Volume of foliage tents affects harem size in Cynopterus sphinx living in a fission-fusion society

<em>Cynopterus sphinx</em> males construct dome-shaped tents in various foliage to form harems with females. It is generally assumed that <em>C. sphinx</em> follows resource-defence polygyny. However, a recent study suggests that these bats mate promiscuously and that forming harems confer no reproductive advantages for males. So, the selective forces maintaining male behaviours amid promiscuity remain poorly understood. For the first time, we show that (1) male body size and tent volume are not correlated, suggesting that the benefits of tent construction for harems may outweigh the costs of maintaining and defending the resource. And (2) tent volume confers a positive effect on the harem size in mating seasons, suggesting that males who choose larger tents have a higher chance of attracting more females into their harems for mating.