Factors influencing nest-site selection
Correlations among predictor variables (water depth, vegetation height,
offshore distance of the nest and grazing intensity) were first
considered to test for multicollinearity. The VIF values were low
(<1.3), and models did not show evidence of overdispersion (Φ
≈ 1), and therefore all predictor variables were included in the model
without correcting for multicollinearity or overdispersion. The model
selection procedure yielded a single best model (ΔAICc <2)
with the predictor variables i) water depth, ii) vegetation height, and
iii) offshore distance of the nest (Table 1). These variables had a
significant influence on nest-site selection: water depth
(p =0.005), offshore distance of the nest (p =0.037), and
vegetation height (p =0.035) (Table 2).
A total of 30 nests out 63 active nests and an equal number of randomly
selected nest-sites, were measured. These nests were distributed in all
the three sections of the lake (north 14, middle 9, south 7), thus were
a representative of crane’s nesting-sites. The nests were located in the
lake’s marshes with varying levels of standing water, the mean water
depths being north (35.76 cm), middle (55.76 cm) and south (64.86 cm),
and a range of 14.2–123.63 cm. Cranes located their nests in water
points above 50 cm deep, vegetation above 60-90 cm, and preferably 100 m
offshore (Figure 3).