Cjz-2020-0210.Pdf

Canadian Journal of Zoology

Forest edges negatively influence daily nest survival rates of a grassland tinamou, the Spotted Nothura (Nothura maculosa)

Journal: Canadian Journal of Zoology

Manuscript ID cjz-2020-0210.R2

Manuscript Type: Article

Date Submitted by the 13-Dec-2020 Author:

Complete List of Authors: Colombo, Martín; Universidad Nacional de la Plata Facultad de Ciencias Naturales y Museo, División Zoología Vertebrados Segura, Luciano ; Universidad Nacional de la Plata Facultad de Ciencias Naturales yDraft Museo, División Zoología Vertebrados Is your manuscript invited for consideration in a Special Not applicable (regular submission) Issue?:

edge effect, breeding success, nest predation, invasive exotic trees, Keyword: habitat alteration, Spotted Nothura, Nothura

1 Forest edges negatively influence daily nest survival rates of a grassland tinamou,

2 the Spotted Nothura (Nothura maculosa)

3 M. A. Colombo* & L. N. Segura

4 M. A. Colombo. División Zoología Vertebrados, Museo de La Plata, Facultad de

5 Ciencias Naturales y Museo, Universidad Nacional de La Plata-CONICET. Paseo del

6 Bosque s/n (B1900FWA), La Plata, Buenos Aires, Argentina.

7 [email protected]

8 L. N. Segura. División Zoología Vertebrados, Museo de La Plata, Facultad de Ciencias

9 Naturales y Museo, Universidad Nacional de La Plata-CONICET. Paseo del Bosque s/n

10 (B1900FWA), La Plata, Buenos Aires, Argentina. [email protected]

11 Draft

12 Corresponding author:

13 M. A. Colombo. División Zoología Vertebrados, Museo de La Plata, Facultad de

14 Ciencias Naturales y Museo, Universidad Nacional de La Plata-CONICET. Paseo del

15 Bosque s/n (B1900FWA), La Plata, Buenos Aires, Argentina.

16 [email protected]

1 © The Author(s) or their Institution(s) Canadian Journal of Zoology Page 2 of 31

17 Forest edges negatively influence daily nest survival rates of a grassland tinamou,

18 the Spotted Nothura (Nothura maculosa)

19 M. A. Colombo & L. N. Segura

21 ABSTRACT

22 Grassland degradation and fragmentation produced by land use have globally impacted

23 biodiversity. In the Neotropics, the Pampas Grasslands have been greatly altered by

24 agriculture and the introduction of exotic trees. To evaluate the effects of changing

25 habitat features on native grassland fauna, we studied a breeding population of a ground

26 nesting bird, the Spotted Nothura Nothura maculosa (Temminck, 1985) in a natural

27 grassland under cattle-grazing in central-eastDraft Argentina. We estimated daily nest

28 survival rate (DSR) and modeled it as a function of habitat (distance to habitat edges,

29 cattle density and nest concealment) and temporal factors. Of the 80 nests found, 64 (80

30 %) failed, predation being the principal cause of failure. DSR was 0.874, estimating a

31 cumulative survival of only 6.8 % throughout egg laying and incubation. DSR increased

32 with distance to continuous forests and decreased with nest age. Nests located near

33 forest edges could have increased predation risk because they are potentially exposed to

34 forest dwelling predators in addition to grassland dependent ones. Considering the low

35 success found and the ongoing invasion of exotic trees in the region, we encourage

36 governments to protect large areas of grassland that ensure adequate nest success for

37 tinamous and other ground nesting birds.

38 Keywords: edge effect, breeding success, nest predation, Spotted Nothura, Nothura

39 maculosa, habitat alteration

2 © The Author(s) or their Institution(s) Page 3 of 31 Canadian Journal of Zoology

41 INTRODUCTION

42 Grasslands ecosystems have provided mankind a number of services since prehistoric

43 times (Baldi et al. 2006; Gibson 2009). The expansion of productive systems over the

44 last centuries has greatly transformed the original grasslands by conversion to cropland,

45 pastures or wood plantations, and the introduction of exotic plant and animal species

46 (Baldi et al. 2006; Medan et al. 2011). These transformations resulted in degradation

47 and fragmentation of the remaining original grasslands, which threatens their

48 biodiversity in several ways, including replacement of native flora (Corbin and

49 D’Antonio 2004), population declines of native herbivores, predators and pollinators

50 (Demaría et al. 2004; Bonmarco et al. 2014). 51 Among grassland fauna, birds have Draftreceived increasing attention because of noticeable 52 declines in their populations over the last decades (Di Giacomo et al. 2010; Rosenberg

53 et al. 2019). Breeding success is a key factor in birds’ population dynamics (Xiao et al.

