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Common Terns

[Note: No eggs, nests, or birds were harmed in the taking of this photo]

Not all birds nest in trees. Here on PEI, you can find nests in shrubs, attached to marsh grasses, on the ground in meadows and forests, and in human habitats such as buildings, lawn furniture, dryer vents, barbeques, or vehicles that have been left to sit awhile. I think one of the most unforgiving nesting areas must be our coastal beaches and sand dunes. Shown here is a nest of a Common Tern (Sterna hirundo).

A Common Tern nest on Prince Edward Island, Canada.

Hurricane Fiona made dramatic changes to the Island’s coastline, removing habitat in some areas and creating new habitat in others. In the location shown, the storm delivered tons of fresh sand and created a new, deep channel making a perfect, isolated spot for a colony of Common Terns to set up shop. I came upon this spot while doing some botanical work, but researchers later returned and found a healthy colony of more than 300 nests!

Like everything in nature, living on a beach has its pros and cons. On the upside, a nest can be very well camouflaged within many square kilometres of sand, seashells, and grass, making it a bit like finding a needle in a haystack for predators. That same topography makes it hard to sneak up on anything, allowing nesting birds to take early evasive actions to lure or drive predators away. Finally, our coastal areas are resource-rich, giving ready access to finfish, shellfish, and tons of tasty insects along the shore. On the downside, there’s the harsh environment: extreme temperatures, little freshwater, no cover, and the risk of being flooded out by storm tides.

Common Terns are well-adapted to exploit the pros and minimize the cons. Their low-profile nests are difficult for predators such as Coyotes, Foxes, Raccoons, or Skunks to spot from any distance along the ground. Avian predators – Ravens, Hawks, Gulls, or Herons for example – have a better chance of finding them, but here too Terns have a plan. As colonial nesters, Common Terns cooperate to aggressively defend their nesting area and drive predators out. You might think a 120-gram (1/4 pound) bird would be no match for a larger foe, but don’t underestimate the power of the group! (Hint: there’s a reason biologists surveying Common Tern colonies often wear hard-hats for protection).

Common Terns can also handle the environmental conditions. Like most seabirds, they can drink seawater, filtering excess salt out of their bloodstream and excreting it through special salt glands near their eyes. Parents share incubation duties, protecting eggs from cool nights and hot days. With no shade available, Common Terns will wet their belly feathers with seawater and use evaporative cooling to prevent overheating of both adults and eggs when needed. Finally, if flood tides threaten nests, parents will quickly go to work to shore up the area with shells and grass just as we would sandbag our own homes.

All this is not to say Tern colonies are entirely safe from threats. If a predator does manage to get in, many eggs, nests – even an entire colony – can be wiped out. Colonies are also sensitive to human disturbance. Off-leash dogs or unwary walkers can damage nests, and anything that keeps adults off the nests for too long can cause the eggs or young chicks to overheat and die. It’s always important to share the shore and be respectful of the wildlife that call it home.

Our Island’s unforgiving coastline and the wildlife adapted to this ever-changing environment are fascinating parts of PEI untamed!

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