Can I use Squawkabilly ex's "Squawk and Seize" Ability if I have no cards in my hand to discard?
Yes, you always have a hand even if it has zero cards in it.
Source: Paldea Evolved FAQ; TPCi Rules Team (2023-06-08)

Relevant cards

Note: All applicable cards may not be listed below.
SV2_169
SV2_169