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1.
We studied the effects of anthropogenic edges on predation and parasitism of forest bird nests in an agriculturally fragmented
landscape and a continuously forested landscape in Ontario, Canada. Nesting data were collected at 1937 nests across 10 species
in the fragmented landscape from 2002–2008, and 464 nests across 4 species in the continuously forested landscape from 2006–2008.
Brood parasitism only occurred in the fragmented landscape, and was positively related to the proportion of rural grassland
and row crop habitats within 500-m of nests. Daily nest survival was negatively related to the density of roads within 500-m
of nests in the fragmented landscape, but was not influenced by distance to anthropogenic edge in either landscape. Predation
rates were higher in the fragmented landscape for Ovenbird and Rose-breasted Grosbeak nests, but did not differ between landscapes
for Veery and American Redstart nests. Uniformly high predation in the fragmented landscape may be a result of (1) matrix
predators that penetrate deep (>300 m) into the forest interior, or (2) the additive effect of forest-dependent and matrix-associated
predators that results in high predation pressure in both edge and interior habitats. Further research focused on the identification
of nest predators, their population dynamics, and habitat use is required to understand the underlying mechanisms leading
to uniformly high nest predation in fragmented landscapes. 相似文献
2.
Rates of nest predation for birds vary between and within species across multiple spatial scales, but we have a poor understanding
of which predators drive such patterns. We video-monitored nests and identified predators at 120 nests of the Acadian Flycatcher
(Empidonax virescens) and the Indigo Bunting (Passerina cyanea) at eight study sites in Missouri and Illinois, USA, during 2007–2010. We used an information-theoretic approach to evaluate
hypotheses concerning factors affecting predator-specific and overall rates of predation at landscape, edge, and nest-site
scales. We found support for effects of landscape forest cover and distance to habitat edge. Predation by Brown-headed Cowbirds
(Molothrus ater) increased, and predation by rodents decreased as landscape forest cover decreased. Predation by raptors, rodents, and snakes
increased as the distance to forest edges decreased, but the effect was modest and conditional upon the top-ranked model.
Despite the predator-specific patterns we detected, there was no support for these effects on overall rates of predation.
The interactions between breeding birds, nest predators, and the landscapes in which they reside are scale-dependent and context-specific,
and may be resistant to broad conceptual management recommendations. 相似文献
3.
Erin L. Koen Jeff Bowman Colin J. Garroway Stephen C. Mills Paul J. Wilson 《Landscape Ecology》2012,27(1):29-43
Landscape heterogeneity can influence animal dispersal by causing a directional bias in dispersal rate, as certain landscape
configurations might promote, impede, or prevent movement and gene flow. In forested landscapes, logging operations often
contribute to heterogeneity that can reduce functional connectivity for some species. American martens (Martes americana) are one such species, as they are considered specialists of late-seral coniferous forests. We assessed marten gene flow
to test the hypothesis that habitat management has maintained landscape connectivity for martens in the managed forests of
Ontario, Canada. We genotyped 653 martens at 12 microsatellite loci, sampled from 29 sites across Ontario. We expected that
if forest management has an effect on marten gene flow, we would see a correlation between effective resistance, estimated
by circuit theory, and genetic distance, estimated by population graphs. Although we found a positive relationship between
effective resistance and genetic distance (Mantel r = 0.249, P < 0.001), marten gene flow was better described by isolation by Euclidean distance (Mantel r = 0.410, P < 0.001). Our results suggest that managed forests in Ontario are well connected for marten and neither impede nor promote
marten gene flow at the provincial scale. 相似文献
4.
Landscape-scale Edge Effect in Predation Risk in Forest-farmland Mosaics of Central Europe 总被引:8,自引:1,他引:7
Avian nest predation is known to increase with the degree of forest fragmentation. A common explanation is that farmland allows
for high densities of generalist predators, and predators penetrating into the forest cause higher nest losses at forest-farmland
edges than in forest interiors. In contrast to numerous patch-level studies of forest edge effects conducted earlier, we broadened
the spatial extent to the landscape. We tested the hypothesis of increased predation near farmland over distances of >4 km
from forest–farmland edges into forest interiors in five mountain ranges in Germany, using artificial ground nests. We considered
two landscape settings: (1) Transitions between a forest matrix and a farmland matrix, and (2) farmland patches within a forest
matrix. Nest losses were not significantly higher in vicinity to a farmland matrix, but proximity to a pasture within the
forest matrix strongly increased predation risk. We speculate that these differences resulted from landscape geometry. Farmland
patches and matrix alike are highly attractive to generalist predators, and are regularly visited by red foxes from the forest.
