Progress 09/01/03 to 06/30/06
Outputs
We have conducted a comprehensive examination of the interactions of invasive fleshy-fruited plants and the fruit-eating birds which may disperse the seeds of such plants. Our aim was to determine if these plants have dispersal advantages which allow them to be especially successful during the invasion process. Our results have shown that both native and invasive birds eat and move the fruits of invasive woody plants (autumn olive, Asiatic bittersweet, multiflora rose) known to disrupt natural and agricultural ecosystems; and that captive birds often prefer fruits of native plants to the those of natives. We have also found that ingestion by starlings increases seed germination rates, thereby potentially increasing plant rates of establishment and spread. We found that in captive birds fed invasive plants most seeds are voided within 40 minutes of ingestion, although some are retained for up to 2.5 hours. Starling movement data collected by radio-tracking over the
course of two fall-winter seasons showed that most of the seeds of all three plants fall within 250 m of the point of origin, but in each case (autumn olive, Asiatic bittersweet, multiflora rose) a small percentage of seeds is moved to distances of over 1 km. During two hour tracking periods, starlings, on average, covered a total of 34 ha. The cumulative distance traveled by the average starling during this time was approximately 1800 m; and the average starling traveled a mean of 541 m away from the point of origin during this time. Analysis of starlings diets over the course of the study has shown that 84% of the seeds voided by starlings at a diurnal starling roost during the late fall and winter were those of Asiatic bittersweet. Small numbers of other seeds of both native and invasive plants were also found. We also measured fruit loads of both the native and invasive plants at our field sites during the last two years of our study. We found that invasive plants both covered
more area, and produced more fruits than did co-occurring fleshy-fruited natives. We are currently in the early stages of using data collected in this study to develop both hierarchical Bayesian and cellular automata models which will elucidate how starlings influence the dispersal process for autumn olive and Asiatic bittersweet.
Impacts
Fleshy-fruited woody invasive plants are serious and costly threats to American agriculture and biodiversity. This project provides empirical information about the nature of the relationship between these plants and the birds which disperse their seeds. The information is of use for producing guidelines for screening new plant introductions for potential bird-assisted invasiveness, and is fundamental to producing models which will accurately predict the rate and direction of spread in new invasives. In addition to reporting the work to the scholarly community (8 presentations at meetings in the last 4 years; see below for publications) we educate the broader community of stakeholders through public presentations (e.g. to amateur natural history organizations; discussions of invasive plant/bird interactions while leading birding walks), cooperation with the media (e.g., Natural New England magazine, issue 7, pgs 24-25), and annual reports to state and federal agencies
(e.g. the Connecticut State Department of Environmental Protection) charged with control of invasives. One co-PI (LaFleur) has completed her doctorate and now occupies a postdoctoral position working with the (USDA-funded) IPANE database, which compiles invasive plant reports from trained volunteers. Project funding has also supported training and research experiences for 2 other graduate students, and 7 undergraduates, including a total of 7 women. Five of the undergraduates who have worked on the project have entered graduate programs; one is a co-author on a submitted manuscript.
Publications
- LaFleur, N., Rubega, M., and Elphick, C.S. 2006. Invasive fruits, novel foods, and choice: an investigation of frugivory in European Starlings and American Robins. In revision for: The Wilson Bulletin.
- LaFleur, N., Rubega, M., and Parent, J. (2006) Do European Starlings (Sturnus vulgaris) Facilitate the Spread of Fleshy-Fruited Invasive Plants? Submitted to the Journal of the Torrey Botanical Society.
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Progress 10/01/04 to 09/30/05
Outputs
Fleshy-fruited woody invasive plants are serious and costly threats to American agriculture and biodiversity. We are conducting a comprehensive examination of the interactions of invasive fleshy-fruited plants and the fruit-eating birds which may disperse the seeds of such plants in order to determine if these plants have dispersal advantages which allow them to be especially successful during the invasion process. We have previously shown that; 1) both native (American robin, northern mockingbird, cedar waxwing, Eastern bluebird) and invasive (European starling) birds eat and move the fruits of invasive woody plants (autumn olive, Asiatic bittersweet, multiflora rose) known to disrupt natural and agricultural ecosystems; 2) captive birds often prefer fruits of native plants to the those of natives; 3) ingestion by starlings increases seed germination rates, thereby potentially increasing plant rates of establishment and spread; 4) most seeds are voided within 40
minutes of ingestion, but some are retained for up to 2.5 hours; 5) analysis of fecal samples collected at a starling roost indicates that starlings move many more seeds of invasive plants than of native plants in the wild. In the last year, we completed measures of fruit-producing plant distribution and productivity. The three most abundant fruit-producing plants at our field sites were all invasives. We measured both the areal coverage and fruit production; these data combined for the three most important invasive species give an estimate for our field sites, which covered an estimated 43.8 hectares, of over 8 million autumn olive fruits, 2 million multiflora rose fruits and 1 million Asiatic bittersweet fruits. We also measured fruit disappearance rates; our data indicate that most of the autumn olive fruits were ripened by early October and were the first to be completely removed from the plants with less than 1% of fruit remaining by December in each of the years of this study.
