2009 SOUTHEASTERN NATURALIST 8(2):277–292 Effectiveness of Call-broadcast Surveys for Breeding Marsh Birds Along Coastal Alabama Eric C. Soehren1,*, James W. Tucker, Jr.2, and D. Garth Crow1 Abstract - Point-count surveys targeting Ixobrychus exilis (Least Bittern), Laterallus jamaicensis (Black Rail), Rallus longirostris (Clapper Rail), Rallus elegans (King Rail), Porphyrio martinica (Purple Gallinule), and Gallinula chloropus (Common Moorhen) were performed using a standardized marsh-bird monitoring protocol along tidally infl uenced emergent marshes of coastal Alabama during the 2004 breeding season. We compared the number of target species detected during an initial passive-listening period to those detected during a subsequent multiplespecies call-broadcast period to evaluate the effectiveness of the call-broadcast period for increasing detections. Additionally, we examined the number of responses of each target species to conspecific and heterospecific calls to determine how marsh birds respond to multiple species call-broadcast sequences. Numbers of new individuals detected during call-broadcast periods were significantly greater (P < 0.05) than those detected during the initial passive-listening period for Clapper Rail, King Rail, and Purple Gallinule, but not for Least Bittern and Common Moorhen. Black Rails were not detected during this study. Conspecific calls were more effective at eliciting responses than heterospecific calls for each of the target species except Least Bittern. Although the calls of Clapper Rail and King Rail are very similar, our data indicate that the advertisement calls of both species should be incorporated within multiple species call-broadcast sequences where populations are sympatric. We also recommend that Purple Gallinule call-broadcasts be applied to marsh-bird inventories or monitoring programs throughout this species’ range as a result of its effectiveness, which was previously uncertain. Introduction North American marsh-bird species, particularly bitterns and rails, are habitat specialists that depend primarily upon emergent wetlands. Because of their dependence on marshes, documented losses of wetlands across North America have raised concerns about the current welfare of this group (Conway 2002, Eddleman et al. 1988, Ford et al. 1997, Ribic et al. 1999). In addition, marsh birds are under-sampled by current long-term, landscapescale monitoring programs such as the USGS Breeding Bird Survey (Conway 2002) because this group of birds is generally reclusive, inhabit dense marshes, vocalize infrequently, and seldom fl y. These limitations have resulted in a paucity of baseline population information for marsh-bird species across the continent (Ribic et al. 1999). To address these data deficiencies, a marsh-bird monitoring protocol was proposed for North America (Ribic 1Alabama Department of Conservation and Natural Resources, State Lands Division, Natural Heritage Section, 64 North Union Street, Suite 464, Montgomery, AL 36104. 2Archbold Biological Station, Avian Ecology Laboratory, 475 Easy Street, Avon Park, FL 33825. *Corresponding author - eric.soehren@dcnr.alabama.gov. 278 Southeastern Naturalist Vol. 8, No. 2 et al. 1999) and later developed (Conway 2002) to adequately sample marsh birds to determine population trends at local, regional, and continental scales (Conway and Gibbs 2005). Detecting marsh-bird presence in wetlands usually requires aural surveys because of their reclusive habits (Conway and Gibbs 2005). Many marshbird studies have used call-broadcast approaches under the assumption that this method increases the number of detections over passive-listening. However, little is known about the degree to which call-broadcasts increase detections compared to passive-listening surveys for many marsh-bird species (Conway and Gibbs 2005) and has been identified as a subject needing further investigation (Ribic et al. 1999). Although numerous studies using call-broadcasts have been performed on marsh birds in other regions of North America (e.g., Allen et al. 2004, Bogner and Baldassarre 2002, Conway et al. 2004, Erwin et al. 2002, Evens et al. 1991, Gibbs and Melvin 1993, Glahn 1974, Lor and Malecki 2002, Manci and Rusch 1988, Rehm and Baldassarre 2007, Swift et al. 1988, Tomlinson and Todd 1973), very few have been conducted in the Southeast (Holliman 1978, Legare et al. 1999, Runde et al. 1990) or have yet been published, especially those focusing on 2 or more species (Cely et al. 1993). Therefore, as part of a broader study along Alabama’s coastline, we compared the number of individuals detected during an initial passive-listening period to those detected during a subsequent