Birds have often played an important role as environmental bioindicators, and different species can be useful due to their bioaccumulating capacity. The micronuclei test is a cytologic technique used for accessing DNA and is a biomarker for damage to DNA. This study analysed the Cerrado avian community, especially the efficiency of the blue-black grassquit (Volatinia jacarina) in responding to pesticide contamination in situ on different-sized coffee farms in southeast Brazil. The micronuclei test was used in erythrocytes of birds. Eighty-two individuals of 21 bird species belonging to 11 families that were found in all study areas were used to evaluate micronuclei (MN) frequency. Two hundred fifty-two MN were counted in every area of study. The MN average count was 3/10,000 erythrocytes, and 17.1% of all bird species exhibited no MN. The average MN was 1.29 ± 0.69 in small farms, 2.59 ± 1.65 in medium farms, and 5.41 ± 1.34 in large farms. Small farms accounted for 14.3% of MN frequency, medium farms 27.8%, and large farms 57.9%. V. jacarina was the most abundant species found and displayed a sensitive response to environmental contamination. Pesticides appear to induce MN formation in a dose-dependent way when farms are analysed according to their area. Therefore, biomonitoring birds remain an efficient means to detect environmental pollutants, especially pesticides. V. jacarina responds as a sensitive biomonitor, showing a dose-dependent response to pesticides used in coffee farms.