Linking calf survival to cow habitat selection

With only 8% of the calves alive at the end of the winter 2013 and a high pregnancy rate of 85-95%, we can legitimately wonder: What happens to the calves?

Assuming that predation is the most important factor of calf mortality: where do female elk go on the landscape to give birth, how do they choose where to hide their calves, and how do they avoid predation, while meeting nutritional requirements? Not only is the current project aiming to describe causes of calf mortality, but it also intends to determine the role of habitat in calf survival.

In summer, the Ya Ha Tinda elk herd splits into three main groups. About half of the herd summers on the ranch while another ~10% goes west into Banff National Park and ~40% heads east of the ranch. This eastern migration is relatively recent. Elk likely follow the new grass produced by fresh clear cuts and/or burns out east, or they may be taking advantage of refuge from predation as a result of higher human activity levels. Preliminary results of this pilot year show that eastern calves have a higher survival rate than that of residents. In September 2013, 40% of the eastern calves were still alive while only 20% of the residents made it through the summer.

Elk calves are hiders not followers (e.g., caribou). Once they are born they hide for about a week to 10 days while their mums graze and rest. They are highly vulnerable to predators during this period. They do not move and are camouflaged in the vegetation. How cows select their birth sites, where calves are hidden, and where they go once the calf follows is likely critical to their survival.

From very dense forests to open grasslands, elk appear to give birth in very heterogeneous landscapes. We visited each birth site and/or hiding site and examined them post-capture to quantify characteristics such as the amount of hiding cover available. Was it easy for a predator to spot the calf from a distance? Which calves were preyed upon? Which ones survived? Are the ones that survived the ones that are carefully hidden, the ones close to human activity, or the ones with difficult access? The next few years of the project should bring some answers to these questions.

We would expect pregnant cows to give birth where predation risk is lower. Ya Ha Tinda resident elk are habituated to human activity and predators tend to avoid humans in daylight. As a result, cows might use anthropogenic infrastructure, such as the ranch, as protection from calf predation.

As you have probably now realized, understanding calf survival is multi-factorial and relies on the interactions of many environmental factors. Because our pilot year’s sample size was small, we cannot draw any definitive conclusions as of yet.

BE13 Birth B

            But stay posted, time flies and it won’t be long before spring is back!



Predator distributions

Since 2008, no predators have been collared in the ranch’s direct vicinity.  Understanding calf mortality cannot happen without also understanding predators’ patterns and routinesSo how do we deal with that?

We are using highly-trained scat detection dogs to augment data on calf mortality with information on relative distributions and diet among predator species. In 48 cells of 5 km² each, a team consisting of dog and handler survey for bear, wolf, coyote, and cougar scats. These dogs are highly motivated and will sit once they detect their target: scat. As a reward, they are allowed to play ball. The cells are spread out over much of the Ya Ha Tinda herd’s range: from east of the ranch, across YHT, and into Banff National Park.

Scats collected using dogs are pinpointed on a map and used to analyze the distribution of canids, ursids and felids. Dogs can process multi-species scents over a large area and precisely detect scats in a short amount of time. Wildlife detection using dogs is not only non-invasive but it also is one of the most reliable methods in use nowadays. Not only can scats be useful for DNA extraction and specific information such as species, age and individual identity, but we are using the scats we collect to validate existing maps of predation risk to the elk by wolves and bears, and in comparison with predator occupancy surveys being conducted with remote cameras…

Field teams also collect scats on a regular basis. Once opportunistically sighted, these scats are collected and used to determine the relative diet between predators. Analyses of wolf, cougar, and bear feces will indicate how much of their diet is made of elk, and more specifically of elk calves.


We might be surprised once the results for YHT come out… Stay with us if you want to know more about them!!

Long-term monitoring

The Ya Ha Tinda elk monitoring project is one of the longest-running elk studies in the world. Since 2000, a collaborative research program has been on-going between researchers at the Universities of Alberta and Montana, Parks Canada, Alberta Conservation Association, Alberta Sport, Recreation, Parks and Wildlife, and other natural resource groups within Alberta to investigate factors influencing the herd’s dynamics such as: human impact (harvest, recreation, habitat management), natural factors (predation, climate), and natural vegetation dynamics .

