Your calculations are a prediction Your calculations are a prediction... How do we know how many there really are? Actually count them all! • US census • ADA at school • Giants game attendance Count evidence of each! • Nests • Scat • Prints

Sample the population Quadrat – a square area Transect – a line through an area

Sample the population Mark and recapture Catch a group, mark them, release; Capture a second group, count # marked vs unmarked Infer total based on number marked in second sample