1. Different taxonomic treatments
Taxonomists use different criteria to classify birds into species, subspecies, and other taxonomic ranks. This can lead to different lists of bird species, depending on which taxonomic treatment is used. For example, some taxonomists consider the eastern and western meadowlarks to be separate species, while others consider them to be subspecies of the same species.
2. Different data sources
Lists of bird species may also disagree because they use different data sources. Some lists are based on museum specimens, while others are based on field observations. Field observations can be less reliable than museum specimens, because birds can be difficult to identify in the field. Additionally, some bird species may be more difficult to find than others, which can lead to biases in species lists.
3. Changes in bird populations
Bird populations can change over time, due to factors such as habitat loss, climate change, and hunting. This can lead to changes in the composition of bird species in a given area, which can in turn lead to changes in lists of worldwide bird species.
4. Human error
Finally, lists of bird species may also disagree due to human error. For example, a typographical error could lead to a species being listed twice, or a species could be misidentified.
Despite these challenges, there is a general consensus on the number of bird species in the world. The International Ornithological Committee (IOC) currently recognizes 10,709 bird species. This number is constantly being updated as new species are discovered and others are reclassified.
