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2015 Vol. 14, Special Issue 7
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Canaan Valley & Environs
2015 Southeastern Naturalist 14(Special Issue 7):357–364
Nesting Birds in Hawthorn-Savannah Habitats of Canaan
Valley, Tucker County, West Virginia
James T. Anderson1,* and Kelly A. Chadbourne1,2
Abstract - A decline in the amount of North America’s early-successional habitats has triggered
a concern for birds that nest in these environments. In West Virginia and throughout
the Northeast, sharp drops have been detected in the populations of early-successional
birds. We monitored the nest success of birds in Crataegus (hawthorn)-dominated areas of
grasslands in the Canaan Valley National Wildlife Refuge (herein called The Refuge) during
the summers of 1999 and 2000. We found 30 nests of six species, including Bombycilla
cedrorum (Cedar Waxwing), Turdus migratorius (American Robin), Pooecetes gramineus
(Vesper Sparrow), Tyrannus tyrannus (Eastern Kingbird), Spizella passerina (Chipping
Sparrow), and Geothlypis trichas (Common Yellowthroat). Hawthorn trees were the
dominant plants used for nest placement. Overall, a similar number of nests fledged young
(n = 17, 56.7%) as failed (n = 13, 43.3%) (P = 0.31). We attributed most nest failures to avian
or mammalian predation, which may reflect an edge effect. The clutch size of the Cedar
Waxwing was greater than for other species (P = 0.03). We recommend that The Refuge’s
managers focus on reducing edge features, studying predator-edge relations, and monitoring
avian use of early-successional habitats.
Introduction
Populations of shrubland songbirds have declined throughout North America,
indicating that greater conservation of shrublands and open habitats are needed
(Askins 2000, Hunter et al. 2001, Sauer et al. 2008). The clearing of the eastern
forest for European settlement allowed a variety of successional habitats to
develop. With fewer of these kinds of disturbances, along with declining natural
habitat conditions, many species may become locally extirpated or extinct
(Askins 2001, Hunter et al. 2001, Trani et al. 2001). Reasons for the decline in the
numbers of early-successional songbirds include habitat loss, changes in logging
practices, and higher predation rates in fragmented and edge habitats (Woodward
et al. 2001). Zegers et al. (2000) noted that the rates of predation along habitat
edges may be attributed to the landscape matrix, structure of the edge, and the
nature of the habitats producing the edge.
Problems associated with habitat edges, the boundary between adjacent
dissimilar habitats, and habitat fragments may negatively affect nesting in shrublands.
Songbirds nesting in edges or fragments are more susceptible to predation
and parasitism because nest predators and Molothrus ater (Boddaert) (Brownheaded
Cowbird) are more abundant and active in these areas (Paton 1994,
1Wildlife and Fisheries Resources Program, Division of Forestry and Natural Resources,
West Virginia University, PO Box 6125, Morgantown, WV 26506. 2 Current address - US
Fish and Wildlife Service, Great Bay National Wildlife Refuge, 100 Merrimac Drive,
Newington, NH 03801.*Corresponding author - jim.anderson@mail.wvu.edu.
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2015 Vol. 14, Special Issue 7
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Woodward et al. 2001). In West Virginia, particularly in Canaan Valley (hereafter,
the Valley), shrubland songbirds use the forest-grassland ecotone. While some
of the cover types in rural landscapes—such as orchards, hedgerows, and pine
plantations—appear to the casual observer to be adequate, evidence suggests that
these areas do not support viable populations of disturbance-dependent songbirds
(Hunter et al. 2001). One such ecotone in the Valley is dominated by hawthorn
savannah, with lesser amounts of Hypericum densiflorum Pursh (Glade St. John’s
Wort) and Spiraea alba Du Roi (Narrow-leaved Meadowsweet) meadows. Although
some data have been collected on the nesting success of shrubland birds
in southern West Virginia (Hunter et al. 2001), little is known about the Valley’s
nesting shrubland songbirds. Our objectives were to measure the breeding activity,
selected life-history features like clutch size, and nesting success of the
songbirds of the Valley’s scrub-shrub habitat.
