are recommended due to high degree of variability.
- Wildlife managers should classify elk during the month of July as survival estimates generated from calf: cow ratios are most representative then because calf: cow pairs have joined massive, visible nursery groups.
- Aerial classifications may be used to estimate survival when ground-based techniques are not appropriate, but estimates must be adjusted.
- As of August 31, 2004 we have documented 7 elk calf mortalities from the 2004 radio-marked sample (14%).
- Summer 2004 aerial calf: 100 cow ratios have ranged from a high of 47:100 (7/2) to a low of 33:100 (7/31) (Figure 2).
- Summer 2004 ground-based calf: 100 cow ratios have ranged from a high of 100:100 (7/14) to a low of 16:100 (6/27) (Figure 2).
- Ground based classifications tended to show large variability relative to aerial classifications (Figure 2).
- Neither 2004 ground-based nor aerial calf survival estimates strongly correlated to calf survival estimates generated from the radio-marked sample; however 2002 and 2003 aerial calf survival estimates did weakly correlate with survival estimates from calf sample (Figure 3).
- Materials and Methods
- From summer 2002 to 2004, we captured, processed, and radio-marked 121 newborn elk with mortality-sensing, radio ear tag transmitters and expandable, break-away radio collars.
- During each of the 3 field seasons, we conducted between 4 and 6 summer radio-telemetry flights from a Supercub aircraft counting and classifying elk as calves, cows, and spike, raghorn, and mature bulls. For each flight we generated a calf: 100 cow ratio to estimate calf survival.
- In addition, during 2002 and 2003 we measured cow elk pregnancy rates, and age and sex structure of herds to determine how many calves are born annually on the study site. We estimate that roughly 67 calves are produced for every 100 cows in the elk herds on our study site.
- During the summer of 2004, I collected 10 ground-based classifications on 2 herds (Kleinschmidt & Murray) on our study site from 6/22/04 to 8/31/04.
- I utilized radio-telemetry techniques in an attempt to locate elk herds at sunrise. Binoculars and a Bushnell 40X spotting scope were used to observe animals. I recorded date, time, weather, herd, UTM’s from a Garmin GPS unit, and counted and classified total animals, including calves, cows, and bulls (spikes, raghorns, and matures). I then generated a calf: 100 cow ratio for each classification.
Figure 2. Summer Radio-marked calf survival overlaid with aerial and ground calf: 100 cow ratios. Every labeled apex represents a sample point.
Photograph of July aerial classification consisting of large calf: cow nursery group
- Literature Cited
- Heisey, D.M., and T.K. Fuller. 1985. Evaluation of survival and cause-specific mortality rates using telemetry data. Journal of Wildlife Management 49(3):668-674.
- Pollock, K.H., S.R. Winterstein, C.M. Bunck, and P.D. Curtis. 1989. Survival analysis in telemetry studies: the staggered entry design. Journal of Wildlife Management 53(1):7-15.
- Samuel, M.D., E.O. Garton, M.W. Schlegel, and R.G. Carson. 1987. Visibility bias during aerial surveys of elk in northcentral Idaho. Journal of Wildlife Management 51:622-630.
Figure 3. Comparison of aerial and ground-based calf survival estimates to calf survival estimated from radio-marked sample throughout summer 2004.
Figure 1. Spring elk counts and calf and bull: 100 cow ratios on our study site from 1988 to 2004 (excluding 2002 because of inappropriate aircraft).
Research Mentors: Jarod Raithel & Nyeema Harris
Funding: Project TRAIN Undergraduate Research Fellowship, Salish Kootenai College, University of Montana
Special Thanks: Penny Kukuk, Pat Hurley, Samantha Grant, Candace Tucker, Kqyn Kuka, Kari Signor, Jeremy Longdon.