54 2017), and knowing how it is influenced by habitat modification is crucial for the

55 management and protection of bird populations (Davis 2005). Birds nesting near edges

56 in fragmented habitats may have reduced nest success, which is interpreted as a being

57 caused by the exposure to a more diverse nest predator community than deeper in their

58 original habitat (Lahti 2001; Stephens et al. 2004). Although this type of edge effect has

59 been well documented in fragmented north temperate forests (Chalfoun 2002), few

60 studies have found it in tropical or subtropical ones (Vetter et al. 2013). In grasslands,

61 some studies found increased predation rates near habitat edges (see Johnson and

62 Temple 1900; Winter et al. 2000) while many others failed to find this trend (Benson et

63 al. 2013; Keyel et al. 2013). This variation seems to be the result of differences in the

64 landscape matrix (Fletcher and Koford 2003), the type of habitat edge (Winter et al.

65 2000) and the ecology of the predator communities of each system (Grant et al. 2006;

3 © The Author(s) or their Institution(s) Canadian Journal of Zoology Page 4 of 31

66 Benson et al. 2013). Therefore, as these patterns are not broadly generalizable and

67 research has focused almost exclusively on north temperate grassland (Pretelli et al.

68 2015), new studies about the effects of fragmentation and habitat edges in less studied

69 regions become necessary. In addition to habitat fragmentation, cattle-grazing is another

70 factor influencing grassland birds’ nest success, mainly indirectly by reducing grass

71 cover, modifying vegetation structure (Cardoni et al. 2012) and favoring the presence of

72 different types of predators (Ribic et al. 2012; Grande et al. 2018). Cattle can also

73 impact nest success directly by trampling nests, with higher stocking densities resulting

74 in greater trampling risk (Fondell and Ball 2004).

75 In South American grasslands, conversion to cropland and cattle grazing have expanded 76 and intensified rapidly over the last Draft20 years (Azpiroz et al. 2012). The Pampas 77 Grasslands ecoregion in Argentina is among the most modified habitats in the world

78 (Baldi et al. 2006), and has experienced an accelerated conversion to cropland and

79 pasture following the advance of new technologies (Herrera et al. 2009). The Flooding

80 Pampa is a sub-region of ~90,000 km2 within the Pampas Grasslands, and ~80% of its

81 extension remains as natural grasslands mostly used for extensive cattle-grazing,

82 because the soil properties and flooding regime make it unsuitable for crop production

83 at a large scale (Perelman et al. 2001). The area has also been greatly altered by the

84 introduction of exotic trees for wood extraction and ornamental purposes (Matteucci

85 2012). Particularly, in the last decades, the Flooding Pampa has been invaded by the

86 Honey Locust (Gleditsia triacanthos L.), a woody species capable of replacing large

87 areas of grassland in few years (Ghersa et al. 2002; Fernandez et al. 2017). The

88 introduction of exotic trees, in addition to urbanization and conversion to cropland

89 (Matteucci 2012), has produced a major fragmentation of the original Pampas

90 Grasslands (Baldi et al. 2006). Although the need of assessing the effects of these

4 © The Author(s) or their Institution(s) Page 5 of 31 Canadian Journal of Zoology

91 modifications on the reproductive success of birds in the region has been highlighted

92 (Azpiroz et al. 2012), almost no studies have attempted to relate habitat features and

93 their reproductive performance (Pretelli et al. 2015).

