Although BIDE models are conceptually simple, reliable estimates of the 5 variables contained therein (N, B, D, I and E) are often difficult to obtain.
Usually a researcher attempts to estimate current abundance, Nt, often using some form of mark and recapture technique.
Estimates of B might be obtained via a ratio of immatures to adults soon after the breeding season, Ri.
These models can give rise to interesting cyclical or seemingly chaotic patterns in abundance over time when fertility rates are high.
The terms Fi and Si can be constants or they can be functions of environment, such as habitat or population size.