Once abundant, but now rare and endangered, the red-cockaded woodpecker is the epitome of the longleaf pine ecosystem. With the virtual disappearance of its habitat, red-cockaded woodpeckers were placed on the forerunner of the present endangered species list in 1968. Since then, despite implementation of various recovery plans, the bird’s status has remained unchanged.
There is little dispute over the reasons for the red-cockaded woodpecker’s decline. The bird is totally adapted to and dependent upon large unbroken tracts of old growth pines, especially longleafs. Now that these have been reduced to a few scattered and isolated pockets, the bird essentially has no place to live, i.e. to find food, to seek shelter, and to reproduce. Its evolution perfectly adapted it to the pre-settlement forests of the southeast, and it cannot now simply look elsewhere for its requirements.
The red-cockaded woodpecker is one of the few birds that excavates nesting and roosting cavities in living trees; the wood of dead trees, in various stages of decay, is softer and much more easily worked. Although the effort required is greater, there is a distinct advantage to placing the cavities in living pines: the sap which surrounds the holes acts as a very effective deterrent against predators. But the effort required to excavate a cavity in a living tree is substantial. Pines are considered as “soft wood” trees, but the term is relative. The wood of the white pine, common in the northeast, truly is soft, but by comparison that of southern pines is quite hard. As a result, it can take a red-cockaded woodpecker anywhere from six months to two years to excavate a cavity. Most are placed in trees affected with a fungus disease which softens the heartwood. Pines are like people in that they become more susceptible to disease as they age, and the so-called “red heart disease” only infrequently occurs in longleaf pines less than 100 years old.
Once the bird has drilled through the sap wood, it makes a small chamber in the softer interior. It then protects the cavity by pecking off patches of bark around the entrance hole. This causes resin to flow, eventually coating the side of the tree around and well below the cavity. As long as this is fresh, it serves as a repellant to predators. When the cavity is abandoned, it is often taken over by other woodpeckers, squirrels, or insects.
Not only must red-cockaded woodpeckers have old growth trees for their nest cavities, they also require a very open understory. It is believed there are two reasons for this. One has to do with nest predators, mostly snakes, many of which have a remarkable tree climbing ability. It is of little benefit to the woodpeckers to expend a great deal of energy in excavating a cavity in a living pine to take advantage of the extruding sap if all a snake need do is climb a close-by neighboring tree to reach the entrance hole. The other reason is related to the dynamics of the bird’s foraging habits. They feed almost exclusively on insects found on and under the bark of pine tree trunks, very rarely even bothering to look for food on hardwood trees. When the understory in pine flatwoods or in uplands grows tall and thick -- as happens when fire is excluded -- it makes it difficult for the birds to fly from tree to tree. They either abandon the site or if it is so isolated that they have nowhere else to go, eventually succumb to weakness or stress brought on by lack of food.
It is the combination of all these factors which has resulted in the bird’s decline. Virtually all of the old growth forest in the southeast was harvested by the 1920s. Fire was largely excluded from the second growth forests, especially when the pine species were shortleaf or loblolly that are not as fire resistant as longleaf. Red-cockaded woodpeckers will excavate cavities in these species, but generally only when they have been infected by red heart disease. The bird’s specialized requirements then come into conflict with timber management practices. As infected trees are commercially less valuable, they are often harvested before they become susceptible, well before they are suitable as cavity trees. Additionally, a general shift to shorter term rotations in forest management has worked against the species.
For further reading: Robert W. McFarlane, A Stillness in the Pines: The Ecology of the Red-cockaded Woodpecker, 1992. |
