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Upper Midwest Environmental Sciences Center

Exploring Patterns of Bird Diversity in a Floodplain River System

Is the changing floodplain landscape linked with bird decline?

Under natural conditions, a floodplain river is a dynamic ecosystem – experiencing seasonal fluctuations in water levels that create the ideal habitat for diverse assemblages of resident and migrating birds. During dry summer conditions, river waters recede from the adjacent floodplain, allowing soil to dry out and lush vegetation to thrive. Breeding waterfowl inhabit the lush grasses and sedges through the fall. When river waters rise between late fall and spring, the floodplain is once again inundated, creating the perfect place for ducks, geese and other migratory birds to stop and feed en route during migration.

From the construction of dams to agricultural development, large floodplain river systems have undergone dramatic alterations over the last two centuries. Once a contiguous landscape of river channel, floodplain forest and wet prairies, most floodplain ecosystems are now a discontinuous mosaic of habitats – and scientists are just beginning to uncover how this habitat loss and fragmentation is connected to declines in avian diversity.

To effectively restore floodplain habitats and bird populations, scientists must first understand how factors such as vegetation (or cover type), season and variation in location influence measures of biodiversity. To gain this knowledge, a team of researchers designed a study to examine how the composition of bird assemblages varies across three successional stages of floodplain habitat including wet prairie, early successional forest and mature forest.

Methods and study site

Ten study sites were chosen within the lower Missouri River floodplain, stretching from northwestern to east-central Missouri. The study sites contained three successional stages of floodplain habitat:

Birds were surveyed during spring migration and summer breeding seasons from 2002 to 2004. Survey data were used to calculate biodiversity indices including species abundance, species diversity and species evenness in each successional stage. The results were analyzed to characterize how location, cover type and season affect patterns of bird diversity within each floodplain habitat.

Key results

In this study of bird diversity in the lower Missouri River floodplain, more than 15 percent of all avian species in North America were recorded. This impressive avian diversity is higher than that found in other Midwestern habitats, highlighting the importance of this river system in supporting bird communities.

Based on the analysis of survey data, the research team identified several important links between floodplain habitat and avian diversity:

Implications for conservation and management

Understanding how floodplain habitats influence avian biodiversity will help biologists best manage floodplain ecosystems that have been acquired for conservation along the lower Missouri River as result of the abandonment of agricultural lands after the flooding of the 1990s. This study reveals the importance of maintaining a variety of floodplain successional stages to conserve avian biodiversity.

While all successional stages of floodplain habitat are important for supporting bird diversity, this research highlights wet prairies as a habitat of considerable importance for threatened bird species, including the endangered American Bittern. Because wet prairies are largely ephemeral (existing for only a short time each year) and no longer experience annual flooding, these systems may need to be specially maintained to prevent ecosystem succession. Allowing succession of wet prairies to forest conditions could lead to a loss of the 20 percent of the bird diversity unique to wet prairies, including several species of conservation concern.

Table 1. Bird diversity and common species within each stage of floodplain habitat.

 

Total number of bird species

Most common bird species

Wet prairie

131

Red-winged Blackbird, Common
Yellowthroat, Dickcissel

Early successional forest

121

Indigo Bunting, Northern Cardinal, Common Yellowthroat

Mature forest

141

House Wren, Northern Cardinal, Indigo Bunting, Red-bellied Woodpecker

Table 2. Indicator species (species representative of a habitat) identified within each stage of floodplain habitat.

 

Indicator species

Wet prairie

Northern Harrier, Bobolink

Early successional forest

Bell’s Vireo

Mature forest

Prothonotary Warbler, Northern Parula

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