In addition, Alberta Fish and Wildlife has been conducting aerial surveys of the herd starting in the 1970s to document the herd’s population dynamics. In the early 2000s, Leslie McInenly, MSc., and Dr. Mark Hebblewhite (now University of Montana), became the first students to work at YHT, and since then many master’s and doctorate students have continued the various components of this long-term research.

The Ya Ha Tinda elk are captured in a corral trap or darted from the ground and equipped with Very High Frequency (VHF) or Global Positioning System (GPS) collars (these collars take and store GPS locations on a regular basis). All elk receive unique ear tags to facilitate identification. The collars allow researchers to monitor the elk from a distance and to record their movements and any mortality events. Elk collars usually emit signals of 38 to 60 pulses per minute. When a collar stays immobile for more than 8 hours, the signal changes to 80 pulses per minute. Sometimes elk drop their collars but most of the time following this signal leads to a carcass.

During mortality investigations, researchers look for  evidence that aid in determining the cause of death, such as: wounds, punctures, signs of a chase, plucked hair, tracks or scats, presence of a collared predator in the vicinity, or unhealthy body condition of the elk. It is essential to investigate mortalities early on before it  becomes really difficult to distinguish predation from scavenging events. Necropsies are conducted on suspicious deaths to look for bruises, hemorrhaging, abnormalities, and to take any useful samples. We also investigate  un-collared elk mortalities. Data is thus available for every age class and gender and can be entered into population models to predict the status of the herd. Documenting mortalities provides information on habitats that may pose high predation risk for the elk, which age classes are the most vulnerable, major causes of death, human impacts, and seasonal patterns

We listen for collared elk  on a daily basis  and record their presence or absence from specific locations. Listening for elk everyday and during flights helps determine an individual’s migratory behavior. Ratios of residents to migrants can be obtained and changes in migratory trends examined. This method is also useful in documenting distribution of the elk.

We determine composition of elk groups that we observe. It is crucial to count how many animals are in each age class to  to model the population dynamics  over time.

Cow and calf pairs are also described to keep track of calf survival through the year. If there are more calves in groups right after calving and not that many in October, something is not right… Since 2009, recruitment of calves into the population has declined from a cow-calf ratio of 27% in 2009 to 17% in 2010 to 8% at the end of winter 2013. Monitoring of group size and composition continues in summer in Banff National Park, on the ranch, and in the eastern part of the study area. Summer 2013 results showed [see Calf survival article] that calf survival was way higher east of the ranch. Are cows not having many calves or are the calves dying early on? In addition, when migrants are back to the ranch in winter, we can compare how migrant calves survive on the ranch versus the resident calves.

Our research also looks into the effects of habitat on the YHT population. We follow the evolution of the grasslands. Elk diet is mostly composed of grass and a reduction of available forage impacts the elk population. In late July – early August, when the highest biomass of grass is produced on the ranch, teams sample plots throughout the grasslands. Vegetative species composition and dry weight of a clipped sample are recorded. Since the beginning of the vegetation monitoring, native Fescue grasses have declined and the grasslands are shrinking, suffering from encroaching shrublands and forests.

Finally, we conduct pellet plots twice a year: in the spring and in the fall. The spring data reflects the winter use of the ranch whereas the fall data displays the summer use. Researchers visit ~400 plots around the ranch in grasslands and in forests. At each plot they determine the number of elk, deer, and horse pellet groups. Results help understand the relative use of the ranch by those three ungulates over time. Hot spots of distribution are highlighted in response to time (year) and habitat modifications (burn, biomass growth).

Overall, by repeating our standardized measurements  over the years, we have been able to document many patterns of the YHT herd and can begin to understand how elk react to changes in their environment. By recognizing these chain reactions, we can work towards efficient and proper management of the Ya Ha Tinda herd.