Herring Gulls: Important ecological indicators

By Tyler Ripku and Courtney Irvine

Herring Gulls, often referred to as ‘seagulls’, are similar to the ‘canary in the coal mine.’ They inform our understanding of both large- and small-scale changes in the ecosystem and are an important indicator of human impacts on the natural world. Learn more about the results of recent investigations at Pukaskwa National Park.

Parks Canada’s Resource Conservation staff have been counting Herring Gull nests since 1977 as part of the Ecological Integrity Monitoring Program. Notably, the number of Herring Gull nests decreased by 70% since the 1970s. In 2015, Pukaskwa National Park began collaborating with Environment and Climate Change Canada and Carleton University scientists to investigate this decline. We measured nest attentiveness using remote cameras and collected eggs and regurgitated pellets to examine diet and potential causes of decline in Herring Gulls within the park.

First, the decrease in Herring Gulls nests (English only) is likely due to a decrease in non-native Rainbow Smelt (a prey fish) due to an increase in native Lake Trout. In the 1970s, the population of Herrings Gulls was artificially high for three reasons: (1) recently introduced Rainbow Smelts provided an all-time high of available food; (2) Lake Trout were at an all-time low due to overharvest and introduced sea lampreys; and (3) predators of Herring Gulls (Peregrine Falcons, Bald Eagles, and Great Horned Owls) were also at an all-time low due to the use of DDT pesticides. As Rainbow Smelt declined, and populations of other predators rebounded, Herring Gulls declined.  Although the decrease in the Herring Gull population was alarming, it may actually indicate the ecosystem returning to a more “balanced” state.

Second, the consumption of human garbage positively impacted nesting success (English only), which was different between northern and southern populations of Herring Gulls in Pukaskwa National Park. Both regurgitated pellets, and molecules within gull eggs (stable isotopes and fatty acids) indicated that northern gulls were consuming human garbage while the southern gulls were consuming a more natural diet of fish. We found that the Herring Gull eggs containing molecules of human garbage were larger in size, had lower stress hormones, and had parents attending to them for a greater amount of time. This increased the chance of chick survival.

Lastly, by monitoring Herring Gull nests with remote cameras, we documented some interesting interactions: scavenging of dead Herring Gulls by Peregrine Falcons, and predation of Herring Gull chicks by Great Horned Owls. This is the first time Peregrine Falcons have been photographed feeding on dead Herring Gulls in this region! This research helps us understand the declines of Herring Gulls within Pukaskwa National Park and shows why long-term monitoring of indicator species is so important.

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