Migration Patterns of Double-crested Cormorants Wintering in the Southeastern United States

Migration patterns of Double-crested Cormorants (Phalacrocorax auritus) wintering in the southeastern U.S. are poorly understood. Movement data were analyzed from 28 cormorants captured in Alabama, Arkansas, Louisiana and Mississippi and equipped with satellite transmitters. Four (three immature, one adult) cormorants did not migrate and stayed in the southeastern U.S. throughout the year. During spring, cormorants captured in Alabama migrated east of the Mississippi River and primarily west of the Appalachian Mountains. Cormorants from Arkansas, Louisiana and Mississippi migrated north along the Mississippi River Valley, the Missouri River Valley and/or the Ohio River Valley. The earliest departure for spring migration was 26 March, whereas the latest departure was 12 May. Adult cormorants departed for spring migration earlier than immature cormorants. The average departure date for fall migration was 1 October. Mean duration of spring migration was twelve days, and cormorants traveled an average of 70 km per day

Individual trophic niche specialization in American beaver (\u3ci\u3eCastor canadensis\u3c/i\u3e)

The American beaver (Castor canadensis) has been described as a choosy generalist at the species/population scale, yet observational studies have shown little variation in diet among individuals. We compared isotopic values of δ13C or δ15N taken from hair of 32 beaver, representing seven colonies in northern Alabama, USA to determine 1) if colonies of beaver show overlap in isotopic niche width as a result of the similar use of food resources and 2) if individual trophic niche specialization occurs within colonies. Total Trophic Niche Width varied across the wetland with the widest being twice the narrowest. Each of the five niche ellipses overlapped with ≥ two other wetlands studied. The percentages of observed variance attributed to Within Individual Component, Between Individual Component, and Between Location Component for δ13C were 37%, 33%, 30%; and those for δ15N were 16%, 56%, and 28%. Dietary nitrogen differentiated the trophic niches of individual beavers. Our results revealed that colonies across the landscape showed separation in trophic niche, lending support that the choosy generalist classification is correct at the colony scale. Our results also support individual trophic niche specialization within colonies, as seen by the substantial amount variation in both δ13C (33%) and δ15N (56%) between individuals

Fish-Eating Birds on Catfish Ponds in the Mississippi Delta

Catfish acreage in the Mississippi Delta has significantly declined in the past two decades, but cormorant density on catfish ponds has remained the same. One possible explanation is that there are fewer cormorants in the region, and this is supported with decreasing roost counts. Cormorant roost harassment can be even more effective today than in the past, because there is less aquaculture acreage to protect and fewer cormorants to move. Roost harassment is important over the entire winter, but even more so around mid-January when cormorant abundance is greatest and when cormorants are more focused on aquaculture ponds. The addition of limited lethal management on ponds and roosts may make dispersal efforts more effective. Understanding which ponds fish-eating birds decide to use is important for effective management at catfish farms. Many pond characteristics influence use by cormorants, herons, and egrets. What is in the pond and what is around the pond are things these birds take into consideration. From this work, it is possible to produce a “heat map” of farms showing the probability that each bird species will use a given pond (Figure 6). Paying more attention to ponds with higher probabilities of damage may help bird harassment efficiency on the farm and reduce depredation

Native Wildlife Adjust Activity Patterns to Temporally Avoid Wild Pigs

Wildlife species have defined activity patterns that are important for conserving biological rhythms and altering these rhythms can cause physiological stress. Species often shift activity patterns to minimize predation risks or to temporally partition competition. Thus, when a new predator or competitor is introduced into a community, the activity patterns of the whole community could be affected, and this effect may increase the stress wild pigs cause to native wildlife. To test the hypothesis that wild pig activity patterns affect those of native wildlife, we monitored activity patterns of native wildlife and wild pigs before and after aerial gunning events that manipulated pig activity patterns. Using the Statistical R-package – Overlap option, we generated species activity curves which showed aerial gunning caused a substantial shift in wild pig activity patterns from peaking near sunrise to peaking near sunset. Native species not directly at risk from aerial gunning, such as raccoon, armadillo, rabbits, squirrels, and opossum, shifted their activity patterns to a lesser degree than that of pigs, but most species adjusted activity peaks to favor lulls in pig activity. Thus, by manipulating swine activity patterns we provide evidence that wild pigs affect the activity patterns of many native wildlife species. Not only does our data demonstrate the flexibility of pigs to alter activity patterns to avoid removal, it also indicates that these animals cause an additional unappreciated stress on native wildlife by altering their biological rhythm

Vertebrate Community Response to Wild Pig Control in an Agroecosystem

Biological invasions often have negative effects on native wildlife and in the case of feral swine, also can cause extensive agricultural damage. As a result, the rapidly increasing swine populations and associated damages have led to wide-spread control efforts focused in agricultural areas. In a previous study, via camera trapping, we determined feral swine reduced observed vertebrate species richness by 26% when they invaded remnant forest patches in the Mississippi Alluvial Valley. To determine the effectiveness of removal efforts in recovering the lost vertebrate richness, in January 2018, we initiated a before-after control-impact designed experiment in 5 forest patches to monitor species richness before and after swine removals with camera traps. Also, we calculated swine activity patterns before and after aerial gunning to determine the degree to which feral swine alter behavior to avoid detection in future efforts. Preliminary data suggests a minimal species recovery following swine removal which may result from a lag in response to decreasing swine abundance or continued suppression from remaining swine populations. Preliminary data also indicate that swine immediately shifted their activity to avoid times of day when aerial gunning occurred. Thus, shifting swine behavior is likely to exacerbate the diminishing returns in removal effectiveness in a patch over a short time period. However, swine activity returned to normal within a year. These results are preliminary to a long-term experiment where we intend to increase patch sample size and continue to monitor species richness recovery as removals decrease swine populations

