The percentage of Harvard College alumni who donated to their alma mater declined last year to reach a 17-year low, according to figures released by the University.

The rate at which alumni give back to their school, known as the “participation rate,” is sometimes viewed as a barometer of alumni confidence in an institution.

Harvard’s rate fell slightly to 39 percent during fiscal year 2006—only a single percentage point lower than the previous year’s rate, but the College’s lowest since 1989.

Fundraising from Harvard alumni still showed signs of strength last year, including a $41 million reunion donation from the Class of 1981. More than three-quarters of the class contributed to that fund drive, which set records as Harvard’s largest 25th reunion gift, according to Charles W. Cardillo ’91, the executive director of the Harvard College Fund.

And the University continued to rake in sizable gifts last year—many from donors who are not alumni—propelling its annual total to $595 million, up $5 million from the previous year.

But the College’s overall participation rate has gradually slid over the past five years—a possible signal of alumni disaffection that threatens to drag down Harvard’s ranking in national surveys.

“[P]rospective students, faculty, and the media view alumni participation as a vote of confidence in the institution,” says a Harvard fact sheet for fundraisers. “[A]lumni capable of giving very large gifts are more willing to do so when a substantial number of their classmates are contributing what they can.”

The alumni giving rate constitutes 5 percent of a school’s overall score in U.S. News & World Report’s annual ranking of America’s best colleges. Harvard dropped to second place—behind Princeton—in the rankings this year. Princeton boasts an alumni giving rate of 61 percent.

The declining rate at which Harvard alumni contribute may reflect greater competition from other charities, which have grown in number and sophistication in recent years, the University says.

“We support and encourage their participation in multiple charities,” Harvard’s vice president for alumni affairs and development, Donella M. Rapier, told The Crimson last year. “In some years, however, it may not be feasible for these donors to give to all of the charities that are meaningful to them.”

And in the Internet age, fundraisers’ attempts to reach alumni are occasionally foiled by junk e-mail filters and unlisted cell phone numbers.

Other colleges face a similar predicament; the average participation rate across institutions of higher education has also declined for the last five years. It stood at 12.4 percent, far below Harvard’s rate, in 2005, the most recent year for which data is available, according to the Council for Aid to Education.

—Staff writer Nicholas M. Ciarelli can be reached at ciarelli@fas.harvard.edu.,