Responses by Steller's Jays to forest fragmentation on southwest Vancouver Island and potential impacts of Marbled Murrelets
Date
2001
Authors
Masselink, Michelle Nella Maria
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Abstract
Steller's Jays (Cyanocitta stelleri) eat eggs and chicks of the threatened Marbled Murrelet (Brachyramphus marmoratus). Clearcut logging, in addition to reducing murrelet nesting habitat, may increase the risk of predation at murrelet nests by drawing jays to recently fragmented landscapes. To assess this risk, I investigated responses by Steller's Jays to man-made edges and clearcut habitat on southwest Vancouver Island in 1996-97.
At three study sites, standard point counts were conducted in old-growth stands bordering artificial (clearcuts and logging roads) and natural (river) edges. Counts indicated that there were significantly more jays in stands adjacent to clearcuts (post-breeding season counts averaged, 1.12 ± 0.23 SE jays per station) than in stands located either by roads (0.69 ± 0.13) or rivers (0.67 ± 0.14). In addition, jay abundance was significantly higher at stand edges (breeding season counts averaged 0.56 ± 0.11 SE and post-breeding counts averaged 1.17 ± 0.16 jays per station) than within stand cores (0.26 ± 0.07 SE and 0.50 ± 0.08 jays per station, respectively) for all stand locations combined. Counts conducted in the middle of clearcuts indicated that there was no significant difference between the number of jays at the centre and edges of clearcuts.
Radio-telemetry and single-point observations of jays that used clearcuts (referred to as cutblock jays, n = 6) and those that did not (referred to as forest-interior jays, n = 5) indicated that there was no difference between groups (mean± SD) in home-range size (24.6 ± 19.6 ha and 19.0 ± 20.9 ha respectively), total size of core area (3.4 ± 2.8 ha and 1.45 ± 1.31 ha, respectively) and the number of cores used (2 .5 ± 0.5 cores per bird for each group). Compositional analysis revealed that edge habitat (50 m on either side of abrupt forest edges) was selected for at the home-range scale (when compared to an area 20 times that of the home range; both groups analysed), and was selected for within jay home ranges ( only cutblock jays analysed).
Patterns of micro-habitat use were similar between groups as well. For cutblock jays, the mean percentage (± SD) of observations (all behaviours) at ground, shrub, subcanopy and canopy strata were 8.8 ± 9.3%, 25.4 ±12.6%, 37.7 ± 19.5% and 27.9 ± 19.2% respectively. For forest-interior jays they were 26.8 ± 21.4%, 22.2 ± 16.4%, 22.2 ± 8.1 % and 28.8 ± 13.8% respectively. Chi-square analysis of observations of randomly selected (nontagged) jays categorized as either cutblock birds (in clearcuts or within 75m of a clearcut/forest edge, n = 30) or forest-interior birds (≥ 200 m from the nearest clearcut/forest edge, n = 24) indicated that the relative frequencies of observations of all four strata were the same. Observations of jays foraging indicated that clearcut jays foraged at the canopy level nearly 10 (tagged jays) and four (randomly-selected jays) times more than forest-interior jays, but this was partly due to the ease of viewing the canopy from cutblocks than from within the forest.
I propose that forest fragmentation does not alter a jay' s response to its environment: spatial requirements, and macro and micro-habitat use were similar between jays that used new open habitat and those that did not. However, fragmentation does lead to a greater number of jays at edges and in stands bordering anthropogenic disturbance. These results suggest that the creation of edges either causes a shift in the distribution of jays across the landscape (moving from undisturbed to disturbed habitats) or attracts jays and causes an overall increase in jay populations in areas managed for timber harvesting. My data were insufficient to resolve these alternatives, but in either case murrelet nests in fragmented landscapes are exposed to more edge habitat and may therefore still be at greater risk to predation by jays. This risk can be minimized by reducing edge habitat through adjustments to harvesting schedules and the spatial distribution of cutblocks, leave-areas and roads.
Steller's Jays (Cyanocitta stelleri) eat eggs and chicks of the threatened Marbled Murrelet (Brachyramphus marmoratus). Clearcut logging, in addition to reducing murrelet nesting habitat, may increase the risk of predation at murrelet nests by drawing jays to recently fragmented landscapes. To assess this risk, I investigated responses by Steller's Jays to man-made edges and clearcut habitat on southwest Vancouver Island in 1996-97. At three study sites, standard point counts were conducted in old-growth stands bordering artificial (clearcuts and logging roads) and natural (river) edges. Counts indicated that there were significantly more jays in stands adjacent to clearcuts (post breeding season counts averaged, 1.12 ± 0.23 SE jays per station) than in stands located either by roads (0.69 ± 0.13) or rivers (0.67 ± 0.14). In addition, jay abundance was significantly higher at stand edges (breeding season counts averaged 0.56 ± 0.11 SE and post-breeding counts averaged 1.17 ± 0.16jays per station) than within stand cores (0.26 ± 0.07 SE and 0.50 ± 0.08 jays per station, respectively) for all stand locations combined. Counts conducted in the middle of clearcuts indicated that there was no significant difference between the number of jays at the centre and edges of clearcuts. Radio-telemetry and single-point observations of jays that used clearcuts (referred to as cutblock jays, n = 6) and those that did not (referred to as forest-interior jays, n = 5) indicated that there was no difference between groups (mean± SD) in home-range size (24.6 ± 19.6 ha and 19.0 ± 20.9 ha respectively), total size of core area (3.4 ± 2.8 ha and 1.45 ± 1.31 ha, respectively) and the number of cores used (2 .5 ± 0.5 cores per bird for each group). Compositional analysis revealed that edge habitat (50 m on either side of abrupt forest edges) was selected for at the home-range scale (when compared