This need to fly great distances for food has been theorized as a reason for the decline of the species. One study reported finding a greater noctule bat on the ground exhausted from flight. Another study of owl droppings found in areas in between GNB roosting sites has shown that the greater noctule bat is susceptible to predation in flight. It has also been noted that the foraging range for the greater noctule bat increases during the lactating period for the greater noctule bat, potentially due to an increased need for energy. The greater noctule bat is also known to increase its foraging range in response to different levels of potential food sources. In the summer and fall months, when water levels and insect abundance is lower in the northern parts of Europe, the greater noctule bat has been found to increase its foraging range south to areas with a larger abundance of insects. The greater noctule bat is also one of the few known species of bat that also preys on nocturnally migrating birds. These birds tend to pause for rest during the day in the marshland fields that the greater noctule bat forages for insects in at night. When the birds start to migrate again at dusk, the greater noctule bat is known to prey on them during flight. These changes in habitat based solely on food source suggest that the greater noctule bat is heavily dependent upon areas that can support its food supply regardless of how far it must travel to get to their prey. The greater noctule bat also interacts with parasites that live in the trees that they roost in and transfer themselves to the bats while they are sleeping. The greater noctule bat also interacts with the few nocturnal flying predators in its area, mainly owls that are much larger than the bat. Evidence of greater noctule bat bones have been found in owl pellets. The most common predators of greater noctule bat are barn owl ("Tyto alba") and Eurasian eagle-owl ("Bubo bubo"). The greater noctule bat generally leaves its roost to forage after it is already completely dark outside, this coincides with the general time that the two mentioned owl species hunt. There is also some risk to the greater noctule from parasitism between bats.In Seville, Spain, one of the largest breeding colonies in Europe, the bats are in danger of obliteration. Rose-ringed parakeets, an invasive species, compete for homes in tree hollows, attacking and killing the bats.