multiplespecies call-broadcast period following Conway (2002) protocols to evaluate the effectiveness of the 2 survey techniques for 6 northern Gulf Coast breeding marsh birds: Ixobrychus exilis (J.F. Gmelin) (Least Bittern), Laterallus jamaicensis (Gmelin) (Black Rail), Rallus longirostris Boddaert (Clapper Rail), Rallus elegans Audubon (King Rail), Porphyrio martinica (L.) (Purple Gallinule), and Gallinula chloropus (L.) (Common Moorhen). Furthermore, we examined the responses detected during the multiple-species call-broadcast period to determine how each target species responded to conspecific and heterospecific call-broadcasts (Conway and Gibbs 2005). Study Area This study targeted the tidally infl uenced marshes occurring along the shoreline of Baldwin and Mobile counties within the jurisdiction of the Alabama Coastal Area Management Program (ACAMP; Fig. 1). Alabama’s coastal emergent marshes are infl uenced primarily by a salinity gradient that progressively transitions from polyhaline inundation (saline) along the Gulf of Mexico proper to mesohaline and oligohaline inundation (brackish) within portions of Mobile Bay inward to the lower reaches of the Mobile-Tensaw River Delta, respectively (Tiner 1999). For the purpose of this study, we classified coastal marsh-types as either “saline” or “brackish” emergent marshes based on representative plant communities described in Stout and Lelong (1981). Saline emergent marshes were characterized primarily by dominant stands of Juncus roemerianus Scheele 2009 E.C. Soehren, J.W. Tucker, Jr., and D.G. Crow 279 (Black Needlerush), Spartina alternifl ora Loiseleur (Smooth Cordgrass), or mixtures of both found in vast expanses or fringing along the mainland coastline, islands, and inlets of Mobile Bay. These marshes are regularly inundated by tidal fl ooding where salinities exceed 15 ppt (Holliman 1978). Brackish emergent marshes were typically characterized by one or several combinations of Typha domingensis Persoon (Southern Cattail), Sagittaria lancifolia L. (Bull-tongue Arrowhead), Cladium mariscus ssp. jamaicense (Crantz) Kükenth (Jamaica Swamp Sawgrass), Spartina cynosuroides (L.) Roth (Big Cordgrass), Peltandra virginica (L.) Schott (Green Arrow Arum), Phragmites australis (Cavanilles) Trinius ex Steudel (Common Reed), Alternanthera philoxeriodes (Martius) Grisebach (Alligatorweed), or other less frequently encountered dominants occurring in the lower portions of the Mobile-Tensaw River Delta (hereafter referred to as the lower Delta) and around Shelby Lakes in southern Baldwin County (Soehren 2005). These estuary marshes occur where freshwater meets saltwater tides and salinities fl uctuate between 5 to 15 ppt or higher depending on tidal stage, weather, Figure 1. Marsh-bird survey point locations along coastal Alabama, April–July 2004. Hollow dots represent points within saline emergent marsh, and solid dots represent survey points within brackish emergent marsh. Regional sampling areas and landmarks denoting sampling area boundaries are represented in boldface font. 280 Southeastern Naturalist Vol. 8, No. 2 and watershed drainage (Holliman 1978). Within both marsh-types, shrubby stands of Baccharis halimifolia L. (Groundsel Bush) and Iva frutescens L. (High-tide Bush) often occurred where elevations were slightly higher than the surrounding marsh (Holliman 1978). Methods Survey route selection Prior to initiating surveys, we identified emergent marsh habitat by reviewing recent USGS black-and-white aerial imagery (1997 or 2001; TerraServer ®, Raleigh, NC) of the entire Alabama shoreline which includes the outer coast, offshore islands, inlets, bays, rivers, and creeks combining for 977 km (607 mi) in total length (NOAA 1979). We then reconciled all identified marshes with described marsh-types mapped south of US Interstate 10 (Stout and Lelong 1981) to designate either saline or brackish emergent marsh classifications. Following marsh designation, we manually marked potential survey points over 1:24,000 digitized USGS topographical maps using ArcGIS software (ESRI®, Redlands, CA) at 800-m increments along the open water-emergent vegetation interface. We placed points at 800-m intervals instead of the recommended 400-m intervals (Conway 2002) to accommodate for the large size of the sampling area. We then linked survey points into groups of 10 and assigned each group a route name and number generating a total of 86 possible survey routes along coastal Alabama (Soehren and Crow 2004). Logistic constraints made it infeasible to survey all 86 routes, so we selected a random subset of 34 routes (21 saline and 13 brackish routes) consisting of 317 total sample points for surveys (Fig. 1). Lastly, we divided the entire coastal Alabama study area into 3 primary sampling regions to better coordinate survey scheduling. Sampling regions included: 1) lower Mobile County (Mississippi state line to Upper Dog River); 2) lower Delta (Blakeley Island to Ducker Bay); and 3) lower Baldwin County (Weeks Bay to Perdido Bay) (Fig. 1). Survey protocol Our sampling methodology followed the North American marsh-bird monitoring protocols (Conway 2002). We performed all surveys once by boat along the water-emergent vegetation interface during the breeding season from late April to late July when adults on territory are most likely to be vocal. We randomly determined the sampling order and starting location (either survey point 1 or 10) for all 34 routes prior to initiating field surveys. We conducted both morning and evening routes to maximize survey opportunity. Morning surveys began 30-min before sunrise or shortly thereafter and were completed by 10:00 AM CST. Evening surveys began 4 hrs before sunset and were completed by dark. We approached each survey point slowly until the bow of the boat rested firmly over marsh vegetation. In cases when tides were low, we lifted the boat motor and used a push pole to quietly move the boat to the marsh edge. We postponed surveys when wind speeds exceeded a Beaufort scale of 3 or during periods of steady rain. 2009 E.C. Soehren, J.W. Tucker, Jr., and D.G. Crow 281 We recorded all marsh birds detected during an initial 5-min passivelistening period followed by a call-broadcast period (Conway 2002). To reduce observer bias, we practiced bird identification, the sampling protocol, and distance estimation prior to initiation of the surveys (Kepler and Scott 1981). To elicit call responses from target species, we used a portable compact disc player equipped with 2 external, amplified speakers. We placed this setup at the bow of the boat facing the marsh. We obtained 2 compact discs with the primary advertising calls of each target species from the national Marsh Bird Survey Coordinator (Dr. Courtney Conway, USGS Arizona Cooperative Fish and Wildlife Research Unit). One compact disc contained the calls of Black Rail, Least Bittern, King Rail, and Clapper Rail for broadcasting in saline emergent marsh habitats (9-min survey), while the other disc contained calls of Least Bittern, King Rail, Clapper Rail, Common Moorhen, and Purple Gallinule for brackish emergent marsh habitats (10-min survey). Both compact discs began with 5-min of silence (for the passive-listening period) before the advertising calls started. Each broadcast consisted of 30-sec of calls followed by 30-sec of silence to listen for responses and to separate subsequent species’ calls. Primary advertising calls were broadcast in order starting from the least intrusive species to the loudest. All calls were broadcast between 80–90 decibels at approximately 1-m in front of the speakers (Conway 2002). Differentiating between Clapper and King Rail calls A challenging aspect of performing coastal marsh-bird surveys in the Southeast is distinguishing between the similar calls of Clapper and King Rails where populations are sympatric. Although both species are identifi- able when observed, distinction between their respective calls can be very difficult, especially at lengthy distances. To reduce the likelihood of misidentification, we performed several trial runs using call-broadcasts in emergent saline and brackish marshes focusing on identifying both species aurally before surveys were initiated. Moreover during surveys, the repetitiveness of listening to the broadcast of both species’ calls over the course of the field season added to our abilities and confidence of distinguishing the subtle differences between the 2 species. Typically, Clapper Rails are restricted to tidal saline marshes (Holliman 1978) and usually do not overlap with King Rails, which occur in both inland fresh and tidal brackish marshes (Meanley 1969). However, both species are occasionally found together in transitional areas where tidal saline marshes converge with tidal brackish marshes, particularly where Uca spp. (fiddler crab) populations persist (Meanley 1969, Meanley and Wetherbee 1962). This transitional condition exists along coastal Alabama within a poorly defined zone ranging from the US Interstate 10 Causeway at the northern edge and extending southward along the eastern and western shores of Mobile Bay (including the inner confl uences of rivers and creeks) to Weeks Bay in lower Baldwin County and Mon Louis Island in lower Mobile County, respectively (E.C. Soehren, pers. observ.). It also 282 Southeastern Naturalist Vol. 8, No. 2 occurs