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Survival of Female White-cheeked Pintails During Brood Rearing in Puerto Rico
Marisel Lopez-Flores, J. Brian Davis, Francisco J. Vilella, Richard M. Kaminski, José A. Cruz-Burgos, and Joseph D. Lancaster

Caribbean Naturalist, No. 10 (2014): 1–12

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Caribbean Naturalist 1 M. Lopez-Flores, J.B. Davis, F.J. Vilella, R.M. Kaminski1, J.A. Cruz-Burgos, and J.D. Lancaster 22001144 CARIBBEAN NATURALIST No. 10N:1o–. 1120 Survival of Female White-cheeked Pintails During Brood Rearing in Puerto Rico Marisel Lopez-Flores1,2, J. Brian Davis1,*, Francisco J. Vilella3, Richard M. Kaminski1, José A. Cruz-Burgos1,4, and Joseph D. Lancaster1 Abstract - Anas bahamensis (White-cheeked Pintail) is widely distributed across the Caribbean islands and South America. The species is classified as threatened in Puerto Rico and a species of least concern across most of its range. Little demographic data exist for the species, particularly during the breeding season. During 2000–2002, we radiomarked 31 incubating females at the Humacao Nature Reserve (Humacao) in southeastern Puerto Rico and estimated daily and interval survival rates of females during brood rearing. Only one of 31 birds died; the average ± 95% CI daily survival rate of pintails was 0.998 ± 0.989–0.999 for all years, and interval survival was 0.913 ± 0.527–0.987 for a 60-day brood-rearing period. High survival of females suggests their mortality during brood rearing does not influence White-cheeked Pintail populations at Humacao, but further studies of reproductive and annual ecology are needed. Introduction Survival of female ducks during nesting and brood rearing has an important influence on their population dynamics (Arnold et al. 2010; Cowardin and Blohm 1992:423; Davis et al. 2001; Hoekman et al. 2002, 2006). Forty percent of adult female Anas platyrhynchos L. (Mallard) may be killed by predators during the breeding season, mostly while hens are nesting (Sargeant and Raveling 1992:399). However, survival of brood-rearing female ducks increases considerably when hens depart nests and use aquatic habitats for brood rearing (e.g., Arnold et al. 2012; Davis et al. 2001, 2007). Nonetheless, as much as 80% of all annual mortality of female Mallards may occur during the breeding season (Arnold et al. 2012, Johnson et al. 1992). Nesting and brood rearing are sequential periods of the waterfowl breeding season and contribute significantly, as mentioned, to fitness prospects of individuals and recruitment into autumn populations of Nearctic waterfowl (Coluccy et al. 2008, Hoekman et al. 2002). Cowardin et al. (1985) estimated survival of female Mallards during the breeding season in two separate intervals, from April to June, 1Department of Wildlife, Fisheries and Aquaculture, Box 9690, Mississippi State, Mississippi, MS 39762, USA. 2Current address - US Fish and Wildlife Service, Puerto Rican Parrot Recovery Program Sub-Office, Box 1600, Río Grande, Puerto Rico 00745, USA. 3US Geological Survey, Mississippi Cooperative Fish and Wildlife Research Unit, Department of Wildlife, Fisheries and Aquaculture, Box 9691, Mississippi State, Mississippi, MS 39762, USA. 4Current address - US Fish and Wildlife Service, Caribbean Ecological Services Field Office, PO Box 491, Boquerón, Puerto Rico 00622, USA. *Corresponding author - Manuscript Editor: Wayne Arendt Caribbean Naturalist M. Lopez-Flores, J.B. Davis, F.J. Vilella, R.M. Kaminski1, J.A. Cruz-Burgos, and J.D. Lancaster 2014 No. 10 2 mostly reflective of the nesting period, and from July to September, intervals approximating brood rearing and molting periods. Cumulatively, survival during these periods was >80% (Cowardin et al. 1985). Kirby and Cowardin (1986) estimated survival of brood-rearing female Mallards at 94%. In other studies of brood-rearing Mallards, survival ranged from 69–74% (Bergmann et al. 1994, Johnson and Sargeant 1977). Kaminski et al. (2013) reported similar rates of survival for female Mallards that ranged from 