Long term monitoring of populations is the traditional way of determining if a species is in danger.
This requires sustained effort over many years.
For migratory or mobile animals, changes in behaviour can also mask population changes.
A detected trend does not explain the cause of said decline
Many shorebird species are thought to have declining populations
Monitoring programs often unable to detect strong trend in many shorebird species
High variability in census counts between years can mask trends.
Vary high variability in counts between sites can increase variation in population estimate
An overarching cause of shorebird declines also remains elusive
Five hypotheses have been generated to explain the decline in census counts:
Avoidance of predators
Habitat Loss and Degradation
(See Butler et al. Shorebird Research Group of the Americas for more information)