Table 2. Summary of explanatory variables for breeding Common Loon presence and absence lakes across New Hampshire. N = 322 lakes. Means were measured for the 150-m zone surrounding each lake. All variables are included to highlight the range of variables considered during the modeling process. We modeled only variables indicated as included at each of the four scales within each ecoregion and statewide.

Mean (SD)
Habitat variable Description Presence Absence Reason for inclusion/exclusion
Lake area Lake surface area, excluding islands (ha) 209 (1125) 33 (34) Included: loons prefer larger lakes for a variety of reasons
Lake perimeter Lake shoreline length (km) 11 (23) 4 (3) Excluded: correlated with lake area
Lake shape Lake configuration and shoreline complexity 2 (1) 2 (1) Excluded: correlated with lake area and perimeter
Maximum depth Maximum lake depth (m) 14 (11) 6 (4) Included: important for fish/prey habitat
Islands Number of islands per lake 4 (13) 1 (2) Included: loons prefer small islands for nesting
Elevation Lake elevation (m) 296 (154) 251 (152) Included: estimate of geographic specification
Lake flushing rate Total volume of water entering a lake per unit time (m³/yr) divided by lake volume (m³) 12 (43) 39 (82) Included: important factor in nest survivorship
Water clarity Secchi depth transparency reading (m) 4.5 (2.1) 2.6 (1.2) Included: loons are visual predators
Total phosphorous Organic and inorganic forms of phosphorus (mg/L) 0.009 (0.005) 0.017 (0.011) Included: estimate of human disturbance
pH Hydrogen ions in the water or acidity (units) 6.6 (0.4) 6.4 (0.6) Included: indicator of fish habitat
Trophic status Categorical: 1 = oligotrophic, 5 = mesotrophic, 10 = eutrophic 3 (3) 6 (3) Excluded: correlated with phosphorous
Conductivity Number of ionic particles present (µmhos/cm) 48 (33) 66 (53) Excluded: negatively correlated with clarity
Loon distance metrics Distance to nearest loon presence lake (upper numbers) and distance to nearest loon absence lake (lower numbers, km) 2 (2.4)
6 (4.5)
5 (5.2)
5 (4.2)
Included: hypothesized loon dispersal factor
Developed-residential/urban Proportion of residential and urban developed land within 150- and 500-m zones surrounding each lake and nest/non-nest site (%) 3 (4) 4 (7) Included: estimate of human disturbance
Agriculture Proportion of pasture, hay, and cultivated cropland cover within 150- and 500-m zones surrounding each lake and nest/non-nest site (%) 1 (2) 2 (3) Included: estimate of human disturbance
Forested Proportion of forested land cover within 150- and 500-m zones surrounding each lake and nest/non-nest site (%) 36 (13) 45 (17) Included: hypothesized habitat factor
Wetland Proportion of forested and nonforested wetland cover within 150- and 500-m zones surrounding each lake and nest/non-nest site (%) 4 (7) 10 (13) Included: hypothesized habitat factor
Open water Proportion of open water with < 25% vegetation or soil within 150- and 500-m zones surrounding each lake and nest/non-nest site (%) 54 (12) 35 (13) Included: hypothesized habitat factor
Cleared and disturbed Proportion of cleared or disturbed land within 150- and 500-m zones surrounding each lake and nest/non-nest site (%) 3 (4) 4 (6) Excluded: correlated with Developed
Road density Density of roads within 150- and 500-m zones surrounding each lake and nest/non-nest site (m/m²) 1798 (1255) 2132 (1759) Included: estimate of human disturbance
Minimum distance to human population center Minimum distance to high-density residential areas and municipal community centers from nest/non-nest site (km) 4 (4) 3 (3) Included: estimate of human disturbance