03/01/2010 Council Packet - Laserfiche WebLink

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Great Blue Heron chicks were found in an active Great Horned Owl nest; also, a Great Horned Owl fledgling was observed perched among the remains of another heron chick which it presumably had just consumed (Figure 21) Heron eggs with holes pecked in the sides (n = 2) were found on the ground, suggesting that American Crows (Corvus brachyrhynchos) had preyed upon these eggs (Figure 22). Based on aerial survey data (MN -DNR, unpubl. data) the Peltier Lake colony had a maximum estimated total of 180 active nests in 2004. An aerial survey conducted on 25 May, 2004, documented a large number of abandoned nests. This observation took place only six days prior to the increased disturbance rate detected on video. A ground survey confirmed that all nests at the Peltier Lake colony were abandoned by 15 June, 2004. Predation Predation has been documented as the primary cause of avian nest failure for many species of birds (Ricklefs 1969) and a cause of waterbird colony abandonment (Kadlec 1971, Shealer and Kress 1991, Whittam and Leonard 1999, D Mock pers. comm.). Presence of predators near and within the heron nests at Peltier Lake was a clear difference from Pigs Eye Lake. All monitored nests failed at Peltier Lake, 75% of which were visited or attacked by a raccoon at least once. Video evidence showed that raccoon predation was the cause of chick mortality in up to 87% of deceased chicks. Cameras on three separate occasions also recorded the presence of >1 raccoon foraging in a single nest -tree (Figure 27). Video and ground survey results also demonstrated that Great Horned Owls at Peltier Lake preyed upon heron chicks. And, two incidences of egg predation were documented during ground surveys (possibly caused by American Crows). The importance of opossum foraging behavior upon heron nest productivity, specifically egg predation, is not known because cameras were not installed until after eggs hatched. However, the ensuing furbearer management in the park (Chapter 3) suggested that opossum density may be higher on the island than raccoon density and could also be important to nest productivity. Protection of active nests and nestlings via a strategy of mesopredator management was recommended based upon the results of this study. Two primary approaches include: (i) preda exclusion from nest -trees and bridge -trees (i.e., those trees providing access to nest - trees) by means of "predator guards "; and (ii) predator removal by means of trapping and /or hunting. for Two primary approaches for predator management were available: (1) predator exclusion and (2) predator removal. Beginning in 2000, a formerly large mixed - species waterbird colony, located at Peltier Lake (Lino Lakes, Minnesota), failed to fledge chicks over five consecutive nesting seasons. During this same time period the number of nesting pairs declined by 74% and two of the original three resident species stopped nesting at Peltier Lake. Previous management efforts, from 2001 to 2003, focused