where the Perdido River empties into the Perdido Bay. Within transitional zones, we differentiated King Rails aurally from Clapper Rails by the former having an overall richer-quality sound of slightly deeper and more evenly-pitched notes given during the “kik” and “clatter” call bouts, the 2 most often detected call-types. Occasionally, we were able to validate some aural identifications when we later observed calling individuals emerging from marsh vegetation after our call-broadcast periods were completed. Although we made pre-survey preparations to address this aural identification challenge (i.e., within the transitional zone), it is possible that some of the individuals we detected aurally may have been misidentified as a result of the variability in calls that exists among individuals of both species. Hence, differentiation between both species can be very difficult and potentially unreliable. Nevertheless, we identified all confusing Rallus spp. calls within the transitional zone as either Clapper or King Rails based upon our initial impression. Statistical analysis We compared the effectiveness of the passive-listening and call-broadcast methods for each of the 6 focal species by calculating the proportion of individuals detected by each method-type. We assigned individuals initially detected during the passive-listening period that later responded during the call-broadcast period as passive-listening detections. Therefore, the proportions responding to call-broadcasts refl ected only the increase in number of individuals detected. We calculated the percent difference in the number of first detections between the 2 periods (i.e., [call-broadcast period – passive-listening period]/passive-listening period x 100; Gibbs and Melvin 1993) to show effectiveness of the call-broadcast period for increasing detections over the passive-listening period. To compare species detections between the two periods in saline marshes, we excluded detections from the 5th-min of passive-listening to standardize sampling effort with the 4-min call-broadcast period. As an additional measure of detection in response to call-broadcasts, we calculated the proportion of individuals detected by passive-listening that later responded to call-broadcasts. This additional measure of detection is the proportion of individuals known present from the passive-listening period that later responded to call-broadcasts; thus, it is a simple estimate of detection probability in response to call-broadcasts. We included all individuals that responded to any call-broadcast, including those first detected during the passive-listening period, to examine responses of individual species to conspecific and heterospecific calls. However, we excluded individuals if they were detected only during the passive-listening period. Some individual birds responded to more than 1 type of call-broadcast; thus, responses across call types often were greater than the number of individuals, and summation of proportions were greater than unity. For statistical analyses, we compared proportions by calculating 95% confidence intervals around the binomial proportions (Zar 1984:378) and concluded significant differences when confidence intervals did not overlap. 2009 E.C. Soehren, J.W. Tucker, Jr., and D.G. Crow 283 Results We surveyed a total of 195 sites in saline emergent marshes and 122 sites in brackish emergent marshes using point-counts between 27 April and 23 July 2004 (Fig. 1). Overall, we detected 604 individuals consisting of 385 Clapper Rails, 50 Least Bitterns, 38 King Rails, 89 Purple Gallinules, and 42 Common Moorhens (Table 1). An additional 16 Clapper Rails and 1 Least Bittern were detected only during the fifth minute of passive-listening in saline marshes, but we excluded these individuals to standardize sampling effort with the latter 4-min call-broadcast period. No Black Rails were detected. Aside from a single detection in a brackish emergent marsh of the lower Delta sampling region, we detected Clapper Rails consistently in saline emergent marshes, and they were the most numerous of the target species encountered (Table 1). Of the 384 Clapper Rails detected in saline marshes, 267 (70%) were initially detected during the call-broadcast period and 117 (30%) were detected during the first 4-min of the passive-listening period (Fig. 2), accounting for a 128% increase in individuals detected (Table 1). For those individuals detected within the multiple-species call-broadcast sequence, the proportion of Clapper Rails responding to conspecific calls was signifi- cantly greater than the proportion responding to King Rail calls. Furthermore, the proportion of individuals