94 In the Neotropics, the family Tinamidae (i.e., “tinamous”) is a group of grassland and

95 forest birds that nest on the ground (Winkler et al. 2020). Despite being well known and

96 having a high commercial importance as gamebirds (Crego and Macri 2009), grassland

97 tinamous have been subject of no studies on how their breeding success is affected by

98 changing habitat characteristics, while their populations are declining in rural areas

99 where they used to be common (Thompson and Carroll 2009). In this contribution we

100 assessed for the first time the effects of habitat features on the reproductive success of 101 the Spotted Nothura Nothura maculosaDraft (Temminck, 1985) in a grassland under cattle- 102 grazing in the Argentinian Flooding Pampa. We estimated nest daily survival rates

103 (DSR) and evaluated the effects of nesting habitat features, focusing on distance to

104 edges, cattle density and vegetation cover. We expected DSR to be negatively affected

105 by proximity to habitat edges, increased cattle density and reduced grass cover.

106 METHODS

107 Study site: the study was conducted on a private farm in north-eastern Buenos Aires

108 province, Argentina (35°21’S; 57°12’W). The property is located within the Flooding

109 Pampa, and as the majority of land in this region, it is dedicated to livestock production

110 in large areas of natural grasslands which have poor drainage properties (Matteucci

111 2012). Grasslands are composed mainly of native species such as Nassella (Trin.) E.

112 Desv., Paspalidium Stapf., Leersia hexandra Sw., Baccharis L. and other native and

113 exotic grasses (Hummel et al. 2009; Roitman and Preliasco 2012). Most of the farm’s

114 grassland surface is used for extensive cattle grazing, which is rotated among plots

115 according to available vegetation biomass and livestock requirements. Native original

5 © The Author(s) or their Institution(s) Canadian Journal of Zoology Page 6 of 31

116 woodland is predominantly arranged in rows (50–100 m wide and up to several

117 kilometers long) parallel to the La Plata River, but also occurs as small isolated patches

118 of forest (10–70 m diameter) surrounded by grasslands (Fig. 1). These forests are

119 dominated by native trees such as Tala (Celtis tala Gillies ex Planch) and Coronillo

120 (Scutia buxifolia Reissek), and some exotic species such as mulberries (Morus L.),

121 Eucalyptus (Eucalyptus L'Hér.) and Honey Locust (Arturi and Goya 2004). The latter is

122 considered an invasive landscape transformer species, capable of replacing large areas

123 of grassland in few years (Ghersa et al. 2002, Fernandez et al. 2017). The region hosts a

124 wide diversity of potential nest predators; some associated to grasslands include snakes

125 (Philodryas spp. Wagler, 1830) and raptors (Circus buffoni (Gmelin, 1788)); some

126 woodland dependent such as medium-sized mammals (Didelphis albiventris Lund,

127 1840; Galictis cuja (Molina, 1782))Draft and small rodents; and others common in both

128 grasslands and woodlands, such as tegus (Salvator merianae Duméril & Bibron, 1839),

129 caracaras (Caracara plancus (Miller, 1777); Phalcoboenus chimango (Vieillot, 1816))

130 and mesocarnivores (Lycalopex gymnocercus Fischer, 1814) (Svagelj et al. 2003;

131 Cozzani and Zalba 2012; Marini and Menezes 2017; L.N. Segura, unpubl. data).

132 Study species: the Spotted Nothura (hereafter “nothura”) inhabits grasslands from

133 north-eastern Brazil to mid-eastern Argentina (Gomes 2020) and is considered to be one

134 of the most common gamebirds in the region (Bump and Bump 1969; Thompson and

135 Carroll 2009). Although the species is said to tolerate moderate hunting pressure, there

136 is a lack of information on its population trend, which may be decreasing in some areas

137 (Crego and Macri 2009; Thompson and Carroll 2009). Males build a simple nest on the

138 ground hidden under or inside clumps of vegetation, where one or more females lay

139 eggs which are incubated by the male during 16–18 days (Bump and Bump 1969; this

140 study). The eggs are immaculate shiny chocolate brown, measuring ~44 mm in length

6 © The Author(s) or their Institution(s) Page 7 of 31 Canadian Journal of Zoology

141 and ~31 mm in breadth, and mean clutch size is 5 eggs (Bump and Bump 1969)1. Egg

142 laying frequency in each nest is one or two eggs per day, while egg laying frequency per

143 female is unknown (Gomes 2020).

