We thank Bartolomé and colleagues for their interest in our recent article, “Rewilding through inappropriate species introduction: The case of European bison in Spain” (Nores et al., 2024). Our work critically evaluated the proposal to introduce European bison (Bison bonasus) into the Iberian Peninsula, considering ecological, biogeographical, conservation, and legal aspects. The reply by Bartolomé et al. presents alternative hypotheses but does not challenge our conclusions with new evidence. Our position relied on what the available data show and on the convergence of paleontological, ecological, climatic, and legal evidence (Nores et al., 2024). In contrast, Bartolomé and colleagues rely on hypothetical scenarios of the presence of European bison in Iberia, such as possible Holocene extinctions or preliminary sedaDNA signals (Gelabert et al., 2025), which, while intriguing, do not offer conclusive support for past presence of extant European bison in Iberia. We emphasize that a huge number of well-studied Holocene sites across Iberia—110 sites with bovine remains—have yielded no remains of European bison. This absence is meaningful, especially when considered alongside the clear presence in many of them of the steppe bison (Bison priscus) and auroch (Bos primigenius). It is difficult to conceive that European bison could have lived throughout Iberia during thousands of years without leaving any recognizable trace, given the extensive Late Pleistocene (197 sites) to Holocene (222 sites) fossil record in the region (Arribas, 2004). Bartolomé et al. suggest that this absence could be explained by sampling bias or by misidentification of bone remains. However, these claims are unsupported. The Iberian fossil record has yielded remains of many other large herbivores—including reindeer (Rangifer tarandus) and muskox (Ovibos moschatus) (see Nores et al., 2024)—that present similar preservation challenges. If European bison had been present, it would be reasonable to expect some traces among this extensive fossil material. The diagnostic morphological features of Bison and Bos are well established and widely applied in paleontology (see references in Nores et al., 2024 and others as Martínez-Navarro et al., 2007) as well as in genomics (Llamas et al., 2025). While isolated misidentifications may not be discarded, they cannot account for a complete absence across hundreds of paleontological sites. The idea that European bison was overlooked remains unconvincing in the absence of supporting evidence. In contrast, Bartolomé and colleagues cited references that, upon closer inspection, align more closely with our conclusions than with their assertions: neither Benecke (2005), Kuemmerle et al. (2012), nor Pilowsky et al. (2023) concluded that European bison were historically present in Iberia or that it offered more than marginal habitat suitability, which explains the low fitness of Spanish bison populations and the failure of 30% of introductions (see Appendix of Nores et al., 2024) (see also Llamas et al., 2025). The nature of sedaDNA findings by Gelabert et al. (2025) does not overturn the weight of multidisciplinary evidence, as they do not provide details of such a discovery (e.g., clade/subclade or species), nor it is supported by identifiable remains. Furthermore, the recent discovery of a bison skeleton in northern Spain, dated around 4000 years B.P. (Gobierno de Navarra, 2026), does not challenge our position. First, the clade/subclade of the bison remains is yet to be confirmed by DNA analyses. It is possible that those remains belong to part of the subclade Bb2 which is extinct (Grange et al., 2018; Massilani et al., 2016). Second, if the remains are identified by molecular evidence as extant European bison, the discovery places this skeleton in the Eurosiberian region of Spain during a Neoglaciation period (García-Ruiz et al. 2020). Accumulated evidence of the absence of the species in Iberian paleontological sites suggests that this discovery would be limited to a narrow area in nothern Spain, only 50 km distant from the French boundary in the Pyrenees. The recent discovery of periodicities in the temporal distribution of European bison during the Holocene, which coincided with colder and wetter phases of the North Atlantic atmospheric circulation (Llamas et al., 2025), could be in line with this recent discovery in northern Spain, and casts doubt on the plausibility of the persistence of this species in warmer climates, such as those occurring in most of the Iberian Peninsula. Sound conservation policies require strong supporting evidence. Basing conservation decisions on uncertainty undermines the scientific standards that must guide the reintroduction (introduction in this case) of species. In contrast, Bartolomé and colleagues fail to demonstrate the presence of European bison across Iberia. A recent study suggests again that the extant European bison was not present in Iberia based on fossil, aDNA, paleoecological, and paleoclimatological evidence (Llamas et al., 2025). These authors also strongly challenge the introduction of European bison in Spain. The burden of proof lies with those proposing the introduction of a species and, to date, while awaiting the genetic results of the skeleton found in Navarra, no study has provided verifiable evidence of current European bison in Iberia. In any case, habitat suitability for European bison is not expected to improve in the Iberian Peninsula. Current and projected climate trends there show a consistent increase in temperature and a reduction in precipitation (AEMET, 2024; IPCC, 2023). These trends are expected to intensify in the coming decades, including a marked increase in the number and intensity of hot days and heatwaves, and a spread of semi-arid conditions across several regions in Spain (see Lorenzo Bugalho et al., 2026). A sound conservation policy should focus on supporting and restoring herbivore populations where justified. There is no demonstrated ecological gap that the European bison alone can fill, especially considering the Mediterranean climate and habitat types, which differ markedly from the species' present range. We acknowledge the conservation value of the European bison; however, introducing them to the Iberian Peninsula, dominated by the Mediterranean biogeographic region, is a high-risk intervention with an uncertain outcome. Any conservation introduction must adhere to the precautionary principle, which requires strong supporting evidence and careful risk assessment. Conceptualization: C. Nores, D. Nogués-Bravo, and J. V. López Bao. Original draft: D. Nogués-Bravo and J.V. López Bao. All authors reviewed the manuscript and suggested additional information. Authors declare no conflict of interest.
Nores et al. (Mon,) studied this question.