Moose with more winter-range fire were likelier to leave

STEP 1 · Year classes

19.4 percent of moose-years stayed resident

Koetke and colleagues classed 836 moose-years from 2012 to 2021. Researchers collared 461 moose from 2012 to 2022 in Big Creek, Bonaparte, Prince George South, the John Prince Research Forest and Entiako. Captures targeted adult females. The 836 moose-years were 42.0 percent mixed migrants, 21.9 percent migrants, 19.4 percent residents, 13.4 percent nomads and 3.3 percent dispersers.

Logging was the main land use in every area. Harvest was extensive at Big Creek, Bonaparte and Prince George South. It was intermediate at the John Prince Research Forest and relatively less at Entiako. Wildfire disturbance was greater at Big Creek and Entiako than in the other areas.

Reported spring departures run from March 1 to June 4, and the mean is April 17. March 1 is also the first day of each classified year. Our read is not to treat that date as the earliest a moose can leave.

In fall the mean departure from summer range was November 4 and the mean arrival on winter range was November 30. Fall departures ran from June 30 to January 1. Winter arrivals ran from July 6 to March 17. Those are study averages for classified movement from 2012 to 2021. They are not an arrival date for a cow on your ground. Our read is to set the November means beside your own season before you pin an early-fall hunt on winter ground.

Migrants averaged 22.2 miles between winter and summer range (35.8 km). Mixed migrants were the largest class. They averaged 14.0 miles in spring (22.5 km) and 11.9 miles in fall (19.2 km).

In the John Prince Research Forest, migrants and residents shared a winter region and migrants used a separate summer region. In Bonaparte and Big Creek a migrant's summer range was distinct from that moose's winter range and often overlapped resident annual ranges. Those migrants did not all move the same direction and the moves did not widen the population. Prince George South and Entiako fell between those two patterns.

STEP 2 · Winter fire

Migration rose with winter-range fire

Koetke and colleagues found that disturbance-avoidance models best predicted migration on all five areas and on a reduced pair. That pair was the John Prince Research Forest and Prince George South. The authors reported the five-area results because that set had more observations.

Spring migration rose with the share of winter locations in wildfire from the previous 40 years and from the previous 5 years. Other terms in those leading models were not statistically significant.

Among migratory moose-years that had winter fire, 76.1 percent had less fire on the summer range than on the winter range. In that same group, 67.2 percent had less fire on the route than on the winter range. Some migrants did not reduce wildfire exposure by moving.

The authors suggest nutritional condition, disease, parasites and age can also push a moose to leave when the winter range did not burn. They say parasites, disease and population density were not accounted for in the analysis.

Human disturbance did not enter the best migration models in these logged landscapes. Our read is to weight 5-year and 40-year fire history above cutblock history when guessing where more moose may leave in spring. That reading follows which terms the comparison kept. It does not show that logging has no effect.

STEP 3 · Modeled births

Previous distance tracked full-data birth calls

Koetke and colleagues estimated births with movement models that had not been validated on moose, and they checked the calls themselves. Of 337 moose-years, 220 were classed parturient (65.3 percent) from 140 moose. The authors call the estimates relatively accurate and say the likely errors are missed births. They see no reason those misses favored migrants or residents. They also say to read the relationships cautiously.

On the full five-area data the best parturition model used previous migration distance. Cows with a long or near-average move the previous year were more likely than residents to be classed as giving birth. Cows with a short previous move showed no detected difference from residents. The paper did not test whether the long and near-average classes differed from each other.

On the John Prince Research Forest and Prince George South subset, the best parturition models were disturbance avoidance and wolf risk. Greater wolf risk was associated with a higher modeled chance of birth on that subset only.

The discussion groups short and near-average migrants with residents. The conclusions credit only a relatively long previous migration. Our read is to follow the full-data results. Long and near-average previous moves were the classes tied to higher modeled births. The later wording conflicts with those results.

The birth calls are movement classifications. They are not a count of calves seen and they do not measure calf survival.

STEP 4 · Adult deaths

Cause differed without a detected survival difference

Of 227 moose classed as migrant or resident, 57 died while monitored (25.1 percent). Koetke and colleagues found that movement strategy was not in the best adult-survival models. On the full data those models used leading tree species, and the second model also included wetland or riparian cover. Mortality hazard was highest in deciduous forest and lowest in mixed forest. On the two-area subset the null model fit best, with Akaike weight above 0.99. The study did not detect a survival difference by strategy. A missed difference is still possible.

Among moose that died, migrants more often died from predation and residents more often died from health-related causes. Those causes include apparent starvation, disease and parasites. Strategy and cause were associated, with a chi-square of 7.89 on 2 degrees of freedom and p = 0.02. Only dead moose entered the test. The authors omitted switchers and deaths classed as other because those samples were small. The paper's overall cause shares do not reconcile with these 57 deaths, so they are left out. The paragraph gives no per-strategy counts.

STEP 5 · Local check

Two pockets show presence, not a named migrant

Our test is on your own ground. Pick one burned pocket and one unburned pocket that both held moose in late winter. On later trips count animals and fresh sign in each. A faster drop on the burn is a local pattern you can weigh if you see it again in another spring. Similar drops over more than one spring suggest burn history deserves less weight there. The counts show presence and sign. They do not name a migrant, separate mixed migrants from residents, or show that fire caused the change.

Koetke and colleagues reported classified spring departures running to June 4, and 19.4 percent of moose-years were resident. Our read is that one quiet visit does not retire a burn and one spring does not lock the next year. The authors note, citing earlier work, that individual moose can change strategy from year to year.

In Bonaparte and Big Creek, migrants moved inside the same country as residents and did not all take one heading. Our read is that a cow gone from the winter pocket can still be in that country. The miles above are sample averages for these collared moose. They are not a circle to search.

The paper reports on targeted adult females. It does not address bulls, calf survival or hunter success. The authors say a lack of support for predation-release and forage models does not rule out forage access or predation risk, and they note those measures were coarse. They also say more severe summer-range fire in a warmer and drier climate could alter migration and its benefits. Rules vary. Check the provincial wildlife agency before you hunt.