Isadore Day, Chief of the Serpent River First Nation in Ontario, said Duncan's decision came at a convenient time for the Conservative government, which is under mounting pressure from aboriginal groups to address treaty rights and other issues.
"It appears he's getting out when the getting's good and that's again being seen as a strategy of proactive disengagement by First Nations leaders," he said in a phone interview Saturday.
"This certainly will buy some time for the government, they'll be able to turn around and now say, 'We've got to brief the new minister on these files,'" he said.
"All the while, there may be opportunities that get missed."
He said many of his counterparts share his concerns, though few are likely to speak out for fear of reprisals.
Day initially voiced his misgivings on Twitter Friday shortly after Duncan's announcement, calling the move a "shell game" and accusing Ottawa of being "tactically strategic" in making Duncan its "sacrificial lamb."
Other First Nations groups expressed shock or even sadness at Duncan's departure and said they look forward to working with his replacement, Heritage Minister James Moore, who is temporarily taking over the portfolio.
A statement by the Assembly of Manitoba Chiefs also strongly urged the government to choose the next minister carefully, adding Canada's indigenous people are "no longer willing to accept the status quo" of the Indian Act.
A spokeswoman for the group was more vocal on Twitter, however, saying Duncan's resignation appeared to be "a bit of a diversion tactic."
The message posted by Sheila North Wilson went on to say: "Either way, we are affecting (sic) change and I think prayers and songs we sing are helping."
She said Saturday the comment reflected her own opinion rather than the chiefs.
The national chief of the Congress of Aboriginal Peoples expressed sadness on Duncan's resignation.
Betty Ann Lavallee called Duncan an honourable man who was doing his best "to improve the lives of all Aboriginal Peoples throughout Canada."
When asked about the minister's decision, a spokesman for the Assembly of First Nations would only say that the organization remains focused on moving ahead with the plans established in last month's talks with the federal government.
Day said it will be hard to overcome the loss of momentum stemming from the repeated change in leadership.
"We need to now figure out how to deal with this and mitigate any impact of not having continuity. This was quite sudden from the minister and now we need to deal with that," he said.
With the prime minister having publicly committed to a new round of negotiations over treaty issues and land-claims settlements, the leadership of the Department of Aboriginal Affairs and Northern Development is likely to take on a much higher profile in the Conservative government.
Duncan announced on Friday he was stepping down after improperly advocating to a tax court on behalf of a constituent.
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