The Mississippi kite demonstrates two different breeding strategies within its range. In the southern Great Plains, Mississippi kites are colonial nesters that often inhabit urban areas. In the Mississippi Valley and further east, they are less colonial and nest singly in large trees in bottomland forest and riparian woodlands. Nests from birds within the eastern population are generally located in large (>22 ha) unfragmented forest near open habitats where birds aerially forage (Parker 1999).
The Mississippi kite habitat suitability model contains six parameters:
- land cover
- successional age class
- forest patch size
- interspersion of forest and open habitats
- dominant tree density
The first suitability function combines landform, landcover, and successional age class into a single matrix (SI1) defining unique combinations of these classes
. We directly assigned suitability index scores to these combinations based on relative habitat quality ranks reported by Hamel (1992) for this species. However, we restricted the species to sawtimber stands based on the preference of Mississippi kites for mature forest stands (Parker 1999).
We also included forest patch size (SI2) in the habitat model and used data from Barber and others (1998) to estimate the influence of forest patch size on suitability scores
Mississippi kites require not only large patches of forest and grassland, but also need to have these patches in a proper landscape context. We used the relative amount of these habitats within a 1-km radius as an index to their interspersion at the landscape scale (SI3). We assumed birds reached highest densities in either open habitats with few trees (characteristic of the Great Plains population) or landscapes containing moderate forest cover interspersed with open habitats
Mississippi kites nest in dominant trees (SI4) that extend above the canopy. We assumed a tree with a d.b.h. >76.2 cm (30”) in a sawtimber stand would extend above the canopy and provide adequate nest substrate for this species. We further assumed 1 dominant tree/ha would satisfy this requirement and Mississippi kites would be absent from stands with a uniform canopy (i.e., 0 dominant trees/ha). We fit an exponential function
to the values between these data points. Stands with ≥14 dominant trees/ha (the maximum observed in the WGCP during the 1992 FIA survey) were associated with maximum habitat suitability (suitability index score = 1.000;
To calculate the overall suitability index score, we determined the geometric mean of SI scores for forest structure (SI1 and SI4) and landscape composition (SI2 and SI3) separately and then the geometric mean of these means together.
Overall SI = ((SI1 * SI4)0.500 * (SI2 * SI3)0.500)0.500