I think that is the cuckoo poem
The cuckoo comes in April
She sings her song in May
In June she changes her tune
In July she prepares to fly
In August she must
I know a slightly different version of the same ditty:
In April come he will;
In May he sings all day;
In June he's out of tune;
In July he starts to fly;
In August go he must,
For a cuckoo in September
No man can remember.
How very irritating for you, as it would appear that cuckoo and emu are equally valid answers.
Thank you for your answers - a difficult choice! but having struggled with that for days I feel quite thick now that you have provided me with two answers so quickly, thanks again - Bumble-line
Cuckoo must be required, otherwise 'August' is otiose and too coincidental ( You would also have a choice of 'emu' or 'emus', so this is probably an unforeseen accident rather than a deliberate trick)