Piscivorous Bird Use of Aquaculture and Natural Water Bodies in Mississippi

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 option

Historic and contemporary use of catfish aquaculture by piscivorous birds in the Mississippi Delta

Piscivorous birds are the primary source of catfish (Ictalurus spp.) depredation at aquaculture facilities in northwestern Mississippi. Of particular concern is the Double-crested Cormorant (Phalacrocorax auritus), which can cost aquaculture producers millions of dollars annually through the depredation of cultured fish. Historical research conducted in the early 2000s estimated cormorant use of aquaculture ponds in the region, but aquaculture area has decreased by more than 70% since those estimates were made. With less aquaculture available, we predicted cormorant densities on aquaculture would be greater today than historically. Applying a similar methodology as in historical studies, we used aerial surveys to collect data on cormorants at night roosts and using catfish aquaculture ponds during 3 consecutive winter seasons, beginning in 2015. Although the mean annual number of cormorants at roosts in the Delta during our study was 64% less than historically, we found no significant change in densities on aquaculture, suggesting that aquaculture area is likely the factor influencing cormorant occurrence in northwestern Mississippi. During contemporary surveys we also measured the abundance of Great Blue Herons (Ardea herodias) and Great Egrets (A. alba) on the aquaculture clusters, and built predictive models of abundance relative to variables associated with forage at and surrounding the clusters. We found abundance of all 3 species was strongly related to the amount of aquaculture area both within and surrounding a cluster, although patterns varied by species. Cormorant abundance was also greater on clusters with proportionately more food fish (≥20 cm in length) than fingerlings (\u3c20 cm) and was positively related to the proximity and size of night roosts. The relationships described here can be used by producers and wildlife managers to predict the abundance of these piscivorous birds at aquaculture facilities and to design efficient management plans to mitigate potential impacts of depredation and disease

Seasonal variation in preference dictates space use in an invasive generalist

The spatiotemporal distribution of resources is a critical component of realized animal distributions. In agricultural landscapes, space use by generalist consumers is influenced by ephemeral resource availability that may produce behavioral differences across agricultural seasons, resulting in economic and production consequences and increased human-wildlife conflict. Our objective was to assess changes in habitat selection across seasons in an invasive generalist omnivore (feral pigs, Sus scrofa). Hypothesizing that pig space use is primarily driven by forage availability, we predicted strong selection for the most nutritionally beneficial crops and resource types as agricultural seasons progressed. We deployed GPS collars on 13 adult feral pigs in the Mississippi Alluvial Valley to study resource selection in a fragmented agricultural landscape. We estimated resource selection using mixed-effect logistic regression to assess variation in selection across planting, growing, harvest, and fallow seasons

Long term changes in aquaculture influence migration, regional abundance, and distribution of an avian species

Agricultural development has been causing changes to the environment and the abundance and distribution of avian species. Agriculture is dynamic with changes in products occurring at large scales over relatively short time periods. The catfish aquaculture industry is one such agriculture industry that has undergone dramatic changes over the last 25 years. The double-crested cormorant (Nannopterum auritum) is a piscivorous bird that has an extensive history with the aquaculture industry of Mississippi due to its depredation of cultured catfish. A large-scale monitoring program began in 1989 to estimate the abundance and location of cormorants at every known roost in the primary catfish producing region of the state, regionally known as the Delta. We used this data set to address hypotheses pertaining to cormorant ecology within the Delta over time, particularly in relation to aquaculture. We found that, although the Midwest breeding population of cormorants has been increasing, the abundance of cormorants wintering in the Delta has been decreasing, closely following the decline of aquaculture, suggesting aquaculture area is the primary reason for cormorant inhabitation of the region. We also modeled cormorant presence and abundance at all roost sites to determine what factors most influenced cormorant distribution. Aquaculture area around roosts was a significant predictor of both cormorant presence and abundance. However, the influence of aquaculture area was seasonally dependent, with greater positive influences occurring prior to migration. Lastly, we found peak cormorant abundance in the Delta is occurring 2.14 days earlier each year, which may be indicative of changes to migration phenology. Information gained using this large dataset aids in cormorant damage mitigation and to further our understanding of cormorant ecology. Data indicate changes in agriculture, and potentially climate change, can influence phenology, distribution, and abundance of avian species at large geographic scales

Fine Scale Characteristics of Catfish Aquaculture Ponds Influencing Use by Double-Crested Cormorants (Phalacrocorax auritus) in Northwest Mississippi

Double-crested Cormorants (Phalacrocorax auritus) are the main source of depredation at catfish aquaculture facilities in Northwest Mississippi, resulting in significant economic loss. Understanding factors related to pond selection by cormorants could aid in mitigation practices to minimize further loss. We constructed occupancy models to estimate the probability of cormorant presence on catfish ponds against multiple variables associated with each ponds physical surroundings and internal conditions. We also explored cormorant use of aquaculture and natural habitat by using logistic regression to model the proportion of cormorants on aquaculture compared to natural habitat and influences of seasonal variation. Cormorant presence data was collected by aerial survey (n=35) from October to April, of 2015-2017, accounting for an average of 973 catfish ponds and 26 natural water bodies each year. Our results indicate ponds located farther away from trees and activity centers, such as farm workshops, have a higher probability of cormorant use. Larger ponds, and ponds nearer the edge of pond clusters also have an increased probability of use. Specific pond contents influenced cormorant use, including fish species cultured, pond systems, and fish types. From October through January cormorants were distributed more on natural habitat. However, cormorants’ proportional use of aquaculture steadily increased beginning in February. This temporal shift from natural habitat toward aquaculture coincides with cormorant spring migration, indicating an increase in foraging of catfish in preparation for the migration north