Abstract. This study examines the effects of forest opening (clearcut) size on the surrounding forest-bird community with the objective of offering management suggestions for foresters who employ the clearcut method. I hypothesized that large and small clearcuts would have different effects on the forest-bird assemblage associated with each. I used the point-count method to assess bird abundance in clearcuts, on the edges, and 100 m into the forest from the edges of large and small clearcuts. I found that Neotropical migrant birds and forest-interior birds were the most affected by large clearcuts showing significantly lower abundance in forest areas 100 m from large clearcut edges than in forest areas 100 m from small clearcuts. Edge-open birds were more abundant in large clearcut openings and edges than in small clearcut openings and edges. Blue jays (an avian nest predator) were more abundant on the edges of large clearcuts than on the edges of small clearcuts. A recent study found that forest-interior bird abundance levels off after 100 m distance from small (0.4 ha) forest openings. This result combined with my findings suggest that small openings in the Second College Grant represent less of a disturbance to Neotropical migrants and forest-interior birds. Additionally, given higher abundances of an avian nest predator in large clearcuts, reproductive success could be much lower in areas associated with large clearcuts. Some species such as the White-throated Sparrow (Zonotrichia albicollis), however preferred large clearcuts suggesting that there are some benefits to overall bird abundance by including large clearcuts in a managed landscape.
Finals of Kant get Marx 2.0 : a general politics quiz
THE EFFECTS OF CLEARCUT SIZE ON THE BIRD COMMUNITY IN THE SECOND COLLEGE GRANT
1. THE EFFECTS OF CLEARCUT SIZE ON THE BIRD COMMUNITY IN
THE SECOND COLLEGE GRANT
JOSHUA R. MOONEY
Abstract. This study examines the effects of forest opening (clearcut) size on the
surrounding forest-bird community with the objective of offering management
suggestions for foresters who employ the clearcut method. I hypothesized that large and
small clearcuts would have different effects on the forest-bird assemblage associated with
each. I used the point-count method to assess bird abundance in clearcuts, on the edges,
and 100 m into the forest from the edges of large and small clearcuts. I found that
Neotropical migrant birds and forest-interior birds were the most affected by large
clearcuts showing significantly lower abundance in forest areas 100 m from large clearcut
edges than in forest areas 100 m from small clearcuts. Edge-open birds were more
abundant in large clearcut openings and edges than in small clearcut openings and edges.
Blue jays (an avian nest predator) were more abundant on the edges of large clearcuts
than on the edges of small clearcuts. A recent study found that forest-interior bird
abundance levels off after 100 m distance from small (0.4 ha) forest openings. This
result combined with my findings suggest that small openings in the Second College
Grant represent less of a disturbance to Neotropical migrants and forest-interior birds.
Additionally, given higher abundances of an avian nest predator in large clearcuts,
reproductive success could be much lower in areas associated with large clearcuts. Some
species such as the White-throated Sparrow (Zonotrichia albicollis), however preferred
large clearcuts suggesting that there are some benefits to overall bird abundance by
including large clearcuts in a managed landscape.
INTRODUCTION
Balancing timber management with bird conservation is a difficult endeavor. However,
given recent evidence of declines in many Neotropical migrant bird species (Robbins et
al. 1989a, Askins et al. 1990) it has become increasingly important to manage forested
lands to maintain avifauna diversity and abundance. Threats to migratory land birds in
their North American breeding ground include habitat destruction, degradation,
fragmentation, and loss of habitat diversity (Germaine et al. 1997). Forest fragmentation
increases the ratio of edge habitat to forest interior. Historically, edge habitat has been
seen as beneficial to a wide array of forest dwelling wildlife (e.g., Leopold 1933);
however, edge zones may contribute to reduced populations of bird species that require
2. large areas of forest interior habitat (Gates and Gysel 1978, Ambuel and Temple 1983,
Robinson 1992).
It is important to study Neotropical migratory birds because these birds provide a
useful model for developing general programs of land management and improving
current management schemes (Martin 1995). Neotropical migratory birds are model
organisms because: (1) they are ubiquitous; (2) they include a wide diversity of
coexisting species with varying ecologies; (3) they are sensitive to environmental
perturbations because they are mobile, short-lived, and differ in their environmental
requirements; and (4) their behaviors, demographic characters (fecundity, survival),
physiology, species interactions, and habitat use can be readily studied for many species
(Martin 1995). In addition, knowledge of their habitat requirements is critical to
conserving forest land to allow for successful breeding.
