Table 2. Research effort and species number in the different orders, ranked in alphabetic order.
| Order | Publication number | Species number | Publication number per species (mean ± SE) |
| Anseriformes | 21449 | 172 | 124.703±18.539 |
| Apodiformes | 3401 | 443 | 7.677±1.520 |
| Caprimulgiformes | 1140 | 125 | 9.120±2.335 |
| Charadriiformes | 39990 | 356 | 112.331±10.243 |
| Ciconiiformes | 10290 | 120 | 85.750±18.555 |
| Coliiformes | 99 | 6 | 16.500±6.350 |
| Columbiformes | 5090 | 336 | 15.149±4.940 |
| Coraciiformes | 2860 | 220 | 13.000±2.997 |
| Cuculiformes | 1872 | 167 | 11.210±3.779 |
| Falconiformes | 28831 | 312 | 92.407±13.107 |
| Galliformes | 13735 | 289 | 47.526±10.037 |
| Gaviiformes | 1142 | 5 | 228.400±63.834 |
| Gruiformes | 7331 | 226 | 32.438±6.726 |
| Passeriformes | 93614 | 5954 | 15.723±1.027 |
| Pelecaniformes | 6092 | 66 | 92.303±26.918 |
| Phoenicopteriformes | 773 | 6 | 128.833±59.165 |
| Piciformes | 4743 | 410 | 11.568±2.120 |
| Pocicepediformes | 2166 | 22 | 98.455±35.569 |
| Procelariiformes | 6543 | 131 | 49.947±6.787 |
| Psittaciformes | 6296 | 375 | 16.789±2.083 |
| Sphenisciformes | 2994 | 18 | 166.333±37.923 |
| Strigiformes | 10769 | 201 | 53.577±14.367 |
| Struthioniformes | 1567 | 13 | 120.538±59.927 |
| Tinamiformes | 215 | 47 | 4.574±1.216 |
| Trogoniformes | 133 | 44 | 3.023±0.756 |