Table 5: Comparison of avian monitoring projects focused on measuring occurrence and abundance (adapted from [10]).

Results from these programs have been used in over 1000 publications

Audubon Christmas Bird CountCount circle (24 km diameter)OpportunisticV (party hours)InternationalAnnual59,918 (2008-09)
North American Breeding Bird SurveyRoadside survey (39.4 km; 50 stops)Stratified randomS (3 min count)InternationalAnnual2,749 (2009)
Project FeederWatchFeeder countsOpportunisticV (2 days, hours, days)InternationalAnnual9,750 (2009)
eBirdOnline checklistsOpportunisticV (hours, distance, and area)InternationalContinuous18,053
Bird AtlasSystematic grid (100 km2 blocks; 4 km2 tetrads) and roving reportsRegular grid and opportunisticS/V (roving, timed visits)Britain and IrelandTwo visits (Winter: Nov./Dec. & Jan./Feb.; Breeding: April/May & June/July)10,000–20,000
Common Birds Census (now replaced by Breeding Bird Survey)Census plots (Farmland: 70 ha; Woodland: 20 ha)Stratified randomS (territory mapping)BritainAnnual (8–10) visits; late March–early July)250–300

a Effort is considered standardised (S) or variable (V). When standardised, the protocol specifications are presented; when variable, the effort variables that were reported during sampling are presented.