A DOUBLE KEYSTONE SPECIES
By Lisa Bate
Have you ever heard what sounds like someone sending a Morse code message through the trees in spring? If so, go take a look and you will likely find that the Red-naped Sapsucker (Sphyrapicus nuchalis) has returned to Montana for breeding season. Their drum sounds like Morse code because of irregular spacing between drum beats which typically starts with five rapid beats followed by slower beats; this slow, irregular drumming pattern is unique to sapsuckers.
Their Greek genus name comes from the words sphura which means “hammer” and pikos which means “woodpecker.” The Latin species name nuchalis means “nape,” referring to the red nape, or patch, on the back of the woodpecker’s head. The common name “sapsucker” refers to the bird’s unique method of feeding.
Red-naped Sapsuckers are a small-medium woodpecker with a white and black checkered pattern on their sides and backs. They are the only woodpecker with a wide, vertical white stripe running up the side. Their heads are red with a white moustache and black line above. They have a red nape. The male’s throat and chin are completely red; the female’s chin is usually white. Juveniles have an overall sooty-brown color to them. This cryptic coloring helps protect them when they first leave the nest and have yet to learn about predators. In addition to drumming, sapsuckers make numerous calls and sounds. Listen on-line to hear some of their different sounds (http://www.allaboutbirds.org/guide/red-naped_sapsucker/sounds).
The Red-naped, Red-breasted, and Yellow-bellied Sapsuckers used to be considered the same species with different distributions: the Red-naped resided in the Rocky Mountains, Red-breasted along the western coast, and the Yellow-bellied in the east and into northern Canada. They have since been separated into three species based on systematic studies, but they can hybridize where their populations overlap. Sapsuckers are a migratory woodpecker wintering in southwestern US, Mexico, and central America. They breed throughout the Rocky Mountains in the US, British Columbia, and Alberta.
Sapsuckers don’t really suck sap; rather, they sip it with a specialized tongue that works like a paintbrush. But first, they have to gain access to the sap! To do this, they drill numerous small holes, close together in a pattern, into the bark of a chosen tree to reach the phloem and xylem tissue. Willows, cottonwoods, birch, aspen, and Douglas fir are some of their favorites.
These unique structures are called sap wells. Sap will continue to seep as long as the wells are kept open. Just as we have clotting constituents in our blood to help seal cuts, when they are bleeding, so do trees. Therefore, sapsuckers have to maintain their sap wells constantly to keep them flowing and will vigorously defend this critical food resource all day. Sap is the primary food of sapsuckers. They also eat insects, spiders, and buds; they frequently can be seen fly-catching, or sallying, around their nest trees.
Sap is so highly nutritious that multitudes of other species also seek out sap wells. This is one reason sapsuckers are considered a keystone species. A keystone species is one that makes up only a small number of the animals in an area, but whose presence allows for the presence of many other animals. For example, the distribution and migration patterns of Rufous Hummingbirds are closely tied to that of the Red-naped Sapsucker. This high-sugar food resource allows hummingbirds to arrive early in Montana, even before flowers are in bloom, to select a breeding territory. Rufous Hummingbirds choose nest sites near sap wells and follow sapsuckers on their sap well runs. Some other species that use sap wells are other hummingbirds, Ruby-crowned Kinglets, White-crowned Sparrow, Nashville, Orange-crowned, and Wilson’s Warblers, mice, bats, and tree squirrels. Wasps, moths, butterflies, flies, ants, and beetles feed at sap wells. Sometimes they also become dinner for sapsucker nestlings.
The second reason sapsuckers are considered a keystone species is because they are primary excavators. Each year sapsuckers excavate cavities in trees or snags with heart-rot. Only the heartwood decays, leaving the tree alive, with a solid layer of sapwood around the nesting cavity to protect the young from weather and predation. Once sapsuckers finish using the cavity, it becomes available to secondary-cavity nesting species: those species that nest in cavities, but are incapable of excavating their own. Swallows, bluebirds, squirrels, mice, weasels, and bats all have been known to use sapsucker holes. Chickadees and nuthatches will also, even though they are capable of excavating their own. Nest tree selection varies with area, but if aspen trees are present, this is their first choice. Aspen trees are highly susceptible to heart-rot making them one of the most important tree species for cavity-nesters.
Sapsucker nestlings cry incessantly for food. This draws in predators like black bears. Yet, bears are seldom successful opening the nest if it is in a live tree with intact sapwood. Look for claw marks on aspen trees with cavities next time you are out, to see how often they try. Surprisingly, the red squirrel is a huge predator on sapsucker nests. Most nests are lost during the egg and early nestling stage. Once chicks are feathered, the squirrels seem to leave them alone. To protect from predators during the night, the male always sleeps in the cavity.
Although sap wells are greatly beneficial to a suite of wildlife species, not all landowners feel as appreciative. So if you find sapsuckers taking over your favorite ornamental tree for their sap wells, wrap the trunk with burlap. Then hopefully, they will find another tree nearby for their food and you will be treated to hosting a double-keystone species in your yard!