frogs.RdCounts of the number of frogs in ponds of the Canton Aargau, Switzerland.
A data frame with 481 observations on the following 10 variables.
count1number of counted frogs during the first visit
count2number of counted frogs uring the second visit
elevationelevation, meters above sea level
yearyear
fishpresence of fish (1 = present, 0 = absent)
waterareaarea of the water body in square meters
vegetationindicator of vegetation (1 = vegetation present, 0 = no vegetation present)
pondidname of the pond, corresponds to observation id
xx coordinate
yy coordinate
The amphibian monitoring program started in 1999 and is mainly aimed at surveying population trends of endangered amphibian species. Every year, about 30 water bodies in two or three randomly selected priority areas (out of ten priority areas of high amphibian diversity) are surveyed. Additionally, a random selection of water bodies that potentially are suitable for one of the endangered amphibian species but that do not belong to the priority areas were surveyed. Each water body is surveyed by single trained volunteer during two nocturnal visits per year. Volunteers recorded anurans by walking along the water's edge with precise rules for the duration of a survey taking account of the size of the surveyed water body and noting visual encounters and calls. As fare as possible, encountered individuals of the Pelophylax-complex were identified as Marsh Frog (Pelophylax ridibundus), Pool Frog (P. lessonaea) or hybrids (P. esculentus) based on morphological characteristics or based on their calls. In the given data set, however, these three taxa are lumped together.
The data is provided by Isabelle Floess, Landschaft und Gewaesser, Kanton Aargau.
Schmidt, B. R., 2005: Monitoring the distribution of pond-breeding amphibians, when species are detected imperfectly. - Aquatic conservation: marine and freshwater ecosystems 15: 681-692.
Tanadini, L. G.; Schmidt, B. R., 2011: Population size influences amphibian detection probability: implications for biodiversity monitoring programs. - Plos One 6: e28244.
data(frogs)