It’s very taxon-specific.
And yes, birds do get identified faster. Other species, especially ones that are distinctive, visually appealing, or otherwise charismatic tend to get more attention. This happens not just on iNaturalist, but in the biological sciences in general:
- The twenty most charismatic species, PLOS One, 2018.
- Plant scientists’ research attention is skewed towards colourful, conspicuous and broadly distributed flowers, Nature Plants, 2021.
You can also see it in iNaturalist data from 2017: The Tres-Zeros Club: Meet the 500 species on iNat with at least 1,000 observations!. More bird species had at least 1000 identified observations than anything else, followed by plants, then insects. Given that there’s something around 50,000 vertebrate species (fish, mammals, birds, etc…) vs over 1 million insect species [source] and 370,000 flowering plant species, one starts to realize how people’s preferences skew things.
There’s a lengthy forum thread related to that: Biases in iNat data.