High-tide habitat choice: insights from modelling roost selection by shorebirds around a tropical bay

High tides force shorebirds from intertidal feeding areas to sites known as roosts. We investigated the roostselection of great knots, Calidris tenuirostris, and red knots, Calidris canutus, on a tropical coastline in northwesternAustralia, assessing several roost attributes and recording the frequency of use of each site throughautomatic radiotelemetry. To model roost choice we used two approaches: (1) conditional logistic regressionmodels that assumed roost selection to be a trade-off based on a probabilistic assessment of severalenvironmental characteristics; and (2) bounds-based models that assumed that birds selected the nearestroost site to their feeding grounds, provided that threshold values for certain environmental characteristicswere met. Bounds-based models were more effective, and we suggest that they offer a closer approach toreal roost choice mechanisms. By day, roost choice was affected by distance from the feeding area and microclimate;birds selected nearby roosts where they could stand on cool, wet substrates. Different roost selectioncriteria were used at night when birds chose safer, but more distant, roosts. Models that assumedthat roost choice was influenced by recent experience of roost sites performed better than models that assumedconstant assessment of roost quality. This effect was significant only at night, suggesting that memorywas used more when information on roost quality was limited. Evidence that roost availability mayinfluence selection of foraging areas is also presented. Our results suggest that shorebirds select roostsby using simple mechanisms, making roost choice models a potentially valuable tool in conservationplanning.