These are among the findings of the 2011 Careers in Research Online Survey, which gathers the anonymous views of research staff in UK higher education institutions about employment and career development issues.
The survey, managed by Vitae, found that universities had made "positive progress" since the first survey in 2009 towards implementing the principles of the Concordat to Support the Career Development of Researchers.
Launched in 2008, the concordat is an agreement between the funders and employers of UK researchers.
It calls for measures such as open recruitment, use of appraisals, provision of career development training and institutional recognition of research staff.
It also appeals for such staff to be appointed on open-ended contracts "unless there is a recorded and justified reason to employ on a fixed-term contract".
Of the nearly 5,600 respondents to the survey, 77 per cent are on fixed-term contracts, down from 82 per cent in 2009.
Of the researchers from institutions that also participated in the previous survey, the proportion also fell slightly, from 82 to 80 per cent.
Young researchers are most likely to be on fixed-term contracts, but more than 60 per cent of respondents who have had five or more contracts with their current institutions are still employed on fixed-term arrangements.
More than 40 per cent of those contracts run for 12 months or less.
A rise in the number of contracts of under two years, particularly at post-1992 universities, is a significant cause of a "distinct shortening" of the average length of fixed-term contracts.
However, staff at post-1992s are still far more likely than their colleagues at pre-1992s to be on open-ended contracts.
Other areas where progress is slow include the take-up by researchers of professional development training and the provision by institutions of external placements and secondments to broaden researchers' experience, the survey has found.
The full report will be launched at the Vitae researcher development international conference in Manchester next week, for which Times Higher Education is the media partner.