Florida Mottled Duck Research Articles

Mottled ducks, feral mallards, and their hybrids in Florida

AbstractThe nonmigratory and endemic Florida mottled duck (Anas fulvigula fulvigula) is facing conservation threats from the combined effects of urbanization and introgressive hybridization with feral mallards (Anas platyrhynchos) and mallard x mottled duck hybrids. In the past, the status of the Florida mottled duck population was assessed during annual aerial surveys and most brown ducks (mottled ducks, mallards, and hybrids of them) detected during the survey would have been mottled ducks. But the release of domesticated mallards for aesthetic purposes has led to increases in the prevalence of mallards‐hybrids (mallards or mallard x mottled duck hybrids) throughout peninsular Florida, USA, and because it is impossible to differentiate among mottled ducks, female mallards, and hybrids during aerial surveys, helicopter surveys were halted in 2009 until state researchers could conduct a range‐wide study to determine what proportion of brown ducks are mottled ducks versus mallards‐hybrids. We used plumage keys and high‐resolution photography to categorize brown ducks from 557 wetland grid points as either mottled ducks or mallards‐hybrids. Of the 5,179 brown ducks categorized, 40.1% were mottled ducks and 59.9% were mallards‐hybrids. We used logistic regression analysis to model the interactive effect of a site's latitude and level of urbanization (urban gradient value within a 2‐km buffer) to generate a predictive raster surface (1‐km resolution) of the study area with values corresponding to the probability that a brown duck observed within a cell is a pure mottled duck. Predicted values will be used as correction factors when estimating final mottled duck population abundance from brown‐duck survey data. Additionally, the predictive raster surface will be used to identify wetlands where mottled ducks remain predominant so that these sites can be targeted for preservation. Overall, mallards‐hybrids outnumbered mottled ducks throughout most of peninsular Florida, especially in more urbanized regions, and their current prevalence rate presents a serious conservation threat, via hybridization, to extant mottled duck populations.

Impacts of Drone Flight Altitude on Behaviors and Species Identification of Marsh Birds in Florida

Unmanned aerial vehicles (hereafter drones) are rapidly replacing manned aircraft as the preferred tool used for aerial wildlife surveys, but questions remain about which survey protocols are most effective and least impactful on wildlife behaviors. We evaluated the effects of drone overflights on nontarget species to inform the development of a Florida mottled duck (MODU; Anas fulvigula fulvigula) survey. Our objectives were to (1) evaluate the effect of flight altitude on the behavior of marsh birds, (2) evaluate the effect of altitude on a surveyor’s ability to identify the species of detected birds, and (3) test protocols for upcoming MODU surveys. We flew 120 continuously moving transects at altitudes ranging from 12 to 91 m and modeled variables that influenced detection, species identification, and behavior of nontarget species. Few marsh birds were disturbed during drone flights, but we were unable to confidently detect birds at the two highest altitudes, and we experienced difficulties identifying the species of birds detected in video collected at 30 m. Our findings indicate that MODUs could be surveyed at altitudes as low as 12–30 m with minimal impact to adjacent marsh birds and that larger-bodied nontarget marsh species can be identified from videos collected during MODU drone surveys.

Variation in Survival and Harvest Rates in Florida Mottled Duck

ABSTRACTThe Florida mottled duck (Anas fulvigula fulvigula) inhabits a relatively small range of approximately 90,000 km2 within peninsular Florida, USA, and is threatened by habitat loss and genetic introgression with feral mallards (Anas platyrhynchos). Moreover, the Florida mottled duck population status has not been assessed for more than a decade. We used band‐recovery and recapture data from 2000–2013 to examine geographic and demographic factors that influence the survival of Florida mottled ducks and to determine whether survival and harvest probabilities have changed over time. Mean survival probabilities were higher for birds banded in the southern portion of their Florida range than for those banded in the northern portion and higher for adult males than for adult females in both areas. Harvest probabilities increased in the northern extent of its range in Florida for adults and juveniles and remained relatively constant in the southern portion of its range during the study period. Mean harvest probabilities for adult males in both areas were higher than for adult females. Mean harvest probability for juvenile females was higher than that for juvenile males in the north but was similar between the sexes in the south. Our results suggest that mortality rates are generally greater in the northern portion of the Florida mottled duck range because of regional differences in habitat distribution and permanence and in how mottled ducks and humans use wetlands in these areas. We suggest increasing conservation efforts in the north portion of the Florida mottled duck range and improving inferences from leg banding by incorporating live recapture data. © 2020 The Wildlife Society.

