Invasive Species or Not?

In Texas, we are all too familiar with invasive species. An invasive species is typically defined by two factors: 1) being non-native to the ecosystem and 2) causing economic or environmental harm. In Texas, we know feral swine (or wild hogs, pigs, etc.) with have spread to all, but 1 county in the state; and the damage that occurs to newly colonized areas. Other well-known invasive species in Texas include zebra mussels, giant salvinia, red fire ants, Asian carp, and nutria. Another species that has spread across the Texas landscape is the Eurasian collared-dove.

Based on sightings, Eurasian collared-doves first appeared in northeast Texas in 1995. But how did they get here? Foremost, it is thought that Eurasian collared-doves first arrived in the Bahamas in 1974 via the pet trade and some birds were released into the wild. Within in a decade, birds were found established in southern Florida and then slowly started creeping northward until an explosion starting about the time they were first observed in Texas. They are now found in all 254 counties in Texas and firmly established throughout much of the US with extreme northeast US states and Hawaii being the exceptions. In fact, a breeding pair was found last summer in King Salmon, Alaska!

Yet, Eurasian-collared doves also have expanded throughout Asia, Europe, and even extreme northern Africa too. They were confined to the Indian subcontinent, Balkans and Turkey at the beginning of the 20th century. By 1955, they were found in England and continued to expand. Another cause for their expansion include the release by local pet traders. Americans have a long-history of being involved in the propagation of pigeons (or rock doves); starting as early as the 1600s and other species followed, including “turtle doves” which is a general name for the Genus that includes Eurasian-collared doves.

Based on Texas Parks and Wildlife Department (TPWD) surveys, there was an estimated breeding population of 4.2 million Eurasian-collared doves within our boundaries in 2015. In the matter of two decades, we went from a few sightings to millions of birds. Based on those surveys, the largest populations exist in the High Plains, Rolling Plains, and South Texas. Due to their increase in numbers, TPWD included them in our Small Game Harvest Survey starting in the 2015-16 hunting season. This survey indicated that Texas hunters harvested approximately 890,000 birds. As our surveys have indicated, they appear to be an increasingly targeted bird across Texas by hunters.

However, we don’t completely understand their impact on native flora and fauna in Texas, so it remains if the “invasive” definition does fit these birds or not. Based on the previous definition, we definitely see them as non-native, but do they cause environmental or economic damage? Across Texas, we do know they are highly susceptible to Paramyxovirus (a virus that is an economic concern to both turkey and chicken producers) since largescale mortality events have been reported in both the Panhandle and South Texas. Yet, at a population level, we continue to see mourning doves and white-winged doves do well in the state. Our their impacts on other flora or fauna in Texas?

Whereas mourning doves are mostly a rural-based population in Texas, white-winged doves are largely an urban-based population. With Eurasian collared-doves, birds are split between both urban and rural locations. As said earlier, rock doves were introduced many centuries prior to Eurasian collared-doves in North America, so there invasion may have preempted any observed changes in native populations. All this said, we continue to investigate their possible impacts, but the jury is still out on their invasive title.

By Shaun L. Oldenburger, Migratory Shore and Upland Game
Bird Program Manager, Texas Parks and Wildlife Department