Climate change alters their distribution across a wide geographical range by impacting habitats and bird populations. For the first time globally, this pioneering research integrates climate data; species presence points from field observations, and the international bird data registry. Utilizing various modeling algorithms, it scrutinizes the distribution changes of Aegithalos caudatus across a significant portion of its Palearctic biogeographical range across five distinct periods: the Last Interglacial, the Last Glacial Maximum, the mid-Holocene, the present, and future scenarios, encompassing both an optimistic outlook with sustainable development policies and a pessimistic projection with ongoing greenhouse gas emissions. The findings revealed that three algorithms, random forest, support vector machine, and maximum entropy, outperformed other modeling methods in discerning suitable and unsuitable habitats for Aegithalos caudatus. Evaluation using these models highlighted that the peak of species distribution, reaching 40%, was observed during the Last Glacial Maximum period. Conversely, its favorable habitat decreased by 29% during the Last Interglacial period. Moreover, climate amelioration during the mid-Holocene and present times has increased the habitat suitability of Aegithalos caudatus t across the Palearctic region to 36% and 35%, respectively. In the optimistic scenario for the year 2080, where sustainable policies are adopted to mitigate climate change, there is a notable increase in the distribution and habitat suitability of the long-tailed tit, covering 47% of the Palearctic biogeographical range. Conversely, in the pessimistic scenario, the distribution of this species diminishes to 35%. Across various periods, the annual temperature range emerges as the most influential climatic factor affecting the habitat suitability of this species.

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