Population genomic data delineate conservation units in mottled ducks (Anas fulvigula)

Large multi-locus data sets provide an unprecedented opportunity for detecting fine-scale population structure and identifying populations that warrant independent conservation and management. In this study, we used 3161 polymorphic loci obtained from double-digest restriction-site associated DNA sequencing (ddRAD-seq) to examine genetic differentiation between populations of mottled ducks (Anas fulvigula) and their close relative, the mallard (A. platyrhynchos). Florida (FL) and western gulf coast (WGC) mottled ducks group into discrete populations in ordination analyses and can be assigned unambiguously to their population of origin based on multi-locus genotypes. Moreover, we find limited evidence of recent admixture between populations, and the range gap separating them is a significant barrier to gene flow. We found no evidence of diversifying selection in the sample of loci we analyzed; instead, the genome-wide pattern of differentiation between mottled duck populations is consistent with historical isolation and divergence by neutral genetic drift. Thus, our results indicate that FL and WGC mottled ducks are discrete populations on separate evolutionary pathways and should be managed as independent conservation units, and perhaps recognized as distinct subspecies given observed differences in plumage and morphology. In contrast, the recently established South Atlantic coastal zone population is indistinguishable from the WGC population but shows evidence of a small amount of admixture from FL mottled ducks. Our study demonstrates a quantitative, operational approach for delineating discrete populations for conservation using ddRAD-seq data; multi-locus genotypes allow for a robust test of historical isolation and evolutionary independence on much shorter evolutionary timescales than the overly conservative standard of reciprocal monophyly in mtDNA.

Is it a mottled duck? The key is in the feathers

ABSTRACTThe Florida mottled duck (Anas fulvigula fulvigula) is threatened by introgression through hybridization with feral mallards (A. platyrhynchos). An essential component in managing this threat is the ability to accurately distinguish mottled ducks from mallards and hybrids in the wild. We provide a genetically cross‐validated phenotype key that accurately identifies mottled ducks. We collected data on structural and plumage traits from museum specimens of Florida, USA, mottled ducks and mallards to identify morphological traits useful in this process. We performed extensive comparisons and discriminant function analysis to identify traits informative in distinguishing the 2 species. We used these traits to preliminarily assign 168 contemporary birds as putative mottled duck, mallard, or hybrid. We collected tissue samples from each contemporary specimen and amplified and genotyped associated DNA. We used microsatellite markers to determine posterior probability species assignments for the 168 specimens. We then performed recursive partitioning of phenotypic traits and posterior genotype assignments to create identification keys based on the most informative traits separating mottled ducks from mallards and hybrids. Finally, we cross‐validated the keys by comparing assignments made using the key to those from genotyping for 339 wild ducks. The keys were >90% accurate, which suggests that their adoption will increase the ability of managers to address the threat of hybridization by mallards by allowing mottled ducks to be distinguished from other ducks in Florida. Our research provides a methodology to develop genetically cross‐validated identification keys for other species threatened by genetic introgression. © 2016 The Wildlife Society.

Movements and seasonal use of habitats by rural and urban female mottled ducks in southeast Florida

ABSTRACTFlorida will continue to undergo high rates of habitat loss, primarily the result of urbanization. In addition, invasive species are a major threat to Florida's biodiversity. The Florida mottled duck (Anas fulvigula), a bird unique to the state, is particularly vulnerable to loss of wetland habitats and hybridization with feral mallards. Because mottled ducks are more likely to encounter feral mallards in urban habitats, we trapped and radiomarked adult females in urban (n = 99) and rural (n = 146) habitats to estimate home ranges and rates of movement into and out of urban areas. We also determined habitat use in urban and rural areas during the breeding (1 Feb–31 Jul), post‐breeding (1 Aug–18 Nov), and hunting (19 Nov–31 Jan) periods and estimated seasonal habitat selection of rural female mottled ducks. Urban females used mostly aquatic habitats in low and high intensity human development year‐round. Rural ducks used freshwater marshes throughout the year, but selection of other habitat types varied seasonally. Use of glades marsh and agricultural habitats by rural ducks peaked during the breeding season. Rural ducks selected artificial impoundments and reservoirs during the post‐breeding and hunting periods. Median home range size of rural females was more than 65 times greater than those of urban females. Our results suggest the spread of mallard genetic introgression caused by females leaving urban areas may be slow because as few as 6% of the adult females moved between urban and rural areas. Focusing wetland conservation efforts on freshwater marshes and artificial impoundments in south Florida would likely benefit mottled ducks. © 2014 The Wildlife Society.

