Progress 10/01/05 to 09/30/08
Outputs
OUTPUTS: Following completion of the Bicknell's Thrush population model, our next objective was to model the effects of climate change on the distribution of Bicknell's Thrush in Vermont. Distributional response to an increase in mean summer temperature will be a useful tool for prioritization of conservation of high elevation forest areas. Identifying the critical patches of montane forest for promoting population persistence into the future by concentrating conservation efforts in those areas. For Vermont, we combined a spatial model of boreal tree species basal area (Beckage et al. 2008) with a model of potential Bicknell's Thrush habitat at the landscape scale (Lambert et al. 2005) to create a new base map of predicted habitat suitability currently and in the future. Future conditions represent potential habitat suitability and availability with 1 deg C of warming of mean July temperature (Hayhoe et al. 2008, Rodenhouse et al. 2008). We used the habitat suitability maps (current and future) as input the variables for the metapopulation model (Frey 2008) to predict probability of occupancy, and local colonization and extinction across Vermont currently and with 1 deg C of warming. Response of population parameters were modeled as a function of changes predicted to occur from climate change at both the local (boreal basal area) and landscape scale (montane forest patch size). Literature cited: Beckage, B., B. et al. 2008. A rapid upward shift of a forest ecotone during 40 years of warming in the Green Mountains of Vermont. PNAS 105:4197-4202. Frey, S. J. K. 2008. Metapopulation dynamics and multi-scale habitat selection of a montane forest songbird. Master's thesis, UVM, Burlington, VT. Hayhoe, K. et al. 2008. Regional Climate Change Projections for the NE USA. Mitigation and Adaptation Strategies for Global Change DOI 10.1007/s11027-007-9133-2 Lambert, J. D. et al. 2005. A practical model of Bicknell's Thrush distribution in the northeastern United States. Wilson Bulletin 117:1-11. Rodenhouse, N. L. et al. 2008. Potential effects of climate change on birds of the northeast. Mitigation and Adaptation Strategies for Global Change 13:517-540. Events and dissemination: This project was presented at an international meeting in Portland, OR (126th Meeting of the AOU & 28th Meeting of the Society of Canadian Ornithologists) and will be presented at a national meeting in 2009 in Philadelphia, PA (127th Annual Meeting of the AOU). PARTICIPANTS: This project supported M.S. research by Sarah Frey, in the University of Vermont's Rubenstein School of Environment and Natural Resources (graduation May 2008). Training on high elevation bird identification and habitat mensuration was provided to two individuals that assisted with data collection (Juliette Juillerat and Hector Slongo). The Vermont Center for Ecostudies (VCE) served as a partner organization throughout the study, as data were used from their Mountain Birdwatch program in the analysis. Several biologists are co-authors on manuscripts in preparation pertaining to the findings from this research. Additionally, Therese Donovan of the Vermont Cooperative Fish and Wildlife Research Unit served as a member of Frey's graduate committee and was instrumental in providing support for data analysis. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
A 1 deg C increase in mean July temperature dramatically reduces the amount of montane habitat available for Bicknell's Thrush in Vermont (67% decrease). The number of montane patches decreased from 128 to 29. However, the average patch size increased by 44.6% (from 90.5 to 130.8ha). Changes in local habitat were less dramatic. Although there were fewer patches under the future scenario, the patches that remained represent higher quality habitat (i.e. higher boreal basal area). This is seen by the higher average boreal tree species basal area (60.6 m2/ha mean pixel value after warming, 29.1m2/ha before) under future predicted local habitat conditions. This is likely because sites at higher elevations have higher boreal basal area (Beckage et al. 2008). A 1 deg C increase in temperature reduced the montane patches by removing the warmer lower elevation sites, which reduced the number of sites (pixels) with lower boreal basal area values. While the total amount of habitat decreased by 67%, the total boreal basal area within all of the montane patches decreased by 31.3% (from 371,500 to 255,295 m2/ha) with 1 deg C of warming. The average probability of occupancy and colonization per site (pixel) did not change much between current conditions and predicted habitat conditions under 1 deg C of MJT increase (% change: occupancy -3.8%, colonization -1.3%). Conversely, average extinction probability per site (pixel) increased by 11.3%. Probability of site colonization was least affected by changes in the landscape scale habitat loss regarding an individual site's (pixel) or patch's likelihood of becoming colonized by Bicknell's' Thrush. However, the total number of suitable sites available for colonization decreased by 66.8%. The population implications for a warming of 1 deg C are primarily related to the total amount of habitat lost. The composition of the montane patches was altered with increased summer temperatures, but less so than the overall amount of habitat available to Bicknell's Thrush. The loss of lower elevation sites probably has less of an impact on the population of Bicknell's Thrush because they contain less of the local habitat conditions favored by this high elevation specialist. With small levels of warming, Bicknell's Thrush may be able to persist given the local habitat conditions are favorable in the remaining patches. More than 1 deg C of temperature increase calls into question ability of Bicknell's Thrush to persist in Vermont due to potentially severe habitat loss. Literature cited Beckage, B., B. Osborne, D. G. Gavin, C. Pucko, T. Siccama and T. Perkins. 2008. A rapid upward shift of a forest ecotone during 40 years of warming in the Green Mountains of Vermont. Proceeding of the National Academy of Science 105:4197-4202.