Predators that traverse the forest and take prey along the way, will cause a concentration of predation risk towards a patch
(pasture), but not towards an adjacent matrix (farming lowlands), of feeding habitat. Contrary to previous evidence that edge
effects in nest predation level off after 50 m, nest fate was related to distance to pastures across the entire study extent
of 4.1 km. Our results suggest that landscape context and predator mobility may greatly affect spatial predation patterns. 相似文献
5.
Edge and area effects on avian assemblages and insectivory in fragmented native forests 总被引:1,自引:1,他引:0
Luc Barbaro Eckehard G. Brockerhoff Brice Giffard Inge van Halder 《Landscape Ecology》2012,27(10):1451-1463
Disentangling the confounded effects of edge and area in fragmented landscapes is a recurrent challenge for landscape ecologists, requiring the use of appropriate study designs. Here, we examined the effects of forest fragment area and plot location at forest edges versus interiors on native and exotic bird assemblages on Banks Peninsula (South Island, New Zealand). We also experimentally measured with plasticine models how forest fragment area and edge versus interior location influenced the intensity of avian insectivory. Bird assemblages were sampled by conducting 15?min point-counts at paired edge and interior plots in 13 forest fragments of increasing size (0.5?C141?ha). Avian insectivory was measured as the rate of insectivorous bird attacks on plasticine models mimicking larvae of a native polyphagous moth. We found significant effects of edge, but not of forest patch area, on species richness, abundance and composition of bird assemblages. Exotic birds were more abundant at forest edges, while neither edge nor area effects were noticeable for native bird richness and abundance. Model predation rates increased with forest fragmentation, both because of higher insectivory in smaller forest patches and at forest edges. Avian predation significantly increased with insectivorous bird richness and foraging bird abundance. We suggest that the coexistence of native and exotic birds in New Zealand mosaic landscapes enhances functional diversity and trait complementation within predatory bird assemblages. This coexistence results in increased avian insectivory in small forest fragments through additive edge and area effects. 相似文献
6.
Effects of landscape structure on nest predation in roadsides of a midwestern agroecosystem: a multiscale analysis 总被引:1,自引:1,他引:0
Bergin Timothy M. Best Louis B. Freemark Kathryn E. Koehler Kenneth J. 《Landscape Ecology》2000,15(2):131-143
Nest predation is an important cause of mortality for many bird species, especially in grassland ecosystems where generalist predators have responded positively to human disturbance and landscape fragmentation. Our study evaluated the influence of the composition and configuration of the surrounding landscape on nest predation. Transects consisting of 10 artificial ground nests each were set up in 136 roadsides in six watersheds in south-central Iowa. Nest predation on individual roadside transects ranged from 0 to 100% and averaged 23%. The relationship of landscape structure within spatially-nested landscapes surrounding each roadside transect (within 200, 400, 800, 1200, and 1600 m of the transect line) to nest predation was evaluated by using multiple regression and canonical correlation analyses. The results of this multiscale landscape analysis demonstrated that predation on ground nests was affected by the surrounding landscape mosaic and that nest predators with different-sized home ranges and habitat affinities responded to landscapes in different ways. In general, wooded habitats were associated with greater nest predation, whereas herbaceous habitats (except alfalfa/pasture) either were associated with less nest predation or were not important. Different landscape variables were important at different spatial scales. Whereas some block-cover habitats such as woodland were important at all scales, others such as rowcrops and alfalfa/pasture were important at large scales. Some strip-cover habitats such as gravel roads and paved roads were important at small scales, but others such as wooded roadsides were important at all all scales. Most landscape metrics (e.g., mean patch size and edge density) were important at large scales. Our study demonstrated that the relationships between landscape structure and predator assemblages are complex, thus making efforts to enhance avian productivity in agricultural landscapes a difficult management goal. 相似文献
7.
Fine-scale landscape change can alter dispersal patterns of animals, thus influencing connectivity or gene flow within a population.