Annual and seasonal survival of adult female Mottled Ducks in southern Florida, USA

Continuing human population growth and urbanization in Florida may impact the survival of native birds, including the Florida Mottled Duck (Anas fulvigula fulvigula). Survival of adult females is an important vital rate that affects population growth rates, thus estimates of female survival as well as sources of variation affecting survival rates are needed for the development of a more informed conservation plan for Florida Mottled Ducks. In this study, we estimated annual and seasonal survival rates of radio-tagged adult female Mottled Ducks (n = 236) using urban and rural areas in southern Florida from 2008 to 2011. Additionally, we tested for differences in survival among ducks using different geographic areas during the breeding season and that were exposed to different hunting regimes during the hunting season. Identifying the geographic areas where higher rates of mortality occur may allow for more effective habitat and harvest management of the Florida subspecies of Mottled Duck. Annual survival was higher for ducks that used urban areas (74%) than for ducks that did not (47%). Daily survival rates were lowest during the breeding season. Females that used Everglades-type habitat during the breeding season had higher seasonal survival rates (78–85%) than those that did not (37–47%). We found evidence of density-dependent mortality during and after the hunting season. Differences in hunting season survival for ducks that used unhunted rural areas (88%) when compared with survival of ducks that used areas with open (87%) or quota hunting systems (85%) were not significant. Differences in survival among study years were negligible. Our results indicate that Florida Mottled Ducks survive at high rates in urbanized areas, but may benefit from increases in the quantity and quality of breeding habitats.

Nesting ecology of Florida mottled ducks using altered habitats

Habitat loss has negatively affected many species of upland-nesting waterfowl. Very few areas contain pristine nesting habitat in Florida because of conversion to agriculture and urban development. Although some species have acclimated to nesting in an altered landscape, little is known about the nesting ecology of Florida mottled ducks (Anas fulvigula fulvigula) that use altered habitats. We located and monitored 77 nests of radio-marked Florida mottled ducks in the Upper St. Johns River Basin (1999–2002) and in south Florida (2009–2011) and tested the effects of nest vegetation characteristics, human disturbance, and temporal variables on estimates of daily nest survival. We also calculated the percent of females that nested each year as a measure of breeding propensity. Nest age at discovery had a positive relationship with daily nest survival. Daily nest survival rates did not vary within or among years and were unaffected by density and height of vegetation at the nest and human disturbance parameters we measured. Breeding propensity ranged from 25% to 56%. Breeding propensities were less than those of other duck species, but our nest success estimate of 28% was greater than most estimates for ducks and is not likely to limit population growth of Florida mottled ducks. © 2013 The Wildlife Society.

Fifty-nine microsatellite markers for hybrid classification studies involving endemic Florida Mottled Duck (Anas fulvigula fulvigula) and invasive Mallards (A. platyrhynchos)

Endemic Florida Mottled Duck (Anas fulvigula fulvigula) appear to be hybridizing introgressively with domesticated Mallards (A. platyrhynchos), which are frequently released or escape captivity and have established feral populations throughout Florida. To investigate this possible conservation threat, we isolated and characterized 59 polymorphic loci from an enriched Florida Mottled Duck microsatellite library and performed cross-amplification assays with Mallard specimens. Average numbers of alleles per locus were 6.0 (ranging 2-23) and 5.6 (ranging 2-15) for A. fulvigula and A. platyrhynchos, respectively; estimates of observed/expected heterozygosity were 0.54/0.63 and 0.52/0.64. Markers developed in this study will be used in conjunction with existing markers to robustly classify hybrids and to assess and monitor the genetic dynamics of introgression between these waterfowl species.

A Comparison of Hybridization between Mottled Ducks (Anas fulvigula)and Mallards (A. platyrhynchos) in Florida and South Carolina using Microsatellite DNA Analysis

Interspecific hybridization has been implicated in population declines for some waterfowl species within the mallard complex, and hybridization with mallards (Anas platyrhynchos) is currently considered the largest threat to mottled ducks (A. fulvigula), one North American member of that complex. We assessed genetic variation among 225 mottled ducks and mallards using five microsatellite loci, and detected significant overall differences between these species within two geographic areas. We characterized hybridization in Florida, where mottled ducks are endemic and mallards are beginning to appear on the breeding grounds, and in South Carolina, where mottled ducks were introduced outside their native range. We used Bayesian genetic mixture analysis in an attempt to distinguish between these closely related species. In Florida, we detected two distinct genetic groups, and 10.9% of our samples from Florida mottled ducks were inferred to have been hybrids. In contrast only 3.4% of Florida mallards were inferred to have been hybrids, suggesting asymmetric hybridization. Populations from different geographic areas within Florida exhibited hybridization rates ranging from 0% to 24%. These data indicate a genetic component would be appropriate in actively managing interspecific hybridization in Florida mottled ducks. In contrast, South Carolina mottled ducks and mallards cannot be differentiated.

