Cormorant - Wildlife Control Information

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20Habitat ModificationNetting and grid wires can prevent or detercormorants from preying on fish in hatcheryor aquaculture ponds. Nets provide a physicalbarrier and are effective as long as the edgesof the nets extend to the ground surroundingthe pond. If nets do not extend to the ground,cormorants may learn to walk into the waterand around the netting. Although netting canbe effective, the cost may be prohibitive forlarge ponds. In some instances, the levies betweenponds are too narrow to hold net supportstructures, and netting may interfere withmachinery needed for daily operations.Overhead wire systems work by making itdifficult for cormorants to land on, and takeoff from, ponds. Although these systems areeffective at preventing large flocks fromlanding, individual birds often learn to flybetween the lines, or land on levies and walkinto the pond despite the wires. However,grid wires may reduce access to people aswell, and present hazards to non-targetspecies like osprey (Pandion haliaetus) orswallows (Hirundinidae), as well as bald eagles(Haliaeetus leucocephalus). Floating ropes,sometimes called bird balls, are a less expensiveand less labor-intensive alternative towire systems. Floating ropes can be strungparallel to each other and 50–55 feet apart.The success of both wire systems and floatingropes depends on the availability of alternativeforaging areas nearby. Birds that are ableto find other food sources easily are morelikely to be deterred.Wire grid systems can also protect nestingcolonies of other waterbirds. Along with gulls,cormorants can out-compete common ternsfor favored nesting islands. Grid wires suspendedabove tern nesting colonies can enhancetern nesting success and productivityby discouraging larger birds from nesting. Thismethod effectively reserves nesting space forcommon terns until they are able to establishand defend a colony.Fisheries ManagementSite-specific impacts on fisheries often occurwhen large concentrations of easily accessiblefish are present. Fish are particularly vulnerablewhen large numbers of hatchery-raised lake fishare released at once, or when natural movements,like salmon smolt runs, or fish spawningbehavior may concentrate fish in small areas.Fish harvest methods that congregate fish inenclosed areas that cormorants can access alsoleave fish vulnerable. Releasing fish at night sothey have time to disperse before cormorantsbegin feeding in the morning can reduce predation.In lakes, releasing fish in deep water ratherthan from the shore can reduce predation. Instreams, fish can be stocked early in the seasonbefore cormorants return from their winteringgrounds. Harassment conducted in coordinationwith stocking may also relieve pressure onrecently stocked fish.
21Lethal ManagementOptionsNest Destructionvariety of methods can be used toreduce or stabilize cormorant populations,or to deter them from taking upresidence in new areas. Any techniquethat involves egg or nest destruction or removalof cormorants will require federal and in manyareas state permits may also be required. Nestsor nesting trees can be removed or physicallybroken up with the hope that adult birds willeither leave the area, or fail to rebuild and renestsuccessfully that season. This method maybe useful for discouraging cormorants fromnesting in new areas, especially if nests are destroyedearly on. It requires more effort in alreadyestablished colonies. Nest destruction isrelatively labor intensive, although can be practicalon smaller colony sites. In order to be effective,control must be repeated throughout thenesting season and likely on an annual basis.Nest removal may shift cormorants to other locationswhere they may cause other conflicts.Egg oiling can be used to prevent or reducepopulation growth and may be useful for eliminatingcolonies at specific location, especially ifcombined with other harassment or populationreduction methods. Spraying eggs with foodgradecorn oil prevents the exchange of gassesthrough the shell, causing asphyxiation. Thebenefit of egg oiling over destroying eggs is thatcormorants will continue to incubate the eggsManagers discourage nesting and encourage cormorants to leaveWantry Island in Oneida Lake, New York by removing their nests.Nest removal is a labor-intensive management activity.JEREMY T. H. COLEMAN
Page 2 and 3: AcknowledgementsFunding for this pu
Page 4 and 5: Lethal Management Options . . . . .
Page 6 and 7: 4IntroductionEven though breeding p
Page 8 and 9: 6Biology andNatural HistoryDescript
Page 10 and 11: 8short time on either side of the h
Page 12 and 13: 10egg hatches after about 25 days.
Page 14 and 15: 12Food Habits and FeedingDouble-cre
Page 16 and 17: 14These fish were collected from th
Page 18: 16Addition of cormorants as a nesti
Page 21: 19RICHARD CHIPMANUsing a variety of
Page 25 and 26: 23Regulation and ManagementAuthorit
Page 27 and 28: 25New Strategies for ManagingCormor
Page 29 and 30: 27SummaryDouble-crested cormorantma
Page 31 and 32: 29the Yellow Perch population of th
Page 33 and 34: 31McCullough, R.D., and D.W. Einhou
Page 35 and 36: Unlike other water birds, the doubl

Cormorant - Wildlife Control Information

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