State of the Greater Fundy Ecosystem - Pileated Woodpecker

GREATER FUNDY ECOSYSTEM RESEARCH PROJECT

UNB Faculty of Forestry and Environmental Management

State of the Greater Fundy Ecosystem

Selection of Trees for Excavation Foraging by Pileated Woodpecker in Fundy National Park and the Greater Fundy Ecosystem

Stephen Flemming, Gillian Holloway, E. Jane Watts, and Peter Lawrence
Fundy National Park, P.O. Box 40 Alma, N.B. E0A 1B0

This study provides baseline data on the foraging habitat requirements of the Pleated Woodpecker in eastern Canada. The study was conducted between 1993 and 1995, in Fundy National Park and in the surrounding fragmented forest.

GOALS

The primary prey of the pileated woodpecker is the Carpenter Ant, which forms galleries deep in the interior of trees. Pileated Woodpeckers gain access to these galleries by excavating deep holes in trees. By examining these foraging signs, it was possible to determine which tree species and tree characteristics were most important to Pileated Woodpeckers for foraging, and to compare differences in the use of these trees between the park and the fragmented forest landscape. Such information provides baseline data on foraging habitat requirements of this species in eastern Canada.

Excavated Balsam Fir with Carpenter Ants
(Photo: C. LeBlanc/Fundy NP)

METHODS

Our study inventoried the structural characteristics (dbh, decay class and height) of 831 foraging trees. Inventories of excavation foraging trees were made during the summers of 1993-95.

In 1993-94, inventories were made of eight continuous forest sites within Fundy National Park and five sites in the fragmented forest outside the Park. The foraging signs were classified as freshly excavated sites or old sites. Freshly excavated sites were less than one year old. If both new and old foraging signs were found on a tree, it was classified as new. For the purpose of comparison, data were collected on trees chosen at random within the same 13 sites in proportion to the number of foraging trees that were sampled. Random trees were selected by walking a straight transect line.

In 1995, the sampling methodology was modified to collect additional data. Linear transects measuring 500 m in length were surveyed in coniferous and deciduous dominated stands both inside and outside the Park. Each transect represented one of four forest age classes (0-25 yrs, 26-50 yrs, 51-75 yrs, and >75 yrs). Three replications were made of each age class in each forest cover type (coniferous and deciduous) and forest status (continuous and fragmented). A forest inventory was conducted at each of the 48 foraging transect sites sampled in 1995 to identify stand-level characteristics.

RESULTS

It was found that Pileated Woodpeckers in southern New Brunswick used both coniferous and deciduous tree species for foraging. The preferred species were Red Spruce and Balsam Fir; however, Sugar Maple, Yellow Birch, Trembling Aspen, and White Birch were also important. When compared with trees chosen at random on the landscape, foraging trees were larger, shorter, and more decayed (Table 1). Trees with these characteristics are usually found in overmature stands.

In our study, foraging trees ranged in size from 6.5 cm to 83.0 cm, with the median dbh being 27.7 cm. Large-sized trees may be important as they have the capacity to contain a greater density of Carpenter Ants. Carpenter Ants usually occupy trees that are damaged or decayed. In our study, the average foraging tree was a standing dead tree with little bark and a broken that are damaged or decayed. In our study, the average foraging tree was a standing dead tree with little bark and a broken top. The shorter heights of foraging trees may be related to decay, as trees with advanced decay usually have broken tops.

In New Brunswick, coniferous species may be preferred for foraging because they decay fairly rapidly once they are dead. In addition, the wood of conifers is soft, making it easier for woodpeckers and Carpenter Ants to excavate. It was found that live or declining coniferous trees were used for foraging more frequently than deciduous trees of the same decay classes. This suggests that Carpenter Ants rarely occupy live or declining deciduous trees, or that it was more difficult for Pileated Woodpeckers to excavate into healthy hardwoods. Consequently, many of the deciduous trees used for foraging in our study were shorter and more decayed (mean decay class for deciduous species = 6.0, for coniferous species = 5.0).

Differences in foraging heights occurred between coniferous and deciduous tree species. For coniferous species, Pileated Woodpeckers foraged primarily at the base of trees (68% of the time), whereas for deciduous species foraging was greatest over the entire tree (28% of the time). In our study, foraging at the base of the tree was not influenced by ground cover.

Red Spruce snag tree near Foster Brook,
Fundy National Park (Photo:A.Skibicki)

IMPLICATIONS FOR MANAGEMENT

Few differences in structural characteristics were evident between the Park and the surrounding fragmented landscape, suggesting that Pileated Woodpeckers have specific foraging habitat requirements that can only be met in older or well-decayed stands. However, a major difference was observed in terms of tree species use. Coniferous species were used far more frequently inside the Park (77% compared to 62%), whereas in the fragmented forest, more deciduous species were used. This may reflect the decreased availability of large-size conifers in the fragmented forest due to the replacement of older stands with monoculture plantations.

Also, the amount of large, decaying Balsam Fir may be limited in the fragmented forest due to the large scale salvage harvest of this species during the Spruce Budworm epidemic. This argument is supported by the more intensive use of individual Balsam Fir trees in the fragmented forest. The mean number of foraging signs per Balsam Fir tree was 16.0 in the fragmented forest, whereas in the park it was only 10.0. In the Park, Pileated Woodpeckers usually foraged at the base of coniferous trees (72% compared to 61%), whereas in the fragmented forest, higher portions of the trunk were more frequently used. As Carpenter Ant galleries concentrate at the base of coniferous trees, Pileated Woodpeckers may be suffering diminished returns for their effort. In addition, Carpenter Ants prefer Balsam Fir as a substrate for their colonies, consequently a shortage of this habitat type could be detrimental to the Pileated Woodpecker.

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