What Signal It May

I see the spring
As atmosphere brings
So many changes
Along with the age.

The garden is bracing
And inviting
All birds to nest
And make habitat look the best.

Morning breeze
Oblige us to use 
Our sense to hear melodious cuckoo
Hiding on top tree of a zoo. 

Flowers boom
With blossom all around
Colours make a wonderful show
River waters make a calm flow. 

These changes make me wonder
The autumn may threaten here
I shall have to pack after spring
What signal it may bring?