Given that a dominant proportion of birds that breed in the Northeast are Neotropical
migrants (MacArthur 1959), it is possible that factors affecting survival in their wintering
habitat may be more important than events in the breeding habitat. Some research has
found that migrants are limited chiefly by events and conditions in tropical wintering
grounds (Lack 1968, Fretwell 1972, 1986, Morse 1980b, Alerstam and Hogstedt 1982,
Baillie and Peach 1992, Morton 1992, Rappole et al. 1992). On the other hand,
fragmentation of forest habitats in eastern North America has been strongly implicated as
one cause of reduced breeding success, and consequently lowered breeding densities of
some songbird populations (Robbins 1979, Whitcomb et al. 1981, Ambuel and Temple
1983, Wilcove and Whitcomb 1983, Lynch and Whigham 1984, Wilcove and Robinson
1990). Long-distance migrants seem to be limited by both breeding and wintering
habitat; however, there is no clear study suggesting one is more important than the other.
Sherry and Holmes (1995) develop the idea of summer and winter limitation for migrant
birds, stating that “migrant bird populations appear to be limited contemporaneously by
their need for quality habitats in which to maintain high fecundity in summer and in
3. which to maintain high survival in winter.” Changes in breeding habitat are therefore at
least one of the important factors that could have profound effects on overall populations
of Neotropical migrant birds. Thus, it is important to study how forest management in
northeastern North America affects bird communities.
Factors associated with timber harvesting that affect bird communities can be
generally categorized in one of two ways: factors associated with increased edge resulting
from habitat fragmentation (“edge effects”), and those associated with reduced area of
suitable forest habitats (“area effects”) (Welsh and Healy 1993). Many studies have been
conducted in highly fragmented forests and have found that fragment area is a major
factor in determining the number and diversity of bird species present (Blake and Karr
1987, Askins et al. 1990). In addition, Donovan et al. (1995) found that small forest
fragments may be sink habitats for some species of Neotropical migrants requiring
immigration from nearby source areas to maintain populations.
Many areas of the Northeast include large tracts of contiguous forest. This is quite
different from many of the highly fragmented regions in which the aforementioned
studies were conducted. In areas of continuous forest, some studies have found increased
bird species richness and density near forest edge created by clearcuts, rivers, fields, or
power lines (McElveen 1979, Strelke and Dickson 1980, Hansson 1983, Germaine et al.
1997). However, other studies have not found such relationships (Kroodsma 1982, Small
and Hunter 1989).
Bird species diversity is often higher in managed forest areas (where timber
harvesting occurs – clearcutting, selective harvesting...) than in reserved forest areas due
to the increase in habitat diversity (Welsh and Healy 1993). However, it is important to
take this question to the next level and ask how bird species diversity (and abundance) is
affected by clearcut size in a managed area. Simply because some studies have shown
that bird species diversity is higher in areas where timber management occurs (Germaine
et al. 1997), should we assume that creating forest openings will increase diversity? The
4. answer to this question will have implications for timber management in the Northeast
and throughout the country. In some cases managing for diversity is not always the
answer. When a sensitive or endangered species is present, it may be more prudent to
ensure its survival. Clearcutting is a relatively common practice in the Second College
Grant and elsewhere in the Northeast. The size of clearcuts varies to a great degree.
Thus, it is important to look at the effects of clearcut size on bird communities, and to
come to some conclusion as to which size affords the greatest benefits.
Communication between researchers and forest managers is essential to designing
appropriate wildlife management schemes. The Second College Grant, where this study
was conducted, is a perfect forum for this type of discourse. Currently, the forester is
implementing a Wildlife Project, the goal of which is to manage the Grant for wildlife
while still harvesting timber. In order to implement a sound program the forester needs
input from researchers. This study will assist the Wildlife Project by providing
suggestions for bird management.
This study reports results of point count censuses of birds conducted in the Second
College Grant, a 10,930 ha parcel of land in northern New Hampshire owned by
Dartmouth College. The objectives were: (1) to examine the differences in bird diversity,
abundance, and species assemblage between large and small clearcuts, (2) to look at these
differences in detail by examining the effects of clearcut size on bird guilds across a
habitat gradient from inside the clearcuts to the edge to 100 m into the surrounding forest,
and (3) to focus specifically on how Neotropical migratory birds were affected. I tested
for these effects by comparing species diversity, similarity of species composition, and
the abundance of birds in several guilds in large (6.0 – 7.0 ha) and small (0.3 – 1.0 ha)
clearcuts. These variables were compared within the clearcuts, on the edges of the
clearcuts, and 100 m into the forest from the clearcut.