75–81%. Additionally, band-recovery analyses revealed that the brood-rearing period was the only other reproductive activity that contributed to lower annual survival of nesting Mallards (Arnold and Howerter 2012). Finally, for Aix sponsa (L.) (Wood Duck), Davis et al. (2001) estimated survival at 90–92% for brood-rearing females at two disjunct study areas. Although reported levels of female mortality may not impose significant constraints on species’ population status and dynamics, evidence indicates variability and risk associated with brood rearing (Arnold et al. 2012). Compared to knowledge of waterfowl in Nearctic ecozones, much less is known about ecology and demographics of Neotropical waterfowl including insular forms of widely distributed species such as White-cheeked Pintail (cf. Weller 1980) in the Caribbean. The White-cheeked Pintail occurs throughout the West Indies and South America, where three subspecies are recognized. Anas bahamensis bahamensis (L.) (Northern White-cheeked Pintail, hereafter, White-cheeked Pintail) occurs from the West Indies to northern South America, A. b. rubrosrostris (Vieillot) (Greater White-cheeked Pintail) is found across Central and South America, and the endangered A. b. galopagensis (Ridgway) (Galápagos White-cheeked Pintail) is restricted to the Galápagos Islands (Raffaele 1998, Sorenson 2005). White-cheeked Pintails are classified as threatened in Puerto Rico by the Department of Natural and Environmental Resources but considered a species of least concern (LC) across most of their range by the International Union for Conservation of Nature (García et al. 2005, IUCN 2012). Taxa included in LC categories are generally widespread and not facing imminent endangerment (IUCN 2012). Although White-cheeked Pintails are native to Puerto Rico and other West Indies islands, their population size remains relatively low in this region and is of concern to wildlife biologists and managers (IUCN 2012). Understanding survival of breeding female White-cheeked Pintails and their broods is needed to identify possible negative effects on annual recruitment. The species’ generally complex mating system heightens the importance of understanding its breeding ecology (McKinney and Bruggers 1983; Sorenson 1992, 2005). The Humacao Nature Reserve in eastern Puerto Rico, the nearby islands of Culebra and Vieques, and the Virgin Islands are key habitats for White-cheeked Pintails in this region (Collazo and Bonilla-Martínez 2001). Previous research has addressed nesting ecology, annual survival rates, density and population size, and adult movements of pintails at Humacao Nature Reserve and other coastal systems (Bonilla-Martínez 1995, Collazo and Bonilla-Martínez 2001, López-Flores 2005, Rivera-Milán and Bonilla-Martínez 2007). However, demographic data from radiomarked nesting females and ducklings have not been published. Caribbean Naturalist 3 M. Lopez-Flores, J.B. Davis, F.J. Vilella, R.M. Kaminski1, J.A. Cruz-Burgos, and J.D. Lancaster 2014 No. 10 Thus, we initiated a 3-year study of the ecology of breeding White-cheeked Pintails and their broods at Humacao Nature Reserve. The refuge contains a diverse complex of fresh, brackish, and marine wetlands (López-Flores 2005, Raffaele 1998), wherein we studied movements, habitat use, and survival of female Whitecheeked Pintails and broods. Here, we present estimates of female White-cheeked Pintail survival during brood rearing using approaches that advance earlier analyses (López-Flores 2005). Knowledge of survival rates for distinct phases of the annual cycle (e.g., nesting, brood rearing) helps identify potential bottlenecks for a species and provides estimates for population modeling (e.g., Coluccy et al. 2008). Field-Site Description The Humacao Nature Reserve (hereafter, Humacao) is located in southeastern Puerto Rico (18°09'01.88˝N, 65°46'19.12˝W; Fig. 1) on a coastal plain estuary formed by three interconnected drainages: Río Blanco, Río Antón Ruiz, and Quebrada Frontera (DNER 1986). The area was officially designated by the Department