A DIPPICULT DECISION ,- TEENS OVER GUI.le by Dan McAakill

The Natural History Society of Prince Edward Island Ltd. began studying the Hillsborough Bridge Tern Colony in 1988 after Greater Black-backed Gulls started nesting in this colony. Between 1988 and 1990, the production of VCommon Terns in this colony steadily declined to a very low number in 1990. The reason'was predation of the Common Terns eggs and young by the Greater Blackrbacked Gulls. Region wide the population of Common Terns has declined-_ while-the population of gulls has increased dramatically because of the amount' Of “aete released by people from processing facilities and homes.

In 1991, the Society, under permit, installed gull exclosure wires on the Hillsborough Bridge Piers to allow the Common Terns attempting nesting at this site to successfully produce young. Mr. Ben Ho ling and others recorded the results of this exclosure experiment and 196 ter nests were tended. .At least 50 recently'fledged young were seen on the adjacent beaches on one day. thus confirming that the colony had successfully fledged terns in 1991. ‘As the nesting was spread out over a considerable time period, success was much higher than the 50 fledged chicks.

The history of this tern colony is reviewed in the Island Naturalist # 111 (July—August, 1990) and the Society will be publishing the 1991 study results later this year. Since the Greater Black-backed Gulls started nesting‘ at this site, the Common Tern fledging suCCess declined to virtually zero by 1990. -While the 1991 efforts may have offered a reprieve to the colony, the condition of the piers has steadily deteriorated. The amount of spelling rock and the state of disrepair of the piers makes the climbing of many of these piers very dangerous due to the probability of a stone block falling on a climber or the boat and carrying workers under the'water's surface. Even if the appropriate diving equipment was on site, it is improbable that a person- could be freed from under one of these large stones before suffocating. The Society's Tern Committee, after evaluating the results of the work and the probability of an accident, has recommended that a safer alternative be! utilized in protecting the tern colony. ’ 7 ‘ .

The Society discussed the situation and potential solutions at the April' 7th, 1992 monthly meeting. The Society had previously contacted the Canadian Wildlife Service and the CWS indicated that it did not have the resources to undertake the work and thus could not take action themselves. They did indicate that they would provide a permit to allow the selective removal of the adult Greater Black-backed Gulls provided that the Fish and Wildlife Division supported this step and.that the police would allow the use of a high powered air rifle at this site. An expert marksman volunteered to assist the Society in carrying out this selective kill. After consideration of the various alternatives to support the continued health of the Hillsborough Tern Colony, the Society voted to remove, under the appropriate permits and by selective means, the small number of nesting Greater Black-backed Gulls (thought to be 8 gulls) from the Hillsborough Piers. An air rifle was tested and proved to have inadequate accuracy at the distance betweenlthe clay road and the piers. The Canadian Wildlife Service recommended the use of a 22

~ caliber rifle and on May 9th and May 11th the pair of Greater Black-backed Gulls nesting on Pier number 1 were successfully removed. Three other pairs of Greater Black-backed Gulls were nesting on the piers on this date. The removal of‘a third Greater Black-backed Gull led to the gulls abandoning the .piers for this spring. Terns have now fully occupied the 8 remaining piers.

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