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Video Surveillance of Painted Bunting Nests to Determine the Effect of Parental Behavior on Nest Success
Phillip L. Vasseur and Paul L. Leberg

Southeastern Naturalist, Volume 15, Issue 1 (2016): 1–11

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Southeastern Naturalist 1 P.L. Vasseur and P.L. Leberg 22001166 SOUTHEASTERN NATURALIST Vol1. 51(51,) :N1–o1. 11 Video Surveillance of Painted Bunting Nests to Determine the Effect of Parental Behavior on Nest Success Phillip L. Vasseur1,2,* and Paul L. Leberg1 Abstract - Declines in populations of Passerina ciris (Painted Buntings) have led to their recent classification as a species of conservation concern. As part of a larger study investigating factors associated with nest success in south-central Louisiana during 2010−2011, we monitored a subsample of nests (n = 14) with video cameras in 2011 to identify nest predators and parasitism events. In addition, we quantified parental activity at the nest to determine if nest attendance and visitation rate during the incubation and nestling stages affected nest success. On average, successful nests were visited less frequently (0.74 ± 0.07 visits/hr) than failed nests (1.04 ± 0.07 visits/hr) during incubation. During the nestling stage, mean nest attendance of successful nests was lower (11.51 ± 1.96 min/hr) compared to failed nests (30.95 ± 3.23 min/hr), and contrary to predictions, mean visitation rate of successful nests (5.46 ± 0.46 visits/hr) was greater than that of failed nests (2.50 ± 0.50 visits/hr). Visitation was positively associated with greater nest concealment, which may have helped mitigate the risk of attracting predators and brood-parasites through increased parental activity. Introduction Loss of breeding habitat due to urban development and land-use changes has contributed to significant declines in populations of Passerina ciris (L.) (Painted Bunting) in portions of its range (Lowther et al. 1999), including a rate of decline in Louisiana of 2.3% per year from 1966 to 2009 (Sauer et al. 2011). Because of declining populations, Painted Buntings have been identified as a species of conservation concern (USFWS 2008). However, few studies have examined the nesting ecology of Painted Buntings, particularly in the western portion of their range (Parmelee 1959, 1964; Vasseur and Leberg 2015). Data on nesting success are critical to better understand the dynamics of nest predation and brood parasitism, which are the primary sources of nest failure for many bird species (Martin 1993, Schmidt and Whelan 1999). Increased parental activity has been hypothesized to increase the risk of nest predation because the act of visiting a nest can attract the attention of visually oriented predators (Ghalambor and Martin 2002, Martin et al. 2000, Skutch 1949). Furthermore, nest predation has the potential to alter parental care strategies and influence the phenotypic expression of life-history traits (Martin and Briskie 2009). To reduce predation risk, for example, incubating adults can increase the length of on- and off-bout duration to reduce nest visits (Conway and Martin 2000, Fontaine 1Department of Biology, University of Louisiana at Lafayette, Lafayette, LA 70504.2Current address - Louisiana Department of Wildlife and Fisheries, Baton Rouge, LA 70898. *Corresponding author - Manuscript Editor: Frank Moore Southeastern Naturalist P.L. Vasseur and P.L. Leberg 2016 Vol. 15, No. 1 2 and Martin 2006). Longer incubation times may also reduce the length of the incubation period by accelerating egg development, thus reducing exposure to predators (Martin et al. 2007). Nest predation may affect parental feeding behavior during the nestling period through reduced visits to the nest (Ghalambor and Martin 2001, Martin et al. 2000). Reduced visitation rates to feed offspring might constrain energy for growth, but this may be offset by increased food loads with each visit (Martin et al. 2000). These trade-offs likely vary across habitats, and understanding their relative influences on nest success can improve management strategies to benefit Painted Buntings. There is insufficient knowledge in many species regarding which nest predators most influence nest failure (Thompson 2007). Identification of predators based on patterns of nest destruction or other visible evidence can yield inconclusive or misleading results (Williams and Wood 2002) due to interspecific similarities and intraspecific variation among predators, as well as unexpected predators and multipredator visits (Stake and Cimprich 2003). Time-lapse, infrared video equipment allows continuous observation of nests and provides indisputable evidence of nest predator and brood-parasite identity. Video surveillance also allows researchers to record the exact date a nest fails or fledges, improving calculations of survival rates (Stake and Cimprich 2003). In Vasseur and Leberg (2015), we discussed the effects of nest-site characteristics on Painted Bunting nest-site choice and nest success. Here, our objective