Spring warmth gave no clear link to missing end-bloom reports in four western US lilac samples from 1956 to 2008

We tested whether spring warmth predicted a missing end-bloom report when a first-bloom date was known. We used 11,052 common lilac reports in four geographic and time samples from the historic western US network in 1956-2008. Models used unit and year effects and winter temperature controls. All four slopes were positive, from 0.29 to 2.61 percentage points per C. All four intervals included zero after correction for four tests. Flag removal, unit trends, a first-date control and a shorter temperature window did not establish a common link. This result does not show that missing reports are random or that duration estimates are unbiased. Few state clusters, unknown visits, coarse weather and small later samples limit inference. We preserve code, source hashes, model inputs, all estimates and separate calculation checks.

phenology · observation bias · common lilac · missing reports · spring temperature · null result