You might pity the fundraising bosses at America’s largest nonprofits. Their pay has inched up only about 2.7 percent over the past five years, according to GuideStar data on groups with annual revenue of $50 million or more.

Yet averages can be deceiving. Plenty of top fundraisers are getting big raises. To gauge how many, The Chronicle analyzed the pay of 260 top development officers at nonprofits that raise $35 million or more from private sources; these are individuals for whom at least three years of compensation figures are available from tax filings by their organizations.

More than 60 percent of these fundraisers got raises of 10 percent or more at least once. Each year in the survey, at least one in five got a pay bump at least that big.

What caused the spikes?

Poachers

It’s the nonprofit CEO’s nightmare: The top development executive gets an offer for a new position — and a lot more money. "It happens all the time" and naturally leads to counteroffers, says Ronald Schiller, head of Aspen Leadership Group, a recruiting firm.

Some organizations try to be proactive about heading off poachers. Amy Purvis, chief development officer at the Museum of Fine Arts, Houston, has marched steadily up the pay ranks since 2010, with her compensation climbing 87 percent to $358,317 in 2015, the last year data is available.

A promotion helped fatten her check, but the museum has moved deliberately to protect what it considers a valuable asset. "I’ve known development directors at museums around the world, and Amy Purvis is simply extraordinary," says director Gary Tinterow, a former longtime executive with the Metropolitan Museum of Art...