Note: Hiked across pasture and got to within 300 m of cliff. For first 2 � hours, adult male was activity hunting swallows and perching. He caught 2 swallows. After he caught the first, he flew behind cottonwoods and I lost him. He cached the 2nd swallow in the big alcove upstream from eyrie and about � way up cliff, south side and out of view. At 10:30, he chased swallows again, no luck, and dropped behind cottonwoods again and lost him. Didn't see him again the rest of survey. About 90 minutes into survey another large falcon flew by and landed upstream on a rock above horizon. Then flew off upstream and out of sight; and not seen again. May have been a PRFA. I sat close enough that if young birds were around I would have heard them. It was quiet, with no falcon noises heard. I strongly suspect this nest failed.