of Natural and Environmental Resources (DNER) as a nature reserve in 1986 (DNER 1995). Six major wetland types occur at Humacao: coastal lagoon (261 ha); herbaceous emergent marsh (364 ha); mangrove forest (25.2 ha) including Rhizophora mangle (Red Mangrove), Avicennia germinans (Black Mangrove), Laguncularia racemosa (White Mangrove), and Conocarpus erectus (Buttonwood Figure 1. Humacao Nature Reserve, Puerto Rico. Caribbean Naturalist M. Lopez-Flores, J.B. Davis, F.J. Vilella, R.M. Kaminski1, J.A. Cruz-Burgos, and J.D. Lancaster 2014 No. 10 4 Mangrove) in order of decreasing salt tolerance; Pterocarpus forest (262 ha); coastal forest (50 ha); and beach scrub (4.4 ha). Forested wetlands were dominated by Pterocarpus officinalis Jacq. (Swamp Bloodwood). This legume tree dominates fresh and brackish coastal regions of the Caribbean basin. Coastal forests were primarily found on sandy soils of fossil dunes at higher elevations, whereas lagoons and emergent wetlands predominated in areas with geological depressions and disturbed areas in forested wetland (DNER1986). Coastal lagoons are mostly surrounded by emergent vegetation, including Typha dominguensis (Cattail) and Achrostichum spp. (aquatic ferns). Estuarine lagoons divide Humacao into two major complexes: Santa Teresa and Mandri. Water depths of lagoons range from 0.5– 2.0 m, and salinity varies seasonally but increases during the dry season (DNER 1986). Water flows into Humacao from nearby rivers fed by rainfall. Seawater enters Humacao during storm periods (i.e., swells) and extreme overflow (DNER 1986). Air temperature at Humacao is nearly constant throughout the year (25 ± 3 °C; Ewel and Whitmore 1973, Rundle et al. 2002). Methods Nest searching Artificial nest tunnel structures were first deployed at Humacao in 1989 to increase waterfowl production, especially by White-cheeked Pintails (M. Córbet, DNER, Humacao Nature Reserve, pers. comm.). Structures were 189-L drums cut lengthwise, which were placed in a soil substrate and ultimately accreted soil. Panicum spp. (panic grass) and other grasses eventually established and provided nest sites for White-cheeked Pintails. Wetland managers of DNER monitored and managed artificial nesting structures and natural nests in decayed Cocos nucifera L. (Coconut Palm) stumps annually to maintain their viability for nesting Whitecheeked Pintails at Humacao (López-Flores 2005). We searched for nesting White-cheeked Pintails in Palmas, Santa Teresa 1–2, and Mandri 1–3 complexes using a kayak from February to August 2000–2002. We also searched managed impoundments from January to June 2001–2002. We observed male behavior as a cue for detecting nests (Sorenson 1992, 2005). In addition, we walked through vegetation from January–June searching for nests in vicinities of White-cheeked Pintail pairs. Upon detecting the approximate location of a nest, we searched intensively in a 20-m radius. We focused our efforts on artificial structures because most White-cheeked Pintails used nesting structures, and, in a previous study (1990–1995), only 8 nests were found in natural vegetation at Humacao (Bonilla- Martínez 1995). We recorded the location of each discovered nest with a global positioning system (GPS) unit (Trimble GeoExplorer II) and recorded data on several variables associated with the nest and its vicinity (López-Flores 2005). We candled several eggs in each nest to estimate hatch date (Weller 1956). Radio transmitters and marking We used a cast net (approximately 0.61 m) with a pole (1.52 m) to capture White-cheeked Pintails on nests in artificial structures or natural vegetation. Caribbean Naturalist 5 M. Lopez-Flores, J.B. Davis, F.J. Vilella, R.M. Kaminski1, J.A. Cruz-Burgos, and J.D. Lancaster 2014 No. 10 We weighed and leg-banded females with a standard Bird Banding Laboratory aluminum leg band, radiomarked the bird, and returned the female to the nest immediately thereafter (Rotella and Ratti 1992). Capture and handling procedures were approved under Protocol 00-048 of the Institutional Animal Care and Use Committee