METHODS
5. STUDY AREAS
This study was conducted from 20 June - 30 July 1997 in the Second College Grant in
northern Coos County, NH. I selected four small and four large structurally similar study
sites by field reconnaissance. These sites were dominated by hardwood trees, but also
included coniferous tree species. Hardwood species included sugar maple (Acer
saccharum), white and yellow birch (Betula papyrifera, B. alleghaniensis), and beech
(Fagus grandifolia). Coniferous species were red spruce (Picea rubens), balsam fir
(Abies balsamea), and some Eastern hemlock (Tsuga canadensis). Aerial photos were
examined to ensure that substantial areas of forest surrounded each cut. The clearcuts
studied were of similar age; all had been harvested within 5 years. Small sites ranged in
size from approximately 0.3 - 1.0 ha. Large sites ranged in size from 6.0 - 7.0 ha (sizes
determined using a Global Positioning System and Trimble’s Pfinder GIS software).
VEGETATION MEASUREMENTS
To test whether my sites were structurally similar, I measured basal area of all trees larger
than 7.5 cm in an 11 m radius around my point count sites which were inside the
clearcuts, on the edges of the clearcuts, and 100 m into the forest from the clearcut edges
(see Figure 1). These measurements were taken in the four large sites and in the four
small sites. One of the large sites was excluded from the study because it differed
strongly in forest composition being composed chiefly of spruce.
BIRD CENSUSING
6. I recorded all birds heard or seen within a 50 m radius of my point count site during a 6
minute period. Point counts were conducted between 05:00 and 08:00 from 29 June
through 19 July. Three census points were established at each site (Fig. 1) and marked by
flagging. One point was located inside the clearcut, 100 m from the edge. The second
was located on the edge. The third was located 100 m into the interior forest. The points
were situated in a straight line to avoid overlap. Each census point was visited four times
throughout the course of the study period.
Figure 1. Clearcut, Edge, and Forest point count layout for a typical
clearcut site in the Second College Grant, New Hampshire.
BIRD GUILDS
To look at finer-scale differences in how birds were affected by clearcut size, I first
categorized the common bird species observed in the Grant on the basis of migratory
group. There were three categories: Neotropical migrants, Nearctic migrants, and
resident species. I then separated these species into groups based on habitat preference.
Forest-interior birds are those species with breeding territories concentrated away from
the forest edge. Interior-edge birds are species with territories both near the forest edge
7. and in the interior. Edge-open species are those with territories both in edge areas and in
openings (Whitcomb et al. 1981). Thirdly, I classified the species into foraging guilds
based on information in the literature (Ehrlich et al. 1988). Foliage-gleaners are those
species that forage insects from the leaves of trees. Ground-foragers are those species
that manipulate the forest floor in search of insects, and bark-probers probe into the bark
of trees with their bills for insects.
DATA ANALYSIS
Basal area, and diversity (Simpson’s Index) were analyzed with an ANOVA model that
included clearcut size, location (clearcut, edge, or forest), clearcut nested within clearcut
size, and clearcut size x location. Abundance within guilds (migratory group, habitat
association, and foraging strategy) was analyzed with an ANOVA model that included all
the above terms and additionally: guild, size x guild, and location x guild. All terms were
treated as fixed effects.
Similarity between large and small habitat groups was determined using the Bray-
Curtis (1957) measurement of species composition and relative abundance measures as
comparison criteria (Germaine et al. 1997), where:
"
similarity = $
(∑ 2Wi ) %
( A + B )' × 100%
# &
and: Wi = lower abundance of each species i present in both plots, A = number of
individuals present in assemblage 1 and B = number of individuals present in assemblage
2.
8. RESULTS
Basal area of coniferous trees was similar in large and small sites (Table 1; Fig 2). Basal
area of hardwood trees was also similar in large and small sites (Table 1; Fig 3).
Table 1. Summary of mean squares and F statistics for ANOVA models run with basal area of coniferous
trees and hardwood trees, and bird diversity as variables.