Materials and Methods
Study sites
We studied four hawthorn-savannah or other early-successional habitats bordering
grasslands in the Canaan Valley National Wildlife Refuge (hereafter called
“the Refuge”), in Tucker County, WV (Fig. 1). The Refuge’s dominant shrubland
vegetation consisted of hawthorn, Glade St. John’s Wort, and Narrow-leaved
Meadowsweet. Summer temperatures averaged 75–79 oF (24 to 26 °C) during the
day and 50–55 oF (10 to 13 °C) in the evenings. Due to its cool climate, the flora
of the Valley is composed of plant species with northern ranges; for some species
the Valley is the southernmost limit of their range (Fortney 1993). In a normal
year, the Valley receives 46 in (114 cm) of rainfall (NOAA 1999). During 1999,
total annual rainfall was 38 in (96 cm), with lower than average rainfall from June
through September. Additionally, West Virginia experienced a statewide drought
during the summer of 1999. In 2000, the Valley’s total rainfall of 45 in (113 cm)
was normal (NOAA 2000).
Field methods
During the breeding seasons of May to August of both 1999 and 2000, we
walked through each of the four tracts daily, recording bird-nesting behaviors and
searching for nests. Each day, we followed a different route to maximize coverage.
We placed flags 16.5 ft (5 m) north of each nest to minimize disturbance from
repetition (Davis and Sealy 1998), except where the nest was obvious and flags
may have offered visual cues to predators. In these situations, nests were either
not flagged or were placed farther from the nests. To minimize disturbance, we
monitored known nests every 3 to 5 days to determine clutch size and nest fate.
When nests became inactive, we scored nest fate as either “success” or “failure”.
If three criteria—nestlings were at fledging age, nest site was in good condition,
and parents were defensive—were met, the nest was considered a success. A nest
was scored as a failure when a complete clutch of eggs or brood of nestlings disappeared
before the species’ average fledging ages.
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Statistical analyses
Because our data set is based on few nests, we combined the data from both
years and four tracts for our analyses by species. We analyzed nest-fate data for
Turdus migratorius L. (American Robin), Bombycilla cedrorum Vieillot (Cedar
Waxwing), Spizella passerina (Bechstein) (Chipping Sparrow), Geothlypis
trichas (L.) (Common Yellowthroat), Tyrannus tyrannus (L.) (Eastern Kingbird),
Figure 1. Canaan Valley National Wildlife Refuge (CVNWR) grassland study sites with
shrub habitat in Tucker County, WV for 1999 and 2000.
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and Pooecetes gramineus (Gmelin) (Vesper Sparrow) by using apparent nest success,
defined as number of successful nests/total nests, and the modified Mayfield
method, which accounts for the length of time a nest is under observation (Johnson
1979, Mayfield 1975). In general, apparent nest success overestimates total
survival because nests lost early in the laying period are less likely to be found.
We compared apparent nest success and average clutch size among species using
the nonparametric Kruskal-Wallis test because low sample sizes precluded our
meeting the assumptions of parametric procedures (Conover 1980). To improve
the reliability of the test, we combined all species for which we found only one
or two nests (Conover 1980). For inferring significance we accep ted P < 0.05.
Results
We found a total of 30 nests of shrubland birds. These included eight nests of
American Robins, 14 of Cedar Waxwings, 4 of Chipping Sparrows, 1 of Common
Yellowthroats, 2 of Eastern Kingbirds, and 1 of Vesper Sparrows. All nests were
used to analyze nest survival and clutch size (Tables 1, 2). Cedar Waxwings began
building their nests at the end of June in 1999 and 2000. American Robins, Chipping
Sparrows, Common Yellowthroats, Eastern Kingbirds, and Vesper Sparrows
built during May through July. The nests of American Robins, Cedar Waxwings,
and Eastern Kingbirds were sited in hawthorn trees. Chipping Sparrows and Common
Yellowthroats commonly used the transition areas, which were dominated
by St. John’s Wort and Narrow-leaved Meadowsweet, both of which usually grew
between hawthorn-savannah and grassland habitats. Although Vesper Sparrows
used hawthorn-savannah for foraging, they nested in the transitional area.
