Bird names in their common form usually have the following syntax: (adjective) (bird-type noun). For example: Sulphur-crested Cockatoo, Grey Catbird, Australian Pelican. There are of course a few exceptions like Emu. For the birds that do have adjectives in their name, what are the most common adjectives that occur in the adjective part?

Black Bittern: Black is the most common adjective in bird names in their common form. Spotted in Australia in Kakadu National Park on the Yellow Water.
If you take the IOC list for example, here are the top 100 starting with the most common:
- black : 101 birds
- gray : 78 birds
- african : 72 birds
- lesser : 71 birds
- common : 66 birds
- white-throated : 66 birds
- brown : 65 birds
- little : 64 birds
- great : 63 birds
- spotted : 63 birds
- northern : 58 birds
- blue : 58 birds
- mountain : 54 birds
- crested : 52 birds
- green : 50 birds
- western : 50 birds
- southern : 49 birds
- new : 49 birds
- greater : 48 birds
- white-browed : 48 birds
- white-bellied : 46 birds
- island : 46 birds
- long-tailed : 46 birds
- rufous : 45 birds
- madagascar : 44 birds
- black-headed : 44 birds
- eurasian : 43 birds
- dusky : 42 birds
- gray-headed : 42 birds
- black-throated : 42 birds
- white-winged : 39 birds
- eastern : 38 birds
- bush : 37 birds
- pied : 36 birds
- cape : 34 birds
- collared : 34 birds
- red-billed : 33 birds
- reed : 33 birds
- black-capped : 32 birds
- indian : 32 birds
- black-faced : 32 birds
- hooded : 31 birds
- philippine : 31 birds
- white-tailed : 31 birds
- leaf : 31 birds
- yellow-billed : 30 birds
- yellow-throated : 30 birds
- long-billed : 28 birds
- golden : 28 birds
- andean : 26 birds
- sooty : 26 birds
- sulawesi : 26 birds
- yellow : 26 birds
- barred : 25 birds
- american : 25 birds
- yellow-bellied : 25 birds
- spectacled : 24 birds
- red : 24 birds
- masked : 24 birds
- javan : 24 birds
- rufous-tailed : 24 birds
- chinese : 23 birds
- australian : 22 birds
- white-headed : 22 birds
- banded : 22 birds
- black-billed : 22 birds
- papuan : 22 birds
- short-tailed : 22 birds
- black-bellied : 21 birds
- pacific : 21 birds
- himalayan : 21 birds
- peruvian : 21 birds
- slaty : 21 birds
- thick-billed : 21 birds
- black-backed : 21 birds
- yellow-breasted : 21 birds
- pygmy : 21 birds
- white-rumped : 21 birds
- slender-billed : 21 birds
- white-fronted : 20 birds
- plain : 20 birds
- chestnut-bellied : 20 birds
- giant : 20 birds
- forest : 20 birds
- striated : 20 birds
- islands : 19 birds
- japanese : 19 birds
- rock : 19 birds
- ashy : 19 birds
- cuban : 19 birds
- red-headed : 19 birds
- south : 18 birds
- andaman : 18 birds
- white-breasted : 18 birds
- sri : 18 birds
- lanka : 18 birds
- rican : 18 birds
- olive : 18 birds
- green-backed : 18 birds
- sunda : 17 birds