Basal Area (H) Basal Area (C) Bird Diversity
df MS F MS F MS F
Size 1 4.52 1.89 1.66 0.73 1.24 0.18
Site (Site) 5 1.39 0.58 1.06 0.46 3.88 0.58
Location 2 6.94 2.90 2.48 1.08 53.01 7.92**
Size x Location 2 0.77 0.32 0.07 1.03 0.91 0.14
Error 10 2.40 -- 2.28 -- 6.69 --
P < 0.05; ** P < 0.01; *** P < 0.001
(H) = Hardwood Trees; (C) = Coniferous Trees
.)tseroF dna ,egdE ,tucraelC( .)tseroF dna ,egdE ,tucraelC(
etis hcae ta snoitacol eerht ta nekat serusaem etis hcae ta snoitacol eerht ta nekat serusaem
aera lasaB .)4=n( setis llams dna )3=n( setis egral aera lasaB .)4=n( setis llams dna )3=n( setis egral
ni seert suorefinoc fo aera lasab naeM .2 erugiF ni seert doowdrah fo aera lasab naeM .3 erugiF
tucraelC egdE tseroF tucraelC egdE tseroF
0 0
).mc .qs( aera lasab naeM
).mc .qs( aera lasab naeM
5.0 5.0
1 1
5.1 5.1 llamS
llamS
egraL egraL
2 2
I registered a total of 39 bird species (Appendix I) within 50 m of 21 point count
stations. Only species for which I recorded more than five individuals throughout the
data collection period (18 species) were included in the analyses. In addition, point
counts were inappropriate for censusing some species (Ruffed Grouse, Cedar Waxwing,
9. Chimney Swifts, hawks), consequently these birds were not included (see Appendix I for
list of all birds encountered).
Bird species diversity did not differ in large and small sites in the three locations
(clearcut, edge, forest) (Table 1; Fig 4). However, there was a highly significant effect of
location when diversity values of large and small sites were pooled (Table 1; Fig 4).
Diversity inside the clearcut (in both large and small sites) was significantly lower than
edge and forest values (F1,10 = 9.52, P = 0.01). There was no difference between diversity
in edge and forest areas (F1,10 = 0.41, P = 0.54).
tucraelC egdE tseroF
.)ES ± naem( 7991 ,erihspmaH weN ,tnarG
0
egelloC dnoceS eht ni setis )4 = n( llams dna )3 = n(
1
egral rof seirogetac tatibah eerht ni )xednI ytisreviD
s'nospmiS( seiceps drib fo ytisrevid naeM .4 erug2 iF
3
4
)xednI s'nospmiS( ytisreviD naeM
5
6
7
8
9
01
llamS 11
21
egraL
Though diversity did not differ with clearcut size, the percent similarity between large
and small sites was low (Table 2). The differences in bird species present can be seen by
looking at the species common in each type of habitat (Table 3). Inside large and small
10. clearcuts, few of the species overlap suggesting very different bird assemblages. In edge
areas of large and small clearcuts more species overlap, and in forest areas a majority of
the species overlap indicating the relative similarity between the assemblages.
Table 2. Percent similarity within the bird community in clearcuts, edge zones, and interior forest zones of
large and small clearcut plots, Second College Grant, New Hampshire, 1997.
Small Clearcut Small Edge Small Forest
Large Clearcut 0.195 -- --
Large Edge -- 0.275 --
Large Forest -- -- 0.325
Table 3. Representation of where each species was relatively common (birds/site > 0.10) in the Second
College Grant, New Hampshire. Point counts were conducted inside clearcuts, on the edges of clearcuts
and in the forest 100 m from clearcut edges. Bird species are separated by migratory group.
Small site: Large Site: Small Site: Large site: Small Site: Large Site:
Migrant Group/Species Clearcut Clearcut Edge Edge Forest Forest
*
Neotropical Migrants
Blackburnian warbler X X X
Black-throated blue warbler X X X X
Black-throated green warbler X X X
Common yellowthroat X X X
Hermit thrush X X X X
Magnolia warbler X X X
Mourning warbler X X X
Northern parula X X X X
Ovenbird X X X
Red-eyed vireo X X X X X
Nearctic Migrants
White-throated sparrow X X X X
Winter wren X X X X
Yellow-bellied sapsucker X
Yellow-rumped warbler X
Residents
Black-capped chickadee X
Blue jay X X
Dark-eyed junco X X X X X X
Golden-crowned kinglet X X X X
The finer details of these differences in similarity are revealed by separating the
species observed into several groupings and analyzing the differences. The most
interesting result from analysis of the effects of size and location on the migratory
groupings (Neotropical migrant, Nearctic migrant, or Resident) was that there were
11. significantly more Neotropical migrant birds in the interior forest surrounding small
clearcuts than in the interior forest surrounding large clearcuts (F1,40 = 10.64, P = 0.002;
Figure 5). The other migratory status groups did not show any significant relationships
with size and location.