Furthermore, dispersal patterns of different species may be influenced by the landscape in varying ways. Our research first
aimed to examine whether the spatial genetic structure within populations of closely related bird species differs in response
to the same landscape. Second, we examined whether individual-level movement characteristics are a mechanistic driver of these
differences. We generated a priori predictions of how landscape features will influence dispersal (particularly the response
of individuals to habitat boundaries both natural and human-induced) based on a movement model developed by Fahrig (Funct
Ecol 21:1003–1015, 2007). This model allowed us to predict genetic relatedness patterns in populations of two passerine bird species with different
life-history traits from Queensland, Australia (yellow-throated scrubwren Sericornis citreogularis, a habitat specialist; white-browed scrubwren Sericornis frontalis, a habitat generalist). We quantified our predictions using cost-distance modelling and compared these to observed pairwise
genetic distances (a
r
) between individuals as calculated from microsatellite markers. Mantel tests showed that our a priori models correlated with
genetic distance. Euclidean distance was most closely correlated to genetic distance for the generalist species (r = 0.093, P = 0.002), and landscape models that included the avoidance of unsuitable habitat were best for the specialist species (r = 0.107, P = 0.001). Our study showed that predictable movement characteristics may be the mechanism driving differences in genetic
relatedness patterns within populations of different bird species. 相似文献
8.
Forest bird species exhibit noticeable seasonal behavioral changes that might lead to contrasting effects of landscape pattern
upon species abundance and performance. We assessed if the effect of patch and habitat attributes on the landscape use of
thorn-tailed rayaditos (Aphrastura spinicauda), a forest bird in a relict patchy forest in northern Chile, varied temporally in association with changes in the behavior
of individuals linked to breeding vs. non-breeding conditions. We also assessed the relationship between nest success and
patch and habitat attributes, as nest success might be associated to the density rayaditos during the breeding season. We
found that density of rayaditos was affected by patch size and functional connectivity but not by habitat structure and that
the magnitude of the effect of patch size was greater during the non-breeding season, thus supporting the existence of a temporally
variable effect of landscape pattern. Similarly, the nest success of rayaditos was positively affected by functional connectivity
and negatively by structural connectivity. We hypothesize that these results emerged from the interaction among territorial
behavior, resource limitation and predation risk. Despite the variable intensity of the effect of patch size upon density,
however, this landscape attribute, in addition to connectivity, is essential for the persistence of rayaditos at this relict
patchy forest landscapes. 相似文献
9.
We measured the activity of mammalian predators, numbers of singing male songbirds, and predation rates on nests of songbirds (152 natural, open-cup nests and 380 artificial nests) on 38 250 m transects located along various types of forest-field edges in a wildlife management area in east-central Illinois. We then related these variables to each other and to measures of the vegetative structure of our transects that we anticipated might influence predator activity or predation rates on nests of birds characteristic of edge and shrubland habitats. Mammalian predators, particularly raccoons (Procyon lotor), were abundant in the wildlife area and present on all transects surveyed. We did not find significant relationships among the variables we measured. Rather, rates of nest predation were consistently high (>70%) and generally evenly distributed around our study site. Medium-sized, generalist mammalian predators in the midwestern United States reach their highest population densities in fragmented landscapes with abundant edge habitat, particularly agricultural edges. Areas of natural habitat in these landscapes dominated by agriculture may concentrate predators and act as ecological traps for nesting birds because they attract high densities of breeding birds that are subjected to high rates of nest predation. 相似文献
10.
Terhi Riutta Eleanor M. Slade Michael D. Morecroft Daniel P. Bebber Yadvinder Malhi 《Landscape Ecology》2014,29(6):949-961
Forest ecosystems have been widely fragmented by human land use, inducing significant microclimatic and biological changes at the forest edge. If we are to rigorously assess the ecological impacts of habitat fragmentation, there is a need to effectively quantify the amount of edge habitat within a landscape, and to allow this to be modelled for individual species and processes. Edge effect may extend only a few metres or as far as several kilometres, depending on the species or process in question. Therefore, rather than attempting to quantify the amount of edge habitat by using a fixed, case-specific distance to distinguish between edge and core, the area of habitat within continuously-varying distances from the forest edge is of greater utility. We quantified the degree of fragmentation of forests in England, where forests cover 10 % of the land area. We calculated the distance from within the forest patches to the nearest edge (forest vs. non-forest) and other landscape indices, such as mean patch size, edge density and distance to the nearest neighbour. Of the total forest area, 37 % was within 30 m and 74 % within 100 m of the nearest edge. This highlights that, in fragmented landscapes, the habitats close to the edge form a considerable proportion of the total habitat area. We then show how these edge estimates can be combined with ecological response functions, to allow us to generate biologically meaningful estimates of the impacts of fragmentation at a landscape scale. 相似文献
11.
