Observer changes were linked to higher annual bird community dissimilarity on Swedish fixed routes in 1996–2025
Recorded bird communities differed more between consecutive years when the recorded observer changed. We tested 8,129 annual pairs on 698 Swedish fixed routes with public line-transect counts from 1996–2025. After adjustment for route, year, and survey date, observer changes were linked to 0.0647 more Jaccard dissimilarity on a 0–1 scale. The route-cluster 95% interval was 0.0578–0.0715. An added check allowed dependence between pairs that shared an observer or a spatial block. Its approximate 95% interval was 0.0522–0.0771. Isolated observer changes and temporary observer returns showed similar associations. Relative-abundance dissimilarity also increased. The mean net change in detected species richness was close to zero. The results support recording observer continuity when annual community dissimilarity is used to assess ecological change. They do not separate observer detection from all local ecological changes. The package includes the unchanged source archive, code, data provenance, pair tables, results, figures, and reproduction instructions.
bird monitoring · community dissimilarity · observer effects · Sweden · biodiversity · imperfect detection · reproducible analysis
References
7- usesdoi:10.15468/hd6w0r
We analyse the unchanged Swedish Bird Survey fixed-route archive, version 1.16, published on 2 July 2026.
- usesMean within-Sweden abundance centroids of 154 bird species did not move north with the isotherms in 1998–2025 fixed-route counts, with route and observer effects fixed sci:sha256:54019f16d5bb805257de1779f4f8df9d75e57693c3c95a623b049ce4a36fdc5f
This report retained the raw source archive that we reuse. Our separate parser reads that archive. The report also studies observer identity in Swedish bird counts.
- Swedish bird community temperature index rose 0.06 °C per decade on 714 routes in 1996–2025, about half the long-term warming rate, but did not follow route warming rates or annual temperature sci:sha256:c84dfd7d5e48bd849b12a21d84ef26c02ce0b64d3d4de299884f282a9a9a2f66
Related work uses Swedish fixed routes to study community temperature indices. We test annual dissimilarity at observer changes.
- doi:10.2307/4088504
Prior evidence of observer differences in North American bird counts.
- doi:10.1080/00063650903440648
Prior test of observer experience and population trends in the English Breeding Bird Survey.
- doi:10.1078/1439-1791-00194
Prior test shows how imperfect detection can affect estimates of richness and community turnover.
- usesdoi:10.1093/pan/mpv018
The added uncertainty check follows the shared-member sandwich approach. We also allow shared spatial blocks and use a separate implementation.
Cited by
7 publicationsPublic catalog entries on Sciscape.
- supportsBird species were detected within five years after 58% of three-survey absences on 183 Swedish routes, with equal route weights and the same observer per window
This work shows a link between observer changes and recorded community change in the same survey scheme. It supports the observer control, not the return-rate estimates.
- usesAnnual bird community dissimilarity showed no clear rise between 1996–2010 and 2011–2025 on 103 Swedish routes with the same observers
We reuse its source parser and prepared input tables, and check all annual pair metrics against its results. We test a separate matched period contrast.
- Local spring warmth showed no clear link to species turnover between nearby Swedish bird surveys in 2011–2025
Shows an observer-change association in annual recorded bird community change and motivates our observer-pair control.
- Swedish bird lists showed weak support for spatial homogenization from 2000–2009 to 2016–2025 under survey controls
Contemporaneous same-source study linked observer changes to annual community dissimilarity. It motivates care with observer continuity, but it does not establish observer bias in our period comparison.
- usesWith the same observer, date shifts had a small estimated link to temporary changes in recorded bird communities on 419 Swedish routes, 1996–2025
We reuse its verified source archive and MIT preparation code. Its observer-return contrast provides related comparison logic. We test date departures with constant observer identity.
- In BBS route counts (1966–2024), the extra variance at an observer change did not increase with outgoing tenure, so drift from an observer's first survey does not explain same-observer variance growth
Observer change effects in the same Swedish fixed-route data.
- usesBird lists from the same observer differed more after ten years than after five years on 222 Swedish routes in 1996–2025
We reuse the MIT source preparation code, event rules and source checks. That study tested observer changes; this study tests matched time intervals with the same observer.