Brown pelican (Pelecanus occidentalis) groundings on a four-lane divided highway in south Texas: a comparative study using citizen science

The population of the once-endangered brown pelican ( Pelecanus occidentalis ) has increased over the past several decades and is now considered fully recovered. However, in south Texas, the combined effects of weather patterns, transportation infrastructure, and brown pelican biology have led to road mortalities on State Highway 48 (SH 48) at the Carl “Joe” Gayman Bridge. To mitigate these mortalities, the Texas Department of Transportation modified traffic barriers on SH 48. We aimed to examine the effect of the barrier change and determine which weather variables influence brown pelican groundings on SH 48. Citizen scientists monitored sections of SH 48 during adverse weather conditions to record how many brown pelicans collided with the road and how many were killed by vehicles. The monitoring continued for 6 years during fall and winter when weather conditions were predicted to adversely affect brown pelican flight. Our results showed a significant decrease in the number of downed brown pelicans after the removal of concrete single-slope traffic railings (SSTRs) and the installation of T2P railings along the bridge and causeway. However, there was no significant change in the number of days when grounded brown pelicans occurred after T2P railings were installed. We also found a positive relationship between downed brown pelicans and daily maximum wind speed, and a negative relationship with daily minimum air temperature and daily average air pressure. Globally, bridge-related avian mortality is essentially unstudied. These findings will aid our understanding of the effects of road infrastructure on pelican groundings in Texas and call international attention to the potential negative effects transportation infrastructure may have on coastal bird populations.