The species primarily roosts in caves, but has also been found roosting in buildings, hollow trees, under palms, and underground chambers (Nowak 1999, Francis 2019). Within a crowded cave, H. diadema may roost on walls or near the floor of wet caves (Bonoccorso 1998). In Australia, it was recorded within three different cave types including fully developed tourist caves, self-guided/underdeveloped tourist caves, and non-tourist caves (Pavey 1998). On the Nicobar Islands, it has been recorded in bunkers with a colony size of 20-25, as well as colony sizes greater than 150 within caves (Aul et al. 2014). Maternity colonies of 8,000 H. diadema have been observed in Papua New Guinea (Bonoccorso 1998). Further, it is known to roost with other species in colonies that may reach over 100,000 individuals (Payne et al. 1985). It has been recorded roosting with Rhinolophus affinis at a cave in Penggerukan, North Sumatra (Whitten et al. 2000). In the Philippines, it was found to co-exist with other species in caves including Hipposideros pygmaeus, Rhinolophus arcuatus, Rhinolophus virgo, and Rousettus amplexicaudatus (Nuñeza and Galorio 2014), and co-roost with Pipistrellus javanicus (Galorio and Nuñeza 2014). Individuals were found to use multiple day roosts but did not change roost every day (Pavey 1998). Ectoparasite loads among H. diadema was recorded to be lowest among individuals within more complex caves and lower densities (Phelps and Kingston 2018), as close contact among females in maternity colonies has been shows to increase parasitism transmission (Christe et al. 2007).

It forages in various forested habitats, including highly disturbed areas (Francis 2019). A study in Australia found some flexibility in its foraging ecology, as some individuals occupied up to three types of vegetation including an open forest and vine thicket, although woodland was the most common (Pavey 1998). However, they still required similar habitat components among each type, specifically an area with leafless twigs for perching overlooking an open space. Its wing morphology and high constant echolocation frequency of 59-66kHz are more efficient for foraging in densely vegetated habitats, as higher frequency calls rapidly attenuate in air (Denzinger and Schnitzler 2013). Therefore, they are less effective in locating prey in more open forests or disturbed habitats such as coffee plantations (Kingston 2003, Meijaard 2005). According to Huang et al. (2019), species similar to H. diadema that roost in caves and have higher constant-frequency calls are more tolerant to coffee plantations than plant-roosting species with lower broadband-frequency calls. However, H. diadema is still less likely to be found in an open disturbed habitat such as a coffee plantation, as vegetation simplification decreases prey availability (Wickramasinghe et al. 2004), limits their echolocation efficiency and may increase predation pressure (Gardner 1998). This hypothesis is supported in a study by Huang et al. (2014) that only recorded sightings H. diadema within the primary rainforests of Bukit Barisan Selatan National Park, Sumatra, Indonesia, and only half of the sampled polyculture plantations, while recording no sightings within the sampled disturbed forest and monoculture plantations.

Hipposideros diadema is an insectivore, mostly feeding on Coleopterans, Lepidopterans, and Orthopteras, however, it has also been classified as an “occasional carnivore” that will occasionally feed on small birds and spiders (Pavey and Burwell 1997). Samples of H. diadema stomach contents in Australia consists of 78% Coleoptera and 20% Lepidoptera (Milne et al.2006). In the Philippines, Galorio and Nuñeza (2014) found fruit bits in their stomachs, suggesting they either consumed fruits or the insects attracted to fruits, as bats can echolocate prey that are hidden on a fruit surface (Korine and Kalko 2005). They also found bird feathers and unidentified hair fibers within the stomachs, supporting the theory of occasional carnivory. The species is a perch hunting species, with continuous flight as a secondary behavior (Pavey 1998). It hangs from a perch and scans the area using echolocation until it detects its prey and then makes a fast, direct flight to catch it (Francis 2019). It typically has 1-3 foraging areas with an average foraging range of 1.08km from the day roost (Pavey 1998) but can range up to 10km (Bonoccorso 1998). It also usually goes out for 1-2 foraging bouts per night (Pavey 1998), selecting several perches over 1km² (Francis 2019).

It has a single breeding season that coincides with warmer temperatures and the maximum quantity of insects (Nowak 1999). The females congregate and form maternity colonies during March and April (Nowak 1998, Francis 2019). In peninsular Thailand, females with young were found in maternity roosts in April (Monadjem et al. 2019). In the southern hemisphere, dependent young and subadult H. diadema were also observed in caves from April through May (Bonoccorso 1998). The females give birth to a single pup and may carry it until it becomes independent enough to fly and feed alone or leave it within the roost when searching for food. Within the Bismarck Archipelago, lactating females are known to carry infants from June through October (Bonoccorso 1998). A young H. diadema will reach sexual maturity after about one year (Nowak 1999). It has an average life span of about four to seven years but can live up to twelve years in captivity (Nowak 1999). 

Hipposideros diadema is known from protected areas throughout its range and there are currently no known species-specific conservation initiatives in place for the species as it is a Least Concerned species. For example, it has been recorded within and around Bukit Barisan Selatan National Park, Sumatra, Indonesia, which is the second most species rich area in Southeast Asia (Huang et al. 2014). Furthermore, the species was also recorded in areas outside the protection of the national park, including local villages, highlighting the importance of protecting this broader diversity hotspot.

Further surveys to identify and protect cave roosts that support the highest populations (Kingston 2010) are needed. Therefore, future management recommendations can focus on effectively providing protection for species as well as maintaining any scientific, cultural, or economic values of caves. Protection of more complex caves would provide more available roost sites for H. diadema, reducing both competition and risk of parasite transmission among individuals. Caves utilized by large maternity colonies should also be identified and protected, as the disturbance of these sites would likely cause local population declines or extirpations.

Research on the current population status and trends of H. diadema is lacking, yet crucial in creating effective conservation actions for the species. Similarly, further research on the ecology of maternity roosts would provide more information regarding the impacts of cave disturbance on their population. Huang et al. states that species differ in vulnerability to anthropogenic land use changes (2019), therefore, further species-specific studies must be performed to better analyze species sensitivity and form effective conservation plans. This is especially critical for H. diadema as it is found near many growing plantations/monocultures (Huang 2019, Huang 2014). Lastly, the extent of hunting of H. diadema is unknown and should be quantified to determine its exact impact on their population. Further taxonomic research on the species is needed.