Food resource availability for American black ducks wintering in southern New Jersey

Abstract

Midwinter waterfowl survey data indicates a long-term decline in the number of wintering American black ducks (Anas rubripes), potentially due to habitat limitations. In order for future estimates of carrying capacity to be determined, it is critical that regional food availability is estimated. We collected pairs of habitat core samples (n ¼ 510) from 5 habitat types in southern New Jersey, USA, during October, January, and April 2006-2008 to estimate resource availability and variability. We collected upper gastrointestinal tracts from hunter-killed birds (n ¼ 45) and late season collections (n ¼ 19) to identify food items and limited our estimates of resource availability to only winter food items; thereby reducing the availability of seed foods found in our core samples by 38% and animal foods by 96%. We did not detect differences in years or sampling period, but did between habitat types. Mudflat habitat had the greatest availability of invertebrate and vertebrate food items and appeared to supply the bulk of energy to black ducks wintering in southern New Jersey. We suggest conservation efforts to be focused on restoring or enhancing mudflat habitat as an integral component of an ecologically functioning salt marsh to increase food availability. ß

A 24-Hour Time-Energy Budget for Wintering American Black Ducks (Anas rubripes) and its Comparison to Allometric Estimations

“…Although black ducks are one of the more extensively studied waterfowl species, little is known about their nocturnal behavior. Studies of black duck movement using radio telemetry have reported nocturnal activity (Albright et al 1983;Hickey and Titman 1983;Morton et al 1989b;Cramer 2009) and in some cases different habitat use patterns between diurnal and nocturnal periods (Conroy et al 1986;Morton 2002). However, researchers have never quantified the actual behavior exhibited across all time periods.…”

Notice: The authors have discovered an error in raw data analyzed in this paper. This article has been retracted. The corrected article is published online early as Ringelman KM, Williams CK, Castelli PM, Sieges ML, Longenecker RA, Nichols TC, Earsom AD. 2018. Estimating waterfowl carrying capacity at local scales: A case study from Edwin B. Forsythe National Wildlife Refuge, New Jersey. Journal of Fish and Wildlife Management 9(1):xx-xx; e1944-687X. doi:10.3996/082017-JFWM-066.

“…We did not model uncertainty in the energy content of waterfowl foods, which could increase variation in energy supply by !10% and likely closer to 30-40% . We did not account for niche differentiation in habitat use, nor species-specific dietary preferences, but focused on habitat and food types selected by black ducks (Cramer et al 2012); this probably had a minimal influence on the outcome of the model given that black ducks comprise the majority of energetic demand at Forsythe. We also did not model depletion through degradation or consumption by nontarget species such as shorebirds or include foraging effectiveness or thresholds (Central Valley Joint Venture 2006, Miller et al 2014Hagy and Kaminski 2015).…”

“…We used data from Cramer et al (2012), Goldstein et al (2016), Fino et al (2017), and newer unpublished data to evaluate foraging resources in high marsh, low marsh, mudflats, subtidal habitats, forested wetlands, and freshwater impoundments within our study area. We used an average value for salt marsh habitats to estimate energy availability in unclassified salt marsh.…”

“…These data sets excluded foods not known to be eaten by black ducks, as well as ribbed mussels Geukensia demissa and killifish Fundulus spp. deemed too large (.21.4mm) to be consumed by black ducks (Cramer et al 2012). Despite this, outlier data points clearly remained in the core sampling data.…”

“…There has been a great deal of waterfowl research conducted at Forsythe over the past decade, much of which has sought to address information gaps in black duck ecology. These include detailed behavioral studies of waterfowl movements (Ringelman et al 2015b), energy expenditure (Cramer 2009;Jones 2012), and food availability (Cramer et al 2012;Ringelman et al 2015a;Goldstein et al 2016). In addition, several different population surveys are available for Forsythe, including the annual Midwinter Waterfowl Survey (MWS), standardized ground surveys from 2005-2014, and aerial transect surveys for black ducks from 2011-2014.…”