ECR feature: Elie Gaget on riparian birds community changes

Elie Gaget is a Postdoc at the International Institute for Applied Systems Analysis (IIASA) – Austria. He is a community ecologist interested in understanding how climate warming and land-use change affect bird communities. Here, Elie shares his recent work that uses a long-term survey to understand latitudinal and altitudinal shifts in riparian birds due to climatic change.

Long-term studies require field monitoring (Photo of Elie Gaget by Pauline Gohier).

Personal links. Research Gate

Institute. International Institute for Applied Systems Analysis (IIASA) – Austria

Academic life stage. Postdoc

Major research themes. Community ecology, Conservation biology, Climate change adaptation

Current study system. Birds! They are amazing! Birds are not only an iconic group easy to monitor and to study, but also fantastic living organisms, relaxing and sources of inspiration. My work partly focuses on birds in wetland ecosystems, which have suffered severe damages because of human activities. Wetlands are spectacular, hosting a high diversity of species and showing different faces following the seasons – at least in Europe where I live. Combining bird observations and wetland ecosystems for scientific conservation purposes is a great satisfaction to me.

Recent paper in JBI. Gaget, E., Devictor, V., Frochot, B., Desbrosses, R., Eybert, M. C., & Faivre, B. (2021). Disentangling the latitudinal and altitudinal shifts in community composition induced by climate change: The case of riparian birds. Journal of Biogeography, 48(3), 526-536.

The great crested grebe (Podiceps cristatus) needs a peaceful place to breed (Photo: Elie Gaget).

Motivation behind this paper. Birds are often used as sentinels of the impact of human’s pressure on ecosystems. This study takes advantage of a very special long-term bird monitoring program that sampled bird communities from upstream to downstream along three major French rivers for 31 years. We investigated whether temporal bird community changes were responsive in a similar way to climate warming and land-use change at different locations along the rivers. The main hypotheses were regarding community elevational shifts over time and how bird communities can adjust to an accumulation of human’ pressures. In theory, climate niche tracking (i.e., local change of relative abundance of species-specific thermal preferences) by high elevation species should closely match a local change in temperature to a higher elevation because species only need to move small distances to find cooler temperatures. Conversely, lowland species must make a greater latitudinal shift to compensate for a local change in temperature – thus, there should be a time lag between climate niche tracking and local change in temperatures for these species.

Key methodologies. We used the Community Temperature Index to reflect the relative abundance of species-specific thermal preferences to measure the temporal lag accumulated by communities according to temperature increase, the so-called climatic debt. In addition, we quantified the temporal changes in the abundance of habitat specialists and generalists using the Community Specialization Index. These metrics allowed us to investigate whether and how the composition of riparian bird communities in lowland versus highland can be related to recent climate warming and reveal a biotic homogenization response. We also assessed the interaction between the thermal and homogenization responses of the communities by calculating species’ contributions (percentage of change related to a specific species) to both community index temporal trends. By doing so, we compared whether the same species drove the shift in Community Temperature Index and Community Specialization Index.

The white wagtail (Motacilla alba) is a fairly common species in Europe, sometimes benefiting from human-made habitats (Photo: Ghislain Riou).

Unexpected challenges. One challenge concerns the spatial design, with three rivers sampled along their stream at different locations. Streams may have their own characteristics and particularities in terms of environmental factors and pressure exposition, which might obscure congruent patterns. We were very impressed by the fact that we observed a remarkably consistent pattern among the rivers for each biodiversity metric used. Not saying that n=3 is a perfect design to investigate spatial heterogeneity, but having such a similar response was important for the conclusions of our study.

Major results. Surprisingly, climatic debt was larger in the highland than in the lowland community, even though temperature increased at a similar rate in both areas. This finding was not primarily expected given thermal niche tracking can be achieved with smaller distances in the highland by performing elevational shifts than in the lowland that requires latitudinal tracking. In other words, for riparian birds, the thermal community adjustment to climate warming was better in lowlands than in highlands. However, a strong homogenization signature was detected in both areas. Interestingly, community changes relative to climate warming and land-use change were uncorrelated, meaning that the species responsible for the community adjustment to climate warming were not the same as those responsible for the community homogenization. In addition, we found a decline in bird abundance in the highlands compared to lowlands that were stable over time. Together, these results highlight the vulnerability of highland species to the accumulation of anthropogenic pressures, particularly in the context of climate warming.

Next steps for this research. Overall, our results support the development of long-term surveys and conservation actions dedicated to riparian bird communities. Not only are these riparian assemblages among the richest in Europe, but they are also highly exposed to both land use and climate change.

The impressive northern giant petrel (Macronectes halli), a sub-Antarctic scavenger characterized by massive nasal tubes (Photo: Elie Gaget).

If you could study any organism on Earth, what would it be? My dream species is the Northern Giant Petrel. Sometimes considered ugly, this bird leaves no one indifferent. Giant Petrel behaviour is amazing, especially on land when feeding as vultures on carrions. This apex species has a great potential for studies investigating the impact of fisheries on the Antarctic and sub-Antarctic food webs, bird olfaction, movement ecology and disease regulation.

Published by jbiogeography

Contributing to the growth and societal relevance of the discipline of biogeography through dissemination of biogeographical research.

Leave a Reply

%d bloggers like this: