Background gardens increase regional bird diversity

Bird populations are decreasing across the United States as their preferred habitats are replaced. This is particularly true in urban areas where impervious surfaces and man-made structures predominate. However, a recent study of bird diversity in six US cities has found that the way in which people manage and landscape their own backyards has the potential to increase habitat for wild birds and improve biodiversity on a regional scale. 

The research was co-led by Susannah Lerman of the USDA Forest Service and Desirée L. Narango from City University of New York. The team recorded bird diversity in four residential yard types and in natural parks across six cities with distinctly different climate conditions, including Baltimore, Boston, Los Angeles, Miami, Minneapolis, and Phoenix.

Urbanization usually leads to the homogenization of biodiversity because fewer different types of habitats are available for birds. In addition, bird communities in urban areas contain fewer indigenous species and have a lower conservation value. But few studies have explored whether or how land management by urban residents can ameliorate the negative effects of this homogenization on species composition. 

The researchers tested the effects of local (back yard land management) and neighborhood-scale (amount of impervious surface and tree canopy cover) features on breeding bird diversity in the six metropolitan areas.  They considered six land management types: two natural area park types (separate and adjacent to residential areas), two yard types with conservation features (wildlife-certified and water conservation) and two lawn-dominated yard types (high- and low-fertilizer application), in addition to the surrounding neighborhood-scale features. 

The results were similar in all six cities; species diversity was higher in yards than in urban parks, although parks supported more species of conservation concern. In addition, yards certified as wildlife habitat through the National Wildlife Federation’s certification program supported a wider variety of bird species when compared with more traditional yard landscaping that was dominated by lawn.

Within yard types, species richness was positively associated with the amount of tree cover in the neighborhood, and negatively correlated with the amount of impervious surface in the neighborhood. 

The experts also found that bird species in backyards generated high public interest within the community of citizen birdwatchers, and this made the management of back yards for the purpose of attracting wildlife very significant. 

“This study shows that when people landscape with wildlife in mind, householders can contribute to conservation right in their own back yards,” said Lerman. “And our yards often support some of our most beloved backyard birds.”

According to the study authors, their results show that preserving natural areas, minimizing impervious surfaces and increasing tree canopy are essential strategies to support bird diversity and conserve regionally important species. 

Back yards – especially those managed for wildlife – support diverse, heterogeneous bird communities with high public interest that can advance successful conservation in American residential landscapes.

“Scientists are finding that we can’t study cities in isolation,” said Narango. “It will improve bird conservation efforts if we can understand which management practices are effective across regions and nationally, and which are effective at a more local level.”

The research findings were published today in the journal Ecological Applications.  

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By Alison Bosman, Earth.com Staff Writer