There are a number of difficulties that make recording hyenas challenging. Many things have to come together at once to allow for a good recording. One of the most important aspects of a good recording is having low background noise in comparison to the sound you are trying to record. That can be difficult to achieve when there are high winds, rain, or you just happen to be in the Maasai Mara at night.
Not only does all this background noise make it difficult for me to get recordings, but hyenas have to be louder than the background noise if they want other hyenas to hear them. For vocalizations to someone close by, the background noise isn’t a huge deal, but if you’re trying to be heard from kilometers away, that background noise becomes very important. Here is the background noise the hyenas have to compete with (and I have to contend with) at night: