A few years ago I did some contract work surveying nesting populations of river birds on the Waimakariri River in New Zealand. We walked along the river bank identifying and counting birds as part of an annual census to look at populations trends over time. We also spent a lot of time leaping in and out of a moving jetboat onto tiny patches of gravel in the middle of the river. That led to some heart-stopping moments!
One of the more abundant species we saw was the black-fronted tern (Sterna albostriatus). These guys nest in colonies and tend to mob anyone or anything that gets too close, including well-meaning scientists! Which makes the counting process somewhat difficult – “Have I already counted the one wheeling around the top of my head or is that a different one?”! Black-fronted terns only breed in the eastern regions of New Zealand’s South Island and are usually found nesting along braided rivers. Nests are very basic, with the eggs laid among the river gravels. Black-fronted terns feed on freshwater fish, invertebrates and worms. Unfortunately their numbers seem to be declining, mostly likely due to predation by introduced mammals and loss of habitat.