Three of 29 Chisana caribou calves released from a wilderness pen into the wild with their mothers last Friday evening were killed by bears within hours.

Caribou biologist Rick Farnell of the Department of the Environment said one of the dead calves was the last to be born inside the 28-hectare enclosure on the shore of Big Boundary Lake, 50 kilometres south of Beaver Creek.

It raises the question of whether the difference in age even a week may play a factor in calf survival during the post-calving period when the newborns are the most vulnerable to predators, Farnell suggested in a news briefing this morning.

There was, he pointed out, a difference in height of about 20 centimetres or more between the calves that were born earliest in the captive rearing experiment and those born latest, in this second year of the Chisana caribou recovery program.

Farnell said it's likely everybody wants the best for the troubled herd, but from the scientific view he must maintain, bear predation on young calves is a fact of life for caribou.

But he also pointed out that of the 35 radio-collared Chisana cows that gave birth in the wild, just eight still have calves by their side, representing a calf survival rate of 23 per cent, according to data collected from aerial of the herd.

'As far as it is looking, bears are playing a major role in patterns of survival with this herd,' Farnell told reporters.

He said all three calves were killed as the herd made its way through the treed area separating the pen site and the upper alpine where the treeless expanses make it more difficult for predators to hide.

Year 2 of the recovery effort began in early April when crews net-gunned the caribou cows from helicopters, then transported them to the enclosure.

Of the 34 cows captured, four were not pregnant and released immediately. Of the 30 pregnant cows, one died of stress from the capture.

As the Chisana herd began a downward spiral in size and age composition in the early 1990s, concern for its well-being rose. Hunting bans were put in place, though the spiral continued.

It was suggested a couple of years ago by Haines Junction regional biologist Michelle Oakley that capturing pregnant cows and placing them in a protective enclosure in their natural range to have their calves may be a way of increasing calf survival.

Information from the first release of 17 calves last year indicates 12, possibly 13, survived for a calf-survival rate of 70 per cent, compared to a dismal average for calf survival in the wild.

This year's $300,000 recovery program is supported by organizations in Canada and the United States.

The Alaska side of the border is contributing approximately $100,000 Cdn.

State wildlife officials, for instance, are doing the aerial monitoring that will be intensive for the first couple of weeks following the release, as the herd moves from its winter range in the Yukon onto its summer range in Alaska. All 29 of the captive-born calves were fitted with radio collars.

Last Friday's scheduled release of the caribou in early afternoon was delayed until evening on account of the caribou, explained Jamie McLelland, the onsite supervisor for this year's program.

He said staff had taken down approximately 50 to 65 metres or more of fencing made from the dark cloth used as subsurface liner during highway construction, and tried to herd the animals out early Friday afternoon. But they wouldn't leave.

'Once they recognized the opening, they stood right on the line of the opening and looked out,' he said.

Instead, the animals made for a hilly area inside the pen where they slept away the afternoon under sunny skies, despite freedom not more than 30 metres away.

But by 7 p.m., knowing aerial monitoring of the released caribou would begin the very next morning, there was another effort to shoo them from the wilderness maternity ward that had been home for the cows since early April, and back into the wild.

'It just took one animal stepping over the line, and the rest followed,' McLelland said.

Whether reluctance to leave the security of the pen was just that, security, the fine food or perhaps knowing a bear or bears were in the neighbourhood, it is difficult to say, Farnell and McLelland suggested.

McLelland did point out the caribou are very aware of their surroundings.

If a staff member was checking the outer perimeter of the enclosure, for instance, an observer watching from the tree stand inside the fenced area could always tell were the person was, even though the person could not see through the heavy cloth material.

The caribou, with their ears perked, would follow the individual with their eyes as he made his way around.

'It's magical, I guess, in some ways,' McLelland said of his first experience with the recovery program, having only joined the staff last fall. 'Because you are watching the calves being born, you are trying to protect the herd and its survival.

'So I guess I feel like real steward and when you let the animals go, there is joy and there is sadness because you have watched all the calves being born; you get to know the cows, all of them have numbered collars, and some of them have personality traits that they exhibit during their behaviour ... but they have to go because their place is not inside a pen.'

From the outset of the recovery plan, wildlife officials maintained they were shooting for three years of captive rearing.

Farnell said it won't be until October when the different supporters of the program meet to review this year's program that a decision will be made whether to go for a third year.

He will, however, have to decide on a gut feeling prior to October whether to have Yukon students again take to the hillsides to collect lichen which is required to ensure the caribou have a natural food to mix with the commercial reindeer feed.

Of the 700 bags picked by Yukon students last fall, 600 were consumed over the last 2 1/2months.

Five days prior to the release, staff began reducing the amount of commercial feed in the diet and increasing the amount of natural food, as a means of preparing the caribou for a return to their regular diet.