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Factors Influencing Behavior and Success of Foraging Reddish Egrets (Egretta Rufescens) Author(S): Elizabeth M

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Factors Influencing Behavior and Success of Foraging Reddish Egrets (Egretta Rufescens) Author(S): Elizabeth M Factors Influencing Behavior and Success of Foraging Reddish Egrets (Egretta rufescens) Author(s): Elizabeth M. Bates and Bart M. Ballard Source: Waterbirds, 37(2):191-202. 2014. Published By: The Waterbird Society DOI: http://dx.doi.org/10.1675/063.037.0213 URL: http://www.bioone.org/doi/full/10.1675/063.037.0213 BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, and environmental sciences. BioOne provides a sustainable online platform for over 170 journals and books published by nonprofit societies, associations, museums, institutions, and presses. Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance of BioOne’s Terms of Use, available at www.bioone.org/ page/terms_of_use. Usage of BioOne content is strictly limited to personal, educational, and non- commercial use. Commercial inquiries or rights and permissions requests should be directed to the individual publisher as copyright holder. BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, research libraries, and research funders in the common goal of maximizing access to critical research. )DFWRUV,QÁXHQFLQJ%HKDYLRUDQG6XFFHVVRI)RUDJLQJ5HGGLVK (JUHWV Egretta rufescens ) ELIZABETH M. BATES1,2 AND BART M. BALLARD1,* 1Caesar Kleberg Wildlife Research Institute, Texas A&M University-Kingsville, Kingsville, TX, 78363, USA 2Current address: Texas Parks and Wildlife Department, P.O. Box 1802, Boerne, TX, 78006, USA *Corresponding author; E-mail: [email protected] Abstract.—The Reddish Egret (Egretta rufescens) is the rarest and least studied species of heron in North Amer- ica and is a species of conservation concern throughout its range. Foraging behavior and foraging success of the Reddish Egret were studied by focusing on whether their foraging behavior or success varied with age, color morph, group size, and habitat measures. Foraging individuals (n = 372) were video-recorded in the Laguna Madre of Texas, USA, from March 2008-April 2010. Adult Reddish Egrets were 30-250% more successful foragers than juve- niles, and groups were 32-44% more successful foragers than solitary foragers. Foraging success was similar between color morphs. The more specialized foraging behaviors of canopy feeding, wing flicking, and foot-stirring had the highest success, but were employed infrequently. Four environmental variables (wind speed, light intensity, water depth, and percent seagrass coverage) were found to influence foraging success, but accounted for only 3% of the variation in foraging behavior. Our results suggest that environmental variables have little influence on foraging behavior of Reddish Egrets in the Laguna Madre, and we suggest that characteristics of the prey have a stronger influence. An understanding of how environmental variables influence foraging behavior and success may allow us to better assess habitat quality or possibly aid in identification of highly productive foraging sites and allow for more targeted conservation actions to those habitats that promote high foraging success. Received 12 September 2013, accepted 14 October 2013. Key words.—Egretta rufescens, foraging behavior, foraging success, group foraging, Laguna Madre, Reddish Egret. Waterbirds 37(2): 191-202, 2014 The Reddish Egret (Egretta rufescens) is re- and lagoons (Lowther and Paul 2002). It is stricted in its distribution, relying primarily the most active forager among North Ameri- on coastal wetland habitats. It occurs along can herons, employing a diverse repertoire of the Gulf of Mexico, Atlantic Coast of Florida, foraging tactics (Rodgers 1983; Lowther and and Pacific Coast of Mexico, as well as in the Paul 2002). There is evidence that species Caribbean. The Reddish Egret has an estimat- employing more active foraging techniques ed 2,000 breeding pairs in the United States (e.g., chasing prey) demonstrate a lower strik- likely making it North America’s rarest species ing efficiency than species that employ less of heron (Kushlan et al. 2002). The majority active techniques (e.g., sit and wait) (Recher of Reddish Egrets breed in the United States et al. 1983; Rodgers 1983; Kent 1987). Also, along the Texas Gulf Coast (Lowther and Paul there is limited information about how forag- 2002). On average, the Laguna Madre sup- ing tactics and success vary between juveniles ports 64% of the breeding population in Tex- and adults. Reddish Egrets typically do not as, with some years as high as 94% (Texas Colo- breed until their fourth year (Lowther and nial Waterbird Society, unpub. data). Because Paul 2002), and this delay could be the re- of the Reddish