EVALUATION OF ALLOZYME AND MICROSATELLITE VARIATION IN TEXAS AND FLORIDA MOTTLED DUCKS

Abstract Genetic variation was evaluated in Florida Mottled Ducks (Anas fulvigula), and Mottled Ducks from the larger Texas population using 22 allozyme and 5 microsatellite loci. Both marker types revealed differences in allele frequencies between populations and each population possessed rare and unique alleles. Overall allelic distributions were significantly different between the two populations, primarily due to significant differences at three allozyme and four microsatellite loci. Significant genetic differentiation was revealed between populations with both marker types, however, over all loci, only 5–6% of the variation detected was partitioned between populations. The Florida population possessed lower levels of allozyme heterozygosity and allelic diversity than the Texas population. In contrast, microsatellite heterozygosities and allelic diversity were similar between populations. These data indicate that there is limited gene flow between populations, suggesting that populations should contin...

Microsatellite Polymorphism and Genetic Structure of Florida Mottled Duck Populations

Abstract Little is understood concerning the effects regional isolation and habitat loss have had upon the genetic structure of Mottled Ducks (Anas fulvigula), a nonmigratory waterfowl species with a limited distribution. Our objective was to identify nuclear DNA-based markers for Mottled Ducks and determine levels of subdivision among populations in Florida. We screened 13 microsatellite primer pairs and identified six microsatellite loci that were variable in Mottled Ducks. These markers revealed a low level of genetic differentiation and a high level of genetic exchange among four Mottled Duck subpopulations within Florida. Over all populations, single-locus expected heterozygosities over the six loci surveyed ranged from 0.13–0.85. There were no significant differences in gene frequencies among the populations examined, and the Fst over 5 biparental loci was not different from zero. Our analysis of the Florida Mottled Duck population indicated high levels of heterozygosity and no evidence of genetic subdivision among breeding units. Polimorfismo en Microsatélites y Estructura Genética en Poblaciones de Anas fulvigula Resumen. Se tiene escaso conocimiento acerca de los efectos del aislamiento regional y de la pérdida de hábitat sobre la estructura genética de poblaciones de Anas fulvigula, un ave acuática no migratoria de distribución restringida. Nuestro objetivo fue identificar marcadores genéticos de ADN para A. fulvigula y determinar los niveles de subdivisión entre poblaciones en Florida. Examinamos 13 pares de iniciadores (i.e., primers) para microsatélites e identificamos seis loci que fueron variables en A. fulvigula. Estos marcadores revelaron un bajo nivel de diferenciación genética y un alto grado de intercambio genético entre cuatro subpoblaciones de A. fulvigula en Florida. Para todas las poblaciones, la heterocigocidad esperada en un locus varió entre 0.13–0.85 para los seis loci examinados. No hubo diferencias significativas en las frecuencias génicas entre las subpoblaciones examinadas, y el valor de Fst para los 5 loci biparentales no fue diferente de cero. Nuestros análisis de las poblaciones de A. fulvigula de Florida indicaron altos niveles de heterocigocidad y no mostraron evidencia de subdivisión genética entre las unidades reproductivas.

MICROSATELLITE POLYMORPHISM AND GENETIC STRUCTURE OF FLORIDA MOTTLED DUCK POPULATIONS

Abstract Little is understood concerning the effects regional isolation and habitat loss have had upon the genetic structure of Mottled Ducks (Anas fulvigula), a nonmigratory waterfowl species with a limited distribution. Our objective was to identify nuclear DNA-based markers for Mottled Ducks and determine levels of subdivision among populations in Florida. We screened 13 microsatellite primer pairs and identified six microsatellite loci that were variable in Mottled Ducks. These markers revealed a low level of genetic differentiation and a high level of genetic exchange among four Mottled Duck subpopulations within Florida. Over all populations, single-locus expected heterozygosities over the six loci surveyed ranged from 0.13–0.85. There were no significant differences in gene frequencies among the populations examined, and the Fst over 5 biparental loci was not different from zero. Our analysis of the Florida Mottled Duck population indicated high levels of heterozygosity and no evidence of genetic s...