Guest Post: The Sapsuckers of East Limestone Island

This post was contributed by Anthony Gaston, co-author of a recent paper in The Wilson Journal of Ornithology on population change and nest tree longevity of a small-island population of Red-breasted Sapsuckers.

A Red-breasted Sapsucker digging sap wells on a western hemlock on East Limestone Island. Photo by Keith Moore.

Woodpeckers are very distinctive birds. Evolution took a lot of trouble to organize a bird that climbs tree trunks and drills holes in wood, and then, having made one such bird, it went on to make 239 different species, 23 of which live in North America. They all share the vital characteristics of having a stiff tail to lean back on and a strong, sharp bill for hacking into trees. Other birds have tried to reach the same niche—nuthatches, creepers, woodcreepers—but none has developed the same skill at woodworking. Watching a big woodpecker hacking at an electrical power pole, spraying large flakes of wood in all directions, is a truly awesome sight and probably a very annoying one for anyone working on the line.

Despite their diversity, woodpeckers tend to live at fairly low densities, making them a challenge to study. So, when you come across a dense population, it provides an unusual opportunity and one that needs to be exploited. The population of Red-breasted Sapsuckers (Sphyrapicus ruber) on small, uninhabited East Limestone Island in the Haida Gwaii archipelago of British Columbia offered just such an opportunity. In 1990, the newly founded Laskeek Bay Conservation Society set up a field camp on the island with biologists and volunteer “citizen scientists” studying the natural history of the area from May to July each year. It soon became apparent to us that, among many interesting aspects of the island’s natural history, there was a relatively high density of breeding sapsuckers. They are noisy and colorful birds, active throughout the daylight hours: it seemed they were almost begging us to study them.

The island was covered in dense coniferous coastal rainforest comprising mainly Sitka spruce and western hemlock and including many trees that were overmature, dying, or dead, making them ideal for sapsuckers to excavate their nesting cavities (Pilgrim et al. 2019). It may be this wealth of elderly trees that enabled the dense population of sapsuckers. The main aim of our project was to monitor long-term ecological changes to the island’s biodiversity, so we looked for questions that would take decades, rather than months, to answer. Luckily, the sapsuckers are easy to see and identify and relatively tame in the presence of people, so they made an ideal subject for inexperienced volunteers and students who visited the camp to learn about ecological field work.

Staff and volunteers outside the Laskeek Bay Conservation Society cabin on East Limestone Island. Photo by Laskeek Bay Conservation Society.

One question that had implications for the management of bird-friendly forests was how long individual trees would remain suitable for sapsucker nesting. The sapsuckers drill a new nest hole each year, but old holes may be used for nesting and roosting by other birds, such as owls, nuthatches and chickadees, so sapsucker-friendly trees are valuable to the bird community in general. Also, the same tree may be used for several years, occasionally as many as ten, ending up with many sapsucker holes.

Our project got underway in 1991, and the island has been scoured for active sapsucker nests every year since. Nest cavities are easy to find during excavation and again after the nestlings hatch, as the young sapsuckers give loud calls whenever the parents arrive. The number of active nests on the 48-hectare island has varied from 5 to 22 (0.11–0.49 per ha). Most are situated in dying trees that have either started to lose their bark or have completely debarked. All identified nest-trees are numbered with plastic tags and checked for five years after their last use. We found that trees, once used, were more likely to be used again subsequently, with runs of continuous use of up to six years. The longest span from first to last use was 21 years but, given that our study has only been running for 30 years, it is possible that some may last even longer, with Sitka spruce being used for longer than western hemlock. Some trees are first used when still at full height, but they may continue to be used even after upper portions have fallen.

Four sapsucker holes close together on a dead spruce on East Limestone Island. Photo by Keith Moore.

When we returned to the island in spring 2011, we found that a major storm over the winter had blown over about a third of the forest, creating the equivalent of a clearcut about 15 hectares in extent, with a few dead poles standing among a tangle of horizontal trunks. It looked as though the area had been a war zone. To our surprise, this substantial reduction in the area of standing forest appears not to have affected the density of sapsuckers, as the mean population of the island over the subsequent ten years was similar to numbers in the decade before the blowdown. That sort of unexpected and intriguing result is something that can only be achieved with long-term monitoring.

As their name suggests, sapsuckers excavate “wells” to access sap, feeding on the sugary exudate. On East Limestone Island, most wells are drilled in western hemlock and red alder, usually in much younger trees than those used for nesting, emphasizing the value of a mixed-age forest, as opposed to the type of second growth forest that develops after a clearcut. The wells are visited by hummingbirds, warblers, and squirrels, as well as insects. By creating nest cavities and sap wells, the sapsuckers are important ecosystem engineers, diversifying the resources provided by the forest trees and increasing the numbers of secondary producers that can be supported. Our study has told us a lot about the lives of the sapsuckers and how they affect the forest ecosystem. Better still, in pursuing it, we have introduced many volunteers and students to the interesting and valuable lives of these delightful birds.

Learn more about the Laskeek Bay Conservation Society at

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About Wilson Ornithological Society

The Wilson Ornithological Society (WOS) is an international scientific society comprising community members who share a curiosity about birds. The WOS produces the quarterly Wilson Journal of Ornithology as the latest iteration of scientific journal publication supported by the Society since 1888. The WOS is committed to providing mentorship to both professional and amateur ornithologists through sponsorship of research, teaching, and conservation. Find us on, Facebook, Twitter, and Instagram (@WilsonOrnithSoc).

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