144 Nest searching and monitoring: we searched for nests during three consecutive

145 breeding seasons (2017–2019) from late September to mid-February. Nests were

146 located by flushing incubating adults either by dragging a 20 m long rope between two

147 people or by systematic walking with sweeping sticks (see Winter et al. 2003). The total

148 area covered was ~270 ha. Once a nest was found, we georeferenced it using a Global

149 Positioning System device, and we placed a small flag (built with a 50 cm wire and a 5

150 cm long red tape) 4 m to the north to facilitate subsequent monitoring. We checked each 151 nest every 2–4 days during the egg Draftlaying and incubation period (~20 days; Bump and 152 Bump 1969, this study), until either the eggs hatched or the nest failed. To minimize

153 disturbance, we avoided flushing the incubating males when they were visible from

154 afar.

155 Nest fate was classified as a) successful when we found empty shells in the nest

156 showing evidence of hatching2, b) depredated when we found the nest empty between

157 two consecutive visits or when egg shells showed signs of predation3, c) trampled when

158 we found the eggs broken and the nest and surrounding area showed signs of being

159 stepped on by cattle and d) abandoned when the eggs were found cold in successive

160 visits. We were extremely careful when classifying nests as abandoned, as males

161 sometimes leave their nests unattended for several hours (M.A.C. pers. obs.) and the

162 eggs can become cold but incubation continues later. In these cases, we confirmed nest

163 abandonment in an extra visit 12–24 hours later.

1 Fig.S1 2 Fig S2 3 Fig S3 7 © The Author(s) or their Institution(s) Canadian Journal of Zoology Page 8 of 31

164 This study was conducted with research permits from the regional nature conservation

165 authority (OPDS #17717, Direccion de Áreas Naturales Protegidas, Buenos Aires

166 province, Argentina).

167 Nest and habitat measures: immediately after the confirmation of nest success or

168 failure, we measured the height of the supporting clump of vegetation and recorded

169 Visual Obstruction Readings by placing a pole graduated in increments of 10 cm in the

170 center of the nest and recording the first section visible from height of 1 m and a

171 distance of 4 m in the four main cardinal directions (NSEW) (modified from Robel et

172 al. 1970). Each reading provided a score from 1 (lowest obstruction) to 10 (highest

173 obstruction) and the scores were averaged to obtain the final VOI (Visual Obstruction 174 Index) for each nest. We also measuredDraft upper visual obstruction by placing a plastic 175 disc divided into 8 black-and-white sections in the nest and recording the visible

176 sections from 1m directly overhead. The score was calculated as 8 minus the number of

177 visible sections, with a higher score indicating greater concealment (Davis 2005).

178 Finally, we measured the distance to the nearest individual woody vegetation or pole >

179 1 m in height, considering that they could provide perching sites with high visibility for

180 avian predators.

181 We repeated the VOI readings at 4 random points between 5 and 50 m from each nest to

182 obtain a measure of grass density in the nesting area. We also measured the distance

183 from each nest to grassland edges using SPOT6 satellite images (1.5 m spatial

184 resolution), provided by the Comisión Nacional de Actividades Espaciales (CONAE).

185 We considered as grassland edges border types that could act as corridors for nest

186 predators (Hovick et al. 2012), including: (a) fencelines, (b) edges of isolated forests

187 (i.e., patches of forest < 100 m in diameter surrounded by grasslands), (c) edges of

188 continuous forest (i.e., borders of interconnected forest rows), (d) roads (road types

8 © The Author(s) or their Institution(s) Page 9 of 31 Canadian Journal of Zoology

189 present in the study-site are small unpaved roads, with low traffic) (Fig. 1). We

190 delimited the edges and obtained all distances in meters using Geographic Information

191 System QGIS (QGIS Development Team 2020). We also considered the cattle density

192 of the plot where each nest was located (number of animals/hectare), provided by

193 livestock owners.

