Read here. Well....the scientists didn't really use the term 'crap' but the terminology 'beaver-pond deposits' sounds awful suspicious, no? Anyways, beavers habitat is adversely affected by drought conditions, which occurred in Yellowstone during both the Roman and Medieval warmings. It became so dry during these warming periods that beaver activity in Yellowstone was severely diminished.

"Persico and Meyer report that "gaps in the beaver-pond deposit record from 2200-1800 and 700-1000 cal yr BP are contemporaneous with increased charcoal accumulation rates in Yellowstone lakes and peaks in fire-related debris-flow activity, inferred to reflect severe drought and warmer temperatures (Meyer et al., 1995)." In addition, they note that "the lack of evidence for beaver activity 700-1000 cal yr BP is concurrent with the Medieval Climatic Anomaly, a time of widespread multi-decadal droughts and high climatic variability in Yellowstone National Park (Meyer et al., 1995) and the western USA (Cook et al., 2004; Stine, 1998; Whitlock et al., 2003)," while we note that the lack of evidence for beaver activity 2200-1800 cal yr BP is concurrent with the Roman Warm Period...Once again, these findings suggest there is nothing unusual, unnatural or unprecedented about the degree of warmth and drought of the Current Warm Period, in contrast to what climate alarmists continually claim."