responding to King Rail calls was significantly greater than the proportion responding to Least Bittern and Black Rail calls (Fig. 2). Of the 117 Clapper Rails detected passively in saline marshes, 76 (65%) later responded to call-broadcasts. We detected Least Bitterns in both saline (n = 15, 0.08 birds per point) and brackish (n = 35, 0.29 birds per point) emergent marshes at nearly a 1:3.6 ratio between the 2 marsh types. We did not find differences between Table 1. Number of individuals detected by point counts for targeted species of marsh birds in brackish and saline marshes of coastal Alabama. Numbers include individuals detected during an initial passive-listening period (Passive) and a subsequent call-broadcast period (Broadcast only). Also included are number of individuals detected by passive-listening that later responded to call-broadcasts (Both), total number detected during call-broadcasts (Broadcast total = Broadcast only + Both), total number of individuals detected (Total = Passive + Broadcast only), and the percent difference between new individuals detected during the call-broadcast and passive-listening periods (% difference). Targeted species were Common Moorhen (COMO), King Rail (KIRA), Least Bittern (LEBI), Purple Gallinule (PUGA), and Clapper Rail1 (CLRA). Brackish marshes Saline marshes Targeted species COMO KIRA LEBI PUGA CLRA KIRA LEBI Passive 25 7 17 30 117 0 7 Broadcast only 17 23 18 59 267 8 8 Both 13 5 8 15 76 0 2 Broadcast total 30 28 26 74 343 8 10 Total 42 30 35 89 384 8 15 % difference2 -32% 229% 6% 97% 128% - 14% 1One Clapper Rail detected in brackish marshes is not shown. 2Calculated as ([Broadcast only - Passive]/Passive) x 100 (Gibbs and Melvin 1993). 284 Southeastern Naturalist Vol. 8, No. 2 the proportion of Least Bitterns detected by passive-listening and call-broadcasts in either saline (Fig. 3A) or brackish marshes (Fig. 3B). Although no differences were found between the proportions, call-broadcasts collectively increased the number of individuals detected after the passive-listening period by 14% and 6% in saline and brackish marshes, respectively. However, Least Bitterns appeared as likely to respond to heterospecific calls as to conspecific calls (Figs. 3A and B). Of the Least Bitterns detected passively, 2 of 7 (29%) in saline marshes and 8 of 17 (47%) in brackish marshes later responded to call-broadcasts. King Rails were the least numerous of all target species encountered, but were detected in both saline (n = 8, 0.04 birds per point) and brackish (n = 30, 0.25 birds per point) emergent marshes at approximately a 1:6.2 ratio between marsh-types. Within brackish marshes, only 7 (23%) individuals were detected during passive-listening periods while the other 23 (77%) were detected after responding to call-broadcasts (Fig. 4), which substantially increased the number of individuals detected after passive-listening by Figure 2. Proportions (± 95% CI) of Clapper Rails detected in saline marshes of Alabama during point-counts by passive-listening and broadcasting recorded calls. Species are coded as follows: BLRA = Black Rail, LEBI = Least Bittern, KIRA = King Rail, CLRA = Clapper Rail. 2009 E.C. Soehren, J.W. Tucker, Jr., and D.G. Crow 285 Figure 3. Proportions (± 95% CI) of Least Bitterns detected during point-counts by passive-listening (P) and call-broadcasts (C-b) in: A) saline marshes and B) brackish marshes of Alabama. Call-broadcasts of species are coded as follows: BLRA = Black Rail, LEBI = Least Bittern, KIRA = King Rail, CLRA = Clapper Rail, COMO = Common Moorhen, and PUGA = Purple Gallinule. 286 Southeastern Naturalist Vol. 8, No. 2 229% (Table 1). King Rails responded to conspecific calls significantly more often than Least Bittern calls, but not significantly more than the calls of Clapper Rail, Common Moorhen, or Purple Gallinule (Fig. 4). Five (71%) of the 7 King Rails detected during passive-listening in brackish marshes later responded to call-broadcasts. Within saline marshes, all 8 King Rails were detected at survey points within the “transitional” zone between saline and brackish tidal marshes and all were detected only during the call-broadcast period (Table 1). Of these, 7 (88%) responded to conspecific calls (95% CI = 0.473–0.997), while the other individual (12%) responded to Clapper Rail calls (95% CI = 0.003–0.527). We detected Purple Gallinules (n = 89) only in brackish emergent marshes. They were the most-encountered target species in brackish marshes and the second-most detected overall. Two-thirds of the individual Purple Gallinules detected (n = 59, 66%) were first detected during the call-broadcast period (Fig. 5A), accounting for a 97% increase in the number of individuals detected after passive-listening (n = 30, 34%; Table 1). Moreover, 15 Figure 4. Proportions (± 95% CI) of King Rails detected during point-counts in brackish marshes of Alabama by passive-listening and broadcasting recorded calls. Species are coded as follows: LEBI = Least Bittern, KIRA = King Rail, CLRA = Clapper Rail, COMO = Common Moorhen, and PUGA = Purple Gallinule. 