Moose population estimates on Kanuti National Wildlife Refuge, Alaska, 1989 – 2008. Error bars represent the 90% confidence interval; narrower bars indicate a higher level of precision.

Large bull seen during a moose survey on Kanuti National Wildlife Refuge, November 2008. FWS photo.

 Kanuti National Wildlife Refuge partnered with the Alaska Department of Fish and Game (ADF&G) in mid-November to conduct a moose population survey with a new twist:  sightability trials.  Using radio-collared moose, we wanted to determine how many moose are not seen during standard surveys.  Biologists know that it is impossible to see every moose in a survey unit (each about 5.3 mi² in area), but they are just starting to document the actual percentage of moose missed.  This can only be accurately done using radio-collared moose.  One plane radio-tracks moose during the survey and knows which units contain collared moose.  Survey planes (two-person tandem aircraft such as a Supercub or Scout) survey a unit and let the tracking plane know whether they saw any collared moose.  If they did, they provide information about group size, sex, and habitat.  If they missed a collared moose that had been tracked in the unit earlier that day, the tracking plane returns to make sure that the moose did not move out of the unit since being tracked.  Results of the sightability survey are pending, but it appears that surveyors missed about 20-25% of the collared moose in units, similar to what has been found by ADF&G in other parts of interior Alaska.  Kanuti Refuge differed from other areas where sightability has been tested in that it is an area of low moose density; other study sites had greater numbers of moose.  Habitat also differed from other study areas in that much of Kanuti Refuge has recently burned.  While this leads to more open habitats where it seems that moose would be easier to see, burns contain numerous stumps and tree root wads that stick out of the snow.  It is surprisingly easy to mistake a moose lying in the snow for a root wad from a distance!

In addition to the sightability tests, a population estimate was also obtained.  Eighty units were surveyed to calculate the estimate, fewer than the 150 units surveyed in 2007 due to the extra cost required for the sightability trials.  Therefore, precision is lower for the 2008 survey compared to last year.  The resulting analyses indicated some promising population trends, however.  The overall estimate grew to 872 moose in 2008 compared to 588 in 2007 (Figure 1) for a moose density of 0.32 moose per square mile.  Calf production was good at 58 calves per 100 cows, and a high yearling bull ratio (14 yearling bulls per 100 cows) indicated that calf survival from last year was also good.  A ratio of 20-30 calves per 100 cows is considered adequate for maintaining a stable population, and ratios of over 30-40 calves per 100 cows promote population growth.  Yearling bulls are identified by their antler characteristics.  It is assumed that a similar proportion of female calves survived, but it is often difficult to distinguish between an adult and yearling cow from the air.  The observed ratio is considered good; in the past, yearling bull ratios have been as low as 4 yearling bulls per 100 cows.  These results are similar to 2007, when there were 53 calves per 100 cows and 13 yearling bulls per 100 cows, and hopefully indicate a growing population.