But that's not at all what the article states:
>“The decline in population density was most severe in areas that were deforested or transformed for industrial agriculture, as orangutans struggle to live outside forest areas,” said a lead researcher for the study, Maria Voigt of the Max Planck Institute for Evolutionary Anthropology in Germany.
This isn't obvious from satellite imagery where it would appear that the jungle is intact, but if there's a logging road nearby then you can be sure poachers, miners, and others are running around underneath the canopy.
[1] https://www.theglobeandmail.com/news/world/amazon-rainforest...
All three of the quotes you added aren't talking about poaching, they are talking about killing of orangutans. This could be done because they are a nuisance or locals see them rummaging through trash or what-not.
Ctrl+F in the article for "poach" - zero hits
EDIT: It's not even that, people are just straight up killing these poor orangutans.
> “Worryingly, however, the largest number of orangutans were lost from areas that remained forested during the study period. This implies a large role of killing.”
> In February, Indonesian police arrested two rubber plantation workers in Borneo, accusing them of shooting an orangutan multiple times, decapitating it and then throwing its body into a river. The men claimed they were acting in self-defense, according to local media reports.
> So, in addition to protection of forests, we need to focus on addressing the underlying causes of orangutan killing. The latter requires public awareness and education, more effective law enforcement, and also more studies as to why people kill orangutans in the first place,” he said.
Source: OP