David B. Lindenmayer Jeff T. Wood Ross B. Cunningham Mason Crane Christopher Macgregor Damian Michael Rebecca Montague-Drake 《Landscape Ecology》2009,24(8):1091-1103
We implemented a replicated before-after-control-impact (BACI) experiment to quantify vertebrate response in native forest
patches to a major change in the surrounding exotic Radiata Pine (Pinus radiata) plantation. We contrasted vertebrate occupancy of patches of native eucalypt forest where the surrounding stands of exotic
Radiata Pine (Pinus radiata) were clearfelled (termed “treatment patches”) with matched “control patches” where surrounding pine stands remained unlogged.
Different species of arboreal marsupials varied in their response to our experimental treatments. The Common Ringtail Possum
was unaffected by cutting of the surrounding pine stands, whereas all sightings of the Mountain Brushtail Possum were in control
patches. For birds, species richness was significantly reduced by 4–9 species in treatment patches. Birds with cup and dome
nests were those negatively affected by the cutting of the surrounding pine stands. They may be susceptible to altered microclimatic
conditions or increasing levels of nest predation when the surrounding pine matrix is clearfelled. Our study emphasized how
the biota inhabiting retained patches of native forest within plantation landscapes can be changed when stands of surrounding
Radiata Pine are clearfelled. In the case of birds, more species will be maintained within eucalypt patches if logging is
scheduled so that not all the surrounding pine plantation is clearfelled at once. 相似文献
12.
Studies dealing with community similarity are necessary to understand large scale ecological processes causing biodiversity
loss and to improve landscape and regional planning. Here, we study landscape variables influencing patterns of community
similarity in fragmented and continuous forest landscapes in the Atlantic forest of South America, isolating the effects of
forest loss, fragmentation and patterns of land use. Using a grid design, we surveyed birds in 41 square cells of 100 km2 using the point count method. We used multivariate, regression analyses and lagged predictor autoregressive models to examine
the relative influence of landscape variables on community similarity. Forest cover was the primary variable explaining patterns
of bird community similarity. Similarity showed a sudden decline between 20 and 40% of forest cover. Patterns of land use
had a second order effect; native bird communities were less affected by forest loss in landscapes dominated by tree plantations
(the most suitable habitat for native species) than in landscapes dominated by annual crops or cattle pastures. The effects
of fragmentation were inconclusive. The trade-off between local extinctions and the invasion of extra-regional species using
recently created habitats is probably the mechanism generating the observed patterns of community similarity. Limiting forest
loss to 30–40% of the landscape cover and improving the suitability of human-modified habitats will contribute to maintain
the structure and composition of the native forest bird community in the Atlantic forest. 相似文献
13.
With expansion of urban areas worldwide, migrating songbirds increasingly encounter fragmented landscapes where habitat patches
are embedded in an urban matrix, yet how migrating birds respond to urbanization is poorly understood. Our research evaluated
the relative importance of patch-level effects and body condition to movement behaviour of songbirds during migratory stopover
within an urban landscape. We experimentally relocated 91 migrant Swainson’s thrushes (Catharus ustulatus) fitted with 0.66 g radio-transmitters to seven forest patches that differed in area (0.7–38.4 ha) and degree of urbanization
within central Ohio, USA, May 2004–2007. Fine-scale movement rate of thrushes (n = 55) did not differ among urban forest sites, but birds in low energetic condition moved at higher rates, indicating an
energetically mediated influence on movement behaviour. In larger sites, Swainson’s thrushes (n = 59) had greater coarse-level movement during the first 3 days and utilized areas farther from forest edge, indicating stronger
influence by patch-level factors. Thrushes exhibited strong site tenacity, with only five individuals (7%) leaving release
patches prior to migratory departure. Movement outside the release patch only occurred at the smallest forest patches (0.7
and 4.5 ha), suggesting that these sites were too small to meet needs of some individuals. Swainson’s thrushes exhibited edge
avoidance and apparent area sensitivity within urban forest patches during stopover, implying that conservation of larger
patches within urban and other fragmented landscapes may benefit this species and other migrant forest birds. 相似文献
14.