Publications
- Frey, S.J., Strong, A.M., Lambert, J.D., and Hart, J.A. 2008. The importance of scale in determining site occupancy patterns for a montane forest songbird in Vermont. Abstracts of the 126th Meeting of the American Ornithologists Union, 78th Meeting of the Cooper Ornithological Society, 28th Meeting of the Society of Canadian Ornithologists, Portland, OR. Page 68.
- Frey, S. J. K. 2008. Metapopulation dynamics and multi-scale habitat selection of a montane forest songbird. Masters thesis, University of Vermont, Burlington, VT.
- Frey, S. J. K., A. M. Strong, J. D. Lambert, and J. A. Hart. 2009. Metapopulation dynamics and multi-scale habitat selection of Bicknells Thrush in Vermont. In prep. To be part of an Ornithological Monographs issue on Bicknells Thrush conservation.
- McFarland, K. P., M. Hartley, S. J. K. Frey, C. C. Rimmer, and J. D. Lambert. 2009. Effects of a pulsed resource on songbird populations in fir forests of northeastern North America. In prep. Target journal for submission: Oecologia.
- Frey, S. J. K., A. M. Strong, and McFarland, K. P. 2009. Population-level implications of climate change for a montane forest songbird, Bicknells Thrush. In prep. Target journal for submission: Conservation Biology.
- Frey, S. J. K., A. M. Strong, and McFarland, K. P. 2009. Population-level implications of climate change on a montane forest songbird, Bicknells Thrush. Symposium on Ecology and Conservation of a Rare, Declining Species, Bicknells Thrush. 127th Annual Meeting of the American Ornithologists Union. Philadelphia, PA.
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Progress 10/01/06 to 09/30/07
Outputs
OUTPUTS: Activities: Detection/non-detection data were collected for Bicknell's Thrush across 88 sites during the breeding seasons in 2006 and 2007. Local habitat characteristics were measured for each site and landscape-level features were calculated using a predictive habitat model. The six local habitat variables were combined using a principal component analysis. Principal component 1 (PC1) described a gradient of increasing coniferous shrub density and proportion of coniferous dominated forest with decreasing canopy height. The landscape covariate was calculated by dividing patch size by patch isolation creating a continuum of small, isolated patches to large, less isolated patches. Thus each site was characterized by a single local habitat (PC1) and landscape metric. From these data, 67 models considering all combinations of landscape and local habitat scores (univariate, additive and interaction) were evaluated for individual estimates of the following parameters: (1) probability of detection, (2) probability of initial site occupancy, (3) probability of site colonization, and (4) probability of local site extinction. AIC model selection techniques were used to rank the models, which represented ecologically plausible hypotheses that compared the strength of local habitat characteristics to large-scale landscape features. Events and dissemination: These findings were presented at one local (Rubenstein School Graduate Symposium) and one international meeting (North American Ornithological Conference, Veracruz, Mexico). PARTICIPANTS: This project supported M.S. research by Sarah Frey, in the University of Vermont's Rubenstein School of Environment and Natural Resources. Training on high elevation bird identification and habitat mensuration was provided to two individuals that assisted with data collection (Juliette Juillerat and Hector Slongo). The Vermont Center for Ecostudies served as a partner organization throughout the study, as data were used from their Mountain Birdwatch program in the analysis. Additionally, Therese Donovan of the Vermont Cooperative Fish and Wildlife Research Unit served as a member of Frey's graduate committee and was instrumental in providing support for data analysis. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Habitat models for the Bicknell's Thrush were assessed using model selection criteria; models within 4 AICc points of the top model were considered plausible. The top eight models were all plausible. Landscape characteristics alone were not significant in driving population dynamics. The relative importance of landscape + local habitat was highest for both probability of initial occupancy and local site extinction. Probability of occupancy increased and extinction decreased with the combination of increased patch size and decreased patch isolation (landscape) and increased coniferous shrub density, proportion of coniferous dominated forest and decreased canopy height (local habitat). Probability of site colonization was driven mainly by local habitat features and increased with increasing habitat quality. These results indicate a complex system with intricate links between landscape and local scales. Preserving large tracts of habitat may not be sufficient in assuring future species persistence, but could minimize local extinction risk. Careful consideration should be given to local habitat features within habitat fragments, particularly to maintain adequate colonization rates. Because important features from both scales are correlated, in intact montane forest patches, landscape-scale attributes alone may serve as a surrogate for identifying quality breeding habitat, assuming processes of natural disturbance can be maintained.
Publications
- Frey, S. J., A. M. Strong, K. P. McFarland, J. D. Lambert, and C. C. Rimmer, C C. 2006. Modeling population dynamics and assessing viability of a montane forest songbird in Vermont. Abstracts of the Fourth North American Ornithological Conference, Veracruz, Mexico. Page 111.
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