.50.0 < P * .)ES ± naem( 7991
,erihspmaH weN ,tnarG egelloC dnoceS eht ni setis
)4 = n( llams dna )3 = n( egral rof seirogetac tatibah
eerht ni sdrib tnargim fo ecnadnuba naeM .5 erugiF
tucraelC egdE tseroF
0
)etis/sdrib#( ecnadnuba naeM
1.0
2.0
3.0
4.0
llamS
5.0 *
egraL
The second grouping was based on habitat associations similar to those of Whitcomb
et al. (1981) and Germaine et al. (1997). There were significantly more forest-interior
birds in the forest 100 m from small clearcuts than in the forest 100 m from large
clearcuts (F1,40 = 5.64, P = 0.02; Figure 6). In contrast, there were significantly more
edge-open birds associated with large clearcuts (F1,40 = 5.05, P = 0.03; Figure 7) and
clearcut edges (F1,40 = 8.07, P = 0.007; Figure 7) than with small clearcuts and clearcut
edges. Interior-edge birds showed a preference for interior and edge zones as expected,
while exhibiting low abundance in clearcut areas (Appendix II). There was no effect of
clearcut size for interior-edge species (Table 4).
12. .50.0 < P * .)ES ± naem( 7991 ,erihspmaH .50.0 < P * .)ES ± naem( 7991 ,erihspmaH
weN ,tnarG egelloC dnoceS eht ni setis )4 = n( weN ,tnarG egelloC dnoceS eht ni setis )4 =
llams dna )3 = n( egral rof seirogetac tatibah eerht n( llams dna )3 = n( egral rof seirogetac tatibah eerht
ni sdrib roiretni-tserof fo ecnadnuba naeM .6 erugiF ni sdrib nepo-egde fo ecnadnuba naeM .7 erugiF
tucraelC egdE tseroF tucraelC egdE tseroF
0 0
)etis/sdrib#( ecnadnuba naeM
1.0
)etis/sdrib#( ecnadnuba naeM
1.0
2.0
2.0
3.0
3.0
4.0
llamS 4.0 llamS
5.0 *
egraL egraL
6.0 5.0 *
*
Table 4. Summary of mean squares and F statistics for ANOVA models run with migratory group, habitat
association, and foraging strategy as variables.
Migratory Group Habitat Association Foraging Strategy
df MS F MS F MS F
Size 1 0.89 0.16 0.48 1.20 0.89 0.14
Site (Site) 5 2.17 0.40 0.43 1.08 2.17 0.34
Location 2 121.52 22.34*** 10.42 26.30*** 121.52 19.27***
Guild 2 234.51 43.11*** 0.57 1.44 359.85 57.07***
Size x Location 2 31.20 5.73** 1.69 4.26* 31.20 4.95*
Size x Guild 2 10.96 2.01 2.13 5.37** 7.35 1.16
Location x Guild 4 76.62 14.08*** 4.70 11.85*** 55.57 8.81***
Error 44 5.44 -- 0.40 - 6.31 -
*P < 0.05; ** P < 0.01; *** P < 0.001
The third grouping was based on foraging strategies (Ehrlich et al. 1988). The
abundance of foliage-gleaning birds increased from clearcut to forest (F4,40 = 8.80 P <
0.001; Figure 8). Ground-foraging birds were most abundant in clearcut areas and edge
areas of large sites and in interior areas of small sites (Figure 9). There were no Yellow-
bellied Sapsuckers (the only commonly encountered bark-probing species) associated
with large clearcuts and they were most abundant in interior areas associated with small
clearcuts (see Appendix II).