was to examine how nest-site characteristics may affect parental nesting behavior and how those behaviors influence nest success. We utilized video surveillance to monitor parental activity at the nest, and to accurately identify nest predators and brood-parasitism events. We hypothesized that successful nests would have significantly higher nest attendance during the incubation stage and lower visitation rates during the nestling stage compared to failed nests. The basis for our prediction is that increased parental visitation rate can increase the risk of nest predation (Skutch 1949). Nest attendance and visitation rate typically are negatively correlated in that longer nest attendance times usually result in fewer visitations thereby reducing the number of opportunities for visual predators to locate nests based on adults returning to or leaving from a nest. Field-Site Description The primary study site was Indian Bayou Recreation Area (IBRA), an 11,533-ha multi-use area owned and managed by the US Army Corps of Engineers (USACE) and part of the 240,788-ha Atchafalaya Basin Floodway System project (USACE 2009). In 2011, record floods of the Mississippi River necessitated the opening of the Morganza Spillway by the USACE to divert floodwaters from the river into the Atchafalaya Basin. As a result, access to IBRA was restricted during the peak of the nesting season. We were later allowed access to IBRA once water levels subsided, but were unable to monitor some of the more productive Painted Bunting nest areas for several weeks. To adjust, we chose an additional study site 29 km from IBRA on private property near Coteau Holmes, St. Martin Parish, LA (Fig. 1), which was Southeastern Naturalist 3 P.L. Vasseur and P.L. Leberg 2016 Vol. 15, No. 1 similar to IBRA in terms of forest cover and habitat fragmentation. The study sites were further characterized in Vasseur and Leberg (2015). Methods As part of a more comprehensive study investigating factors associated with Painted Bunting nest success in south-central Louisiana during 2010−2011, we utilized video surveillance on a subsample of nests in 2011 to more accurately determine nest fate, identify nest predators and parasitism events, and quantify parental activity at the nest. Specific details of our nest searching and monitoring methods are described in Vasseur and Leberg (2015). Because only female Painted Buntings tend to the nest (Lowther et al. 1999), all future references to nest attendance and visitation rates refer to female nest activity. For the incubation and nestling stages, we defined nest attendance as the duration of an on-bout (i.e., time spent at the nest) and visitation rate as the number of visits/hr made to the nest. We also recorded the clutch size, day of stage, and nest fate of each nest. We ascertained nest fate following Martin and Guepel (1993) and Martin et al. (1997), defining successful nests as those that fledged at least 1 young. After nest fate was determined, we quantified microhabitat variables within a 5-m-radius subplot (Martin and Roper 1988) and an 11.3-m-radius (0.04-ha) circular plot (James and Shugart 1970), both of which were centered on the nest. Figure 1. Location of study sites in Louisiana. Southeastern Naturalist P.L. Vasseur and P.L. Leberg 2016 Vol. 15, No. 1 4 We used a reduced version of the Breeding Biology Research and Monitoring Database (BBIRD) field protocol established by Martin et al. (1997) to obtain nestsite measurements including nest height, substrate height, substrate diameter at breast height (dbh), nest concealment, distance to substrate edge, distance to habitat edge, and canopy cover. We measured all heights and substrate-edge distances to the nearest cm and all habitat-edge distances to the nearest m. Nest height was the distance from the ground to the rim of the nest cup. We estimated heights for nests placed well overhead and tall nest substrates using a laser rangefinder. Nest concealment was an ocular estimate of the percent of the nest hidden by vegetation 1 m from the nest in each cardinal direction and 1 m above and below the nest when possible; we used the mean of the estimates in analyses. We measured distance to substrate edge from the outside rim of nests to the nearest outer edge of nest substrates. Habitat edge was the distance from the nest to the nearest ecotone. We used digital orthoimagery (1-m resolution) and the measure tool in ArcGIS 9.3 to estimate distances for nests >15 m from the nearest habitat edge. We used the average of four measurements taken with a convex spherical densiometer 1 m from nests in each cardinal direction to estimate percent canopy cov er. We followed the protocol for a user-built digital video monitoring system similar to “System One” described by Cox et al. (2012). Surveillance equipment consisted of cameras (50 × 91 mm; Model BB70WIRC, Rainbow, Costa Mesa, CA) with infrared light-emitting diodes (940 nm) that allowed filming in low-light conditions. A power cable (~17 m long) connected the camera to a digital video recorder (DVR; Detection