Minnesota study hampered by cows that leave collared calves to die
DULUTH — Minnesota moose researchers the past two springs have tried to capture and place radio collars on newborn calves, only to have many of the moose mothers abandon their young.
The problem surfaced in 2013, during the first year of a major scientific study to find out why northeastern Minnesota’s moose population, including calf survival, has been crashing in recent years.
The situation became so dire last month that officials nearly canceled the entire project.
The study is the first ever in Minnesota to look so closely at calves, and the first worldwide using real-time GPS devices to track the calves for their first year. Another study underway has expanded research into why adult Minnesota moose are dying.
Last year, researchers placed GPS transmitters on 49 calves. Crews in helicopters homed in on the GPS-collared cows, landed and found the newborn calf. They weighed the young, took blood samples and body temperature readings, in addition to attaching the GPS collar.
“It was all done in matter of minutes and we were out of there,’’ said Glen DelGiudice, lead moose researcher for the Minnesota Department of Natural Resources and head of the calf project.
Despite efforts to move quickly, however, nine of the 49 – more than 18 percent of the GPS-collared calves – were abandoned and left to die.
Flight, not fight
Most of the cows would run away when crews approached. Some returned as if nothing had occurred and resumed nursing the calf. But some cows never came back, even after crews left the woods. Others returned to the calf or twin claves multiple times but then ultimately left for good. Researchers saw it all because both mother and calf were transmitting their locations.
“We just didn’t understand what was going on, why they would come back but then leave again,’’ DelGiudice said. “We knew there would be some (abandonment) but there’s no research on anything like this. Nobody had real data on what we were seeing.”
In past studies in Alaska, for example, crews sometimes had to fend off aggressive cow moose that were trying to protect their calves. In Minnesota, the cows are almost always running away, and some are staying away. The Minnesota team figured that researchers in past studies, who didn’t have real time data to confirm if abandonment occurred, may have drastically underestimated the frequency with which cows left their young.
Over the winter, DelGiudice and other Minnesota researchers tried to figure out what had gone wrong. They compared data on both mother and young involved in abandonments and those that stayed together. They found no biological or circumstantial differences. They consulted with moose experts in Canada and Sweden and came up with a new plan for this spring’s effort: Ditch the helicopter.
“We really thought that would solve the problem; if we went in on foot and didn’t have that added disturbance of having the helicopter involved,’’ DelGiudice said. “Nobody said before, ‘Don’t use a helicopter.’ But that’s sort of what we boiled it down to after the fact.”
But they were wrong.
When cow moose began to give birth early last month, crews drove back roads in trucks and used GPS to home in on the new mothers, waiting 48 hours or so for the pair to bond before they walked in. But they ended up with the same problem.
By May 15, a dozen calves had been collared and seven had already been abandoned. Five of the nine cows involved had walked away from their newborns and ultimately didn’t return.
DelGiudice ordered the entire project stopped.
“As of May 15, I was going to pull the plug. That would have been the end of our calf research project,’’ DelGiudice said Thursday.
One last try
DelGiudice came up with one more idea. He would shrink the work crew down to just two people “and instead of getting a blood sample and weight and rectal temperature, all we did was put the collar on and get out … less than 60 seconds,’’ he said, figuring the reduced disturbance and minimal handling time would bring cows back to their calves.
That strategy appears to have worked.
Since the study started up again May 21, 10 calves have been collared, with eight cows involved, and none of the calves has been abandoned. It’s not the 50 calves researchers had hoped to follow for the next year, to see how many survive and how many perish, but 11 was better than none, DelGiudice noted.
Already, one of the 11 calves has been eaten by wolves. But early indications are that this year’s calf crop is doing better than last year, when all but nine calves were dead by winter. Collars were removed or were programed to fall off those remaining nine calves over the winter.
Eleven “is a small sample size. But we think we now have a way to do this,” DelGiudice said, noting that funding for 50 calf collars already has been approved for 2015. “We’re not getting all the information we had hoped to. … But having the collars on them is by far the most important thing.”
In the meantime, six of the seven abandoned calves this year were captured and taken to the Minnesota Zoo in Apple Valley. The seventh perished before crews could find it. Last year, all of the abandoned calves died in the woods.
“We don’t want to see any capture-related mortality. But we know there is going to be some and we have to look at the bigger picture. We need to find out what’s wrong with the moose situation here,’’ DelGiudice said.
Brent Patterson, field researcher and moose expert for the Ontario Ministry of Natural Resources, said he’s seen similar reaction by some Ontario moose, but not all. Cow moose in Algonquin Provincial Park are very defensive of their calves, he said, but those just outside the park did occasionally leave and did not come back.
“In Algonquin, we had zero abandonment, it just didn’t happen. We had a hard time collaring calves the cows were so aggressive,’’ Patterson said. “But outside the park, we had some of the same issues Minnesota is having. ... We really don’t know for sure why it happens.”
Patterson said the only differences between the two, geographically close populations are that moose in the park are never hunted, but they also had more predation, namely wolves, than the moose outside the park. It’s also not clear why some moose abandon calves that have been collared while abandonment is almost unheard of among fawn deer that are handled and collared.
“The only thing we can say is that keeping that disturbance to a minimum and the handling time as short as possible seems to be the difference. But we don’t know why,’’ he said.
Ron Moen, moose researcher for the Natural Resources Research Institute at the University of Minnesota Duluth, said GPS tracking of cows that were not approached by people showed they rarely strayed more than a few yards from the calving site. “It just didn’t happen,’’ he said. “It’s amazing how they held tight.”
He said the abandonment rate in Minnesota “was a surprise. It’s a mystery to us. You’d think that the maternal bond would be so strong that the cows would stay, or at least come back,’’ Moen said.
Minnesota moose decline
Northeastern Minnesota’s moose population has dropped to an estimated 4,000 or fewer animals, less than half the estimated 9,000 moose in 2006. Scientists say moose may be the victims of multiple problems, including warmer temperatures, increased parasites like ticks and brain worm, heightened predation by wolves, a decline of prime habitat and other factors.
The situation became so bleak by 2013 that the DNR canceled the state’s long-running moose hunting season and began two major research projects to find out what was wrong. In addition to the calf study, another team of researchers is watching about 100 GPS-collared adult moose. Researchers want to know where they go to eat, sleep, give birth and, especially, where and when they die, and why. Crews are homing in on dead moose within hours to recover the bodies for lab tests before predators and scavengers eat the evidence.
Data so far shows that 21 percent of adult moose are dying in the first year they are collared. Moreover, 74 percent of the calves fitted with radio collars perished in the first year, most in the first few months. That's considered far too low a survival rate to sustain a viable population.
“The good news is that, so far this year, we’re seeing better survival for both the adults and the calves we have collared,” DelGiudice said. “It’s still early, and we really don’t know why … but, even though it was a tougher winter, we’re seeing less natural mortality.”