The more species contribute to the indicator, the more reliable that indicator is. Many species may show interannual changes in abundance that reflect various environmental factors – for example, extreme weather conditions during the breeding season, poor conditions on the winter grounds, changes in predation pressure, etc. Consequently, indicators based on one or a few species are prone to be unreliable. Indicators based on scarce, threatened species will probably respond to variables specific to that species or conservation actions targeted at them. To reduce such variability, we use a more representative ´basket´ of as many common species as possible that breed or feed in the focal habitat. Genuine directional changes in the abundance of a whole suite of birds become more apparent, and a balanced picture of what is happening in the environment arises.