Community modeling reveals the importance of elevation and land cover in shaping migratory bird abundance in the Andes

Abstract

The tropical Andes are characterized by extreme topographic and climatic complexity, which has likely contributed to their outstanding current species diversity, composed of many range‐restricted species. However, little is known about how the distribution and abundance of highly mobile organisms, like long‐distance migratory birds, varies across different land covers, elevations, and climatic conditions within the Andes. We conducted 1,606 distance‐sampling point counts across the Colombian Andes, spanning elevations from 253 to 3,708 m, a range of precipitation regimes and representative land covers. We then employed a novel application of a multispecies hierarchical modeling approach to evaluate how elevation, local land cover, aboveground woody biomass, cloud cover, precipitation, and seasonality in precipitation shape the abundance of the migratory land bird community in the Andes. We detected 1,824 individuals of 29 species of migratory land birds, six of which were considered incidental in our study region. We modeled the abundance of the remaining 23 species, while considering observer and time of day effects on detectability. We found that both elevation and land cover had an overriding influence on the abundance of migratory species across the Andes, with strong evidence for a mid‐elevation peak in abundance, and species‐specific responses to both variables. As a community, migratory birds had the highest mean abundance in shade coffee plantations, secondary forest, and mature forest. Aboveground woody biomass did not affect the abundance of all species as a group, but a few showed strong responses to this variable. Contrary to predictions of a positive correlation between abundance and precipitation, we found no evidence for community‐level responses to precipitation, aside for a weak tendency for birds to select areas with intermediate levels of precipitation. This novel use of a multispecies model sheds new light on the mechanisms shaping the winter distribution of migratory birds and highlights the importance of elevation and land cover types over climatic variables in the context of the Colombian Andes.

An environmental habitat gradient and within-habitat segregation enable co-existence of ecologically similar bird species

“…Elevation niche partitioning was identified as a potential coexistence mechanism in over half of the species pairs in the community. Together with the estimated reduction in residual pairwise correlations in the extended warbler model (figure 4), these results provide strong evidence of niche partitioning along this Grinellian mechanism for ecologically similar bird species in the Virunga volcanoes, consistent with previous studies in the Cameroonian mountains [61], Himalayan highlands [26], tropical Andes [62,63] and in New Guinea highlands [64,65]. A recent survey of birds covering a third of the study area (Parc National des Volcans in Rwanda) identified 57% of species to be associated with narrow elevation bands (less than 300 m; [66]).…”

Opportunities for the conservation of migratory birds to benefit threatened resident vertebrates in the Neotropics

“…Global amphibian declines have been the subject of much recent attention due to a range of threats including infectious disease, climate change and habitat loss (Beebee & Griffiths, 2005 ; Hof et al., 2011 ). The impacts of chytrid fungi may be the most serious risk to amphibians within the montane ecosystems of Central America and northern South America (Fisher & Garner, 2020 ) where there is also considerable attention directed towards Neotropical migrants given their use of mid‐elevation montane forests (Blake & Loiselle, 2000 ; Céspedes‐Arias et al., 2021 ). Although reducing the impact of chytrid and other diseases on amphibians requires a multifaceted approach, protecting, restoring and managing habitat is still expected to benefit amphibian populations at serious risk of extinction.…”

Habitat protection and restoration: win-win opportunities for migratory birds in the Northern Andes

“…Our study region encompassed the elevation belt between 1000-2300 m asl (hereafter Montane Forest or Montane elevations). We chose this elevation belt for four reasons: 1) Several Neotropical migrants showing population declines depend on forest and agroecosystems located across that range in South America (Céspedes et al, 2021; Céspedes and Bayly, 2019; Colorado et al, 2012; González et al, 2020b; Kramer et al, 2018), 2) the range has a persistent history of loss of natural habitat driven by pastoral, agricultural and urban development that continues today across South America (Armenteras et al, 2011; Tejedor-Garavito et al, 2012), 3) drivers of habitat loss here differ from regions located below 1000 m asl (González et al, 2018, Supplemental Material Table 1), and 4) this range is the geographic focus of ongoing efforts for the conservation of declining Neotropical migrants (Partners In Flight, 2019).…”