13. large clearcuts than in small sites (Figure 10).
predators. They were more abundant in edge areas and interior areas associated with
Finally, I looked at the abundance of blue jays, which are potentially important nest
egraL
5.0 5.0
llamS
* egraL
* 4.0 llamS 4.0
3.0 3.0
*
2.0 2.0
1.0 1.0
)etis/sdrib#( ecnadnuba naeM
)etis/sdrib#( ecnadnuba naeM
0 0
tseroF egdE tucraelC tseroF egdE tucraelC
sdrib gnigarof-dnuorg fo ecnadnuba naeM .9 erugiF sdrib gninaelg-egailof fo ecnadnuba naeM .8 erugiF
llams dna )3 = n( egral rof seirogetac tatibah eerht ni llams dna )3 = n( egral rof seirogetac tatibah eerht ni
weN ,tnarG egelloC dnoceS eht ni setis )4 = n( weN ,tnarG egelloC dnoceS eht ni setis )4 = n(
erew snaem - * .)ES ± naem( 7991 ,erihspmaH .)ES ± naem( 7991 ,erihspmaH
.)50.0 < P( tnereffid yllacitsitats
14. .50.0 < P * .)ES ± naem( 7991 ,erihspmaH weN
,tnarG egelloC dnoceS eht ni setis )4 = n( llams dna
)3 = n( egral rof seirogetac tatibah eerht ni )srotaderp
tsen( syaj eulb fo ecnadnuba naeM .01 erugiF
tucraelC egdE tseroF
0
)etis/sdrib#( ecnadnuba naeM
1.0
2.0
3.0
4.0
5.0
6.0
* llamS
7.0
egraL
DISCUSSION
Clearcuts of different sizes affect the forest-bird community in different ways.
Neotropical migrant bird species and forest-interior species appear to be the most
sensitive bird groups to large (6.0 - 7.0 ha) clearcut disturbances in the Grant. Nearly all
bird species in eastern North America that showed declining trends from the late 1940s
until the late 1980s were Neotropical migrants or forest-interior birds and interior-edge
birds (Whitcomb et al. 1981). In light of this finding and others showing declining trends
in migratory songbirds and birds associated with forest-interior (Askins et al. 1990,
Robbins et al. 1989a) management strategies in the Second College Grant should reflect a
concern for these groups of birds.
Forest-interior and bark-probing birds are able to maintain relatively high abundances
around small clearcuts while they are at low abundance or are absent from areas
associated with large clearcuts. In addition, though ground-foraging birds showed high
abundances in large clearcuts and edge associated with large clearcuts, they also
15. maintained high abundances in forest 100 m from small clearcuts. This suggests that
large open areas are not necessary for maintaining high abundances of these species.
Edge-open birds did prefer large clearcuts and edge areas of large clearcuts over
small clearcuts and edge areas. These species were also present in small clearcuts (Table
3) suggesting that overall bird diversity in the Second College Grant does not benefit
from the presence of large openings. The overall abundance of birds, however, is
enhanced by the presence of large clearcut openings given that species such as the White-
throated Sparrow (Zonotrichia albicollis), Red-eyed Vireo (Vireo olivaceus), and Winter
Wren (Troglodytes troglodytes) were much more abundant in large clearcuts than in
small clearcuts (Appendix II). Of course, just how large openings should be to support a
higher abundance of edge-open birds must be determined for the Grant. This study
suggests that 6.0 – 7.0 ha clearcuts are more beneficial to edge-open species although
clearcuts smaller than 6.0 ha may support equally high abundances of edge-open species.
This question is important given that there may be some intermediate size clearcut that
Neotropical migrants, and forest-interior birds and edge-open species can all utilize.
Large clearcuts represent a major disturbance to the local landscape in which they are
carried out. Relative to small clearcuts, they destroy a larger amount of habitat for forest-
interior birds. Most importantly, it appears from my data that the effects of these large
disturbances extend further into the surrounding forest than the effects of a small clearcut.
Germaine et al. (1997) found that forest-interior bird abundance leveled off after 100 m
distance from small (0.4 ha) forest openings. My abundance measures 100 m from small
clearcuts in the Grant may therefore be representative of areas even further from clearcuts
(interior forest). If this is so, birds must be further away from large clearcuts than from
small clearcuts in order to maintain high abundance. Of course, we must note the
cumulative effect of many small clearcuts totaling to equal the size of one large clearcut.
It could be possible that many small clearcuts disturb more habitat for Neotropical
migrants and forest-interior birds. To assess this we must know the distance from a large
16. clearcut at which the abundance of migrants and forest-interior birds equals the
abundance 100 m away from a small clearcut. This information would be very useful for
developing a strategy to manage for Neotropical migrants and forest-interior birds which
are showing declines recently.