Dynamics, Austin, TX) set to record 10 frames/sec at a resolution of 352 × 240 pixels. A voltage converter was necessary because the DVR and camera operated at different voltages. The camera setup was powered by a 12-V 26-Ah deep-cycle battery (Batteries Plus, Hartland, WI) housed in an equipment case (Model 1450, Pelican Products, Torrance, CA). Cameras were fastened with matte-black gaffer tape to sturdy vegetation ~1–2 m from nests. If there was no sturdy vegetation around a nest, we attached cameras on top of a telescopic metal pole placed in the ground that could extend to 3 m. We routed cables so they were inconspicuous to humans and potential predators, and positioned the equipment case with the recorder, voltage converter, and battery as far from the nest as possible. To reduce chances of nest abandonment, we deployed cameras after egg laying but as close to the onset of incubation as possible to maximize the number of days observed (Reidy et al. 2008, Stake et al. 2004, Thompson and Burhans 2003). We monitored nests after initial camera deployment to determine if females resumed normal nest activities within 1 hr. Most females resumed nest activities within 10–15 min of camera placement, and no females abandoned nests due to the presence of the cameras during the initial deployment. All cameras were left in place until nest fates were determined. Due to our small sample-size, we modified Pope’s (2011) protocol for viewing nest video footage. We watched two 4-hr video segments each day a nest was active, instead of every fourth day, to record nest attendance and visitation rate. We restricted video viewing to the time between 0600 hrs and 2000 hrs when birds are Southeastern Naturalist 5 P.L. Vasseur and P.L. Leberg 2016 Vol. 15, No. 1 active and when there is enough daylight to accurately observe nest activity. We watched a 4-hr morning segment (beginning at 0600, 0700, 0800, or 0900 hrs), as well as a 4-hr afternoon segment (beginning at 1300, 1400, 1500, or 1600 hrs). We used a random-number table to determine the start time for each video segment, and viewed video segments in Windows Media Player 11 (Microsoft Corporation, Redmond, WA) typically at 6–8x normal speed to increase viewing efficiency. In some cases, the nest fate could not be determined within the randomly selected video segment. In those instances, we watched additional footage until the fate could be ascertained, but did not include observations made during these extra viewing periods in bout-duration or visitation calculations. For the nest-camera data analysis, we based our methods on those described by Pope (2011). We used the duration of on-bouts for each observation period to calculate nest attendance (min/hr at the nest). We determined visitation rates by calculating the number of visits/hr made to the nest. When 2 video segments were watched for 1 day (i.e., a morning and afternoon observation period), we averaged nest attendance and visitation rates over both segments so that we had 1 value per variable for that day. We then grouped nest attendance and visitation rates by nest stage (i.e., incubation or nestling), and took the average of all the days observed at a nest for each stage to avoid pseudoreplication (Hurlbert 1984 ). We used SAS Enterprise Guide 4.2 OnDemand for all statistical analyses of habitat data (SAS Institute 2011). We performed a linear regression using PROC REG to determine if nest attendance and visitation rates were influenced by several microhabitat variables including mean percent canopy, vine, shrub, and herbaceous cover. We also included mean percent nest concealment, clutch size, and distance to habitat edge in the analysis. To determine if nest attendance and visitation rates affected nest success, we used logistic regression in an informationtheoretic framework (Burnham and Anderson 2002) to evaluate the support for a set of candidate models, which were ranked by Akaike’s information criterion corrected for small sample size (AICc) and calculated Akaike weights (wi) for each model. Separate analyses were conducted for the incubation and nestling stages because we expected nest attendance and visitation rates to differ between stages and throughout the nestling stage, especially as a result of the increased nutritional requirements of chicks as they age. For the nestling stage analysis, almost all the variation in nest success was explained by the independent variables. This situation interferes with likelihood estimation, so we performed a randomization test (10,000 iterations) to estimate model parameters. Results We monitored 14 Painted Bunting nests with video cameras in 2011 (8 at the private site and 6 at IBRA) for a total of 128 camera-days. Young fledged from 7 camera-monitored nests. We observed predation at 3 nests: Elaphe obsoleta lindheimeri (Baird & Girard) (Texas Rat Snake) depredated 2 nests, and a Quiscalus sp. (grackle) depredated the contents of another. Two nests failed at the onset of incubation for unknown reasons, and 2 nests were abandoned—1 late in the incubation Southeastern