Density in PRESENCE

[CJWM]

Greetings all,

I have point count data consisting of 6 occasions from 338 points, as well as habitat covariates at each point, and need to calculate the density of each bird species at each point. I've been using the Repeated Count Data (Royle Biometrics) analysis to this. My first question is: am i justified in interpreting lambda as the density at each point? and second: lambda is often lower than the raw count at the site, is that cause for concern?

Thanks,
Chris

[darryl]

lambda is the expected or average density for that type of site according to the model. It's not impossible that your observed count is greater than that value though. You also have to look very closely at the assumptions of the model and how they relate to your sampling to consider whether the numbers that PRESENCE produces could really be interpreted as a meaningful density estimate.