And FRI and SP both have articles on wild animals, not sure which is better for purposes here. SP’s is a bit more introductory/accessible maybe, and also expresses more philosophical arguments for why we should care; FRI’s a bit more academic and does not address some typical introductory reactions.
FRI’s: https://foundational-research.org/the-importance-of-wild-animal-suffering/
“Altruism, numbers, and factory farms”: https://sentience-politics.org/philosophy/altruism-numbers-factory-farms
Sentience Politics recently published a page on the significance of factory farms, which also includes discussion on why it’s important to consider numbers and compare suffering.
(Disclaimer, I work at SP/EAF.)