Context
Species distributions are driven by a wide variety of abiotic and biotic factors, including nest placement for breeding individuals. As such, the spatial distribution of nests within a landscape can reflect environmental heterogeneity, habitat preferences, or even interactions with predators and other species.Objectives
We determined the extent to which environmental heterogeneity and predation risk accounted for the observed spatial distribution of nests.Methods
We assessed the spatial distribution of 112 nests of a migratory shorebird, the Hudsonian Godwit (Limosa haemastica), at Beluga River, Alaska, from 2009 to 2012, and explicitly tested for the relative influence of habitat characteristics and predation risk on nest locations. We also evaluated the effect of nest location, distance to conspecific nests, and proximity to roads on nest fate using 64 nests that were monitored through completion.Results
Hudsonian Godwit nests were clustered across the landscape despite a lack of significant spatial autocorrelation (i.e., patchiness) in vegetation characteristics at either the micro- or landscape scale. Nest fate also was not predicted by either the distance to the nearest conspecific neighbor or proximity to roads. Thus, neither habitat characteristics nor predation risk explained the clustering of godwit nests.Conclusions
These results suggest that godwits may select nest locations based more on social cues than underlying heterogeneity in vegetation or predation risk. As such, intra- and inter-specific interactions should be considered when developing management plans for species of conservation concern.15.
Matthew J. Smith Matthew G. Betts Graham J. Forbes Daniel G. Kehler Maryse C. Bourgeois Stephen P. Flemming 《Landscape Ecology》2011,26(5):709-721
Landscape composition and configuration, often termed as habitat loss and fragmentation, are predicted to reduce species population
viability, partly due to the restriction of movement in the landscape. Unfortunately, measuring the effects of habitat loss
and fragmentation on functional connectivity is challenging because these variables are confounded, and often the motivation
for movement by target species is unknown. Our objective was to determine the independent effects of landscape connectivity
from the perspective of a mature forest specialist—the northern flying squirrel (Glaucomys sabrinus). To standardize movement motivation, we translocated 119 squirrels, at varying distances (0.18–3.8 km) from their home range
across landscapes representing gradients in both habitat loss and fragmentation. We measured the physical connectedness of
mature forest using an index of connectivity (landscape coincidence probability). Patches were considered connected if they
were within the mean gliding distance of a flying squirrel. Homing success increased in landscapes with a higher connectivity
index. However, homing time was not strongly predicted by habitat amount, connectivity index, or mean nearest neighbour and
was best explained as a simple function of sex and distance translocated. Our study shows support for the independent effects
of landscape configuration on animal movement at a spatial scale that encompasses several home ranges. We conclude that connectivity
of mature forest should be considered for the conservation of some mature forest specialists, even in forest mosaics where
the distinction between habitat and movement corridors are less distinct. 相似文献
16.
Measuring edge effects in complex landscapes is often confounded by the presence of different kinds of natural and anthropogenic
edges, each of which may act differently on organisms inhabiting habitat patches. In such landscapes, proportions of different
habitats surrounding nests within patches often vary and may affect nesting success independently of distance to edges. We
developed methods to measure and study the effects of multiple edges and varying habitat composition around nests on the breeding
success of the Acadian flycatcher (Empidonax virescens), an understory, open-cup nesting songbird. The Kaskaskia River in Southwestern Illinois was our study area and consists
of wide (>1000-m) floodplain corridors embedded in an agricultural matrix with a variety of natural (wide rivers, backwater
swamps, and oxbow lakes) and anthropogenic (internal openings, and agricultural) habitats. We also measured vegetation structure
around each nest. Nest survival increased with increasing nest concealment, and probabilities of brood parasitism increased
with increasing distances from anthropogenic and natural water-related openings surrounding nests. The magnitude of these
effects was small, probably because the landscape is saturated with nest predators and brood parasites. These results illustrate
the importance of considering both larger landscape context and details of natural and anthropogenic disturbances when studying
the effects of habitat fragmentation on wildlife. 相似文献
17.
David J. Augustine Stephen J. Dinsmore Michael B. Wunder Victoria J. Dreitz Fritz L. Knopf 《Landscape Ecology》2008,23(6):689-697
Sylvatic plague is a major factor influencing the dynamics of black-tailed prairie dog (Cynomys ludovicianus) colonies in the western Great Plains. We studied the nesting response of the mountain plover (Charadrius montanus), a grassland bird that nests on prairie dog colonies, to plague-driven dynamics of prairie dog colonies at three sites in
the western Great Plains. First, we examined plover nest distribution on colonies that were previously affected by plague,
but that had been recovering (expanding) for at least 6 years. Plovers consistently nested in both young (colonized in the
past 1–2 years) and old (colonized for 6 or more years) portions of prairie dog colonies in proportion to their availability.