Naturalist P.L. Vasseur and P.L. Leberg 2016 Vol. 15, No. 1 6 stage and another shortly after being parasitized by a Molothrus ater (Boddaert) (Brown-headed Cowbird). Nest attendance and visitation rates varied significantly between incubation and nestling stages (Figs. 2 and 3, respectively). During the incubation stage, nest Figure 3. Nest attendance (min/hr) and visitation rate (visits/hr) during the nestling stage of successful (n = 7) and failed (n = 2) video-monitored Painted Bunting nests at IBRA and at a private land site in 2011. Figure 2. Nest attendance (min/hr) and visitation rate (visits/hr) during the incubation stage of successful (n = 4) and failed (n = 4) video-monitored Painted Bunting nests at IBRA and at a private land site in 2011. Southeastern Naturalist 7 P.L. Vasseur and P.L. Leberg 2016 Vol. 15, No. 1 attendance and visitation rates were not influenced by any of the variables included in the linear regression analysis (P > 0.10). During the nestling stage, however, nest attendance decreased as mean percent nest concealment and herbaceous cover increased (F1, 7 = 35.06, r2 = 0.83, P < 0.001, and F1, 7 = 5.31, r2 = 0.43, P = 0.055, respectively). The number of visits/hr a female made to the nest during the nestling stage increased as mean percent nest concealment and herbaceous cover increased (F1, 7 = 5.50, r2 = 0.44, P = 0.052, and F1, 7 = 4.20, r2 = 0.38, P = 0.080, respectively). It is not surprising that nest attendance and visitation rate were both related to the same habitat variables because these 2 measures of female activity have a strong negative correlation (r = -0.93, P = 0.003). Based on AIC model-selection, Painted Bunting nest success during the incubation stage was supported most by a lower visitation rate (Table 1), although there was limited support for the null model. On average, successful nests (i.e., nests that remained active throughout the incubation stage) were visited less frequently (0.74 ± 0.07 visits/hr) compared to the visitation rate of failed nests (1.04 ± 0.07 visits/ hr). Although similar, mean nest attendance during the incubation stage tended to be greater for successful nests compared to failed nests (43.07 ± 2.68 and 39.18 ± 2.33 min/hr, respectively). During the nestling stage, the best-supported models included the main effects of nest attendance and visitation rate. Mean nest attendance was 11.51 ± 1.96 min/hr for successful nests compared to 30.95 ± 3.23 min/hr for failed nests. The average visitation rate of successful nests (5.46 ± 0.46 visits/hr) was approximately twice as high as that of failed nests (2.50 ± 0.50 visits/hr) during the nestling stage. We evaluated the strength of these and other predictors by examining odds ratios and their corresponding confidence intervals (Table 2); odds ratios have an advantage over proportions as a measure of effect size in logistic regression because they are constant over the range of values of the predictor variable (Quinn and Keough 2002). The odds-ratio confidence interval for visitation rate (CI: ≤0.001–0.124) during the incubation stage and the odds-ratio confidence intervals for nest attendance (CI: 0.0–0.874) and visitation rate (CI: 2.614 to >999) during the nestling stage did not include 1.0, indicating that these parameters had a strong effect on nest success. While we can be confident that the odds of nest success increased with Table 1. Support for logistic-regression models predicting the probability of success for Painted Bunting nests based on parental activity during the incubation and nestling stages at Indian Bayou Recreation Area and at a private land site in 2011. Models are ranked based on Akaike’s information criteria (AICc), ΔAICc, and Akaike weights (wi). K is the number of parameters estimated by the model. Nest stage Model parameters K AICc ΔAICc wi Incubation Visitation rate 2 11.50 0.00 0.67 Intercept only 1 13.76 2.26 0.22 Nest attendance 2 16.10 4.60 0.07 Nestling Nest attendance 2 6.01 0.00 0.47 Visitation rate 2 6.01 0.00 0.47 Intercept only 1 12.11 6.10 0.02 Southeastern Naturalist P.L. Vasseur and P.L. Leberg 2016 Vol. 15, No. 1 8 visitation rate during the nestling stage, we can have little confidence in the upper bounds of the CI of the estimate. The odds of a nest being successful decreased 0.20 for every min/hr increase in nest attendance and increased by a factor of 3.18 for every visit/hr increase in visitation rate. Discussion We utilized nest cameras to monitor Painted Bunting nest attendance and visitation rates during incubation and nestling stages to examine the effects of parental activity on nest success. Our results provide mixed support for the hypothesis that increased parental activity increases the risk of nest predation. During the incubation stage, females who generally incubated for shorter periods of time and made more frequent nest visits tended to have unsuccessful nests, which we predicted. Yet parental activity during incubation did not appear to be affected by the nestsite characteristics we considered, which means that some factor other than