Summer warmth gave no clear nitrogen contrast in butterfly index failure in four British samples in 1986-2012

We tested whether summer warmth had a different link to butterfly index failure for species with low-nitrogen host plants at sites with more nitrogen deposition. We used 333,501 original UKBMS records in two British regions and two periods in 1986-2012. Failure means that a recorded species lacked enough monitoring within its flight period for an accurate annual index. No absent records were filled. Four fixed-effect models controlled shared site-year conditions, persistent site-species differences and regional species-year changes. Main contrasts ranged from -0.155 to +0.283 percentage points per C, per 5 kg N/ha/year, per unit lower host-plant nitrogen score. All four adjusted working intervals included zero. This does not establish random missingness or unbiased abundance estimates. Conditioning on source records, static pollution, coarse weather, few year clusters and covariance instability limit inference. The package gives exact evidence, source hashes, code, checks and a figure.

butterflies · observation bias · missing indices · nitrogen deposition · summer temperature · regional replication · null result