density

Accounting for detectability when estimating avian abundance in an urban area

Urban areas can support significant bird populations, including species of conservation concern, but urban ecologists have been slow to apply detectability-based counting techniques. We compared abundances and relative abundances of eight urban birds, derived using two commonly applied techniques (fixed-radius point and strip sampling) and distance sampling. We evaluated the influence of habitat and two covariates (observer and whether birds were seen or heard) on detectability. Due to built-up structures in urban areas, point counts are appropriate.

Line-transect distance sampling compared with fixed-width strip-transect counts for assessing tomtit (Petroica macrocephala) population trends

Distance sampling and fixed-width strip-transect counts were compared as methods for estimating population trends of the tomtit (Petroica macrocephala) from late September / early October to early November 2004, before and after aerial 1080-poisoning for control of the brushtail possum (Trichosurus vulpecula). Two observers independently recorded the distance and compass bearing to tomtits detected along 36 transect lines in each of two forests (one prefed with non-toxic bait and one not prefed).

Morphology, distribution and desiccation in the brown garden snail (Cantareus aspersus) in northern New Zealand

Size, density and distribution of the brown garden snail (Cantareus aspersus) were observed relative to cover at a coastal reserve on the North Island, New Zealand. Cover variables depended on vegetation height and available debris (rubbish, wood, cow dung). Air temperature, ground temperature, and relative humidity were recorded continuously during the field survey for the various cover types. Live snails used debris disproportionately as resting habitat, where relative humidity and temperature were the least variable.