Birds currently with holy cow aboard ship heading for Egypt (4,5)

'birds' is the definition.
(snow goose is a kind of bird)

'currently with holy cow aboard ship heading for egypt' is the wordplay.
'currently' becomes 'now' (I've seen this in other clues).
'with holy cow' becomes 'gee' (I can't explain this - if you can you should believe this answer much more).
'aboard' indicates putting letters inside.
'ship' becomes 'ss'.
'heading for' suggests taking the first letters.
The initial letter of 'egypt' is 'e'.
'now'+'gee'='nowgee'
'nowgee' inserted into 'ss' is 'snowgees'.
'snowgees'+'e'='SNOW GEESE'