So, let’s say you’re out banding migratory birds with unique color bands so you can tell individuals apart. You continue your study over several years to see how often the same birds come back, and for how long, to determine how long they live. Cormack-Jolly-Seber (CJS) models are designed to do help with that estimation: CJS is a type of capture-recapture model used to estimate abundance/population size and survival. Most commonly, it is implemented in program MARK.
But, what happens if you go back to the same place and don’t see your bird in a subsequent year? Did it die, or did it just go elsewhere? This is a limitation of your methodology. Schaub and Royle (2013) tried to find a way around this by adding a spatial component to their models.
James J. Gilroy, Thomas Virzi, Rebecca L. Boulton, and Julie L. Lockwood. 2012. A new approach to the “apparent survival” problem: estimating true survival rates from mark–recapture studies. Ecology 93:1509–1516.
Schaub, Michael, and J. Andrew Royle. “Estimating true instead of apparent survival using spatial Cormack–Jolly–Seber models.” Methods in Ecology and Evolution 5.12 (2014): 1316-1326.