2009 E.C. Soehren, J.W. Tucker, Jr., and D.G. Crow 287 (50%) Purple Gallinules that were initially detected during passive-listening later responded to call-broadcasts. For all individuals that responded to call-broadcasts (n = 74; Table 1), 65 (88%) responded to conspecific calls, which was a significantly greater proportion than those responding to heterospecific calls (Fig 5A). Like Purple Gallinules, Common Moorhens (n = 42) were detected only in brackish marshes. Interestingly, more individuals (n = 25, 60%) were detected during the passive-listening period than during the call-broadcast period (n = 17, 40%; Table 1), but this difference was not significant (Fig. 5B). Of the 25 individuals detected during the passive-listening period, 13 (52%) later responded to call-broadcasts. For those detected within the multiple-species call-broadcast sequence (n = 30, Table 1), Common Moorhens responded to conspecific calls significantly more than King Rail calls, but not more than the calls of the other target species (Fig. 5B). Discussion Along coastal Alabama, the call-broadcast period significantly increased detections for Clapper Rail (128%), King Rail (229%), and Purple Gallinule (97%) (Figs. 2, 4, and 5A, respectively), but was less effective for Least Bittern (6–14%; Figs. 3A and B) and Common Moorhen (-32%; Fig. 5B). We acknowledge that the sequential sampling protocol we used did not allow for a direct analysis of the effects of call-broadcasts on detection rates of targeted species. For example, our estimates of percent increase assume that an equal number of individuals were detected during the two survey periods and the additional individuals detected during the call-broadcast period resulted from responses to the call-broadcasts. As a general rule, the rate that new birds are detected by passive-listening rapidly declines after approximately 5 min of sampling (Bibby et al. 1992, Lynch 1995, Petit et al. 1995, Scott and Ramsey 1981). Although we cannot conclude that all individuals detected during call-broadcast periods strictly resulted from their response to the broadcast of calls, the increase in the number of individuals detected using call-broadcasts suggests an improvement in the effectiveness of sampling over passive-listening. The percent differences we report should be viewed as conservative estimates because we did not include individuals responding to call-broadcasts if they were detected during the passive-listening period (see Table 1). We propose a stronger and more direct approach to compare the effectiveness of the two survey methods would consist of repeated sampling and alternating between methods at adjacent points within sampling dates, returning to those points as quickly as practical at approximately the same time of day on a subsequent date, and repeating the survey using the method not used previously. This approach would minimize confounding effects of temporal variation, and using the same observer and equipment to conduct the repeated surveys would minimize observer bias to produce a paired-sample design to allow direct testing for the effects of call-broadcasts. Despite the aforementioned shortcomings of the sequential sampling protocol we used to measure the effects of call-broadcasts on detection 288 Southeastern Naturalist Vol. 8, No. 2 Figure 5. Proportions (± 95% CI) of detections during point-counts by passive-listening (P) and broadcasting recorded calls (C-b) for A) Purple Gallinule and B) Common Moorhen in brackish marshes of Alabama. Species are coded as follows: LEBI = Least Bittern, KIRA = King Rail, CLRA = Clapper Rail, COMO = Common Moorhen, and PUGA = Purple Gallinule. 