Context:

• The majority of Himalayan birds migrate downslope during the winter, while a small proportion of species in low elevations migrate upslope, a study published in the journal Global Ecology and Biogeography. 

Key Findings of Study

• Himalayan birds show the greatest elevational shifts remain within the narrowest thermal regimes.
  • The data of 37,944 Himalayan birds from the western Himalayas and 9,992 from the eastern regions, totalling 47,936 were examined.
  • In the eastern Himalayas, the elevational distribution among 198 species showed that 55 per cent of the birds had significant lower shifts while 59 per cent reflected median shifts and 56 per cent recorded upper elevations limits.
  • The study examined seasonal elevational shifts among 302 Himalayan bird species using eBird, a community science dataset, for the years 2011 through 2022. 
• Factors influencing Elevational Shift
  • Availability of food: The availability of food was a deciding factor for the birds to determine the elevational shift. 
    • In the eastern Himalayas, granivores (species eating grain and seeds) shifted further downslope which was significant at their lower limit while omnivores shifted shorter distances downslope which was significant at their upper limit.
  • Dispersal Availability: As for dispersal ability or the ability of the species to establish itself in that area, fruit-eating species (frugivores) shifted shorter distances compared to invertivores, that feed on invertebrates.
  • Land use & Climate Change: Change in land use and climate change can have a combined effect of elevational migration migrating birds in the future.
  • Thermal Regime: Urocissa flavirostris, Dendrocopos darjellensis, Garrulax ocellatus, and Alcippe vinipectus are four of 37 species known to have a summer median elevational limit of over 2,500 meters. 
    • Temperate mountains, especially at high altitudes with cold winters and warm summers, experience a significant shift in seasonality.

News Source: Down to Earth