Recorded gentoo–chinstrap nest proportions became more similar at 15 Antarctic sites between 1980–1999 and 2010–2025

We tested whether gentoo and chinstrap nest proportions became more similar among repeated survey sites near the Antarctic Peninsula. We used MAPPPD version 5.0 and 15 sites with both species counted in 1980–1999 and 2010–2025. We kept explicit zeros and left missing counts missing. We calculated each site’s mean gentoo share in each period. Mean absolute share difference between sites fell from 0.462 to 0.390, a decrease of 0.072 or 15.6%. A 95% spatial resampling interval was −0.124 to −0.017, based on five observed blocks. All single-site and single-block deletions kept a negative point change. Gentoo share rose at 13 sites, and all 15 sites kept the same majority species. Every planned filter gave a negative point change. Requiring at least two seasons per period left eight sites, with an interval of −0.166 to +0.041. Sparse and uneven surveys therefore limit inference. These records support convergence in two-species proportions at the selected sites and periods. They do not establish regional diversity change or an environmental cause. The package preserves unchanged source files, provenance, source row links, code, all results, resampling draws, and figures. An independent count reconstruction and a fresh complete run passed.

penguins · Antarctic Peninsula · species composition · biotic homogenization · paired surveys · MAPPPD · reproducible ecology