of Mississippi State University and permit 00-IC-045 from the DNER Terrestrial Resources Division. We used prong- and suture-style radiotransmitters (Model 2032 Advanced Telemetry Systems, Isanti MN) to mark incubating females (Davis et al. 2001, Mauser and Jarvis 1991). Transmitters weighed approximately 7.2 g (less than 2% female body mass), measured 28 x 23 x 10 mm, and had a 10-mm steel prong and a 20-cm nylon coated stainless-steel wire antenna (Davis et al. 2001). Monitoring White-cheeked Pintail females We monitored females daily, beginning 1 day after transmitters were attached. We monitored radiomarked birds via kayak or other boat or on foot. We monitored females until the transmitter expired, birds emigrated from the study area, females died, or termination of the study in a given year (Davis et al. 2001, López-Flores 2005). During the 2000 pilot season, we only marked females in June and tracked females until July 29. In 2001 and 2002, we tracked birds from March through midlate August. White-cheeked Pintail nests in Puerto Rico have been reported from February to June with a second nesting peak in October. However, most nesting activity occurs from March–July (Meier et al. 1989, Sorenson 1992). Statistical analyses We defined the brood-rearing period as that from hatch until female mortality, total brood mortality (Davis et al. 2001), or until we ceased monitoring broods at 30–50 days of age (Arnold et al. 2012). With protracted breeding seasons in the Caribbean, White-cheeked Pintails will renest if they lose initial nests, although reports of double brooding are rare (Sorenson et al. 1992). We did not detect any radiomarked females that double-brooded during the study. We used a known-fate model in program MARK to estimate daily survival rates (DSRs) of female White-cheeked Pintails within and across years (Cooch and White 2012:616). Because female White-cheeked Pintails were released into the study at different periods of the breeding season (i.e., left-censored staggered entry), we invoked a simple binomial approach in MARK based on maximum likelihood estimation (Cooch and White 2012; Pollock et al. 1989a, b). Known-fate was our best choice of models because not all radiomarked White-cheeked Pintails were detected on all monitoring days, although birds’ fate was known with certainty. Our data did satisfy three important assumptions of the known-fate model: 1) an animal survives to the end of the study; 2) an animal dies sometime during the study; and 3) an animal survives to some point in the study, until thereafter it is censored (Cooch and White 2012; Pollock et al. 1989a, b). With the left-censored data, we treated released birds as “groups” in the known-fate model (Cooch and White 2012:638). We assumed left-censored individuals had survival distributions similar to birds marked previously, and that survival was not affected by capturing, handling, or Caribbean Naturalist M. Lopez-Flores, J.B. Davis, F.J. Vilella, R.M. Kaminski1, J.A. Cruz-Burgos, and J.D. Lancaster 2014 No. 10 6 radiomarking (Davis et al. 2001; Pollock et al. 1989a, b). We also assumed survival times were independent for all individuals, and that censorship (i.e., emigration, transmitter failure) of females was random and independent of the fate of radiomarked females (Pollock et al. 1989a, b). We right-censored females if they emigrated from the study area and were never encountered after marking or if transmitters were lost or failed (Davis et al. 2001; Pollock et al. 1989a, b). We also right-censored brood rearing females on the day we confirmed the last duckling in a brood had died. We developed a priori a number of candidate models in an attempt to explain variation in DSR relative to measured environmental and other covariates. However, only one White-cheeked Pintail female died during our study, which eliminated most opportunity to model variation in DSR among females. Thus, we evaluated three candidate models to estimate DSR: a null model, with data pooled for 2000– 2002 (S); a model to evaluate between-year variation (2000–2001 [2000 being the abbreviated pilot year of monitoring] versus 2002) because mortalities did not occur both years (S[year 2000–2001, 2002)]); and a model with year as the only effect (SYEAR). We assessed models using Akaike’s information criterion (AIC; Burnham and Anderson 2002). In addition to DSRs, we estimated an interval (brood-rearing period) survival rate for these birds with MARK. The brood-rearing period may last several months in this species (Sorenson 2005). However, White-cheeked Pintail ducklings fledge in 45–60 days (Sorenson 2005), therefore, we raised our DSR estimate to the power of 60 to derive an interval survival rate and associated confidence intervals. A different estimate of interval survival could be obtained by raising DSR to the desired number of interval days. Prior to MARK and perhaps other analytical methods, no clear standard existed for estimating variances for survival rates of 1.0, particularly with staggered entry (Davis et al. 2001, Flint et al. 1995). Thus, if no radiomarked birds died during brood rearing in a given year of our study, we used the profile-likelihood option in MARK to estimate confidence intervals (Cooch and White 2012). The profile likelihood is based on the log-likelihood function of a parameter and is the preferred approach to derive 95% CI values (Cooch and White 2012). Results We found a total of 43 nests of White-cheeked Pintail from 2000–2002 (López- Flores 2005). Twenty-seven of the nests occurred in artificial structures, and all contained broods that hatched. The other 16 nests were constructed in natural vegetation, and their apparent nest success was 0.471 (López-Flores 2005). We radiomarked 35 female White-cheeked Pintails during 2000–2002, but excluded 4 birds from analyses because of transmitter failure, nest abandonment after marking, or other logistical reasons. Therefore, we estimated survival for 31 radiomarked females during brood-rearing seasons 2000–2002. All radiomarked females survived in 2000–2001. In 2002, one female was killed by a raptor, and we suspected Falco peregrinus Tunstall (Peregrine Falcon). Caribbean Naturalist 7 M. Lopez-Flores, J.B. Davis, F.J. Vilella, R.M. Kaminski1, J.A. Cruz-Burgos, and J.D. Lancaster 2014 No. 10 We recorded 633 exposure days for females, or approximately 20.4 exposure days per monitored bird (range = 2–50 days). Together, two of three survival models provided most (≈85%) weight of evidence in explaining variation in DSR of female White-cheeked Pintails (Table 1). Of the three candidate models, the null model contributed the most weight of evidence (≈44%) and best explained survival of brood-rearing White-cheeked Pintails (Table 1). Across all years, DSR (mean ± 95% CI) was 0.998 ± 0.989–0.999. Because female mortality only occurred in 2002, the model comparing variation in DSR in 2000–2001 versus 2002 also contributed substantial weight of evidence (≈41%) in explaining DSR (Table 1). Because only one female died during the study, we could not perform additional modeling to explain variation in DRS within or among years. Including data from all years, the interval survival rate for a 60-day brood rearing period was 0.913 ± 0.527–0.987. Discussion Our results suggest mortality of brood-rearing female White-cheeked Pintails is not a significant influence on annual population dynamics of this species at Humacao, despite the fact that pintails at this reserve coexist with indigenous (i.e., waders, raptors) and exotic (i.e., Herpestes auropunctatus (É. Geoffroy Saint-Hilaire) [Small Indian Mongoose]) predators. Similar conditions may occur in other wetland systems in the West Indies (López-Flores 2005). However, number of exposure days per female in our study was low (≈20) because brood survival was only 30.5% (López-Flores 2005). Thus, predation seems to be a significant source of duckling and brood mortality at Humacao (López-Flores 2005). We do not know what proportion of the White-cheeked Pintail female population at Humacao attempted to nest annually during our study, although we acknowledge this