DOI: 10.5061/dryad.rjdfn2zj2
title: Data for: Considerations for fitting occupancy models to data from eBird and similar volunteer-collected data

description: An occupancy model makes use of data that are structured as sets of
 repeated visits to each of many sites, in order estimate the actual
 probability of occupancy (i.e., proportion of occupied sites) after
 correcting for imperfect detection using the information contained in the
 sets of repeated observations. We explore the conditions under which
 preexisting, volunteer-collected data from the citizen science project
 eBird can be used for fitting occupancy models. The data archived here are
 used to explore two ways in which the single-visit records could be used
 in occupancy models. First, we use empirical data contained within this
 archive to assess the potential for space-for-time substitution:
 aggregating single-visit records from different locations within a region
 into pseudo-repeat visits. The archived data are used to illustrate that
 the locations chosen for data collection by observers were not always
 representative of the habitat in the surrounding area, which would lead to
 biased estimates of occupancy probabilities when using space-for-time
 substitution. Second, create a large set of simulated data (output from
 the simulations contained in this archive) that we used to explore the
 utility of including data from single-visit records to supplement sets of
 repeated-visit data.
description: The seven data files archived are of three different
 types: <strong>Raw data:</strong> records
 of bird watching events in which observations of wild bird were made by
 volunteer participants in eBird and entered into eBird's database.
 These data have not undergone subsequent processes, aside from being
 associated with identifier variables that can be used to connect records
 of observations made at the same locations or by the same
 observers. <strong>Combination and derivation
 from primary data:</strong> information from eBird observation
 events (location, date, time, observer effort) are combined with summaries
 of landcover in the immediate area surrounding each location of an eBird
 observation. The landcover information is derived from the MODIS
 MCD12Q1v006 data product, with derived estimates of landcover percentages
 calculated by summarizing information from multiple pixels within the
 immediate areas around all locations of eBird observations.
 <strong>Simulation output:</strong> records of
 parameter estimates and their precision from occupancy models fit to large
 numbers of sets of simulated data, with the goal of understanding how
 variation in conditions (the conditions examined in the paper with which
 the data are associated) affected the accuracy and precision with which
 detection and occupancy probabilities were estimated. The simulated study
 was needed because true detection probability and true occupancy
 probability are never known for empirical data.
description: All data files can be viewed as plain text within a text editor,
 although the archived tables are better viewed within computer programs
 designed to display and manipulate tabular data.  The archived data are
 almost all comma-delimited value (.csv) tables, with one tab-delimited
 value (.txt) table. In our use of these data we have read them into the
 statistical software R, and at least one aspect of the format of some of
 the data tables is the use of the letters "NA" to denote missing
 values as is the convention in R.