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Habitat Fragmentation: Viewing 40 Years of Land Use Change in Texas and Oklahoma through the Eyes of the Northern Bobwhite

Date: 11/16/16

What is happening to quail in the Southeast?  Within the span of a lifetime, people who love that perky “Bob-WHITE!” call -- sportsmen, hunters, and even backyard birders -- have seen populations of the Northern Bobwhite decline by more than 80% range-wide, and even more in Texas and Oklahoma, with continuing declines that could result in another halving of the population in 10 years or less (K. V. Rosenberg, et al., 2016. Partners in Flight Landbird Conservation Plan: 2016 Revision for Canada and Continental United States. Partners in Flight Science Committee).  

 

Many point their finger at changes on the landscape, particularly habitat fragmentation, as one of the primary causes of this decline.  But until recently, no one could put numbers together to explain those changes.

 

“The Gulf Coast Prairie Landscape Conservation Cooperative (GCP LCC) is the first organization to put serious dollars on the table to actually quantify fragmentation effects on Bobwhite populations,” says Leonard Brennan, the C.C. Winn Endowed Chair for Quail Research at Texas A&M University’s Caesar Kleberg Wildlife Research Institute.  “For 30 years, we’ve had qualitative and anecdotal evidence implicating fragmentation, but until we began working with the GCP, no one had been able to quantify the extent to which fragmentation may be driving Bobwhite declines.”

 

Leonard’s study, conducted in collaboration with Humberto Perotto-Baldivieso, Assistant Professor at the Caesar Kleberg Wildlife Research Institute, set out to develop a framework to help understand how different drivers are acting at different scales to affect Bobwhite numbers.  Their LCC-sponsored study, completed in summer 2016, assessed how changes in land cover (measured as woodland, cropland, pasture), development (measured as population growth, road density, and impervious surface), and the size of habitat patches correlates with changing Bobwhite quail populations, based on survey data over 40 years.  

 

Everywhere you look: loss of diversity

 

“If there is a theme to what we found, it is a loss of diversity,” says Brennan, “a declining diversity in land uses, in plants on the landscape, in associated insect communities, and in habitat structure have all contributed to the Bobwhite’s decline.”   

 

Humberto Perotto-Baldivieso explains that they set about this task by collecting data at three different spatial levels:  at the discrete field or study plot level, at the county level, and across the entire Gulf Coast Prairie region (an area encompassing western Louisiana, eastern Texas, and central Oklahoma).  By analyzing changes across a span of 4 decades, they were able to discern patterns that show how Bobwhite declines and changes on the landscape have interacted.

 

“What’s really interesting is that patterns in the data seem to coincide accurately with some of the suspected land use changes and policy drivers that may have contributed to Bobwhite declines,” explains Brennan.  

 

Perotto-Baldivieso continues, “For example, in Figure A we see that from 1974 to 2002 cropland remained relatively static, while Bobwhite populations declined.  The decline occurred during the 1980s and 90s, when more intensive application of herbicides and pesticides began to occur.  Then in 2012, we see that both agriculture and Bobwhite have declined, reflecting a development boom in central and southeastern Texas.

 

“On the other hand, Figure B shows that from 1974 to 2012, Bobwhite declines occur almost in tandem with an increase in pastureland.”

 

Farming and pasture practices matter

 

“In many parts of Texas, ‘clean farming’ and other management techniques introduced in the 80s and 90s may have resulted in collateral damage to plant-eating insects,” says Brennan.  With the elimination of native grasses and scrubby borders on cropland and along roadsides, native insects were left without cover and without anything to eat.  This, in turn, is a likely contributor to the decline of species, such as Bobwhite, whose diet during the breeding season relies on insects.

 

“What’s really interesting,” continues Brennan, “is that the patterns and data tell us broadly about some potential policy drivers of Bobwhite decline:  namely, over the years of decline, the amount of farmland went down and pasture went up.”  

 

This may seem counterintuitive until you realize that there have been no requirements for native grasses in the Conservation Reserve Program (CRP), a key factor in the trend toward pasture.  “The intention of CRP from the beginning was to control erosion, and the focus has been taking highly erodible land out of production,” Brennan clarifies.  “I applaud the current efforts of the National Bobwhite Conservation Initiative to include incentives for native warm season grasses in these programs -- CRP would then have the potential to provide two important benefits on the same piece of ground.”

 

Informing conservation delivery on the ground

 

With Quail Forever setting up a new office in San Antonio , TX, an obvious question is how can these results be used to improve and focus conservation delivery?  The investigators point to their county-level analyses to inform landscape conservation design by using some of the county metrics and applying them to other areas of interest.  For example, the metrics that appear related to declining vs. stable populations can be used to (a) prioritize areas for habitat restoration and vegetation improvement or (b) focus on management needs (e.g. woody cover or connectivity) in areas that are already high priority.    

 

“There needs to be a recognition of uniqueness of the data at each level,” Brennan  points out.  “It needs interpretation, and the local perspective must be blended with expert knowledge.  We absolutely intend to keep working with Ben Kahler (GCP LCC Science Coordinator) to benefit quail through landscape conservation design and possible future projects.”

 

View the recorded webinar presenting results of this project on the Gulf Coast Prairie YouTube channel at http://bit.ly/NOBO40years.