2007 SOUTHEASTERN NATURALIST 6(2):283–292 Nest Success of Grassland Birds in Florida Dry Prairie Dustin W. Perkins1,2,* and Peter D. Vickery3 Abstract - This paper represents the first study of reproductive success for Sturnella magna (Eastern Meadowlark) and Columbina passerina (Common Ground-dove) in Florida dry prairie and, to our knowledge, the first published study of reproductive rates of Chordeiles minor (Common Nighthawk) in North America. We located 34 Eastern Meadowlark, 13 Common Ground-dove, and 14 Common Nighthawk nests during the 1997 and 1998 breeding seasons. We estimated daily nest success (standard error) to be 0.93 (0.01), 0.94 (0.02), and 0.93 (0.02) for Eastern Meadowlarks, Common Ground-doves, and Common Nighthawks, respectively. Subsequently, total nest success was 0.16, 0.22, and 0.28 for Eastern Meadowlarks, Common Ground-doves and Common Nighthawks. Predation was the most common cause for nest failure. Our estimates of nest success for Eastern Meadowlarks and Common Ground-doves are generally lower than reported for other regions, which could be due to the small and fragmented nature of Florida dry prairie. Introduction Grassland birds have received increased attention in recent years as their populations have declined. Grassland bird declines in North America are well documented (Brennan and Kuvlesky 2005, Peterjohn and Sauer 1999), with the best-supported explanation being the loss of breeding habitat (Goriup 1988, Herkert et al. 1996, Vickery et al. 1999). Florida dry prairie has similarly suffered substantial declines. Historically, dry prairie was the dominant grassland in central Florida, occurring from the southwest shoreline of Lake Okeechobee, north and east to Lake Kissimmee and Osceola County (Howell 1932). Florida dry prairie is endemic to the state and is ranked as a G2 (globally imperiled) community type (FNAI and FDNR 1990, Grossmann et al. 1994) due to its rarity. Shriver and Vickery (1999) reported that at least 81% of the dry prairie habitat in central Florida has been converted to other uses, primarily improved pasture and citrus plantations. Perkins et al. (1998, 2003) have previously reported nest success rates in Florida dry prairie for 2 rare species Aimophila aestivalis Lichtenstein (Bachman’s Sparrow) and the federally endangered Ammodramus savannarum floridanus Mearns (Florida Grasshopper Sparrow). While conducting fieldwork on these 2 rare species we monitored nests of 3 other 1Department of Forestry and Wildlife Conservation, University of Massachusetts, Amherst, MA 01003. 2Current address - 1175 Texas Avenue, Biology Department, Mesa State College, National Part Service, Grand Junction, CO 81501 3Current address - Center for Ecological Research, PO Box 127, Richmond, ME 04357. *Corresponding author - dustin_w_perkins@nps.gov. 284 Southeastern Naturalist Vol. 6, No. 2 ground-nesting grassland species, Sturnella magna L. (Eastern Meadowlark), Chordeiles minor Forster (Common Nighthawk), and Columbina passerina L. (Common Ground-dove). While none of these species are restricted to dry prairie in Florida, this ecosystem was historically a major breeding habitat for these species, but one for which there are no reported reproductive rates. In addition, studies of reproductive rates for Common Nighthawks and Common Ground-doves are rare. The objective of this study was to document nest success rates for these 3 ground-nesting grassland birds in Florida dry prairie. Methods Native dry prairie is characterized as flat, unforested, fire-dependent grasslands with scattered shrubs (Abrahamson and Hartnett 1990). Dominant graminoids include Aristida beyrichiana Trin. & Rupr. (wiregrass), Ctenium aromaticum (Walt.) Wood (toothache grass), Andropogon spp. (bluestem), and Rhynchospora spp. (beak rush). Dominant shrubs include Serenoa repens (Bartr.) Small (saw palmetto), Quercus minima (Sarg.) Small (dwarf oak), Lyonia lucida (Lam.) K. Koch (fetterbush), and Ilex glabra (L.) Gray (gallberry). Dominant forbs include Polygala spp. (bachelor’s button), Xyris spp. (yellow-eyed grass), Eriocaulon decangulare L. (hat pin), Rhexia spp. (meadow beauty), and a variety of milkweeds, orchids, and asters. We used 3 dry prairie sites for this study: Delta Trail/OQ Range at Avon Park Air Force Range in Highlands and Polk counties, (27°37'N, 81°19'W), Three Lakes Wildlife Management Area in Osceola County (27°47'N, 81°06'W), and Kissimmee Prairie Preserve State Park (27°34'N, 81°02'W) in Okeechobee County, hereafter referred to as Delta/OQ, Three Lakes, and Kissimmee Preserve. The 3 study sites are less than 30 km from each other. To simulate the natural fire frequency, all thee sites conduct prescribed fires on a 2–3 year rotation throughout the prairie, resulting in a mosaic of burn classes available in each year. Delta/OQ, owned by the Department of Defense, is approximately 700 ha in size, and conducted only winter prescribed fires during this study. Three Lakes, owned by the Florida Fish and Wildlife Conservation Commission, contains approximately 4000 ha of dry prairie, and was burned with summer and winter prescribed fires. Kissimmee Preserve, owned by the Florida Park Service, is approximately 19,000 ha, and was burned with summer and winter fires. We located nests opportunistically from March through August, during the 1997 and 1998 breeding seasons, as we conducted spot-mapping surveys and banding exercises for Florida Grasshopper Sparrows and Bachman’s Sparrows (Perkins and Vickery 2001, 2005; Perkins et al. 2003). We usually found nests after flushing birds from the nest or after watching them land with food. After we located nests, we marked them with flags 3 m from the nest and checked nests every 2 to 3 days. We classified a nest as successful if at least 1 nestling left the nest. We also calculated mean clutch size for each species. 2007 D.W. Perkins and P.D. Vickery 285 We used Mayfield’s (1961, 1975) method to determine nest survival rates and Johnson’s (1979) method to calculate standard errors and 95% confidence intervals around nest success rates. A nest was considered a failure only if the whole brood was lost. Losses were assumed to have occurred at the midpoint between 2 visits. We considered nests successful if young were expected to leave the nest between nest visits, and on the later visit, we found the nest empty with no evidence of disturbance. In order to increase sample size, we combined both sites and years to give an estimate of nest success for each species for Florida dry prairie. This method assumes that rate of nest loss is constant. Eastern Meadowlark incubation lasts 13–14 days (Saunders 1932), with nestlings remaining in the nest for an additional 10–12 days before fledging (Lanyon 1995). Common Ground-doves have a 12–14 day incubation period (Nicholson 1937) and 12-day nestling period (Bowman and Woolfenden 1997). Common Nighthawks have a 16–20 day incubation period (Campbell et al. 1990, Dexter 1977), with hatchlings being semi-precocial and capable of self-locomotion in response to female’s call during the first day after hatching (Weller 1958). They generally move an average of 0.5 m per day just 2 days after hatching (Fowle 1946). We used nesting periods of 24, 26, and 18 days for Eastern Meadowlarks, Common Ground-doves, and Common Nighthawks, respectively. We determined annual productivity rates and estimated the survival rates necessary in order for these populations to be sustainable. We fully acknowledge that these estimates have wide confidence intervals due to the small number of nests. However, we still think this provides additional useful information beyond reporting only nest success