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Raccoon predation caused all of these nests to fail during both seasons. Raccoons were able to thwart the predator guards by pushing off of one trunk to gain climbing traction on its neighbor (Figure 29B). Prior to 2007, a concerted effort was made to secure this tree complex by raising the metal flashing to a height at which the trunks were angled too far apart to offer a climbing advantage. This tree complex had high nest occupancy during the 2007 and 2008 seasons (six and five nests respectively). However, no successful climbs or nest predation by mesopredators was documented. This tree complex produced a total of 17 fledglings during the 2007 and 2008 seasons. Another tree ( #714), which produced fledglings annually since 2005, provides a different perspective. Its configuration and distance from other trees made it easy to protect. In 2005, an audio recorder attached to the base of this tree clearly recorded the sound of an animal attempting to climb past the metal flashing. In the background, the alarm calls of Great Blue Heron chicks were also clearly audible. Upon inspection the following morning, muddy tracks and scratches indicated that a raccoon had attempted but failed to circumvent the flashing. This securely guarded tree was one of only two that produced fledglings in 2005. This appears to be the first time since Hjertaas (1982) that a tree nesting wader colony has been successfully protected using predator exclusion. Because no trapping has occurred since the 2007 nesting season, I anticipated that evidence of raccoon foraging activity might increase. Alternately, residual effects from trapping may have resulted in a continued decline in tree climbing activity through elimination of the learned foraging behavior in resident mesopredators. If predator guards made tree climbing sufficiently difficult within the colony, then the learned association between climbing and the reward of an available food source should weaken in the absence or reduction of positive reinforcement (Thorndike 1911).