Has the cull begun? New data show that after remaining more or less steady for a decade, the number of investigators with National Institutes of Health (NIH) funding dropped sharply last year by at least 500 researchers and as many as 1000. Although not a big surprise—it came the same year that NIH’s budget took a 5% cut—the decline suggests that a long-anticipated contraction in the number of labs supported by NIH may have finally begun.

Although NIH publicizes the number of grants it funds each year, it does not routinely disclose the number of principal investigators—the leaders of the labs these grants support. But in response to a request from ScienceInsider, NIH shared these data for two sets of grants: research project grants (RPGs), which include all research grants, and R01 equivalents, a slightly smaller category that includes the bread-and-butter R01 grants that support most independent labs.

These data show that despite minimal budget growth at NIH since a 5-year doubling ended in 2003, the number of investigators with R01-equivalent grants has held steady at about 22,000. (That number does not necessarily include researchers who received funding from a $10 billion, one-time spending boost that NIH got as a result of stimulus programs designed to combat the recession.)

But the numbers fell sharply last year when NIH’s budget plummeted $1.55 billion due to sequestration. As NIH has reported, new R01-equivalent awards fell by 534. The new data show that the number of investigators with these awards dropped in sync by 605, from 22,116 to 21,511 (raw data here). The decline for RPGs was 511. The loss was a staggering 1001 when all R grants are tallied, according to an analysis by American Society for Biochemistry and Molecular Biology President Jeremy Berg, a former director of the National Institute of General Medical Sciences (NIGMS), now at the University of Pittsburgh in Pennsylvania. (Berg’s data include smaller grants such as R21s but not large ones such as P01s.)

Regardless of which data you go with (Berg advised ScienceInsider to stick with the figures from NIH), the number of investigators fell by hundreds last year, or by 2.7% for R01 equivalents or 3.8% using Berg’s R grant data. That suggests that after years of propping up grant numbers by squeezing the size of existing grants, the agency could not avoid a tumble last year.

These labs aren’t all necessarily shutting down. They could have bridge funding from their institution or be “surviving by other means,” such as foundation support, Berg says. Moreover, NIH’s budget rose 3.5% this year, so the number of investigators could rebound somewhat in 2014 or later years, as DrugMonkey notes.

But the drop in investigators does suggest some contraction in labs. If so, Berg asks, “is this a wise culling of the herd, or is this a destructive loss of productive investigators and talent?” Some of the grants are probably R01s that the investigator has held for decades, Berg says. But others “are probably people in the prime of their careers.”

NIH has been thinking about ways to avoid relatively random culling of experienced lab chiefs. One idea is to offer willing senior scientists enough funding to wind down their labs over a few years. That might encourage more to retire and free up money for younger scientists. It’s “a potentially reasonable idea,” Berg says.

He thinks NIH should also come clean about a policy it put in place in 2012 to spread its money further—reviewers give extra scrutiny to applications from investigators who already receive more than $1 million in direct support from NIH. NIH has not revealed whether the policy has significantly affected grant decisions, Berg notes. And he’s concerned that most institutes look only at the funding that well-funded grantees receive from NIH, and not the total including other sources. (An exception is NIGMS, which looks at the whole picture.) For instance, scientists supported by the Howard Hughes Medical Institute, which lavishes their investigators with funding, usually have grants from NIH as well, Berg recently found.