rates. Juvenile survival rates for birds are one of the hardest parameters to estimate. Based on demographic data and extrapolation, Perkins and Vickery (2001) estimated juvenile Florida Grasshopper Sparrow survival to be 35% (66–73% of adult survival) at the same study sites as this study. Kershner et al. (2004a) estimated juvenile Eastern Meadowlark survival at 56–69% during the first 90 days after fledging. Others have estimated juvenile survival to be between 25% and 50% of adult survival (Donovan et al. 1995, McCoy et al. 1999, Ricklefs 1973). We assumed that juvenile survival would be 50% of adult survival and then estimated the adult survival rates that would be needed to maintain stable populations assuming both 2 and 3 nest attempts. Double broods (17%, 4 of 23 nests) have been reported for Eastern Meadowlarks in Wisconsin (Lanyon 1957), and they can have as many as 4 nest attempts (Lanyon 1995). Kershner et al. (2004b) followed radio-marked Eastern Meadowlarks in Illinois and found only 9% (3 of 34) to have double broods, and only 6% (2) attempted 3 nests. Common Ground-doves are thought to breed year round in Florida (Baynard 1909 in Howell 1932, Johnston 1962, Landers and Buckner 1979), with Bailey (1925) and Bowman and Woolfenden (1997) reporting that 3–4 successful broods are possible. Pairs of Ground-doves have been observed re-nesting in the same 286 Southeastern Naturalist Vol. 6, No. 2 nest within 20 days of successfully fledging young (Nicholson 1937). There is little information on Common Nighthawks, but Weller (1958) and Walbeck (1989) noted that 2 broods are possible. Results We found 35 Eastern Meadowlark, 13 Common Ground-dove, and 14 Common Nighthawk nests. We estimated daily survival rate to be 0.927 (SE = 0.013), 0.944 (SE = 0.020), and 0.932 (SE = 0.023), for Eastern Meadowlarks, Common Ground-doves, and Common Nighthawks, respectively. With a nesting cycle length of 24, 26, and 18 days for these 3 species, we calculated nest success rates over the entire nesting cycle to be 0.16 (95% confidence interval = 0.08–0.32), 0.22 (0.07–0.68), and 0.28 (0.11–0.68) for Eastern Meadowlarks, Common Ground-doves, and Common Nighthawks, respectively (Table 1). Nest predation was the major cause of nest failure (40 of 42 failed nests, 95%); one Eastern Meadowlark nest was abandoned and 1 Common Ground-dove nest was flooded. We observed no Molothrus ater Boddaert (Brown-Headed Cowbird) or Molothrus bonariensis Smelin (Shiny Cowbird) parasitism, which was consistent with our findings for Florida Grasshopper and Bachman’s Sparrows at the same study sites during the same time period (Perkins et al. 1998, 2003). Mean clutch size was 3.65 ± 0.73 (􀂗 ± SD, n = 20), 2 ± 0 (n = 6), and 1.93 ± 0.28 (n = 14) for Eastern Meadowlarks, Common Ground-doves, and Common Nighthawks, respectively. If each species had 2 nesting attempts 1.14 (95% Confidence interval 0.57–2.28), 0.81 (0.26–2.44), and 0.85 (0.34–2.03) young would be produced Table 1. Eastern Meadowlark, Common Ground-dove, and Common Nighthawk nesting estimations derived from nests at Avon Park Air Force Range, Kissimmee Prairie Preserve State Park, and Three Lakes Wildlife Management Area during the 1997 and 1998 breeding seasons. Eastern Common Common Estimation Meadowlark Ground-dove Nighthawk Nests 35 13 14 Nest failures 27 7 8 Nest exposure days 371.5 125.5 118 Daily nest survival (SE)A 0.927 (0.013) 0.944 (0.020) 0.932 (0.023) Nest successB 0.16 (0.08–0.32) 0.22 (0.07–0.68) 0.28 (0.11–0.68) Fledglings/successful nest (SE) 3.5 (0.19) 1.8 (0.17) 1.5 (0.22) Productivity/nest attemptC 0.57 (0.28–1.14) 0.40 (0.13–1.22) 0.42 (0.17–1.01) Productivity—2 nest attemptsC 1.14 (0.57–2.28) 0.81 (0.26 –2.44) 0.85 (0.34–2.03) Productivity—3 nest attemptsC 1.72 (0.85–3.41) 1.21 (0.38–3.66) 1.27 (0.51–3.04) Adult survival—2 nest attemptsC 0.64 (0.47–0.78) 0.71 (0.45–0.89) 0.70 (0.50–0.86) Adult survival—3 nest attemptsC 0.54 (0.37–0.70) 0.62 (0.35–0.84) 0.61 (0.40–0.80) ACalculated following Johnson (1979). BNumbers in parentheses are 95% confidence intervals calculated based on the daily nest survival rate ± one standard error. CNumbers in parentheses are 95% confidence intervals calculated from the lower and upper confidence limits on nesting success. 