could be another factor that limits population growth in the species. Collazo and Bonilla-Martínez (2001) used mark-resight to study movements and estimated survival rates of adult White-cheeked Pintails on Vieques and Culebra islands east of Puerto Rico during eleven 3-month intervals from October– June 1996–1999. Their estimated period survival rate was 0.87, similar to our period estimate (0.913 ± 0.527–0.987) for brood-rearing White-cheeked Pintails at Table 1. Product-limit estimates of daily survival ratesA (DSR, Ŝ) of radiomarked female whitecheeked pintails (n = 31) during brood rearing at Humacao National Refuge, Puerto Rico, 2000–2002. ModelB KB ΔAICc C ωi D DevE Null 1 0.000 0.441 11.176 Years (2000–2001 vs. 2002) 2 0.149 0.409 9.313 Year 3 2.168 0.149 1.922 ADSRs estimated with known-fate model, program MARK (Cooch and White 2012). BNumber of parameters. CTop-ranking model had AICc = 17.001. DRelative likelihood of the current model (i) based on AICc value. EModel deviance. Caribbean Naturalist M. Lopez-Flores, J.B. Davis, F.J. Vilella, R.M. Kaminski1, J.A. Cruz-Burgos, and J.D. Lancaster 2014 No. 10 8 Humacao. In a study of 229 marked birds in the Bahamas, Sorenson (2005) found mean annual adult survival rates was 0.75 (± 0.19) for males and 0.74 (± 0.03) for females. These estimates are valuable because some White-cheeked Pintail populations in the Caribbean are declining, and understanding survival rates is relevant to population management and species conservation (IUCN 2012). Our study was designed to expand findings of Collazo and Bonilla-Martínez (2001) by investigating White-cheeked Pintail breeding female and duckling ecology, because survival of these population components had not been estimated but are well known to influence population dynamics of Nearctic duck species (Coluccy et al. 2008, Hoekman et al. 2002). Hence, we delayed radiomarking female White-cheeked Pintails until late incubation, which precluded us from estimating female survival during the entire breeding period (Davis et al. 2007). Nonetheless, brood rearing is a critical period for female waterfowl because of depleted energy reserves following egg laying and incubation, exposure to predators, and other exogenous factors (Afton and Paulus 1992, Arnold et al. 2012). Further, this phase of their annual cycle may be particularly stressful for females of Neotropical waterfowl species given the extended nesting periods and physical environmental conditions of tropical wetlands (Tieleman et al. 2004). In one of the most comprehensive and contemporary studies of northern prairie nesting Mallards, Arnold et al. (2012) studied 927 brood-rearing females that generated 30,631 observation days. Mortality risks of females were least while brood rearing in a diversity of wetlands, despite females investing in important parental activities compared to non-breeding females (Afton and Paulus 1992, Arnold et al. 2012). Daily mortality risk of brood-rearing female Mallards was 0.00032, translating into an annual survival probability of 0.890 (Arnold et al. 2012). Similar high survival rates also were found in another study of breeding Mallards, where only 7 (4.2%) of 168 radiomarked females died during brood rearing (Amundson and Arnold 2011). In the southern United States, Wood Ducks and Lophodytes cucullatus (L.) (Hooded Merganser) nest and rear broods in predator-rich environments (Davis et al. 2007, 2009). Despite sometimes low and variable duckling survival (Davis et al. 2007), only 5 (3.7%) of 135 brood-rearing females died over 4 years, resulting in a composite survival estimate of 0.90 (SE = 0.043; Davis et al. 2001). Future analyses that address duckling and brood survival and resource use by White-cheeked Pintails in this local breeding population and throughout their annual cycle and range are needed, especially where populations are threatened or endangered (López-Flores 2005). In particular, attention should be paid to populations where females use offshore cays for nesting. Rats, e.g., Rattus rattus (L.) (Black Rat), and other