Abstract
Studies of bird phenology can help elucidate the effects of climate change on wildlife species but observations over broad spatial scales are difficult without a network of observers. Recently, networks of citizen volunteers have begun to report first arrival dates for many migratory species. Potential benefits are substantial (e.g., understanding ecological processes at broad spatial and temporal scales) if known biases of citizen data reporting are identified and addressed. One potential source of bias in bird phenology studies is the tendency for more “first” migratory arrivals to be reported on weekends than on weekdays. We investigated weekend bias in data reporting for five common bird species in North America (Baltimore Oriole, Icterus galbula; Barn Swallow, Hirundo rustica; Chimney Swift, Chaetura pelagica; Purple Martin, Progne subis; and Ruby-throated Hummingbird, Archilochus colubris), and assessed whether this bias affected mean arrival dates reported using data from historical (1880–1969; N = 25,555) and recent (1997–2010; N = 63,149) Citizen Science databases. We found a greater percentage of first arrivals reported on weekends and small but significant differences in mean arrival dates (approximately 0.5 days) for four of five species. Comparing time periods, this weekend bias decreased from 33.7 % and five species in the historical time period to 32 % and three species in the recent, perhaps related to changes in human activity patterns. Our results indicate that weekend bias in citizen data reporting is decreasing over time in North America and including a ‘day of week’ term in models examining changes in phenology could help make conclusions more robust.
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Acknowledgments
We thank L. Chambers and hummingbirds.net, E. Howard and Journey North (with funding from the Annenberg Foundation), J. Tautin and the Purple Martin Conservation Association, and P. D. and G. Z. Kyle and the Driftwood Wildlife Association, for collecting and compiling thousands of recent first arrival reports. We are also grateful to the countless contributors to these Citizen Science projects for more than a decade of careful observation, without which, a study of this magnitude would not be possible. We thank J. Zelt and S. Droege for their commitment to providing and protecting historical migration records through the North American Bird Phenology Program (USGS, Patuxent Wildlife Research Center) and for their expertise and support, which underscores the vision of the hundreds of early naturalists who faithfully contributed arrival cards from 1880 to 1970. We thank Clemson University students K. Auman, C. Boaman, J. Burroughs, J.H. Collins, B. Crawford, M. Kynoch, E. Purcell, D. Stone, M-K. Spillane, and S. Taylor for transcribing arrival cards and for help with our analysis. This study was funded primarily by Clemson University and the Clemson University Creative Inquiry Program, with additional support from a Carolina Bird Club grant.
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Courter, J.R., Johnson, R.J., Stuyck, C.M. et al. Weekend bias in Citizen Science data reporting: implications for phenology studies. Int J Biometeorol 57, 715–720 (2013). https://doi.org/10.1007/s00484-012-0598-7
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DOI: https://doi.org/10.1007/s00484-012-0598-7