LLWart 1963 8 Aimophila mystacalis August 12 km. 616 on Pan Am Hwy. S. of Cayaco, Cayaco. mandibulating nest material but has not actually started building. Very difficult to follow birds when they are low in shrubs or when they fly so could be building + be very secretive about approach. 11:15 - 0 giving introductory note downhill + lower than song perch #1. Q walked downhill from above #1. heard chweet, chweet -- "reunion" call. saw Q hover + pluck at top of 12' shrub as flew by. Did not see if she caught anything, but she bit wiped when landed 3 feet further on. flew across slope + began singing fast song 50 yards t away. I walked in series of short flights across slope in same direction. When I reached area where I thought nest might be she turned 90° + began working uphill. Never dropped to ground after starting across slope but always stayed 2-5 feet up in shrubs or trees. Several times hopped around shrubs like a vireo - gazing about thru to another perch, gazing about, etc. - but never saw any movements like trying to capture prey. Left area at 11:35. See journal for afternoon + evening.