non-native predators may be a significant source of mortality for eggs and entire nests on offshore cays (Sorenson 2005), and removal of invasive predators could improve nest success, as has been shown for nesting seabirds (e.g., Offshore Islands Conservation Project; Glen et al. 2013, Lawrence 2012). Glen et al. (2013) endorsed removal of rats from cays or islands to enhance nest success of local birds. However, they also cautioned that removal of rats can exacerbate populations of mice, which can also increase mortality of eggs of nesting birds Caribbean Naturalist 9 M. Lopez-Flores, J.B. Davis, F.J. Vilella, R.M. Kaminski1, J.A. Cruz-Burgos, and J.D. Lancaster 2014 No. 10 (Angel et al. 2009, Glen et al. 2013). Nonetheless, data on nesting and broods of White-cheeked Pintail are essential for modeling population dynamics and guiding conservation of this waterfowl species. Additionally, effects and economics of artificial nesting structures on reproductive performance of nesting female White-cheeked Pintails and other Neotropical waterfowl are not well known (Blanco et al. 1996). This lack of understanding is particularly relevant given the greater diversity of predators in the mainland Neotropics and the establishment of several species of invasive predators in Puerto Rico and the Virgin Islands (Martin 1995, Pimentel et al. 2005). Rats occur on virtually every island and most cays in the Caribbean, and mongoose, feral dogs and cats, Procyon lotor (L.) (Raccoon), etc. may also be prevalent (Hays and Conant 2007, Simberloff 2001). Lastly, because legal hunting of White-cheeked Pintails and other resident waterfowl species has been banned since the early 1980s (García et al. 2005), hunting-related mortality should be minimal to nonexistent for the species in Puerto Rico. However, White-cheeked Pintails are hunted elsewhere in the Caribbean (e.g., Cuba, Hispaniola) and mainland South America, but demographic studies of these ducks have not been conducted. Other populations and periods of the annual cycle of White-cheeked Pintails should be investigated to determine if hunting is an additive or compensatory agent of mortality and if survival of females and males varies between breeding and non-breeding seasons. Acknowledgments We were supported by the Federal Aid in Wildlife Restoration Program from the US Fish and Wildlife Service (USFWS) through the Puerto Rico Department of Natural and Environmental Resources (PRDNER; W-22, Study 2), the Mississippi Cooperative Fish and Wildlife Research Unit, and the Forest and Wildlife Research Center (FWRC), Mississippi State University. We thank Messrs. C. Diaz and F. Núñez-García, USFWS, Region 4, and Mr. J. Berríos, PRDNER, Federal funds program coordinator. Thanks to F. Schaffner for reviewing an earlier version of the manuscript. We are especially grateful to Manuel “Maño” Córbet, Humacao Nature Reserve manager, and his staff for logistic support and assistance during our research. M. Ortiz, H. Lopez, and R. Rivera provided field assistance. Animal capture and handling procedures were conducted under the auspices of permits 00- IC-58 from the Puerto Rico Department of Natural and Environmental Resources, USGS Bird Banding Laboratory Master Station Permit 22456, and protocol 00-048 of the Mississippi State University Institutional Animal Care and Use Committee. The use of trade names or products does not constitute endorsement by the US Government. This manuscript has been approved for publication by the FWRC as WF386. Literature Cited Afton, A.D., and S.L. Paulus. 1992. Incubation and brood care. Pp. 62–108, In B.D.J. Batt, A.D. Afton, M.G. Anderson, C.D. Ankney, D.H. Johnson, J.A. Kadlec, and G.L. Krapu (Eds.). Ecology and Management of Breeding Waterfowl. University of Minnesota Press, Minneapolis, MN, USA. 635 pp. Amundson, C.L., and T.W. Arnold. 2011. The role of predator removal, density-dependence, and environmental factors on Mallard duckling survival in North Dakota. Journal of Wildlife Management 75:1330–1339. 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