Wf. Andelt et Sn. Hopper, EFFECTIVENESS OF ALARM-DISTRESS CALLS FOR FRIGHTENING HERONS FROM A FISH REARING FACILITY, The Progressive fish-culturist, 58(4), 1996, pp. 258-262
We evaluated the effectiveness of using alarm-distress calls of the bl
ack-crowned night heron Nycticorax nycticorax and the great blue heron
Ardea herodias for frightening these piscivorous bird species from a
rearing unit for rainbow trout Oncorhynchus mykiss. Heron alarm-distre
ss calls reduced black-crowned night heron numbers 48% during the 11-d
treatment period, compared with the pretreatment period, but did not
affect the number of great blue herons. The number of black-crowned ni
ght herons using the rearing unit and the proportion that remained imm
ediately after the broadcast of alarm-distress calls increased from ni
ghts 1 through 11 of the treatment period, which indicates that this p
redator quickly habituated to the calls. We did not find any differenc
es between the proportions of black-crowned night herons and great blu
e herons that remained on the rearing unit immediately after playing c
alls of the respective species. Alarm-distress calls were mostly ineff
ective in reducing heron predation on rainbow trout fingerlings.