State of the Greater Fundy Ecosystem - Hayward Brook breeding birds

GREATER FUNDY ECOSYSTEM RESEARCH PROJECT

UNB Faculty of Forestry and Environmental Management

State of the Greater Fundy Ecosystem

Hayward Brook Watershed Study:
Breeding Birds

Gerry Parker1 and Denis Hache2
1Environment Canada - Canadian Wildlife Service
P.O. Box 1590, 17 Waterfowl Lane, Sackville, N.B., E0A 3C0
2Universite de Moncton, Moncton, N.B., E1A 3E9

This summary presents the results of the breeding birds study for the pre-treatment period (1993-94) of the Hayward Brook Watershed Study. Breeding birds were not censused during 1995 when the plots were harvested. A summary of the response of these bird species to harvesting will be completed by 1998.

GOALS

To identify the spatial arrangement of territories and habitat preferences of breeding birds in the Hayward Brook Watershed Study area.

METHODS

A standard territory mapping method was used to sample bird communities on all the plots. Each plot was surveyed 6-7 times during the breeding season (May - July). Bird observations also extended 50 m outside of plot boundaries in order to identify bird territories which extended outside the plot area. Data collected included species and sex of bird, use of song, use of calls, displays of courtship behaviour, aggressive interactions, nest building, nest use and food carrying. The information was plotted on species maps which showed which species were present, where and when observed, and - if possible - what their behaviour was like.

The Blackburnian Warbler prefers forest
stands dominated by conifers
(Photo: G. Forbes)

RESULTS

During pre-harvest seasons in 1993 and 1994, 66 species of birds were observed. Forty-two of these species were breeders and had at least one territory within the study plots during one of these seasons. The other 24 species were either visitors from other habitats or forest birds that were either not breeding, breeding outside of the study plots, inconspicuous because of low density, nocturnal, discreet, or had an extremely large home range. The number of bird species found breeding on individual plots averaged about 25 for both years. Parulid warblers dominated the breeding bird community. Fifteen species of warblers accounted for more than one-half of the territories mapped for both years. The most common warblers were the Magnolia Warbler, Black-throated Blue Warbler, Ovenbird, Blackburnian Warbler, Northern Parula, Bay-breasted Warbler and Canada Warbler.

An average decline of 15.8% in territory density was observed between 1993 and 1994 on plots surveyed in both years. Breeding bird densities tended to be lower in the upper reaches of the watershed than on the lower reaches. Species richness was lower at all but two plots in 1994.

The overall densities of breeding birds did not vary by distance from the stream (0 - 150 m). This may be because the riparian zone at Hayward Brook is very narrow and shows little difference from the adjacent forested habitat. As such, the contrast in habitat types is not that obvious. Although the densities of some species did change as one moved away from the stream, no bird species was observed to be limited to, or totally dependent on, the riparian area (i.e. the open canopy over the stream and/or the stream-side strip of alders). Significant decreases in densities of Yellow-bellied Sapsucker, Winter Wren, Solitary Vireo, Yellow-bellied Flycatcher, American Robin and Bay-breasted Warbler were seen in one or both years as one moved away from the stream. The reason for the higher densities of the first three birds near streams is not known but may be tied to vegetation, topography, microclimate, food abundance and social interaction. In contrast, the densities of Black-throated Blue Warbler and Ovenbird increased with distance from the stream. It may be that these interior forest birds are responding to stream corridors in a similar negative manner as to abrupt forest edges.

Territory densities appeared to decline for many of these species as one moved away from the stream. Territory densities for most species were generally higher from 0 to 60-90 m from the stream.

The frequencies with which birds occurred in specific forest stand types allowed us to measure stand preference for each bird species, if any existed. Use of different stand types remained relatively constant over the two years with the exception of stands classified as INHW (stands greater than or equal to 70% intolerant hardwoods) which seemed to be frequented less during the second year.

Breeding bird territories were unevenly distributed among different forest stands over both years. Birds appeared to favour stands of IHTH/THIH (50-75% intolerant hardwoods/50-75% tolerant hardwoods) and SPTH/THSP (50-75% spruce, 25-50% tolerant hardwoods/ 50-75% tolerant hardwoods, 25-50% spruce) for establishing territories. They appeared to disfavour stands of SPIH (50-75% spruce, 25-50% intolerant hardwoods) and PINE (greater than or equal to 50% white and/or red pine). PINE stands may, however, be important habitat for Brown Creeper, Golden-crowned Kinglet, Yellow-rumped Warbler and Blackburnian Warbler. Stands of IHSP (50-75% intolerant hardwoods, 25-50% spruce) did not appear to be an important habitat for any bird species. Stands of SPBF (50-75% spruce, 25-50% balsam fir) and BFSP (50-75% balsam fir, 25-50% spruce) appeared to only be used when available and thus do not appear to be critical habitat for any of the 23 species studied.

It is important to note that only the Magnolia Warbler, Canada Warbler, Bay-breasted Warbler, Ovenbird and Yellow-bellied Sapsucker showed specific habitat selection in both years. Some birds did, however, show specific habitat needs. Yellow-bellied Flycatcher may be strongly dependent on forest stands which have a high presence of coniferous stems and Red-breasted Nuthatch may be closely dependent on coniferous stems and snags. It appears that many species may be habitat generalists, or they may be selecting habitat features that are not precisely described by the forest classification system. However, with few exceptions, the existing system of forest classification was seen as useful for describing habitat use by most of the 23 bird species that were studied and appears to be useful as a management tool for avian habitat.

The selection of forest stands by specific birds appears to be strongly correlated with basal area of specific tree species. The basal area of Red Maple, Trembling Aspen and Balsam Fir influenced 15 of 16 species found in stands where these trees were components. The association of many breeding birds and densities with large stems appears to indicate selection for a mature forest structure.

IMPLICATIONS FOR MANAGEMENT

To summarize, none of the birds breeding at Hayward Brook were exclusively associated with riparian habitat. Breeding birds could be assigned to three general groups: i) those which prefer mature deciduous and mixed coniferous-deciduous stands; ii) those which prefer conifer dominated stands, and; iii) those which are non-selective to specific forest stands (Table 1).

More research is needed to better describe bird/habitat relationships and to refine population predictions in the Fundy Model Forest. As our knowledge develops, it may be possible to predict the avifaunal communities over a defined landscape by knowing the forest stand composition of that landscape.

Although this study estimated the availability of avian habitat over a prescribed landscape, many questions remain unanswered. We do not know what length of time is required following timber harvest for full recovery of the reproductive success of all forest-dwelling birds. We know little about the impact of forest fragmentation and the different rates of reproductive success of birds. The impact of minimum area size of breeding habitat is most measurable in areas where fragmentation has resulted from agriculture and urbanization, but is less apparent where forested habitat is a patchwork of regenerating blocks of different ages following disturbance. These questions are important when developing a forest-wildlife habitat management plan.

Further reading:

Parker, G., J. Pomeroy, and A. Chaisson. 1997. The Hayward Brook Watershed Study (a research project of the Fundy Model Forest): Interim Report (1993-1995). Fundy Model Forest. Sussex, N.B.

Parker, G.R., D.G. Kimball, and B. Dalzell. 1994. Bird communities breeding in selected spruce and pine plantations in New Brunswick. Canadian Field-Naturalist 108: 1-9.

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