How To Count Arctic Shorebirds
Posted on: June 24, 2019
Author: Stephen Brown
One of our three projects this season is conducting surveys across the Arctic Refuge coastal plan to find out how many shorebirds are there. We do this for many reasons, primarily as part of a large and coordinated arctic-wide survey that is part of the Program for Regional and International Shorebird Monitoring or PRISM. This program developed out of the U.S. and Canadian Shorebird Plans and aims to track populations of all the shorebirds that breed in North America. We use the data to track the health of shorebird species, and also to measure increases from conservation action or decreases from threats they face. We also use the data to identify critical sites based on what percentage of the population uses them, and we need the entire population count to find out what sites have a large proportion of the population. For arctic nesting shorebirds, the best time to count them is while they are breeding, because individuals spread themselves out across the landscape and set up nesting territories where they sing and display.
Shorebird nests are incredibly well hidden, they have to be to survive the many arctic predators, especially foxes and Jaegers. That means it’s very hard to find them, so we can’t count shorebirds by counting nests. While normally quiet when we see them on migration, arctic shorebirds sing energetically and display aggressively on their nesting grounds, adding a delightful side to their otherwise demure behaviors, and also making them possible to count.
To find out how many shorebirds use habitats of different types across the tundra, we first categorize the many different types of tundra into classes, mostly related to how wet or dry they are. Habitats that are wetter are generally better for both shorebirds and waterfowl, but we have to visit all types to figure out how many birds are using the entire landscape. So we randomly select plots that are representative of different habitat types and visit them all during the course of our survey.
We also survey habitats along the rivers and streams, where gravel bars are common, and where you find birds adapted to nest on gravel. Semipalmated Sandpipers are one of my personal favorites.
For all these nesting shorebirds, the period when they are singing and displaying is short, usually confined to the time when they are finding mates, setting up territories, and defending their territories from others. That means the window for doing this work is very short, usually around 10 days in the early spring. It is very difficult to time the survey precisely because the onset of spring varies from year to year, and we need to plan our travel and reserve dates with a helicopter company many months in advance. This year spring came early on the tundra, so we were rushing to get our crew in place in time to see and count the birds while they were still displaying.
Because we have to cover a very large area during our survey (the coastal plain is the size of the state of Delaware), we depend on a small helicopter to access the remote plots. This year we flew with Pollux Aviation, who does an amazing job working with us and our partners at USFWS. Our pilot Nick was just great and worked with us to safely access all of our plots during the times in between the foggy weather when we could make it to our widely scattered survey areas. The helicopter is quite small, and just barely has room for the pilot and three surveyors with their gear for the day.
But even with the birds singing up a storm and doing all their displays, they aren’t always visible at any given time, so we miss some during our brief visits to each plot that last only about an hour and a half. So we need a way to correct for birds we missed, which is called a detection rate. Over the many years we have been doing PRISM surveys, we have studied some plots the same size as our survey plots very intensively, and we very cleverly call these Intensive Plots. On these plots, shorebird scientists spend the whole season carefully finding and tracking each nest, and then the rapid surveys are carried out as usual by other scientists who have no idea what birds are there, just like at our regular survey locations. From those intensive plots, we can calculate how many of each species we miss, and on average it turns out that we see and count about 80 percent of the birds on a plot. We use those data, updated each year, to calculate the total populations, including the birds we likely missed.
We have now finished our PRISM surveys, and are starting the process of entering all the data. Soon we will have new population estimates, both for the Arctic Refuge coastal plain itself and also as a part of the overall population estimate for each species for the entire Arctic. As we wrap up this first project, we are very grateful to all our supporters, especially the National Fish and Wildlife Foundation, and the many private donors who provided matching gifts, for making the work possible. Next up, the crew is shifting to the second and third major projects of the season, tracking how long nests of various species survive on the tundra, and tracking their movements and habitat use after the nesting season with satellite tags. We will be reporting on those efforts soon.