to an area 20 times that of the home range; both groups analysed), and was selected for within jay home ranges ( only cutblock jays analysed). Patterns of micro-habitat use were similar between groups as well. For cutblock jays, the mean percentage(± SD) of observations (all behaviours) at ground, shrub, subcanopy and canopy strata were 8.8 ± 9.3%, 25.4 ±12.6%, 37.7 ± 19.5% and 27.9 ± 19.2% respectively. For forest-interior jays they were 26.8 ± 21.4%, 22.2 ± 16.4%, 22.2 ± 8.1 % and 28 .8 ± 13 .8% respectively. Chi-square analysis of observations ofrandomly selected (nontagged) jays categorized as either cutblock birds (in clearcuts or within 75m of a clearcut/forest edge, n = 30) or forest-interior birds (~ 200 m from the nearest clearcut/forest edge, n = 24) indicated that the relative frequencies of observations of all four strata were the same. Observations of jays foraging indicated that clearcut jays foraged at the canopy level nearly 10 (tagged jays) and four (randomly-selected jays) times more than forest-interior jays, but this was partly due to the ease of viewing the canopy from cutblocks than from within the forest. I propose that forest fragmentation does not alter a jay' s response to its environment: spatial requirements, and macro and micro-habitat use were similar between jays that used new open habitat and those that did not. However, fragmentation does lead to a greater number of jays at edges and in stands bordering anthropogenic disturbance. These results suggest that the creation of edges either causes a shift in the distribution of jays across the landscape (moving from undisturbed to disturbed habitats) or attracts jays and causes an overall increase in jay populations in areas managed for timber harvesting. My data were insufficient to resolve these alternatives, but in either case murrelet nests in fragmented landscapes are exposed to more edge habitat and may therefore still be at greater risk to predation by jays. This risk can be minimized by reducing edge habitat through adjustments to harvesting schedules and the spatial distribution of cutblocks, leave-areas and roads.
Steller's Jays (Cyanocitta stelleri) eat eggs and chicks of the threatened Marbled Murrelet (Brachyramphus marmoratus). Clearcut logging, in addition to reducing murrelet nesting habitat, may increase the risk of predation at murrelet nests by drawing jays to recently fragmented landscapes. To assess this risk, I investigated responses by Steller's Jays to man-made edges and clearcut habitat on southwest Vancouver Island in 1996-97. At three study sites, standard point counts were conducted in old-growth stands bordering artificial (clearcuts and logging roads) and natural (river) edges. Counts indicated that there were significantly more jays in stands adjacent to clearcuts (post breeding season counts averaged, 1.12 ± 0.23 SE jays per station) than in stands located either by roads (0.69 ± 0.13) or rivers (0.67 ± 0.14). In addition, jay abundance was significantly higher at stand edges (breeding season counts averaged 0.56 ± 0.11 SE and post-breeding counts averaged 1.17 ± 0.16jays per station) than within stand cores (0.26 ± 0.07 SE and 0.50 ± 0.08 jays per station, respectively) for all stand locations combined. Counts conducted in the middle of clearcuts indicated that there was no significant difference between the number of jays at the centre and edges of clearcuts. Radio-telemetry and single-point observations of jays that used clearcuts (referred to as cutblock jays, n = 6) and those that did not (referred to as forest-interior jays, n = 5) indicated that there was no difference between groups (mean± SD) in home-range size (24.6 ± 19.6 ha and 19.0 ± 20.9 ha respectively), total size of core area (3.4 ± 2.8 ha and 1.45 ± 1.31 ha, respectively) and the number of cores used (2 .5 ± 0.5 cores per bird for each group). Compositional analysis revealed that edge habitat (50 m on either side of abrupt forest edges) was selected for at the home-range scale (when compared to an area 20 times that of the home range; both groups analysed), and was selected for within jay home ranges ( only cutblock jays analysed). Patterns of micro-habitat use were similar between groups as well. For cutblock jays, the mean percentage(± SD) of observations (all behaviours) at ground, shrub, subcanopy and canopy strata were 8.8 ± 9.3%, 25.4 ±12.6%, 37.7 ± 19.5% and 27.9 ± 19.2% respectively. For forest-interior jays they were 26.8 ± 21.4%, 22.2 ± 16.4%, 22.2 ± 8.1 % and 28 .8 ± 13 .8% respectively. Chi-square analysis of observations ofrandomly selected (nontagged) jays categorized as either cutblock birds (in clearcuts or within 75m of a clearcut/forest edge, n = 30) or forest-interior birds (~ 200 m from the nearest clearcut/forest edge, n = 24) indicated that the relative frequencies of observations of all four strata were the same. Observations of jays foraging indicated that clearcut jays foraged at the canopy level nearly 10 (tagged jays) and four (randomly-selected jays) times more than forest-interior jays, but this was partly due to the ease of viewing the canopy from cutblocks than from within the forest. I propose that forest fragmentation does not alter a jay' s response to its environment: spatial requirements, and macro and micro-habitat use were similar between jays that used new open habitat and those that did not. However, fragmentation does lead to a greater number of jays at edges and in stands bordering anthropogenic disturbance. These results suggest that the creation of edges either causes a shift in the distribution of jays across the landscape (moving from undisturbed to disturbed habitats) or attracts jays and causes an overall increase in jay populations in areas managed for timber harvesting. My data were insufficient to resolve these alternatives, but in either case murrelet nests in fragmented landscapes are exposed to more edge habitat and may therefore still be at greater risk to predation by jays. This risk can be minimized by reducing edge habitat through adjustments to harvesting schedules and the spatial distribution of cutblocks, leave-areas and roads.