Keystone Birds (& Plants)

When considering the essential value of keystone species in our home habitats, imagine being gathered around a table with family or friends playing Jenga. Blocks are stacked on top of one another. Each rectangle has a role to play in supporting the ‘wildlife’ tower, with some of the blocks having more critical roles than others. Early in the game, the tower feels stable. As players remove one piece at a time, the structure may sway or falter, but it remains standing. Then, the “keystone” block is pulled and a large chunk or sometimes the entire tower, comes falling down. This is similar to a keystone; the block in the Jenga tower that numerous other species depend on. Remove it and the ecosystem begins to falter.

Primary Cavity Nesters (Woodpeckers) as Foundational Keystones

The keystone concept exists across taxonomic groups. Take birds for example: woodpeckers are an avian group we can consider as keystones. While each species has a slightly different foraging behavior, all of them generally use their hammer-head-like-beaks to drill holes into trees or woody plants. Most woodpeckers require mature trees or cacti in their ecosystems to do what they do best–forage on insects, sap, nectar, fungus, and seeds–by making holes or cavities. The size of these holes varies by species and foraging niche. Larger holes are often made by woodpeckers for roosting or nesting. In their inaugural year, woodpeckers tend to use the large holes for raising their own young. Thus they are referred to as primary cavity nesters.

Secondary Cavity Nesters Need Woodpecker Hardware for Nest Cavities

Large holes made by woodpeckers are sought after by secondary cavity nesters for raising their young. Common secondary cavity nesting songbirds include chickadees, nuthatches, titmice, wrens, bluebirds, swallows, and Purple Martins. Though non-native to North America, House Sparrows and European Starling are also common songbird cavity nesters. Some of these secondary cavity nesters will do a bit of excavating, but they generally lack the correct “equipment” to carve out their own nest cavity from scratch – they rely on the better-equipped woodpeckers to do this.

New Cavities Rated Better Than Old

If tomorrow, woodpecker populations in their native ranges disappeared or rapidly declined, so too would the number of nesting habitat options for secondary cavity nesters. A prime example of this is the American Three-toed Woodpecker, which is commonly seen in disturbed forest in some mountainous areas of the western United States and large swaths of Canada. Research reveals that not only are these woodpeckers critical cavity creators, but that the “fresh cavities”– meaning those made in five years or less–were preferred and more frequently used by secondary cavity nesters. Holes that were 15 years or older were infrequently used. Thus, the continuous creation of cavities is critical, even when numerous older cavities are available.

Hummingbirds That Stalk Woodpeckers?

Another unique keystone example is the Red-naped Sapsucker, which subsists predominantly on the sap from aspen and willows. These birds can be found in the Rocky Mountains and some southwestern states. Red-naped Sapsuckers fill the traditional cavity-creator role of woodpeckers, but they have an additional behavior that feeds numerous others. When sapsuckers drill into trees they create sap wells. Other songbirds “rob” the remains of these sap wells, “stealing” a sugary sticky meal. Various species of hummingbirds, Orange-crowned Warblers, chipmunks, and a variety of other species have been documented feeding on the dripping sap. Rufous Hummingbirds, pictured above, have been known to follow foraging Red-naped Sapsuckers in the hopes of sneaking a sample of the sweet syrup left behind.