Apparent nest success ranged from zero percent for Common Yellowthroats to
100% for Eastern Kingbirds and Vesper Sparrows; it averaged 56.7% (SE = 16.3)
for all nests (Table 1). Because we found only one or two nest(s) for each species,
Mayfield nest success could not be calculated for Common Yellowthroats,
Eastern Kingbirds, and Vesper Sparrows. Mayfield nest success ranged from 25%
for the Cedar Waxwings to 51% for Chipping Sparrows (Table 3) and averaged
Table 1. Number and fate of nests for each bird species and year in the scrub-shrub habitat of the
Canaan Valley National Wildlife Refuge, Tucker County, West Virginia for the 1999 and 2000
breeding seasons.
No. nests monitored Nest fateA
Species Total 1999 2000 Depredated Fledged Abandoned
American Robin 8 2 6 3 (37.5) 5 (62.5) 0 (0)
Cedar Waxwing 14 6 8 5 (36) 8 (57) 1 (7)
Chipping Sparrow 4 3 1 3 (75) 1 (25) 0 (0)
Common Yellowthroat 1 0 1 1 (100) 0 (0) 0 (0)
Eastern Kingbird 2 1 1 0 (0) 2 (100) 0 (0)
Vesper Sparrow 1 0 1 0 (0) 1 (100) 0 (0)
Total 30 12 18 12 (40) 17 (56.7) 1 (3.3)
ANumbers in parentheses indicate percent based on total number of nests for each species in 1999
and 2000 combined.
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33.64% (SE = 21.4) across all species. The percent of nests that fledged young
(56.7%) did not differ (G2 = 2.34, P = 0.31) from the percent of unsuccessful
nests (43.3%) for each species. Mean clutch size was greater (χ2 = 8.79, P = 0.03)
for Cedar Waxwings than for the other species (Table 2). No nests were parasitized
by Brown-headed Cowbirds.
Discussion
Nest success, estimated as the Mayfield nest success, varied among species,
but overall the proportions of successful and unsuccessful nests were similar.
Although 13% more nests were successful than unsuccessful, low sample sizes
may have contributed to our inability to infer a significant difference (Cohen
1977). Total and daily nest survival rates were high for all species and similar
among species. Our observed rates were similar to those for songbird communities
in shrubland habitats of the Northeast and Midwest (King and Byers 2002,
Woodward et al. 2001). Cedar Waxwing nests typically failed during incubation,
and thus led to complete brood failure. Some studies indicate that Cedar Waxwings
are so abundant that they are considered to be a pest in farm areas (Witmer
et al. 1997). While Cedar Waxwings were not overly abundant in the Valley, 57%
of their nests were successful, producing >30 fledglings. Their large average
clutch size may compensate for high nest losses during incubati on.
Table 3. Number of active nests, exposure days (ED), Mayfield (1975) nest success (OSR), and
daily survival rate (DSR) for bird nests in the shrublands of the Canaan Valley National Wildlife
Refuge, Tucker County, WV in 1999 and 2000.
Species n ED OSR DSR
American Robin 8 100 0.31 0.96
Cedar Waxwing 14 266 0.25 0.98
Chipping Sparrow 4 14 0.51 0.85
Common YellowthroatA 1 2 . .
Eastern Kingbird 2 27 . .
Vesper Sparrowa 1 5 . .
AMayfield (1975) nest success could not be calculated because >1 nest is needed.
Table 2. Average clutch size in nests of shrubland birds found on the Canaan Valley National Wildlife
Refuge, Tucker County, WV during 1999–2000.
Species nA MeanB SE
American Robin 8 3.12B 0.29
Cedar Waxwing 14 4.14A 0.21
Chipping Sparrow 4 3.25AB 0.48
Common Yellowthroat 1 2.00B .
Eastern Kingbird 2 3.00B 0.00
Vesper Sparrow 1 2.00B .
ACommon Yellowthroat, Eastern Kingbird, and Vesper Sparrows were combined for analyses due
to low samples sizes.
BMeans with the same letter were not different based on G-tests at P < 0.05.