2009 E.C. Soehren, J.W. Tucker, Jr., and D.G. Crow 289 rates, the protocol enabled us to compare the responses of targeted species to conspecific and heterospecific call-broadcasts. Both Clapper and King Rails responded more often to their conspecific calls than to each other’s calls within the multiple-species call-broadcast sequences (Figs. 2 and 4). Prior to this study, there had been a question on whether use of 1 of these 2 species’ calls would be sufficient to elicit responses from both species where populations are sympatric (Ribic et al. 1999:7). Our findings suggest that both species’ calls should be incorporated into multiple-species callbroadcast sequences during the breeding season along the northern Gulf Coast, but additional study is probably needed to better evaluate responses in other regions. In addition, the effectiveness of using call-broadcasts for detecting Purple Gallinules was classified as uncertain prior to this study due to a paucity of information about it (Ribic et al. 1999). Our data clearly indicate that call-broadcasts significantly improved detections for Purple Gallinules over passive-listening, and they responded to conspecific calls consistently more often than to heterospecific calls placed within a multiplespecies call sequence (Fig. 5A). Hence, we recommend that Purple Gallinule call-broadcasts should be applied to marsh-bird inventories or monitoring programs throughout this species’ range. Although call-broadcasts appeared less effective for Least Bittern and Common Moorhen than for the other target species, other studies have shown that Least Bittern (Bogner and Baldassarre 2002, Gibbs and Melvin 1993, Swift et al. 1988) and Common Moorhen (Conway and Gibbs 2005, Ribic et al. 1999:50) are detected more effectively using call-broadcasts than by passive-listening. The lower responses from Least Bittern and Common Moorhen during the call-broadcast period that we observed may have resulted from several factors including the conservative approach we used to calculate percent differences. For example, we did not include 13 Common Moorhens that responded to call-broadcasts in our calculations because those individuals had been detected previously by passive-listening (Table 1). Thus, we actually detected 30 Common Moorhens during callbroadcasts versus 25 during passive-listening, but those 13 individuals detected via call-broadcasts did not contribute to increased efficiency by addition of call-broadcasts to the sampling protocol. Similarly, our calculations for Least Bitten also appear conservative (Table 1). Other factors that possibly limited the responses of Least Bitterns and Common Moorhens to call-broadcasts include the timing of surveys within the breeding season (Rehm and Baldassarre 2007) and the length of time each call-broadcast segment was played within the multiple-species call-broadcast sequence. For example, Bogner and Baldassarre (2002) recommend 5-min of broadcasting vocalizations with 15-sec bouts of calls separated by at least 15-sec of silence to survey for Least Bitterns due to their slow responses to call-broadcasts. Conversely, our call-broadcast segments lasted only 30-sec for each target species and may have been too short to elicit adequate responses from Least Bitterns and Common Moorhens. 290 Southeastern Naturalist Vol. 8, No. 2 Furthermore, broadcasting calls of multiple species in succession may increase or decrease the probability of detecting the targeted species (Conway and Gibbs 2005). Although we found that King Rail, Clapper Rail, and Purple Gallinule were detected much more frequently during call-broadcasts than during passive-listening, Least Bittern and Common Moorhen simply may not have responded to call-broadcasts as readily for reasons unknown. Subtle factors such as the number and order of species on a call-broadcast sequence, dialects of the calls broadcasted, and time of day may have played a role in the limited responses. Such factors will require more study to better understand how multiple-species call-broadcasts affect targeted marsh-bird responses in different regions of North America (Conway and Gibbs 2005). Lastly, although call-broadcasts increased the number of individual marsh birds detected, only 71% or fewer of the individuals detected during the passive-listening period later responded to call-broadcasts. Therefore, detection probability for target species was less than perfect using callbroadcasts, attesting to the secretive nature of these species. Acknowledgments Initial funding for this project was provided in part by ACAMP Project Award #NA17OZ2324 through the Coastal Zone Management Act of 1972, as amended, administered by the Office of Ocean and Coastal Resource Management, National Oceanic and Atmospheric Administration and in conjunction with the Alabama Department of Conservation and Natural Resources (ADCNR), State Lands Division, Coastal Section. Additional matching funds and equipment use was provided by the ADCNR, State Lands Division. We gratefully acknowledge the efforts of Courtney Graydon for assisting with surveys and preparing the study area figure. Additional thanks are extended to Kelly Brinkman, Carl Ferraro, Greg Lein, Bruce Stewart, and Steven Threlkeld for field assistance. 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