Strange little story from Arabia

As I have said, I am reading the Gutenberg version of Seven Pillars of Wisdom, T E Lawrences's memoir. It is chock full of the strange little stories. Here is one of Lawrence and his Arab irregulars camping within the walls of an old Arab fortress:

In these slow nights we were secure against the world. For one thing, it was winter, and in the rain and the dark few men would venture either over the labyrinth of lava or through the marsh--the two approaches to our fortress; and, further, we had ghostly guardians. The first evening we were sitting with the Serahin, Hassan Shah had made the rounds, and the coffee was being pounded by the hearth, when there rose a strange, long wailing round the towers outside. Ibn Bani seized me by the arm and held to me, shuddering. I whispered to him, 'What is IT?' and he gasped that the dogs of the Beni Hillal, the mythical builders of the fort, quested the six towers each night for their dead masters.

We strained to listen. Through Ali's black basalt window-frame crept a rustling, which was the stirring of the night-wind in the withered palms, an intermittent rustling, like English rain on yet-crisp fallen leaves. Then the cries came again and again and again, rising slowly in power, till they sobbed round the walls in deep waves to die away choked and miserable. At such times our men pounded the coffee harder while the Arabs broke into sudden song to occupy their ears against the misfortune. No Bedouin would lie outside in wait for the mystery, and from our windows we saw nothing but the motes of water in the dank air which drove through the radiance of our firelight. So it remained a legend: but wolves or jackals, hyasnas, or hunting dogs, their ghost-watch kept our ward more closely than arms could have done.

He offers no explanation beyond that last half sentence. But his Arabs knew all about wolves, jackals, and the rest, and they were scared out of their daring. As was Lawrence, apparently.