Blue jays, potentially important nest predators, are also more of a concern in large
clearcuts than in small clearcuts in the Grant. Their greater abundance in large sites may
explain why forest-interior birds and Neotropical migrants were more abundant in forest
100 m from small clearcuts than in forest 100 m from large clearcuts. In addition, forest
associated with large clearcuts may be more detectable or exploitable than forest adjacent
to small clearcuts by nest predators such as chipmunks, squirrels and avian nest predators
than the more discontinuous edges of small clearcuts (Germaine et al. 1997). An
increased presence of nest predators could have serious implications for reproductive
success. I did not measure nest success, but the differences I saw in abundance may be
even more pronounced in terms of reproductive success. Measuring reproductive success
in and around large and small clearcuts would provide land managers with an important
insight into the nature of the effects of clearcut size on the bird community.
This study shows the importance of looking beyond diversity measures as an
indication of management success. If management in the Grant based assessment of
different strategies strictly on the diversity of the bird assemblage present, much would
be overlooked. For instance, sensitive groups such as Neotropical migrants and forest-
interior species showing population declines would not show up in such an analysis.
To manage for Neotropical migrant and forest-interior species in the Second College
Grant, managers should limit clearcut size. Additional timber could be harvested using
selective cutting although the effects of this practice should be examined in future studies
as well. Such a strategy may be prudent given the nature of surrounding timber
management schemes. The land immediately east of the Grant is owned by a large paper
mill that harvests large tracts of forest (much larger than 6.0 – 7.0 ha) using the clearcut
17. method. Thus, in terms of larger landscape dynamics, edge-open birds may have an
abundance of habitat outside the Grant’s borders while Neotropical migrants and forest-
interior birds are more limited.
To manage for overall bird abundance within the Grant, management strategies
should include large and small clearcuts. This would benefit the most number of species
in terms of abundance. Again it is important to remember, however, that reproductive
success may be lower in forest associated with large clearcuts and one must be hesitant in
adopting a strategy that includes large clearcuts if the goal is to manage for edge-open
bird abundance.
Of course, it is important to consider the habitat requirements of wildlife other than
birds such as moose, bear, deer, and aquatic organisms. In addition, timber production
and the economics driving it are important factors to consider.
Future studies should attempt to synthesize concerns for other organisms with my
results for forest birds to provide the forester at the Grant with the necessary information
to implement a sound and effective Wildlife Program. In addition future work could
attempt to determine whether many small clearcuts which add up to the same amount of
area as one large clearcut would be more beneficial to the bird assemblage.
LITERATURE CITED
Alerstam, T., and G. Hogstedt. 1982. Bird migration and reproduction in relation to
habitats for survival and breeding. Ornis. Scand. 13:25-37.
Ambuel, B., and S. A. Temple. 1983. Area-dependent changes in bird communities and
vegetation of southern Wisconsin forests. Ecology 64:1057-1068.
Askins, R. A., J. F. Lynch, and R. Greenberg. 1990. Population declines in migratory
birds in eastern North America. Current Ornithol. 7:1-57.
Baillie, S.R., and W. J. Peach. 1992. Population limitation in Palearctic-African migrant
passerines. Ibis 134 (Suppl. 1): 120-132.
Blake, J. G., and J. R. Karr. 1987. Breeding birds of isolated woodlots: area and habitat
relationships. Ecology 68:1724-1734.
Bray, J. R., and J. T. Curtis. 1957. An ordination of the upland forest communities of
southern Wisconsin. Ecol. Monogr. 27:325-349.
18. Donovan, T. M., F. R. Thompson III, J. Faaborg, and J. R. Probst. 1995. Reproductive
success of migratory birds in habitat sources and sinks. Conserv. Biol. 9:1380-1395.
Ehrlich, P. R., D. S. Dobkin, and D. Wheye. 1988. The Birder’s Handbook: a field guide
to the natural history of North American birds. Simon & Schuster Inc., New York.
Fretwell, S. D. 1972. Populations in a seasonal environment. Princeton University
Press, Princeton, NJ.
Fretwell, S. 1986. Distribution and abundance of the Dickcissel. Curr. Ornithol. 4:211-
242.
Gates, J. E., and L. W. Gysel. 1978. Avian nest dispersion and fledgling success in
field-forest ecotones. Ecology 59:871-883.
Germaine, S. S., S. H. Vessey, and D. E. Capen. 1997. Effects of small forest openings
on the breeding bird community in a Vermont hardwood forest. The Condor 99:708-
718.
Hansson, L. 1983. Bird numbers across edges between mature conifer forest and
clearcuts in central Sweden. Ornis Scand. 14:97-103.
