Hybrid Clark's x Western Grebe- How to distinguish between non-hybrid and hybrid individuals? (1 Viewer)

[Bewick]

A post on the gallery of the Clark's grebe seems to show both western and clark's grebe traits, with black that stops just short of the eye and rather dark sides. Is there anyway to effectively remove the possibility of an individual being hybrid if it shares some similarities with both species?
Apparently hybridisation doesn't occur often so is it better to just ignore the possibility of an individual being a hybrid.

Here's a link to the gallery post- Plane-spotter story part 1: Distant grebe

And here's a link to a few online resources that I'm currently reading up on:
1. Western Grebe x Clark's Grebe
2. https://www.researchgate.net/publication/319492006_Clarks'_Grebes_and_Suspected_Western_X_Clark's_Grebe_Hybrids_in_Manitoba
3. Western Grebe vs. Clark’s Grebe- An Easy Tip for Distinguishing the Two

Any links to other useful resources would be appreciated.