Weald monitors are the largest predators the gryphons in Eyrie
Weald monitors were once a common food source for gryphon and opinicus alike. One year, a disease spread through the local population. It killed not only the monitors infected with it but also the gryphons and opinici who ate the dead monitors, hitting the youngest the hardest. This began the Redwood Valley Eyrie’s research into food preparation and preservation, saving the lives of many opinicus chicks. The gryphons weren’t nearly as lucky. An entire generation of chicks and fledglings ate the monitor meat. Only three survived. Hatzel went on to become the leader of her own pride partially because she’d built up an immunity to the disease and was able to clear the monitors form what later became her hunting grounds. Vosk went on to become the taiga pride leader, maintaining a good trade relationship with Hatzel. The third gryphon hasn’t been mentioned by name in the series yet.
In real life, the weald monitors are based on megalania, an ancestor of the komodo dragon that lived 50,000 years ago. The lace monitor is its closest living relative. While it’s not clear if megalania was venomous or not, many of its relatives were, making it potentially the largest venomous animal we know of. An overview can be found on the wikipedia page for megalania.