State of the Greater Fundy Ecosystem - Hayward Brook cavity-nesting birds

GREATER FUNDY ECOSYSTEM RESEARCH PROJECT

UNB Faculty of Forestry and Environmental Management

State of the Greater Fundy Ecosystem

Forestry and Cavity-nesting Birds
in the Hayward Brook Watershed

Gerry Parker1 and Denis Doucette2
1 Environment Canada - Canadian Wildlife Service
P.O. Box 1590, 17 Waterfowl Lane, Sackville, NB, E0A 3C0
2 Universite de Moncton, Moncton, NB, E1A 3E9

The cavity-nesting birds project of the Hayward Brook Watershed Study sought to identify habitat requirements for cavity-nesting birds. New Brunswick's present commercial forest guidelines are based upon inadequate knowledge of the habitat requirements of cavity nesting birds. These guidelines do not address species, sizes, conditions or emplacement of snags to be retained during commercial harvesting operations.

Both primary cavity-nesters and secondary cavity-nesters use tree cavities for nesting and roosting. Primary cavity-nesters, such as Woodpeckers, excavate the cavities they use. Secondary cavity-nesters, such as Nuthatches and Chickadees use naturally occurring cavities or cavities that have been abandoned by primary cavity-nesters. Secondary cavity-nesters may, on occasion, excavate their own cavities in very decayed wood.

Cavity-nesters are believed to seek out different nesting habitat depending on forest type and composition. As such, the birds found in New Brunswick may have greatly different nesting habitat needs when compared with cavity-nesters in other parts of North America. Quantifying the use of nesting habitat for these birds in New Brunswick may ensure the proper management of these birds in the Acadian forest.

GOALS

The objectives of the project were: 1) to gain greater knowledge on the nesting habitat requirements of cavity nesters, and 2) to incorporate these findings into sustainable forest ecosystem management guidelines and regulations. The three-year study focused on the nesting microhabitats of cavity-nesters in the Hayward Brook and Holmes Brook drainage basins and attempted to quantify primary and secondary cavity-nesting microhabitat.

Black-capped Chickadees are secondary cavity-nesting birds that
utilize naturally occurring or abandoned tree cavities
(Photo: G. Forbes)

METHODS

A preliminary cavity search was conducted in 1993. Active cavity-nests were identified with flagging tape and mapped for future reference. The first season of extensive cavity searching began in 1994. Searches were mostly confined to the breeding bird survey plots during this period. The forest habitat adjacent to the breeding bird survey plots was also searched for evidence of cavity-nester breeding behaviour. Regular visits every 4-5 days were made to trees that were flagged from May 11 to July 4 to give a general breeding chronology and to see if any predation had occurred. The degree of cavity and cavity-tree re-use was also documented. In 1995, cavity searches were conducted from May 2 to July 6. Microhabitat around nest trees was sampled with 11.3 m radius circular plots centred on the cavity-trees. All trees and snags with stems larger than 8 cm diameter dbh were measured and mapped. Foliage profiles were measured by looking through an ocular tube. Descriptions and measurements were also made of potential cavity-trees in the area.

Principal component analysis was used to quantify the nesting habitat of cavity-nesters. Data analysis will also be performed using Arc/Info, a computerized Geographic Information System (GIS). Locations of nesting cavity trees will be digitized into the Fundy Model Forest GIS and matched with the existing forest stand classification.

RESULTS

Over the course of the three seasons, 121 active cavities used by 7 cavity-nesting species were found. The Yellow-bellied Sapsucker was the most common species with 67 cavity nests. Trembling Aspen was by far the most favoured tree used, accounting for over 80% of all nesting cavities found (Figure 1). The Hayward Brook study area appears to offer suitable habitat for most species of woodpecker due to its large number of largeAspen (25 - 45 cm dbh). The importance of Trembling Aspen as a nesting substrate is therefore apparent.

The apparent selection of certain trees for nesting may be greatly influenced by tree availability. In northern New Brunswick, Beech appears to be the most frequently selected tree species by Yellow-bellied Sapsucker. In the Hayward Brook study area, large diameter Beech are rare but large diameter Aspen are very common.

Trembling Aspen is a pioneer tree after fires, logging and farm abandonment. If left undisturbed, much of the early to mid-successional Aspen component of these 80-year-old mixed stands would eventually be replaced by later successional Spruce,Pine, Maple and Yellow Birch. It is not known if cavity nesting species would revert to other trees for nesting, such as Maple and Birch, or move to other areas where Aspen were more common. Because we found few nests in other species of trees, we think that populations of cavity nesters would change relative to the availability of Aspen trees suitable for nesting.

Many trees used by primary cavity-nesters were not dead and decadent snags. Most were fully or partially alive (70%)(Figure 2). It is likely that primary cavity nesters "test" certain trees by tapping or short excavations to search for the most favourable conditions for cavity nest building. Such conditions may include a degree of early rot in the centre of a tree which would aid in excavation. Such tree conditions are often not obvious from the simple visual examination of sites done during most site visits by professional foresters and biologists.

IMPLICATIONS FOR MANAGEMENT

The Hayward Brook study raises important questions about the value of certain forestry management practices and their effects on species of cavity nesting birds. For instance, leaving a few large, mature and often dying White Pine or Yellow Birch in the middle of clearcuts to serve as nesting substrate is of little value to most species. A few secondary cavity nesters, such as Kestrels and Flickers, may benefit from such trees and they may also serve as foraging and roosting sites for other species, however, their limitations must be recognized. It is likely that potentially suitable cavity nesting trees, such as large diameter Aspen, need to be left in treed islands or within corridors between contiguous forest, if they are to be of any value to most species. More comment on forest management strategies may be possible once the microhabitat data collected at Hayward Brook is analyzed.

Large-diameter Trembling Aspen
trees may be important nesting
substrate for cavity-nesting birds
(Photo: Fundy NP)

Further reading:

Parker, G., J. Pomeroy, and A. Chaisson. 1996. The Hayward Brook Watershed Study (a research project of the Fundy Model Forest): Interim Report (1993-1995). Fundy Model Forest. Sussex, N.B.

Annotated bibliography on cavity-nesting birds research (1992-97)

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