State of the Greater Fundy Ecosystem - Forest bird monitoring

GREATER FUNDY ECOSYSTEM RESEARCH PROJECT

UNB Faculty of Forestry and Environmental Management

State of the Greater Fundy Ecosystem

Forest Bird Monitoring in
Fundy National Park

David Christie
Mary's Point Research Station
R.R. #2, Albert, N.B.
E0A 1A0

Regular bird monitoring has been conducted in Fundy National Park (Fundy NP) and parts of the Greater Park Ecosystem (GFE) over the past 30 years. The bird monitoring provides a short-term historical perspective on bird population fluctuations in the GFE, especially in relation to the Spruce Budworm outbreak of the 1970s.

METHODS

The only monitoring activity in the area that has continued regularly for a reasonable length of time is the Christmas Bird Count. The Christmas Bird Count has become an annual event since its inception in 1965. The roadside Breeding Bird Survey method has also been used, although irregularly, to monitor bird populations. Other surveys include the intensive spot-mapping studies of breeding populations which were conducted at a single site in 1970, and at several sites in 1979 and 1992. The 1992 spot-mapping was conducted as a follow-up or comparison to the 1979 survey but also augmented the control portion of a GFE study of forestry plantations between 1992-94 (see Johnson and Freedman, this volume). There have also been some roadside surveys for single species, such as Ruffed Grouse and American Woodcock, and for species groups, such as thrushes. An annual Spring Bird Survey of breeding birds was initiated in June 1993, and is now in its fifth year.

The Christmas Bird Count is a loosely structured survey method, consisting of a varying number of people spending one day counting all the birds they can find within a 24-km diameter circular area. For widespread small- to medium-sized species, indications of population trends are obtained by relating the number of birds counted to the amount of survey effort. Comparing the average figures for 5- or 10-year periods provides more confidence in cases where a species is uncommon or the effort is small.

A 50-stop, 39.4 km-long Breeding Bird Survey route was established in 1966 but has been inconsistently used since then. Only nine surveys were conducted over a 27-year period by four different observers on three variations of the route. Thus, the Breeding Bird Survey can only be used to indicate very obvious changes.

A plot surveyed in a mixed forest by the Canadian Wildlife Service (CWS) in 1970 was the first spot-mapping census of breeding birds in Fundy NP. This plot remains the most thoroughly surveyed site in the Park.

In 1979, near the end of the budworm outbreak, spot-mapping censuses were conducted by the author at 18 sites. In 1992, 15 sites (including 14 from 1979) were surveyed. These two surveys provided "snap-shots" of breeding populations thirteen years apart.

RESULTS

Winter bird populations at the latitude of the GFE typically show considerable fluctuation from year to year. Combining the Christmas Bird Count results for the Fundy area for 24 species of forest birds, shows that about 50 - 100 birds are recorded per 10 party-hours (Figure 1). This number may be exceeded in years where there are incursions of certain species due to the greater availability of tree seeds in the area or the failure of a food source or sources elsewhere. The peak in 1968 was due to an abundance of Pine Grosbeaks and Common Redpolls. The peak in 1991 was due to an abundance of White-winged Crossbills and Common Redpolls.

Winter bird populations were consistently low during the Spruce Budworm outbreak of the 1970s, except for 1974 when there was a large crop of spruce cones. During most of this period, coniferous forest habitat was in poor condition. Black-backed Woodpecker, which is associated with recently dead or dying conifers, was the only winter species which increased to a peak (1978-80), and then declined markedly. Since the outbreak, Pileated Woodpecker, Black-capped Chickadee, Red-breasted Nuthatch, and Golden-crowned Kinglet all show a trend of increased numbers, while Gray Jay and Boreal Chickadee have decreased. These variations are likely due to changes in tree condition and forest structure. Northern Goshawk has declined but for unknown reasons.

General changes in the area indicated by the more infrequent Breeding Bird Survey include greater numbers of Yellow-bellied Sapsucker, Cape May Warbler, Dark-eyed Junco, and Evening Grosbeak near the start of the budworm outbreak, a decline and subsequent recovery of Winter Wren, and a great reduction in numbers of Tennessee Warbler after the budworm outbreak had crashed. Like the Christmas Bird Counts, these surveys also suggest an increasing trend for Black-capped Chickadee and decreasing trend for Boreal Chickadee.

The CWS spot-mapping census of breeding birds in 1970 indicated that population densities of species that feed on larval insects was high when budworm were abundant.

A comparison of the spot-mapping surveys conducted by the author in 1979 and 1992 showed a large reduction in breeding numbers, mainly of warblers. Warblers tend to increase in numbers when Spruce Budworm is abundant. Population densities in each habitat type were extrapolated to produce estimates of breeding populations in the Park in 1979 and 1992 (Figure 2). Bay-breasted, Tennessee and Blackburnian Warblers each declined and Golden-crowned Kinglet increased by several thousand pairs. Other changes were smaller in magnitude but some were large in relation to population size.

IMPLICATIONS FOR MANAGEMENT

To examine the possible influence of habitat changes in the tropics on bird populations in the GFE, relative population change was charted against winter range (Figure 3). This showed increases in birds that winter in Canada and the northern United States, slightly greater increases than decreases among birds that migrate to the southern United States, and a preponderance of declines among species that winter in tropical regions. Resident northern species benefitted by the healthier conditions of coniferous trees since the end of the budworm infestation and also by a heavy cone crop in 1991.

Since the tropical pattern may be biased by the fact that warblers that feed heavily on Spruce Budworm migrate to the tropics, tropical migrants were compared against their degree of association with budworm numbers (Figure 4.). All the categories showed declines, supporting the results of other studies (i.e. Robbins et al., 1989) that neotropical are faring less well than other North American birds. This is a reminder that the GFE is affected by the even greater ecosystem beyond.

Further Reading:

Christie, D.S. 1993. Survey of breeding birds in Fundy National Park 1992. Volume I. Survey methods and results. Unpublished report of the Canadian Parks Service. Contract No. FNP/92-004. 159 pp.

Christie, D.S. 1997. Status of the avian community of Fundy National Park and its greater ecosystem. In: D. Clay (ed.) Resources of Fundy National Park: A primer of ecosystem studies. Part II. Chapter II. Pks. Can. Eco. Sci. Rev. Report. No. 007. 36 pp.

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