Depletion of Rice as Food of Waterfowl Wintering in the Mississippi Alluvial Valley

Abstract

Waterfowl habitat conservation strategies in the Mississippi Alluvial Valley (MAV) and several other wintering areas assume carrying capacity is limited by available food, and increasing food resources is an effective conservation goal. Because existing research on winter food abundance and depletion is insufficient to test this hypothesis, we used harvested rice fields as model foraging habitats to determine if waste rice seed is depleted before spring migration. We sampled rice fields (n = 39 [winter 2000–2001], n = 69 [2001–2002]) to estimate seed mass when waterfowl arrived in late autumn and departed in late winter. We also placed exclosures in subsets of fields in autumn (n = 8 [2000–2001], n = 20 [2001–2002]) and compared seed mass inside and outside exclosures in late winter to estimate rice depletion attributable to waterfowl and other processes. Finally, we used an experiment to determine if the extent of rice depletion differed among fields of varying initial abundance and if the seed mass at which waterfowl ceased foraging or abandoned fields differed from a hypothesized giving‐up value of 50 kg/ha. Mean seed mass was greater in late autumn 2000 than 2001 (127.0 vs. 83.9 kg/ha; P = 0.018) but decreased more during winter 2000–2001 than 2001–2002 (91.3 vs. 55.7 kg/ha) and did not differ at the end of winter (35.8 vs. 28.3 kg/ha; P = 0.651). Assuming equal loss to deterioration inside and outside exclosures, we estimated waterfowl consumed 61.3 kg/ha (48.3%) of rice present in late autumn 2000 and 21.1 kg/ha (25.1%) in 2001. When we manipulated late‐autumn rice abundance, mean giving‐up mass of rice seed was similar among treatments (48.7 kg/ha; P = 0.205) and did not differ from 50 kg/ha (P = 0.726). We integrated results by constructing scenarios in which waterfowl consumed rice at different times in winter, consumption and deterioration were competing risks, and consumption occurred only above 50 kg/ha. Results indicated waterfowl likely consumed available rice soon after fields were flooded and the amount consumed exceeded our empirical estimates but was ≤48% (winters pooled) of rice initially present. We suggest 1) using 50 kg/ha as a threshold below which profitability limits waterfowl feeding in MAV rice fields; 2) reducing the current estimate (130 kg/ha) of rice consumed in harvested fields to 47.1 kg/ha; and 3) increasing available rice by increasing total area of fields managed, altering management practices (e.g., staggered flooding), and exploring the potential for producing second or ratoon rice crops for waterfowl.

Avian Foods, Foraging and Habitat Conservation in World Rice Fields

“…Eadie et al (2008) and Remsen et al (1991) reported that 15 species of waterfowl regularly used rice fields during the non-growing season in California and the Gulf Coast, USA, whereas at least nine species were commonly observed in MAV fields (Delnicki and Reinecke 1986;Reinecke et al 1992;Twedt and Nelms 1999;Huner et al 2002;Greer et al 2009). Additionally, authors have reported that waterfowl using rice fields in winter feed heavily on waste rice (Singleton 1951;Reinecke et al 1989;Miller and Newton 1999;Dabbert and Martin 2000;van Groenigen et al 2003;Manley et al 2004;Mugica et al 2006a;Greer et al 2009). …”

Waterfowl foraging in winter-flooded ricefields: Any agronomic benefits for farmers?

“…More recent studies in Spain have shown that similarly crushed and flooded fields have a waste rice density of 24.5 g m -2 (Toral 2011), while in North America the values range from 6.6 to 67.2 g m -2 (Stafford et al 2010). In any case, we found an abundance of seeds well above the giving-up density of 5 g m -2 , under which waterfowl are considered to cease foraging (Reinecke et al 1989;Greer et al 2009). Therefore, ducks should have considered the experimental plots as a valuable feeding habitat.…”

“…It has been demonstrated that winter flooding is highly effective in controlling some weeds such as weedy rice (Oryza sativa L., Fogliatto et al 2010) and in inhibiting dormancy break of other seeds such as the exotic Heteranthera limosa (Baskin et al 2002). Greer et al (2009) attributed 44-47 % of waste rice seed loss over the winter to deterioration due to flooded conditions. Another factor of seed bank decrease may potentially be waterfowl foraging.…”

“…Measuring the weed seed bank, we expected greater effects, since not all the seeds present in winter will germinate during the subsequent growing season. Greer et al (2009) estimated that wild waterfowl consumed between 25 and 48 % of waste rice seeds. Concerning weed biomass, the estimated decrease was of 48 % with a medium waterfowl activity (0-21.3 birds ha -1 ) during the winter (van Groenigen et al 2003).…”

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 used an average true metabolizable energy content for waterfowl foods of 1.55 kcal/g to back-calculate an average kg/ha over our entire study site (outliers-removed data). Our high (mean þ 1 SE) estimate of food availability roughly equates to 112 kg/ha, which is below the observed foraging threshold in many other systems (Naylor 2002;Greer et al 2009;Hagy and Kaminski 2012). Simply stated, the threshold at which ducks cannot (or will not) forage (profitably) could appear as a horizontal line anywhere on Figure 4.…”