194 Data analysis: we obtained incubation time (in days) directly for nests found during

195 egg laying that survived until hatching. Clutch size was calculated directly for nests that

196 remained active and had a constant number of eggs after two successive visits (i.e., no

197 new eggs were laid and incubation had already started), and laying period was estimated

198 as clutch size minus 1 day, assuming that one egg is laid per day (Bump and Bump 199 1969; this study). Hatching dates wereDraft established directly in two cases where we 200 observed the nestlings at the nest right after hatching. In most nests, where hatching

201 occurred between two visits, we assumed that it occurred in the midpoint between those

202 visits.

203 We estimated the average daily nest survival rate (DSR) using generalized linear models

204 with a logistic-exposure link function (Shaffer 2004). We first created a null model for

205 which DSR is constant across nests and then we calculated the cumulative nest survival

206 probability by raising the DSR to a power equal to the length of a complete nesting

207 cycle for an average size clutch (20 days including the duration of egg laying and

208 incubation for an average size clutch; Bump and Bump 1969; this study).

209 To identify habitat variables influencing nest DSR, we built a set of candidate models

210 with explanatory variables based on factors that a priori may influence nest survival.

211 Nest-site features included clump height (height of clump used as cover), VOI

212 (averaged visual obstruction readings at the nest), upper obstruction (concealment score

213 directly overhead) and distance to nearest perch (woody vegetation or pole > 1 m in

9 © The Author(s) or their Institution(s) Canadian Journal of Zoology Page 10 of 31

214 height). The horizontal and upper nest-concealment measures were evaluated separately

215 because both terrestrial and aerial predators are known to feed on tinamou nests

216 (Salvador 2016). On a broader scale (i.e., study-site scale) we included grass density

217 (averaged VOI of 4 random points around nest), and four distances to edges, including

218 fencelines, continuous forest, isolated forest patches and roads. We also included cattle

219 density as the maximum number of animals/hectare in the plot during the nesting cycle

220 for each nest. We used Spearman’s rank correlation coefficient to control for correlation

221 among vegetation variables and between vegetation and border types4.

222 Additionally, as time-specific factors can influence nest DSR (Grant et al. 2005; Segura

223 and Reboreda 2012), we evaluated effects of year (a three-level factor, one 224 corresponding to each season), linearDraft and quadratic effects of time of breeding (day 225 since the beginning of the season, standardized as day 1 = October 1) and nest age (days

226 after the first egg of each nest was laid). For nests found during egg laying, we

227 calculated nest age by back-dating considering that one egg is laid per day (Bump and

228 Bump 1969; this study). For successful nests found during incubation, we back-dated

229 from the hatching date, using the average incubation period of 17 days (Bump and

230 Bump 1969; this study). For unsuccessful nests found during incubation, we assumed

231 that they were found halfway through the incubation period (see details in Segura and

232 Reboreda 2012).

233 We used a stepwise approach to reduce the complexity of the final model set (Arnold

234 2010), first building subsets based on combinations of variables within each category

235 (i.e., nest-site, study-site and time-specific variables) and ranking models using

236 Akaike’s Information Criterion corrected for small sample sizes (AICc) (Burnham and

237 Anderson 2002). We report all models within 2 units of ΔAICc (estimated as the

4 TablesS1 and Table S2 10 © The Author(s) or their Institution(s) Page 11 of 31 Canadian Journal of Zoology

238 difference between the top ranked model and each other model) in each subset. The

239 variables included in the best model (i.e., lowest AIC value) of each subset were used to

240 build a final model set, including all possible combinations. To account for model

241 selection uncertainty, we model-averaged parameter estimates from models within 2

242 AIC units of best model in the final set (Burnham and Anderson 2002), and report them

243 as means ± standard error (SE), 95 % confidence intervals (CI) and relative importance

244 of each averaged parameter, calculated as the sum of weights of the averaged models

245 where that parameter occurs (Burnham and Anderson 2002). We report parameters

246 based on input variables standardized to a mean of 0 and 0.5 SD to allow for a direct

247 comparison of their magnitudes (Grueber et al. 2011). Variables not included in a model

248 were assigned an estimate of zero in that particular model, but included in model

249 averaging (“Zero method”, BurnhamDraft and Anderson 2002). We predicted DSR for nests

250 based on model-averaged parameters of the meaningful variables, using values within

251 the range of observations while holding the other variables at their mean. We conducted

252 all statistical analyses in software R (version 3.6.3 R Core Team 2020).

