It's amazing to encounter wildlife datasets spanning multiple decades. These rare studies can make powerful statements about changes occurring in our environment. Researchers from University of Texas Austin have looked at the abundance of the 28 most common species of coastal birds on Mustang Island, Texas over a 29-year period (1979-2007).
They found that during these three decades, 10 species experienced significant declines in abundance ranging from 39 to 88%. Other studies have found similar results over a broader area indicating that the decline of coastal birds is widespread.
This study sheds some light on a key question: What's causing the decline in coastal birds? Over the three-decade time span of the study, Mustang Island saw a major increase in human activity - from no large developments prior to 1978 to 15 condominiums, four residential communities, several private residences, and a recreational vehicle park 30 years later - all with direct beach access for pedestrians over the dunes.
But is development causing the decline...?
The study looked at data from bird surveys along a 11.7 kilometer stretch of barrier island coast line. Other data was collected including the number of people, dogs, and vehicles. The study found significant correlations between increases in abundances of people on the beaches and decreases in the population of four of the bird species. These results suggest that human activity may be causing the declines. But the results are far from conclusive:
- Ten species faced significant declines (Forster’s tern, royal tern, gull-billed tern, Caspian tern, black skimmer, great blue heron, red knot, and black-bellied plover). The delines of two other species were marginally significant (piping plover and double-crested cormorant)
- However four species, experienced increases in abundance during the same time period (Brown pelican, American oystercatcher, laughing gull, and sanderling).
- Six of the ten declining species are migratory. It's possible that factors outside of Mustang Island are causing their decline.
Implications for conservation...
This study has important implications from both a local and global perspective:
- Mustang Island is an important place for birds. It lies along the Central Flyway and serves as a stopover point.
- What's happening on Mustang Island may be indicative of a much larger trend. From 1980 to 2003, coastal population in the United States increased from 120 to 153 million people. 53% of the people in the US now live on the coast even though it makes up only 17% of the land mass and the population figures are growing. This may be particularly problematic for many coastal birds whose characteristics make them vulnerable to human population trends.
--Reviewed by Rob Goldstein
Foster, C., Amos, A., & Fuiman, L. (2009). Trends in Abundance of Coastal Birds and Human Activity on a Texas Barrier Island Over Three Decades Estuaries and Coasts DOI: 10.1007/s12237-009-9224-2