The same need exists for birds in general. Declines in bird populations, especially of more vulnerable largebodied species that have disproportionate and sometimes irreplaceable ecological functions, can rapidly diminish certain ecosystem processes before we can study the underlying
mechanisms. Therefore, long-term, experimental and community-level investigations that compare efficiencies (Table 1) of intact and reduced bird populations are urgently required. We also need studies that simultaneously measure the magnitude of an ecological function (e.g. invertebrate consumption) and that of the consequent ecosystem service benefiting humans (e.g. pest control),hence providing ‘exchange rates’ between ecological functions and ecosystem services. In addition to generating exciting findings, research on avian ecological functions
and ecosystem services could help us predict, prepare for and possibly prevent the ecological and economical consequences of bird population declines worldwide.