Second, we examined changes in plover nest frequency at two sites following plague epizootics, and found that mountain plover
nest numbers declined relatively rapidly (≤2 years) on plague-affected colonies. Taken together, our findings indicate that
available plover nesting habitat associated with prairie dog colonies closely tracks the area actively occupied by prairie
dogs each year. Given the presence of plague throughout most of the mountain plover’s breeding range in the western Great
Plains, important factors affecting plover populations likely include landscape features that determine the scale of plague
outbreaks, the distance that plovers move in response to changing breeding habitat conditions, and the availability and quality
of alternate breeding habitat within the landscape. 相似文献
18.
Frauke Ecke Pernilla Christensen Ralf Rentz Mats Nilsson Per Sandström Birger Hörnfeldt 《Landscape Ecology》2010,25(4):551-560
Changes in forest landscape structure have been suggested as a likely contributing factor behind the long-term decline in
the numbers of cyclic grey-sided voles (Clethrionomys rufocanus) in northern Fennoscandian lowland regions in contrast to mountain regions due to the absence of forest management in the
mountains. This study, for the first time, formally explored landscape structure in 29 lowland (LF) and 14 mountain forest
(MF) landscapes (each 2.5 × 2.5 km) in northern Sweden, and related the results to the cumulated spring trapping index of
the grey-sided vole in 2002–2006. The grey-sided vole showed striking contrasts in dynamics close in space and time. The MF
landscapes were characterized by larger patches and less fragmentation of preferred forest types. The grey-sided vole was
trapped in all of 14 analyzed MF landscapes but only in three out of 29 of the LF landscapes. MF and LF landscapes with grey-sided
vole occurrence were characterized by similar focal forest patch size (mean 357 ha, minimum 82 ha and mean 360 ha, minimum
79 ha, respectively). In contrast, these MF compared to the LF landscapes were characterized by larger patches of preferred
forest types and less fragmented preferred forest types and by a lower proportion of clear-cut areas. The present results
suggest that landscape structure is important for the abundance of grey-sided voles in both regions. However, in the mountains
the change from more or less seasonal dynamics to high-amplitude cycles between the mid 1990s and 2000s cannot be explained
by changes in landscape structure. 相似文献
19.
Responses of Chilean forest birds to anthropogenic habitat fragmentation across spatial scales 总被引:1,自引:1,他引:0
Although it is recognized that anthropogenic forest fragmentation affects habitat use by organisms across multiple spatial
scales, there is uncertainty about these effects. We used a hierarchical sampling design spanning three spatial scales of
habitat variability (landscape > patch > within-patch) and generalized mixed-effect models to assess the scale-dependent responses
of bird species to fragmentation in temperate forests of southern Chile. The abundances of nine of 20 bird species were affected
by interactions across spatial scales. These interactions resulted in a limited effect of within-patch habitat structure on
the abundance of birds in landscapes with low forest cover, suggesting that suitable local habitats, such as sites with dense
understory cover or large trees, are underutilized or remain unused in highly fragmented landscapes. Habitat specialists and
cavity-nesters, such as tree-trunk foragers and tapaculos, were most likely to exhibit interactions across spatial scales.
Because providing additional sites with dense understory vegetation or large habitat trees does not compensate the negative
effect of the loss of forest area on bird species, conservation strategies should ensure the retention of native forest patches
in the mixed-use landscapes. 相似文献
20.
Habitat for wide-ranging species should be addressed at multiple scales to fully understand factors that limit populations.
The marbled murrelet (Brachyramphus marmoratus), a threatened seabird, forages on the ocean and nests inland in large trees. We developed statistical relationships between
murrelet use (occupancy and abundance) and habitat variables quantified across many spatial scales (statewide to local) and
two time periods in California and southern Oregon, USA. We also addressed (1) if old-growth forest fragmentation was negatively
associated with murrelet use, and (2) if some nesting areas are more important than others due to their proximity to high
quality marine habitat. Most landscapes used for nesting were restricted to low elevation areas with frequent fog. Birds were
most abundant in unfragmented old-growth forests located within a matrix of mature second-growth forest. Murrelets were less
likely to occupy old-growth habitat if it was isolated (> 5 km) from other nesting murrelets. We found a time lag in response
to fragmentation, where at least a few years were required before birds abandoned fragmented forests. Compared to landscapes
with little tono murrelet use, landscapes with many murrelets were closer to the ocean's bays, river mouths, sandy shores,
submarine canyons, and marine waters with consistently high primary productivity. Within local landscapes (≤ 800ha), inland
factors limited bird abundance, but at the broadest landscape scale studied (3200 ha), proximity to marine habitat was most
limiting. Management should focus on protecting or creating large, contiguous old-growth forest stands, especially in low-elevation
areas near productive marine habitat.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献