253 RESULTS

254 We found 80 nests during three breeding seasons (40 in 2017–2018, 31 in 2018–2019

255 and 9 in 2019–2020). Nine nests were found during egg laying and 71 during

256 incubation. Including all seasons, the earliest nest was initiated on October 10 and the

257 latest on February 1, the first and last hatching dates were October 30 and January 21

258 respectively, and the last active nest was depredated on February 15. Incubation period

259 was 17 days (range = 16 – 18 days, n = 2) and clutch size was 4.45 ± 1.30 eggs (range 2

260 – 10 eggs, n = 72).

261 Sixteen nests (20 %) were successful. Among failures, 50 nests (78 %) were depredated,

262 9 (14 %) were abandoned and 5 (8 %) were trampled by cattle. Of the abandoned nests, 11 © The Author(s) or their Institution(s) Canadian Journal of Zoology Page 12 of 31

263 two were flooded after intense rains and seven were abandoned due to unknown causes.

264 Constant DSR estimated by the null model was 0.874 ± 0.015 (95 % CI = 0.843–0.900),

265 which provided a cumulative survival estimate of 6.8 % for the entire nesting period.

266 Distances to continuous forest, height of supporting clump and nest age were included

267 as covariates in the final model set (Table 1). Parameter estimates from model-

268 averaging showed that nests located near the edges of continuous forests had lower DSR

269 than those located far from them, and that DSR decreased linearly with nest age (Table

270 2; Fig. 2). The effect of clump height suggested a positive relationship with DSR,

271 although the confidence intervals for this parameter included zero and it had low

272 relative importance, providing little evidence that this variable affected DSR in our

273 study (Table 2). Draft 274 DISCUSSION

275 Our models indicated that nest survival rates of the nothura increased with increasing

276 distance from the continuous forest patches parallel to the La Plata River and decreased

277 with nest age. The effect of forest edges has major implications for grassland birds

278 given the poor conservation status of grasslands in the Neotropics (Azpiroz et al. 2012).

279 Large and continuous forest areas can favor the presence of some nest predators

280 (Andrén 1992; Pita et al. 2009), and nests near their edges are potentially exposed to

281 both grassland predators and woodland dependent ones that travel intro grasslands to

282 feed (Renfrew and Ribic 2003). Also, some generalist predators could be particularly

283 active in these edges due to a greater prey diversity and habitat heterogeneity or because

284 they use edges as travel lanes (Chalfoun et al. 2002; Hovick et al. 2012). In some north

285 temperate grasslands, for example, medium-sized mammals associated with forest are

286 believed to depredate grassland birds’ nests near forest edges (Winter et al. 2000; Ribic

287 et al. 2012). This could be the case of similar species common at our study site, such as

12 © The Author(s) or their Institution(s) Page 13 of 31 Canadian Journal of Zoology

288 Didelphis albiventris or Galictis cuja (L.N. Segura, pers. comm.). In addition, forests

289 could provide additional lookouts for avian nest predators (Söderström et al. 1998),

290 such as Caracara plancus and Phalcoboenus chimango in our study area. However,

291 studies about nest predators in the Pampas Grasslands are scarce and have mostly relied

292 on indirect clues (see for example Svagelj 2003; Cozzani and Zalba 2012), which are

293 not reliable to identify them (Renfrew and Ribic 2003). Given that predator

294 communities are unique to each region and respond differently to habitat features

295 (Benson et al. 2013; Vetter et al. 2013), further research about the identity and ecology

296 of important nest predators in the Pampas Grasslands is needed to understand the effects

297 of forest edges and will be helpful to design management strategies for grassland

298 species (Thompson and Ribic 2012). Draft 299 Nest survival was also strongly influenced by nest age, as DSR decreased from clutch

300 initiation to hatching. In most birds, this trend is associated with increased parental

301 activity at the nest, which provides more visual cues for predators (Grant et al. 2005).