Kroodsma, R. L. 1982. Edge effect on breeding forest birds along a power-line corridor.
J. Appl. Ecol. 19:361-370.
Lack, D. 1968. Bird migration and natural selection. Oikos 19:1-9.
Leopold, A. 1933. Game management. C. Scribner’s Sons, New York.
Lynch, J. F., and D. F. Whigham. 1984. Effects of forest fragmentation on breeding bird
communities in Maryland, USA. Biol. Conserv. 28:287-324.
MacArthur, R.H. 1959. On the breeding distribution pattern of North American migrant
birds. Auk. 76:318-325.
Martin, T. E. 1995. Summary: model organisms for advancing understanding of ecology
and land management, p. 477-484. In T. E. Martin and D. M. Finch [eds.], Ecology
and Management of Neotropical Migratory Birds. Oxford University Press, Inc.,
New York, NY.
McElveen, J. D. 1979. The edge effect on a forest bird community in North Florida.
Proc. Annu. Conf. Southeastern Assoc. Fish and Wildl. Agency 31:212-215.
Morse, D. H. 1980b. Population limitation: breeding or wintering grounds? p. 505-516.
In A. Deast and E.S. Morton [eds.], Migrants in the Neotropics: ecology, behavior,
distribution and conservation. Smithsonian Institution Press, Washington, DC.
Morton, E. S. 1992. What do we know about the future of migrant landbirds? p. 579-
589. In J. M Hagan III and D. W. Johnston [eds.], Ecology and conservation of
Neotropical migrant landbirds. Smithsonian Institution Press, Washington, DC.
Rappole, J. H., E. S. Morton, and M. A. Ramos. 1992. Density, philopatry, and
population estimates for songbird migrants wintering in Veracruz. p. 337-344 In J.
M. Hagan III and D. W. Johnston [eds.], Ecology and conservation of Neotropical
migrant landbirds. Smithsonian Institution Press, Washington, DC.
Robbins, C. S., J. R. Sauer, and R. Greenberg. 1989a. Population declines in North
American birds that migrate to the Neotropics. Proc. Natl. Acad. Sci. 86:7658-7662.
Robbins, C. S. 1979. Effect of forest fragmentation on bird populations. p. 33-48. In R.
M. DeGraaf and K. E. Evans [eds.], Management for non-game birds. Gen. Tech.
Rep. NC-51, North Central Forest Exp. Stn., US Forest Serv, St. Paul, MN.
Robinson, S. K. 1992. Population dynamics of breeding birds in a fragmented Illinois
landscape, p. 408-418. In J. M. Hagan III and D. W. Johnston [eds.], Ecology and
conservation of Neotropical migrant landbirds. Smithsonian Institution Press,
Washington, DC.
Scott, S. L. 1987. Field Guide to the Birds of North America. National Geographic
Society, Washington, DC.
Sherry, T. W., and R. T. Holmes. 1995. Summer versus winter limitation of populations:
what are the issues and what is the evidence? p. 85-120. In T. E. Martin and D. M.
Finch [eds.], Ecology and Management of Neotropical Migratory Birds. Oxford
University Press, Inc., New York, NY.
19. Small, M. F., and M. L. Hunter, Jr. 1989. Response of passerines to abrupt forest-river
and forest-powerline edges in Maine. Wilson Bull. 101:77-83.
Strelke, W. K., and J. G. Dickson. 1980. Effect of forest clear-cut edge on breeding
birds in east Texas. J. Wildl. Manage. 44:559-567.
Welsh. C. J. E., and W. M. Healy. 1993. Effect of even-aged timber management on
bird species diversity and composition in northern hardwoods of New Hampshire.
Wildl. Soc. Bull. 21:143-154.
Whitcomb, R. F., C. S. Robbins, J. F. Lynch, F. L. Whitcomb, M. K. Klimkiewicz, and
D. Bystrack. 1981. Effects of forest fragmentation on the avifauna of the eastern
deciduous forest. p. 125-205. In R. L. Burgess and D. M. Sharpe [eds.], Forest island
dynamics in man-dominated landscapes. Springer-Verlag, New York.
Wilcove, D. S., and S. K. Robinson. 1990. the impact of forest fragmentation on bird
communities in Eastern North America. p. 319-331. In A. Keast [ed.], Biogeography
and ecology of forest bird communities. SPB Academic Publishing, The Hague.
Wilcove, D. S., and R. F. Whitcomb. 1983. Gone with the trees. Natural History
9/83:82-91.