This species is usually found in large roosting colonies in large, canopy trees. It has been recorded in tropical moist forest, cloud forest, mangrove forest, small islets and large islands (Mickleburgh et al. 1992, Flannery 1995, Scanlon et al. 2013). P. tonganus has a broad dietin Fiji, feeding on a wide range of forest genera including the flowers of Alpinia, Barringtonia, Decaisnina, Dillenia, Erythrina, Fagraea, Faradaya, Freycinatia, Geissois, Pandanus, and of Syzygium and the fruits of Aglaia, Amaroria, Faradaya, Ficus, Freycinetia, Garcinia,Myristica, Pandanus, Palaquium, Planchonella, Parinari and Syzygium, (Scanlon et al. 2014). It also feeds on plantation crops such as banana and papaw (Mickleburgh et al. 1992, Flannery 1995) and is often considered a pest in affected agricultural areas (Scanlon et al. 2013). Females most commonly give birth to a single young, twins are found occasionally (A. Brooke pers. comm.). In Fiji, maternity camps were observed in July-September, pregnant females were also captured in August and females with pups in September. Subadults were captured on Rennell Island in October.

It was previously reported to be relatively common in some island groups (e.g., Vanuatu), however, current abundance is unclear for many populations and it is known to have declined in some areas. Colonies can be large, and the species migrates between islands. The population is thought to be declining on the islands of Rarotonga and Mangia. In 2002, surveys estimated 1,730 on Rarotonga and only 78 on Mangia (Cousins and Compton 2005). This species is plentiful and widespread on both large and small Fijian islands, with more than half of the global population attributed to the islands of Fiji (Palmeirim et al. 2005). In Fiji, the species readily flies over water and among islands (A. Scanlon pers. obs.). In Tonga during 1995, surveys found a robust population of about 6,000 individuals on 14 islands in the Vava’u group (Grant 1998). After cyclone Waka hit the area in 2001, McConkey et al. (2004) recorded a decline of more than 80% of bats they had recorded moving between six islands (A. Brooke pers. comm.). Another study found no overall decline in biomass of resources available for bats following cyclone Tomas, but this availability depended on large tracks of intact rainforest (Scanlon et al. 2018). In April 2018, a camp close to the airport on Nendö contained 260 ± 45 individuals, and three camps on Mota contained 105 ± 10.6, 76 ± 7.2 and 602 ± 135.6 individuals.

It is listed on Appendix I of CITES, effectively prohibiting international trade in this species since 1989. It is protected by domestic legislation or wildlife laws in a few range states (e.g., Fiji), and like all bats, this species is protected by a hunting ban in American Samoa (A. Brooke pers. comm.). Hunting regulations and enforcement are needed still throughout much of the species' range. The species is present in a number of protected areas. Monitoring of declines throughout its range is important and further study of Papua New Guinea populations distribution would be worthwhile.