Analysis of radio-tracking data, now complete, shows that starlings, on average, cover a total of 34 ha in a two-hour period. The cumulative distance traveled by the average starling during this time was approximately 1800 m; and the average starling traveled a mean of 541 m away from the point of origin during this time. These data, combined with our data on passage rates of seeds through the digestive systems of starlings, provide estimates of the distances starlings may move the seeds of the invasives studied. While most of the seeds of all three plants fall within 250 m of the point of origin, in each case a small percentage of seeds is moved to distances of over 1 km. Tthe average distance starlings moved the seeds of all three plants were similar. Because ingestion by starlings significantly increases seed germination rates for these plants, consumption of these fruits by starlings is likely facilitating rates of plant establishment and spread.
Impacts
This project will facilitate the development of methods to screen and control invasive fleshy-fruited woody plants by providing practical and predictive information about the nature of the relationship between these plants and the birds which may disperse their seeds. It will ultimately provide specific information of use for producing guidelines for screening new introductions of fleshy fruit-producing ornamentals for potential bird-assisted invasiveness. In addition to disseminating the results of the work to the scholarly community (7 presentations at meetings in the last 3 years; 1 manuscript in revision for a peer-reviewed journal, 2 more close to submission) we are working to educate the broader community of stakeholders through public presentations (e.g. to amateur natural history organizations; discussions of invasive plant/bird interactions while leading birding walks), cooperation with the media (see Natural New England magazine, issue 7, pgs 24-25), and
annual reports to state and federal agencies (e.g. the Connecticut State Department of Environmental Protection) charged with control of invasives. Project funding has also made possible training and research experiences for 3 graduate students, and 7 undergraduates; 5 of the undergraduates, and all of the graduate students, have been women. Three of the undergraduates who have worked on the project have entered graduate programs; 2 more are applying to graduate programs now.
Publications
- LaFleur, N., Rubega, M., and Elphick, C.S. 2006. Invasive fruits, novel foods, and choice: an investigation of frugivory in European Starlings and American Robins. In revision for: The Wilson Bulletin.
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Progress 10/01/03 to 09/30/04
Outputs
Fleshy-fruited woody invasive plants are serious and costly threats to American agriculture and biodiversity. We are conducting a comprehensive examination of the interactions of invasive fleshy-fruited plants and the fruit-eating birds which may disperse the seeds of such plants in order to determine if these plants have dispersal advantages which allow them to be especially successful during the invasion process. To date, our work has shown that both native (American robin, northern mockingbird, cedar waxwing, Eastern bluebird) and invasive (European starling) birds eat the fruits of invasive woody plant (autumn olive, Asiatic bittersweet, multiflora rose) known to disrupt natural and agricultural ecosystems. Analysis of fecal samples and seeds collected at a starling roost indicates that starlings move many more seeds of invasive plants than of native plants; 60% of all fecal samples contained Asiatic bittersweet, suggesting this invasive is a mainstay of their
winter diet. Our data show that the invasive fleshy-fruited plants cover more ground, and produce much greater densities of fruits, than the native fleshy-fruited plants (silky dogwood, red-panicled dogwood, winterberry) on our survey plots. Fruit phenology measures show that the fruits of invasive plants are ripe, and available to birds, from September through April. Birds removed from 15-79% of the fruit crop from invasive plants; the remainder fell to the ground under the parent plant, undispersed. Experimental work with captive birds revealed that both starlings and robins will eat unfamiliar foods, and that they often prefer the fruits of invasive plants to those of natives. Thus, birds should be considered potential dispersers for newly introduced fleshy-fruited woody plants. Ingestion by starlings increases seed germination rates, thereby potentially increasing plant rates of establishment and spread. Most seeds are voided within 40 minutes of ingestion, but some are retained
for up to 2.5 hours. To determine whether birds move seeds to sites favorable to germination, and the distances seeds are moved, we must understand patterns of bird movement in the landscape, and how far birds travel in the time during which seeds are retained. We are now in our second season of radio-tracking starlings in order to obtain this information. Preliminary results, based on two hour tracking periods, with positions of birds estimated no less than every 20 minutes, indicate that in the first 20 minutes after being located starlings moved an average of 323 meters. Our movement and passage rate data combined suggest that the majority of invasive plant seeds ingested by starlings are deposited within 200 meters of the parent plant; however, some seeds may be moved as far as 2 km. Because our standards for including a tracked bird in the analysis are conservative, the maximum distance a seed may be moved is likely to be underestimated; thus the rate of spread of fleshy-fruited
woody plants may be on the scale of kilometers per year. Together, these results suggest that new introductions of fleshy-fruited woody plants for horticultural or other purposes should be tightly regulated.
Impacts
This project will facilitate the development of methods to screen and control invasive fleshy-fruited woody plants by providing practical and predictive information about the nature of the relationship between these plants and the birds which may disperse their seeds. It will ultimately provide specific guidelines for screening new introductions of fleshy fruit-producing ornamentals for potential bird-assisted invasiveness. In addition to disseminating the results of the work to the scholarly community (4 presentations at meetings in the last 2 years; 2 manuscripts are close to submission) we are working to educate the broader community of stakeholders through public presentations (e.g. to amateur natural history organizations; discussions of invasive plant/bird interactions while leading birding walks), cooperation with the media (see Natural New England magazine, issue 7, pgs 24-25), and annual reports to state and federal agencies (e.g. the Connecticut State
Department of Environmental Protection) charged with control of invasives. Project funding has also made possible training and research experiences for 3 graduate students, and 7 undergraduates; 5 of the undergraduates, and all of the graduate students, have been women. Two of the undergraduates who have worked on the project have either entered, or are applying to, graduate programs.
Publications
- No publications reported this period
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