Land Cover and Area Influence Bird Biodiversity in Geographically Isolated Wetlands

Aim

Geographically isolated wetlands, wetlands surrounded by upland habitat, harbour high amounts of bird biodiversity but are rapidly being lost across the United States. Yet, we do not know which characteristics, such as wetland area or land cover, influence the level of bird biodiversity supported. We assessed the influence of wetland area and local (size of the wetland, 0.001–4.20 km²) and landscape (25 km) land cover on bird biodiversity in geographically isolated wetlands.

Location

Conterminous United States.

Methods

We quantified the impacts of the wetland area and different land cover on overall bird species richness and richness estimates within five functional groups. We integrated 207 geographically isolated wetlands, selected based on eBird sampling locations with over 100 total checklists. We computed land cover metrics within wetland sites and landscape buffers (25 km) around each site. Using a generalised linear modelling approach, we examined how species richness was impacted by area and six remotely sensed land cover variables.

Results

Species richness increased with area for all species and functional groups of birds, but aquatic (e.g., ducks) and terrestrial (e.g., wading birds) functional groups had the steepest species–area slopes. Constructed wetlands exhibited a steeper species–area relationship slope compared to natural wetlands. Species richness was negatively correlated with built land cover at the local and landscape scales and was positively associated with flooded vegetation at the local scale and grass cover at the local and landscape scales. All functional group richness estimates responded negatively to build land cover but showed unique responses in their associations with other land cover variables.

Main Conclusions

Anthropogenic disturbance at the local and landscape scales significantly reduces species richness. Land managers looking to create or restore wetlands, which have steeper species–area curves, should consider local-scale management changes in flooded vegetation or grass cover to improve habitat for birds.