2007 D.W. Perkins and P.D. Vickery 287 for Eastern Meadowlarks, Common Ground-doves, and Common Nighthawks, respectively. In order to be sustainable at 2 nest attempts, adult survival would need to be 64% (47–78%), 71% (45–89%), and 70% (50–86%) for Meadowlarks, Ground-doves, and Nighthawks, respectively (Table 1). For 3 nesting attempts, 1.72 (0.85–3.41), 1.21 (0.38–3.66), and 1.27 (0.51–3.04) young would be produced for Eastern Meadowlarks, Common Ground-doves, and Common Nighthawks, respectively. In order to be sustainable at 3 nest attempts, adult survival would need to be 54% (37–70%), 62% (35–84%), and 61% (40–80%) for the Meadowlarks, Ground-doves, and Nighthawks, respectively (Table 1). Discussion Our estimate of nest success for Eastern Meadowlarks (16.4%) was generally lower than estimates for this species in other parts of the country, but was similar to those found for Florida Grasshopper Sparrows (10–33%) and Bachman’s Sparrows (7–38%) from the same study sites (Perkins et al. 1998, 2003). For Eastern Meadowlarks, Lanyon (1957) reported 33% in Wisconsin and Kershner et al. (2004b) reported 46% in Illinois, while Knapton (1988) reported 30% for monogamous females and 52% for polygynous females in Ontario. Granfors et al. (1996) reported Eastern Meadowlark nest success rates for 1990 and 1991 of 20 and 25%, respectively, in Kansas rangelands, and 17 and 10%, respectively, in Kansas Conservation Reserve program fields. McCoy et al. (1999) reported Eastern Meadowlark nest success rates of 25–42% in Missouri CRP fields. Two studies found low Meadowlark nest success rates similar to our study; however, they both attributed the low numbers to anthropogenic reasons. Roseberry and Klimstra (1970) attributed low nest success of 18% in Illinois to high predator densities, and Kershner and Bollinger (1996) suggested that low nest success rates (14%) at Illinois airports were due to mowing. Our nest success estimate for Common Ground-doves (22.5%) was also lower than has generally been reported. Mitchell et al. (1996) reported nest success rates of 25% and 38% for Common Ground-doves nesting in trees in 2 citrus groves along the Florida coast. Bowman (2002) reported nest success varying from 25 to 48% in the Florida Keys. Passmore (1984) reported 42% nest success in Texas. One published estimate was lower than ours; in dry coastal Puerto Rican forests, only 17% of nests fledged at least 1 young (Rivera-Milán 1996). We did not find any published estimates to compare with our Common Nighthawk nest rate of 28.3%. Poulin et al. (1996) reports that no information is known about annual reproductive success or annual survival for this species, and suggest that studying reproductive effort is a priority for future research. Our nest success rates may be low due to the small and fragmented nature of the study sites. Florida dry prairie once occupied 5000 km2 in central Florida (Orzell and Bridges 2006), but 81% of the dry prairie has been converted to other land uses such as citrus plantations and improved 288 Southeastern Naturalist Vol. 6, No. 2 pastures seeded with exotic grasses (Shriver and Vickery 1999). At 700 and 4000 ha, Delta/OQ and Three Lakes are relatively small compared to the historic extent of dry prairie. Perkins et al. (2003) reported higher nestsuccess rates for ground-nesting Florida Grasshopper Sparrows in core areas (> 400 m from edge) than in edge areas in the same