Stock pond forage resource relationships for nonbreeding ducks in the rolling plains of Texas

Abstract

Trends in midwinter waterfowl survey data, collected by Texas Parks and Wildlife (TPWD), indicate an increase in annual abundance estimates of waterfowl in the Rolling Plains Ecological Region since 1997. Stock ponds created within in the Rolling Plains provide small, but regionally widespread features, and currently supply aquatic habitat in this semi-arid rangeland landscape; however, limited data exists regarding the availability of resources for nonbreeding waterfowl on stock pond systems. In an effort to address existing information gaps associated with waterfowl use and stock pond systems in the Rolling Plains, research was initiated from August 2014 through March 2015. My objectives for the study were to: 1) investigate and define aquatic invertebrate and vegetative communities, 2) estimate energetic carrying capacity for dabbling ducks, 3) provide waterfowl use inferences from waterfowl survey data, and 4) suggest stock pond management recommendations for state agencies and landowners interested in managing for waterfowl. In an effort to assess the first and second objective, data were collected from 32 study ponds to target potential forage items through quadrat sampling for mature seeds, and water-column and benthic sampling methodologies for aquatic invertebrates. From the collected data, a bioenergetics model was applied to estimate energetic carrying capacity, which is based on energy supply and demand relationships. Three stock pond construction types were recognized during the research effort: embankment, excavated, and combination, and the relationships of forage provision were compared between construction types. Waterfowl visual ground surveys were conducted to provide a baseline for potential waterfowl use relationships for inference toward the third objective. After incorporating food items sampled from three forage groups (water-column invertebrates, benthic invertebrates, and seeds) into a Duck-Energy-Day (DED) model, I yielded conservative carrying capacity estimates of 12,495 DED, moderate estimates from 23,057 – 32,955 DED, and liberal estimates of 45,478 DED among the study stock ponds. The results suggest high variability regarding stock pond forage availability and provision. While some stock ponds displayed a relative high capacity to support nonbreeding waterfowl, others contributed less than 2% of the total DED estimates within each of the three forage categories. Trends associated with construction type partially explain DED estimates, where embankment type are generally greater contributors to total DED. Characteristics associated with each construction type likely influenced differences in DED provision. Additionally, seasonal averages of water-column invertebrate abundances, for excavated ponds, were approximately 50% or less, than those of other construction types. Differences were observed between waterfowl average abundance data and construction type (F 2, 29 = 9.771; P = < 0.001), where embankment pond type was significantly different from combination (P < 0.001) and excavated types (P < 0.001); however, excavated and combination type did not differ (P = 0.753). Information collected over the duration of this project suggests that embankment construction types may provide more waterfowl forage and thus, more attractive to nonbreeding waterfowl.