Adaptive radiations, where a lineage diversifies into multiple species exploiting different niches, are key drivers of biodiversity. It is therefore important to understand the factors that drive such radiations and how changing environmental conditions affect their persistence. Using a size-structured model, I study how changing environmental conditions impact the persistence of a six-species flock. At birth, individuals are constrained to feed on a shared resource. As they mature, individuals diversify into six specialized forms, each adapted to feed on specific resources. Environmental changes affecting one species can trigger a cascade, altering the size structure of the focal species and subsequently affecting resource availability for other species. Under these altered ecological conditions, coexistence of all species becomes impossible. Importantly, once species are lost, they cannot re-establish even when environmental conditions return to their original state, resulting in irreversible biodiversity loss. These findings underscore the vulnerability of species flocks to environmental change and highlight the potential for unexpected outcomes in the face of shifting ecological conditions due to climate change.