dry prairies as this study. Herkert et al. (2003) studied 39 prairie fragments (24 to > 40,000 ha) in Illinois, Kansas, Missouri, North Dakota, and Oklahoma and reported that Eastern Meadowlarks, as well as Grasshopper Sparrows, Ammodramus henslowii Audubon (Henslow’s Sparrows), and Spiza americana Smelin (Dickcissels), all experienced increasing nest predation as the size of the prairie fragment declined. Predation is considered to be the most common cause of nest failure for many songbirds (Martin 1992). Predation was the major cause of nest failure in common Ground-doves in Florida citrus groves (Mitchell et al. 1996), Eastern Meadowlarks in Illinois (Kershner et al. 2004b), and Florida Grasshopper Sparrows and Bachman’s Sparrows on Florida dry prairie (Perkins et al. 2003). There are at least 12 bird species, 10 mammalian species, and 12 snake species present in the dry prairie of Florida that could be predators of ground nests. We only observed 1 nest that failed due to flooding, but this could be an additional major, but infrequent, reason for nest failure in Florida dry prairie (Perkins and Vickery 2005, Pranty 2000). We do not think that rates of nest predation were artificially inflated by our activities at the nests because our study sites had extensive human activity throughout the breeding season, therefore scent trails would be of little use to mammalian predators. Nest flags would not likely have provided clues to visual predators such as Corvus brachyrhynchos Brehm (American Crows) because the same flags were used to mark 50-m grids across almost the entire study area. Our Eastern Meadowlark clutch sizes (3.65) were lower than those reported in other areas of the country. Clutch sizes for Eastern Meadowlarks have been reported at 4.8 in Wisconsin (Lanyon 1957), 4.2 in Illinois (Roseberrry and Klimstra 1970), and 5.2 in Kansas (Johnston 1964). Common Ground-doves (Bowman 2002) and Common Nighthawks (Dexter 1952, 1956, 1961; Fowle 1946; Howell 1959; Kantrud and Higgins 1992) almost always lay 2 eggs. All 6 Common Ground-dove nests had two eggs. We found 13 Common Nighthawk nests with 2 eggs and 1 nest with 1 egg. It is possible that depredation had occurred at this nest prior to our detection. Assuming that fledgling survival to the first breeding season is 50% of adult survivorship, Eastern Meadowlarks, Common Ground-doves, and Common Nighthawks would need adult survival rates of 0.64, 0.71, and 0.70 with an average of 2 attempts, and 0.54, 0.62, and 0.61 with an average of 3 nest attempts, respectively, in order to be sustainable in dry prairie. Kershner et al. (2004b) similarly estimated that Eastern Meadowlark annual survival would need to be between 59–61% for a stable population in Illinois. Little is known about the annual survival rates for Eastern Meadowlarks (Lanyon 2007 D.W. Perkins and P.D. Vickery 289 1995), Common Ground-doves (Bowman 2002),and Common Nighthawks (Poulin et al. 1996). Perkins and Vickery (2001) reported annual survival rates for Florida Grasshopper Sparrows as 0.48 and 0.53 at Delta/OQ and Three Lake's respecively. While an average of 2 or 3 nest attempts per breeding season is high, it may be possible in Florida dry prairie due to the long breeding season. We acknowledge that these numbers reflect assumptions of juvenile survival and uncertainties in the nest success data due to limited sample sizes. However, these types of data are rare, and we present them in hope that it will encourage other researchers to build on our data. Acknowledgments The authors thank the Department of Defense and the Environmental Flight at Avon Park Air Force Range for financial and logistical support. The Massachusetts Cooperative Fish and Wildlife Research Unit assisted in administrative and logistical support. 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