Selection Indicates Preference in Diverse Habitats: A Ground-Nesting Bird (Charadrius melodus) Using Reservoir Shoreline

Animals use proximate cues to select resources that maximize individual fitness. When animals have a diverse array of available habitats, those selected could give insights into true habitat preferences. Since the construction of the Garrison Dam on the Missouri River in North Dakota, Lake Sakakawea (SAK) has become an important breeding area for federally threatened piping plovers (Charadrius melodus; hereafter plovers). We used conditional logistic regression to examine nestsite selection at fine scales (1, 3, and 10 m) during summers 2006–2009 by comparing characteristics at 351 nests to those of 668 random sites within nesting territories. Plovers selected sites (1 m 2) that were lower than unused random sites, increasing the risk of nest inundation. Plovers selected nest sites that were flat, had little silt, and at least 1 cobble; they also selected for 3-m radius nest areas that were relatively flat and devoid of vegetation and litter. Ninety percent of nests had,38 % coverage of silt and,10 % slope at the site, and,15 % coverage of vegetation or litter and,31 % slope within the 3-m radius. Gravel was selected for at nest sites (11 % median), but against in the area 10-m from the nest, suggesting plovers select for patches or strips of gravel. Although elevation is rarely evaluated in studies of ground-nesting birds, our results underscore its importance in habitat-selection studies. Relative to where plovers historically nested, habitat at SAK has more diverse topography, substrate composition, vegetation communities, and greater water-level fluctuations. Accordingly, our results provide an example of how habitat-selection results can be interpreted as habitat preferences because they are not influenced by desired habitats being scarce or absent. Further, our results will be useful for directing habitat conservatio

Median and 10^th and 90^th percentiles of nest and random sites for variables that influence nest-site selection of Piping Plovers on Lake Sakakawea.

a<p>Percent coverage of silt in substrate at site.</p>b<p>Percent coverage of gravel in substrate at site.</p>c<p>Presence or absence of a cobble.</p>d<p>Relative elevation of the nest above the pool level at initiation.</p>e<p>Slope within 1 m of the site.</p>f<p>Percent bare substrate obstruction (vegetation+leaf litter+small debris).</p>g<p>Slope within 3 m of the site.</p>h<p>Percent coverage of gravel in substrate 10 m from the site.</p

The most supported 5 of 20 models evaluated to examine factors that influence intra-territory nest-site selection of Piping Plovers at Lake Sakakawea, North Dakota, including number of parameters (K), Akaike's Information Criterion for small sample size (AIC_c), increase over the lowest AIC_c (ΔAIC_c), and Akaike model weight (<i>w</i>_i).

a<p>Percent coverage of silt in substrate at site.</p>b<p>Percent coverage of gravel in substrate.</p>c<p>Site measurement.</p>d<p>Presence or absence of a cobble.</p>e<p>Distance (m) to shoreline of Lake Sakakawea.</p>f<p>Relative elevation (m) of the nest above the pool level at initiation.</p>g<p>Percent bare substrate obstruction (vegetation+leaf litter+small debris).</p>h<p>Mean of 4 measurements taken 3 m from the site.</p>i<p>Mean of 4 measurements taken 10 m from the site.</p>j<p>Percent coverage of pebble in substrate.</p

Mean and standard deviation (SD) and 25^th, 50^th, 75^th, 90^th, and 100^th percentiles for variables of available Piping Plover nesting habitat at Lake Sakakawea (SAK), sandbars of the Missouri River (MR), and the Atlantic Coast (AC).

a<p>Percent coverage.</p>b<p>Sherfy et al. 2012.</p>c<p>Percent coverage of pebble, gravel, and cobble.</p>d<p>Cohen et al. 2008.</p>e<p>Not reported.</p

Model averaged parameter estimates, standard errors (SE), lower 95% confidence limits (LCL), upper 95% confidence limits (UCL), and standardized odds ratios for variables from 20 candidate models we used to examine potential influences on nest-site selection of Piping Plovers at Lake Sakakawea.

<p>Variables with 95% confidence limits that do not overlap 0 are depicted in bold.</p>a<p>Percent coverage of silt in substrate at site.</p>b<p>Percent coverage of pebble in substrate.</p>c<p>Site measurement.</p>d<p>Percent coverage of gravel in substrate.</p>e<p>Presence or absence of a cobble.</p>f<p>Percent bare substrate obstruction (vegetation+leaf litter+small debris).</p>g<p>Distance (m) to shoreline of Lake Sakakawea.</p>h<p>Relative elevation (m) of the nest above the pool level at initiation.</p>i<p>Mean of 4 measurements taken 3 m from the site.</p>j<p>Mean of 4 measurements taken 10 m from the site.</p

Lake Sakakawea study area.

<p>Map of North Dakota depicting our study area (shaded in gray) at Lake Sakakawea and an example of our segmentation of our study area.</p