Sixty per cent are working longer than their contracted hours, compared with 43 per cent last year, and 65 per cent are satisfied with their work-life balance, compared with 82 per cent in 2007.
Dissatisfaction with flexible working is also growing: only 62 per cent are happy with their current arrangements, compared with 74 per cent last year.
The figures, from the Charity Pulse survey by Third Sector and Birdsong Charity Consulting, suggest the economic downturn is beginning to bite.
"We are starting to see signs of fundraising becoming more concerned about income, and of more pressure on targets," said Frances Hurst, founder of Birdsong. "Maybe things are getting tougher, and that is having an impact on staff."
More than 500 fundraisers responded to the staff satisfaction survey.
The findings are not all doom and gloom: 52 per cent of respondents said they felt supported in developing their careers, up 6 percentage points on last year, and 74 per cent would recommend their charity as an employer, compared with 69 per cent last year.
But there are staff retention problems in London, where the average length of tenure for a fundraiser is only 1.1 years, and staff are relatively young compared with other charity employees - 51 per cent are under the age of 30. The national average length of tenure for the profession is 3.3 years.
"It's a big issue," said Hurst. "There is a loss of knowledge and expertise when people leave, and a significant cost. The Chartered Institute of Personnel Directors estimates that the recruitment process costs £4,500, which is a lot."
One possible reason is bullying: 12.2 per cent of fundraisers say they have been bullied in the past year, a figure marginally above the sector average.
- 52 per cent of fundraisers are happy with their pay, compared with 57 per cent last year, the survey shows
- Fundraisers are earning less than a year ago. Last year, 65 per cent earned more than £30,000;
this year the figure is 61 per cent
- 48 per cent of fundraisers in London earn below £30,000, compared with 77 per cent elsewhere