SAS global macro vs local macro

[Ksharp]

%let a=cat;
%macro animal(a=frog);
%let a=bird;
%mend;
%animal(a=pig)
%put a is &a;

Here keyword marco parameter 'a=' create a LOCAL macro variable &a in macro "%animal". 

So the GLOBAL macro variable &a. would not be updated.

But in your macro,you don't have it, therefore you only have a GLOBAL macro variable and this GLOBAL macro variable would be updated.

[Kathryn_SAS]

Here is some additional documentation:

https://blogs.sas.com/content/sgf/2015/02/13/sas-macro-variables-how-to-determine-scope/