Bird survey data from time to detection surveys across Uganda, 1985 to 2011

These data include time-to-detection results from bird surveys undertaken across Uganda from 1985 to 2011 at 28 sites. Sites include protected and unprotected areas that differ in land cover. Site density is highest in NW and SW Uganda. Not all sites were surveyed in all years, and many sites were surveyed primarily from 2003 to 2010. There were often multiple surveys per year at a given site.

Surveys consisted of one or more observers walking (together) around a (very approximately) 1 km x 1 km area at a site for one hour. For each bird species identified (by sight or sound) the observers recorded the first 10-minute period in which it was detected. Period '6' was the first 10 minutes of the hour, down to period '1', the last 10 minutes of the hour, such that higher values indicate earlier detections. Taxonomy has been standardized to HBW/BirdLife checklist v.8. 

This data release also includes information on each site (Lat, Lon, name, protected y/n, categorical general landcover from our field observations) and survey (date, time, observer initials, number of observers). We include 'local' woody plant cover estimates based on global tree cover and forest gain/loss data layers (Hansen et al. 2013b) described in Hansen et al. (2013a). These layers provide three types of information for each 30 x 30 m grid cell: (a) percentage tree cover in year 2000, (b) forest gain 2000-2012 (binary), and (c) forest loss, indicating the year in which forest loss occurred (if any; 2000-2012). We created 500 m radius buffers around each study site, roughly corresponding to the area that was typically surveyed. We then extracted values from each of the tree cover data layers for all pixels within these buffers for each site and used them to estimate mean percent tree cover for 2000 to 2011. For surveys that occurred prior to 2000 (28% of all surveys) we used 2000 mean tree cover values.

To quantify landscape-scale tree cover in each site’s surroundings, we used annual tree cover layers (Hansen and Song 2018) from Song et al. (2018). These data offer a greater temporal extent than Hansen et al (2013b) and are provided at annual intervals from 1982 to 2016. The spatial resolution, however, is lower (0.05° × 0.05° resolution globally; ~5 x 5 km in Uganda), hence our decision to use them only for landscape (rather than local site) woody cover. We extracted values for each year from the pixel containing each of our sites.

Also included is information about each species: Order, family, genus, species (HBW and BirdLife checklist v.8, 2023), IUCN red list status (2023), Uganda red list status (2018), preferred habitat (forest, grassland, generalist; based on species accounts in Birds of the World - Cornell Lab of Ornithology), and ease of detection/identification (easy, medium, difficult; based on our subjective experience). The latter two pieces of information was included only for species detected 5 or more times and each of five or more sites.

To standardize taxonomy we relied heavily on Avibase to determine splits and mergers of taxa that have occurred through time and between checklists. We confirmed that each final name from HBW and BirdLife checklist v.8, 2023 in this dataset represents a species that occurs in Uganda using maps in the BirdLife datazone: https://datazone.birdlife.org/home