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In some of our study sites, the contiguous area covered by scrub-shrub habitat
was less than 5 ac (2 ha). Many scrub-shrub birds avoid habitat patches of
that area and smaller; they begin to increase in density in patches >30 ac (12
ha) (Hunter et al. 2001). However, patches ≥100 ac (40 ha) may be more desirable
(Hunter et al. 2001). Many of the scrub-shrub habitats on the Refuge are
small patches interspersed through grasslands or open areas. They do not form
the large blocks of contiguous habitats that seem to be preferred by many bird
species (Freemark and Merriam 1986, Vickery et al. 1994). Additionally, small
patches may increase nest depredation (Andrén 1992, Andrén and Angelstam
1988, Bolger et al. 1991).
Overall, we attributed 92% of the nest failures of the Refuge’s shrubland birds
to predators. Direct evidence of such predation included observations of nests that
had been removed from shrubs, from which all of the eggs had disappeared before
their estimated fledge date, and which contained the remains of smashed or partly
consumed eggshells (reviewed by Heske et al. 2001, Jiménez and Conover 2001).
Other studies have also cited predation as the main reason for nest failure (Patterson
and Best 1996, Winter 1999, Wray 1979). In West Virginia, Wray (1979) found
that 78% of unsuccessful nests resulted from bird or snake depredation.
Potential nest predators in the Valley include Elaphe obsoleta (Say in James
1823) (Rat Snake), Coluber constrictor constrictor L. (Northern Black Racer),
Cyanocitta cristata (L.) (Blue Jay), Corvus brachyrhynchos Brehm (American
Crow), Corvus corax L. (Common Raven), Troglodytes aedon Vieillot (House
Wren), Mephitis mephitis Schreber (Striped Skunk), Vulpes vulpes L. (Red
Fox), Peromyscus leucopus Rafinesque (White-footed Mouse), Tamias striatus
L. (Eastern Chipmunk), Procyon lotor L. (Raccoon), and Odocoileus virginianus
Zimmermann (White-tailed Deer) (USFWS 1979, Witmer et al. 1997). Most of
these predators have been observed on the Refuge and may have contributed to
nest losses. While depredation is probably the largest factor contributing to the
losses of nests in the Valley, it appears that the shrubland songbirds monitored in
this study have maintained or even increased their populations.
Management Implications
Nests in edge habitats are assumed to have higher depredation rates. Therefore,
managers should remove internal edges, like remnant fence lines, hedgerows,
and windbreaks, from the shrubland parts of the Refuge. These internal edges
concentrate predators (Heske et al. 2001). Creating feathered edges (i.e., intermixing
of horizontal and vertical strata to create more complex edges) rather
than maintaining distinct breaks in habitat types may also benefit shrubland birds
by decreasing predation rates due to the greater availability of nesting sites that
reduce the search efficiency of predators.
Determining the densities of the various predators, such as small mammals,
reptiles, and raptors, would help us understand the scope of nest losses. Focusing
on predator populations would also provide data for a comprehensive management
plan that would benefit the Refuge’s shrubland birds. Another potential
threat is nest parasitism by Brown-headed Cowbirds. While it was not a problem
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2015 Vol. 14, Special Issue 7
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during our study, it could become an issue in the future in those places where
Cowbirds occur in the Valley.
Additionally, little is known about songbird success in early shrub-dominated
habitats in the Valley. Because we studied only a small part of the Refuge, about
20–25 ac (8–10 ha), our findings may not accurately reflect the overall nesting
success of songbirds throughout the Valley. Accordingly, we recommend further
study of the Valley’s early-successional shrub habitats and the consideration
of the adjacent grassland species (Warren and Anderson 2005). It is important
to evaluate the status of songbird species that use these habitats in the Valley
because of (1) their general decline throughout North America and (2) the abundance
of early-successional habitats in the Valley.
Acknowledgments
For funding, we thank the Canaan Valley National Wildlife Refuge of the US Fish and
Wildlife Service; West Virginia Division of Natural Resources; West Virginia University’s
Division of Forestry and Natural Resources and the Davis College of Agriculture, Natural
Resources, and Design (Brown Faculty Development Fund); and the West Virginia
Agricultural and Forestry Experiment Station (McIntire-Stennis). We also thank R.C.
Whitmore and L. Butler for reviewing an early draft of the manuscript. This is Paper No.
3095 of the West Virginia University Agricultural and Forestry Experiment Station.
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