Egret’s small population size sult of a lower foraging efficiency of juveniles and reliance on coastal wetlands, it is listed as making them unable to provide sufficient a species of concern by the U.S. Fish and Wild- food for developing young. This association life Service and as threatened by the state of between deferred maturity and age-related Texas (Texas Parks and Wildlife Department foraging efficiency has been suggested for 2003; U.S. Fish and Wildlife Service 2008). other waterbirds as well (Recher and Recher The Reddish Egret is described as mostly 1969; Bildstein 1984; MacLean 1986; Shealer a solitary forager that defends feeding territo- and Burger 1995). ries (Palmer 1962). The Reddish Egret feeds The Reddish Egret has two color morphs on small fish in relatively shallow coastal flats that may select different foraging habitats 191 192 WATERBIRDS (Green 2005). Difference in foraging habi- METHODS tat selection by the color morphs may justify different management strategies in different The study was conducted in Laguna Madre, a large parts of their range. This is plausible because (185 km long, 4-12 km wide), shallow (average depth < 1 m) lagoon along the lower Texas Coast (Fig. 1). Foraging there is a north-south change in the propor- habitat for wading birds is abundant as seagrass meadows tion of color morphs of Reddish Egrets, with and wind tidal flats are the two main habitat types found dark morphs being dominant in northern ar- in the lagoon (Tunnel 2002). In particular, wind tidal eas (e.g., upper and central Texas coast) and flats are believed to provide the primary foraging habitat white morphs becoming more dominant in for Reddish Egrets (Lowther and Paul 2002), and they cover over 930 km2 of the Laguna Madre (Quammen and southern areas (B. M. Ballard, unpubl. data). Onuf 1993). The lagoon is an open-water system domi- Recent interest in developing conserva- nated by seagrasses, which cover about 357 km2 of the tion strategies for the Reddish Egret has basin (Quammen and Onuf 1993). Shoalgrass (Halod- focused on increasing knowledge of impor- ule wrightii) is the dominant species with other species tant habitats used by this species (Green et including wigeongrass (Ruppia maritima), manatee-grass (Cymodocea syringodium), clovergrass (Halophila engelman- al. 2013). However, much remains unknown nii), and turtlegrass (Thalassia testudinum) (Quammen about the foraging ecology of the Reddish and Onuf 1993). Seagrass habitats provide nursery and Egret. This lack of information limits the abil- cover for a large array of baitfish that comprise the major- ity to develop sound conservation strategies. ity of the diets of wading birds. For instance, understanding how environ- The lower Texas Coast has a subhumid to semiarid, subtropical climate, typically with long hot summers and mental variables (e.g., water depth, benthic short mild winters (Fulbright et al. 1990). Average rain- habitat) influence foraging behavior and fall throughout the region is 68 cm. Southeastern winds success may allow us to better assess habitat predominate with north winds occurring during winter quality or possibly aid in the identification of frontal passages (Tunnel 2002). Historically, the Laguna highly productive foraging sites (Fretwell and Madre routinely experienced hypersaline conditions with salinities in excess of 60 ppt (Tunnel 2002). Channeliza- Lucas 1970). This would allow for more tar- tion has resulted in lower salinities by allowing for more geted conservation actions to those habitats connectivity to the Gulf of Mexico. Today, salinities in the that promote high foraging success. The pro- lower Laguna Madre are usually below 40 ppt, and salini- tection of key foraging habitats is particularly ties in the upper Laguna Madre are usually around 50 ppt relevant given recent energy development with freshwater inflow primarily coming from rainfall and municipal or industrial discharges (Tunnel 2002). projects in several regions important to Red- We divided the Laguna Madre into six zones dish Egrets (Green et al. 2013). and systematically chose one zone each survey day Herein, we investigate the foraging ecology to video-record foraging Reddish Egrets. On each of the Reddish Egret with the largest sample survey day, we systematically searched a zone by of individuals to date, and in a region that boat (outboard or airboat) for foraging individuals. We sampled each month from March 2008 through supports over half the North American popu- April 2010 and throughout the diurnal period. We lation (Texas Colonial Waterbird Society, un- video-recorded foraging individuals with a 1-40x digi- publ. data). Our objectives were to investigate: tal camcorder for 20 min or until the bird stopped 1) the relationship between the foraging be- foraging. Color morph, age
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