The influence of weather conditions on the detection of birds during Common Birds Census fieldwork

Assessment of Counting Techniques

“…Although all methods for estimating numbers of birds include caveats about sampling during periods with extreme weather conditions, surprisingly little research has addressed the magnitude of bias introduced by weather. To summarize, these biases can be reasonably controlled by avoiding periods of (1) strong wind (> 11 km/hr: Dawson, 1981a;Emlen and Dejong, 1981;Robbins, 1981b; but see Anderson and Ohmart, 1977, for a recommended threshold of 20 km/hr), (2) light to heavy precipitation (O'Connor and Hicks, 1980;Dawson, 1981a;Robbins, 1981b), (3) extreme temperatures « 7°C or > 24°C) (Robbins, 1981b), and (4) fog (Robbins, 1981b). Some of these recommended levels were not specifically identified in the literature cited, but represent my interpretation of results therein.…”

Fifty years ofBird Study

“…Bird census methods continue as a theme in the journal, with several papers investigating and testing the methodology of the Common Birds Census (e.g. Taylor 1965, O'Connor & Hicks 1980. A whole supplement (Baillie et al 1999) was devoted to large-scale studies of marked birds, with many important papers on methodology.…”

The effects of census date on the results of intensive Common Birds Census surveys

“…The census plot itself contained much scrub and held many bird species normally found either on farmland or in woodland. For greater detail of this work see O'Connor and Hicks (1980). In each of the two years the sequence of 40 census visits could be used to compare the results which would have been obtained from shortterm intensive surveys akin to the expeditions of Williamson (1971Williamson ( , 1974 with those of standard CBC work; sub-sets of visits within different time periods were extracted to mimic an expedition to the census plot and thus to examine the relative efficiency of intensive surveys conducted at different times of year.…”