Final answer:
The best methods for quantifying the density of mobile organisms like birds or bats are line transects and mark and recapture. Quadrats work well for immobile organisms and pitfall traps are for terrestrial invertebrates.option c is answer.
Step-by-step explanation:
To quantify the density of birds or bats, a good sampling method would be the use of line transects or mark and recapture. Mist nets might be useful for physically capturing bats for measurement, but they not specifically for determining the population density. Quadrats are typically used for immobile organisms such as plants or very small, slow-moving animals. Pitfall traps are generally used for terrestrial invertebrates, not for birds or bats.
The mark and recapture method is particularly useful for mobile organisms like mammals, birds, or fish. In this technique, a subset of the animal population is captured, marked, and then released back into the environment. After some time, another sample of the population is captured and the ratio of marked to unmarked individuals is used to estimate total population size and density. The method is advantageous for mobile species that can move throughout a large study area, making it difficult to obtain counts directly.