For small sessile organisms, ecologists frequently use a , which is a small square frame that is used to standardize the area being measured. quadra

for larger sessile organisms or organisms whose populations are spread out, ecologists tend to utilize . line transects

mobile animals, like lizards or salamanders are more likely to be caught in , or if they are aerial species like birds or bats, ecologists tend to use . pitfall traps; mist nets

the technique estimates densities based on the number of returned captures. if 50 birds are caught and marked in year one and in year two 50 birds are caught and five of those were marked, the estimated population size would be . mark-recapture; 500