Why does Les say he is careful about reports of scavenger birds multiplying?
He is careful about reports of scavenger birds multiplying because people can write almost anything, sometimes without proof, so such reports should be taken with a grain of salt. A later account claims the bird's multiplication is more or less documented in the Middle East.
Les explains that he is careful when saying things like this because he has concluded people can write just about anything, and sometimes they write it without proof. He recalls that years ago someone told him of an article saying one of the major scavenger birds in the Middle East normally laid only two eggs at a time, usually had only one brood, and thus only two offspring a year. Later, someone told him that same species suddenly had doubled, laying four eggs and producing four instead of two. Les says he takes such things with a grain of salt. Then not too long ago he read again that it is more or less documented that this specific species of scavenger bird is indeed multiplying at a rate almost double normal in the Middle East. This fits the broader context of scavenger birds being summoned to the supper of the great God.