302 Precocial birds may increase the frequency of incubation breaks as they begin to deplete

303 their energy reserves and must leave more often to feed themselves (Grand et al. 2006).

304 If that is the case of the nothura, increased departures from the nests could give more

305 cues for predators and also leave the conspicuous eggs exposed for a longer time

306 (Brennan 2009). Also, as the incubation period progresses and the adults have spent

307 more time at the nest site, the accumulation of feather smells can increase the chance of

308 being found by olfactory predators, including mammals (Bytheway et al. 2013;

309 Mihailova et al. 2018) and tegus (Yanosky et al. 1993).

310 We present for the first time data on nest survival rates for the Spotted Nothura and for

311 grassland tinamous in general. There are few studies on nest success of tinamous and

312 species with similar nesting characteristics (i. e., grassland ground-nesters with similar

13 © The Author(s) or their Institution(s) Canadian Journal of Zoology Page 14 of 31

313 nest materials, incubation periods and nest attendance) in South American grasslands,

314 although some comparisons can be made with grassland galliformes in other areas

315 (Thompson 2004). Predation was the principal cause of nest failure, and it occurred at

316 similar rates as in other ground-nesting species (Pitman et al. 2005; Brennan 2010).

317 Although cattle density was not relevant in our DSR models, livestock trampling caused

318 a relatively high proportion of nest failures (8 %) compared to other studies in sites with

319 similar cattle-grazing intensity (~2 %, Pitman et al. 2005; but see also Bleho et al.

320 2014). Nothura nests could be particularly prone to trampling given their large size and

321 the random nature of trampling events, which will also depend on stocking density,

322 timing and duration of grazing in each plot (Jensen et al. 1990; Bleho et al. 2014). 323 The average nothura nest had an estimatedDraft probability of survival below 7 %, which is 324 considerably low compared to the only other study available on tinamous (Great

325 Tinamou ~16 %, Brennan 2010) and to studies on grassland galliformes (see for

326 example Davis et al. 2014; Grisham et al. 2014). While the nest success necessary to

327 sustain a stable nothura population is unknown, it was estimated at ~15 % for duck

328 species under similar hunting pressure in North America (Klett et al. 1988), which is

329 considerably higher than the value we found. Bump and Bump (1969) suggested that

330 this could be compensated by a high productivity based on the high number of nesting

331 attempts per male, high renesting frequency with no incubation costs for females and

332 the possibility of males breeding in the same season they were born. However,

333 considering that the value we report does not include survival of chicks after fledging,

334 which usually have a high mortality rate (Colwell et al. 2007), the low nest survival rate

335 in our study site may not be enough to sustain the population.

336 Another aspect of concern in light of the negative effect of forest edges is the

337 continuous invasion of the Honey Locust in this region (Fernandez et al. 2017). This

14 © The Author(s) or their Institution(s) Page 15 of 31 Canadian Journal of Zoology

338 exotic tree is able to invade grasslands and rapidly form large patches of forests in few

339 years (Ghersa et al. 2002). Moreover, the dispersal of this plant is favored by cattle and

340 horses (Warren 2016), and local efforts of land managers are insufficient to prevent its

341 expansion. The new patches formed by this invasive tree could also connect forest areas

342 that are currently isolated, thus incrementing the extent of grassland–woodland edges,

343 which negatively influenced nest survival of the nothura. Considering the low coverage

344 of protected grassland areas in the Pampas Grassland (Azpiroz et al. 2012) and the

345 uncontrolled invasion of Honey Locust in the region (Ghersa et al. 2002), we encourage

346 governments to preserve and protect large areas of grassland that ensure adequate nest

347 success for tinamous and other ground nesting birds at these sites. In addition, we

348 recommend continuing research and monitoring this population to better understand the

349 potential decline it faces and take appropriateDraft conservation actions.

350 AKNOWLEDGEMENTS

351 We thank M.L. Shaw for allowing us to conduct this study in Estancia ‘Luis Chico’. We

352 also thank C. Tiernan, A. Wolf, B. Vidrio, A. Valencia, T. Lansley, C. Dudley, A.