the vegetation in the immediate nest vicinity may have driven lower nest attendance and higher visitation rates. One possibility is that females with unsuccessful nests occupied lower-quality habitat, which necessitated travelling greater distances in search of food resulting in shorter incubation periods and more frequent foraging trips to satisfy the energetic demands of their young (Tremblay et al. 2005). Unfortunately, we lack information on foraging habitat quality, age of nesting females, and their previous nesting history that would allow us to more fully evaluate causes of variation in parental behavior. Contrary to predictions, greater parental activity during the nestling stage was not associated with lower nest success. The higher visitation rate observed for successful nests during the nestling stage may be attributable to certain nestsite characteristics. For example, visitation rate tended to increase with greater percent concealment and herbaceous cover around the nest. The Skutch (1949) hypothesis assumes that increased parental activity at the nest attracts the attention of predators; however, nest-site characteristics that better conceal nests could “mask parental activity effects on nest predation” (Martin et al. 2000). Alternatively, the higher visitation rates observed for successful nests in this study could be due to the fact that unsuccessful nests failed relatively early during the nestling Table 2. Model-averaged parameter estimates, unconditional standard errors (SE), and odds ratios (OR) for factors from supported models predicting the probability of success for Painted Bunting nests based on parental activity during the incubation and nestling stages at Indian Bayou Recreation Area and at a private land site in 2011. Lower (LCL) and upper (UCL) 95% confidence limits for the odds ratios of the covariates are also presented. Nest stage Parameter Estimate SE OR LCL UCL IncubationA Visitation rate -14.754 9.711 ≤0.001 ≤0.001 0.124 Nestling Nest attendance -1.630 4.677 0.196 0.000 0.874 Visitation rate 10.120 28.110 3.182 2.614 >999.000 AThe estimate of the nest attendance effect during the incubation stage is not presented because this parameter provided low information about the probability of nes t success. Southeastern Naturalist 9 P.L. Vasseur and P.L. Leberg 2016 Vol. 15, No. 1 stage (mean = 2 d). Because the nestlings from successful nests were older, they required more provisions and thus resulted in more foraging trips. Our findings may have been different had we been able to monitor unsuccessful nests that survived longer in the nestling stage. Texas Rat Snakes were responsible for 2 of the 3 video-recorded nest-predation events in this study. Previous studies that have used video cameras to monitor nests suggest snake predation is widespread and impacts many species of birds (Thompson 2007, reviewed in Weatherhead and Blouin-Demers 2004). Moreover, there is evidence suggesting that increased parental activity could elevate levels of exposure to snake predation because snakes may locate nests visually (Lillywhite and Henderson 1993, Mullin and Cooper 1998). Rat snakes, in particular, have been implicated as important nest predators and may have “serious negative effects on bird species of conservation concern” (Weatherhead and Blouin-Demers 2004). Both snake predation events in our study occurred within 6 m of a habitat edge. Increased nest predation has been associated with habitat fragmentation and edges (Heske et al. 2001), but recent studies have found no evidence that nests closer to edges were at a greater risk of snake predation (Sperry et al. 2009, Weatherhead et al. 2010). Identifying important nest predators and understanding the response of parents to mitigate predation risks, as well as the habitat features that reduce such risks will help protect birds of conservation concern like Painted Buntings. Acknowledgments Funding for this study was provided by the Coypu Foundation and the Louisiana Department of Wildlife and Fisheries’ Natural Heritage Program. Additional support was provided by the Louisiana Ornithological Society, Eastern Bird Banding Association, Graduate Student Organization at the University of Louisiana at Lafayette, US Army Corps of Engineers, US Geological Survey National Wetlands Research Center, and Center for Ecology and Environmental Technology. We thank the many volunteers and field assistants who helped make this study possible. Literature Cited Burnham, K.P., and D.R. Anderson. 2002. Model Selection and Multimodel Inference: A Practical Information-Theoretic Approach, 2nd Edition. Springer-Verlag, New York, NY. 488 pp. Conway, C.J., and T.E. Martin. 2000. Effects of ambient temperature on avian incubation behavior. Behavioral Ecology 11:178−188. Cox, W.A., M.S. Pruett, T.J. Benson, S. Chiavacci, and F.R. Thompson III. 2012. D e - velopment of camera technology for monitoring nests. Pp. 185−210, In C.A. Ribic, F.R. Thompson III, and P.J. Pietz, (Eds.). Video Surveillance of Nesting Birds. 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