Piscivorous Bird Use of Aquaculture and Natural Water Bodies in Mississippi. Issue 8 (1st September 2020)

• Record Type: Journal Article
• Authors: Burr, Paul C.; Avery, Jimmy L.; Street, Garrett M.; Strickland, Bronson K.; Dorr, Brian S.
• Is Part Of: Journal of wildlife management. Volume 84:Issue 8(2020)
• Page Start: 1560
• Page End: 1569
• Publication Date: 2020-09-01
• Subjects: aquaculture -- Ardea alba -- catfish -- depredation order -- double‐crested cormorant -- forage use -- great egret -- human‐wildlife conflict -- Mississippi -- Phalacrocorax auritus; Wildlife management -- Periodicals; Zoology -- Periodicals; 333.954
• DOI: 10.1002/jwmg.21948
• Languages: English
• ISSNs: 0022-541X

Abstract

ABSTRACT: Double‐crested cormorants ( Phalacrocorax auritus ) and great egrets ( Ardea alba ) have an extensive history of human‐wildlife conflict with the aquaculture industry of western Mississippi, USA, due to their depredation of cultured catfish ( Ictalurus spp.). Although aquaculture is abundant, western Mississippi also contains naturally occurring water bodies that offer alternative forage opportunities to these species. How cormorants or egrets distribute themselves among these 2 foraging options is unknown, but it has been generally assumed each species uses aquaculture disproportionately more because of the high density of available prey. To test this assumption, we surveyed these species on aquaculture and naturally occurring water bodies using aerial surveys from October through April of 2015–2016, 2016–2017, and 2017–2018. We modeled the proportion of each species on aquaculture as a function of year, date, and weather‐related variables using quasi‐binomial generalized linear models. Egrets used aquaculture consistently more than what was proportionally available to them and use was not influenced by any of the variables we measured. Proportional use of aquaculture by cormorants was lowest during October through January but steadily increased through April, indicating a distribution shift toward aquaculture in the months immediately prior to their migration. The highest proportional use of aquaculture by cormorants occurred in 2016, a year when lethal control measures were not allowed against cormorants. Conversely, the least proportion of cormorants on aquaculture was in 2015 when cormorants could be lethally controlled under authority of an Aquaculture Depredation Order. This trend highlights the potential influence of changes in mortality risk, caused by changes in policy regarding lethal take of cormorants, on cormorant distribution between foraging options. © 2020 The Wildlife Society. Abstract : We found greater proportions of double‐crested cormorants on aquaculture ponds relative to natural water bodies seasonally during spring, under wetter conditions, and in years when lethal management was limited, suggesting mortality risk altered cormorant distribution and reduced depredation. Great egret use of aquaculture was consistently more than proportionally available and was not influenced by other measured environmental factors.