353 Banges, M. Gilles, A. Hodges, L. Haag, S. Musgrave, A. Miller, B. Ewing, K. Depot

354 and K. McPartlin for help with fieldwork. We appreciate the improvements in English

355 usage made by K. Depot. We are also grateful to the CONAE for providing the satellite

356 image used for this study. Fieldwork was supported by the Agencia Nacional de

357 Promoción Científica y Tecnológica, Grant [PICT-2014-3347].LNS is a CONICET

358 Research Fellow.

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Draft

579 TABLES

580 Table 1. Akaike’s Information Criterion corrected for small sample size (AICc),

581 number of parameter estimates (K) and model importance weight (wi) among models

582 within 2 AICc units explaining daily nest survival rate (DSR) of the Spotted Nothura

583 Nothura maculosa in grazed grasslands in central-eastern Argentina. The variables in

584 the top model for each model subset (i.e., nest-site features, study-site features and time-

585 specific variables) were included in the final model set and used in all possible

586 combinations. AICc null model = 241.85.

Model K AICc ΔAICc wi

Nest-site features S(~Clump) Draft2 242.00 0.00 0.09 S(~Perch) 2 243.11 1.11 0.05

S(~Upper obstruction) 2 243.31 1.31 0.04

S(~Clump + Perch) 3 243.41 1.41 0.04

S(~VOI) 2 243.42 1.42 0.04

S(~Clump + Upper obstruction) 3 243.66 1.66 0.04

Study-site features

S(~Forest) 2 240.36 0.00 0.23

S(~Fenceline) 2 241.84 1.44 0.11

S(~Forest + Fenceline) 3 241.92 1.52 0.11

S(~Forest + Roads) 3 241.97 1.57 0.10

S(~Forest + Patches) 3 242.39 1.99 0.08

Time-specific variables

S(~NestAge) 2 240.10 0.00 0.16

S(~NestAge + Time + Year) 5 240.31 0.21 0.14

S(~NestAge + Year) 4 240.43 0.33 0.13

S(~NestAge + Time) 3 241.09 0.99 0.10

S(~Time) 2 241.84 1.74 0.07

S(~Time + Year) 4 241.96 1.86 0.06

Final model set

S(~NestAge + Forest) 3 237.10 0.00 0.39

S(~NestAge + Forest + Clump) 4 237.76 0.66 0.28

S(~NestAge) 2 240.10 2.94 0.09

S(~Nest Age + Clump) 3 240.17 3.05 0.08

S (~Forest) 2 240.36 3.24 0.07

S (~Forest + Clump) Draft3 240.93 3.81 0.06

S (~Clump) 2 242.00 4.93 0.03

587

588 Table 2. Standardized model-averaged parameters estimated from the models within 2

589 ΔAICc units in the final model set, including Standard Errors, 95% Confidence

590 Intervals and Relative Importance of each variable, calculated as the sum of weights of

591 averaged models where that parameter occurs.

Standard 95% Confidence Relative Parameter Estimate Error Interval Importance

Intercept 2.086 0.164 (1.762, 2.409) -

Nest Age -3.198 1.62 (-6.373, -0.023) 1

Forest 0.608 0.291 (0.035, 1.182) 1

Clump 0.138 0.236 (-0.327, 0.604) 0.42 592 Draft

593 Fig. 1 Overview of study area in north-eastern Buenos Aires province, Argentina,

594 indicating the edges of continuous and interconnected forest rows (continuous black

595 line), roads (wide dashed white line) and fencelines (dotted white lines). “A” indicates

596 continuous and interconnected forest rows and “B” isolated patches of forest. Figure

597 created using QGIS version 3.10.2 and base map courtesy of CONAE (Comisión

598 Nacional de Actividades Espaciales).

599 Fig. 2 Variation in Daily Survival Rates (DSR) of Spotted Nothura Nothura maculosa

600 nests based on model-averaged parameters during three breeding seasons (2017–2020).

601 DSR was modeled as a function of nest age (day 0 = laying of the first egg) for a nest

602 located at 50 m (dotted line), 100 m (dashed line) and 1000 m (solid line) from forest 603 edges. Clump height was held at theDraft mean of the observed values. 604

605 FIGURE 1

Draft

606

607

608 FIGURE 2

609 Draft