DOI: 10.5061/dryad.vt4b8gtrn
title: Temporal and scalar variations affect resource use of northern bobwhite broods

description: Disparate resource use originating from phenology of biotic resources,
 abiotic conditions, and life cycles of exploiting organisms underscores
 the importance of research across time and space to guide locally relevant
 management practices. Our goal was to evaluate resource use of northern
 bobwhite (Colinus virginianus; bobwhite) at two spatial scales and across
 three age classes, from hatching through a period of the post-juvenile
 molt. Our study was conducted at Tall Timbers Research Station,
 Tallahassee, FL, USA– situated in a pyric landscape subjected to biennial
 prescribed fire. We predicted prescribed fire, disking, and supplemental
 feeding would dictate resource use, but effects would depend on time since
 fire, brood age, and time of day. We predicted vegetation and temperature
 would govern roost use by broods, but these effects would also depend on
 age. We radio-tracked 62 broods 21–35 times / week during May – October
 2018 and 2019. Broods were less likely to use areas with large proportions
 of hardwood drains but favored sites with greater proportions of burned
 uplands, regardless of the time of day. Broods were less likely to use
 areas at greater distances from supplemental feed; this relationship had
 no interaction with age. The effect of supplemental feed was stronger
 later in the nesting season (&gt; July 15). Broods were more likely to
 use areas with greater proportions of fallow fields during the day than
 for roosting. Broods used roosts with more woody cover and visual
 obscurity than at available sites. Roosts consisted of less grass and bare
 ground. However, these effects interacted with age; broods used sparser
 cover at older ages. Neonate broods were more likely to use cooler roosts
 with greater thermal stability, but this effect was reversed for
 juveniles. Broods may alter resource use with changes in vulnerabilities
 to threats such as thermal risks and predation.
description: <b>Field
 Methods</b> <i>Radio Telemetry
 </i> Adult bobwhites were trapped in
 walk-in funnel traps during January, March, and November as part of a
 long-term population monitoring study at Tall Timbers (Palmer and Sisson
 2017, Palmer et al. 2019, Terhune et al. 2019). A subsample of trapped
 individuals was marked with 6-g necklace-style VHF transmitters (American
 Wildlife Enterprises, Tallahassee, FL, USA) and monitored via radio
 telemetry at a rate of 3 times / week during October – April and daily
 during the nesting season (May – September). Locations were obtained via
 homing (White and Garrott 1990) and recorded on a portable-document format
 (PDF) map (Avenza Systems, Inc., Toronto, ON, Canada) using a GPS-enabled
 mobile device (e.g., iPad, iPhone, or Android device). Maps were
 georeferenced with respective landcover types (e.g., burned upland, drain,
 disked field, etc.). When individuals were documented in the same location
 after 2 consecutive visits, we assumed they were incubating. Incubating
 bobwhite were monitored daily until a nest fate was recorded (e.g., hatch,
 depredation). Upon a hatched nest, the incubating adult was tracked at a
 rate of 3 times per day. One location was obtained during the morning
 (0800 hrs –1130 hrs), one in the afternoon (1300–1700 hrs), and one at
 night during roosting hours (2000 hrs – 0700 hrs). At 10–12 days of age, broods were
 captured using a corral method (Smith et al. 2003). All chicks that were
 captured were marked using patagial wing tags (National Band and Tag Co.,
 Newport, Kentucky, USA) (Carver et al. 1999). If adults were captured
 without a brood, tracking ceased for that brood and tracking reverted to
 adult monitoring protocol. For broods captured with greater than 5 chicks,
 a subsample was marked with 0.75-g VHF radio tags (American Wildlife
 Enterprises, Monticello, FL, USA), using a modified suture technique
 (Terhune et al. 2017, Lunsford et al. 2019, Terhune et al. 2020). Chicks
 were tagged individually to ensure tracking persisted despite brood
 amalgamations, which are common among bobwhite (Faircloth et al. 2005,
 Brooks and Rollins 2007, Faircloth 2008). Thus, if chicks were adopted by
 another brood or orphaned by the brooding adult, we retained the ability
 to track chicks without the presence of a marked adult. After chicks were
 individually tagged, tracking intensity increased to a rate of 5 locations
 per day during the week and 3 times per day on the weekends. The tracking
 schedule during the week consisted of 5 time slots: early morning (0700 –
 1000 hrs), mid-morning (1000–1200 hrs), early afternoon (1200–1500 hrs),
 late afternoon (1500–2000 hrs), and roost (2000 – 0700 hrs). During
 weekend checks, the times slots included a morning (0700–1200 hrs),
 afternoon (1200–2000 hrs), and roost location (2000–0700 hrs). Daily
 tracking of broods continued until all chicks within a brood died or until
 42 days of age. If brood size was less than 5 during capture and
 individual chicks were not tagged, we continued to monitor broods until 42
 days of age by tracking the adult and ensured brooding status by the
 occurrence or absence of brood feces at the roost.
 <i>Temperature
 Sampling</i> We sampled ground
 surface temperature at roost sites at predefined age intervals. At 3, 7,
 14, 21, 28, 35, and 42 days of age, we marked roosts with flagging tape in
 each cardinal direction so they could be found the following morning. The
 morning (0730 hrs) following locating roosts, observers returned to the
 marked location and located the roost disk (identified by fecal dropping)
 within the flagged area. To evaluate the relative differences in
 temperature at roost sites to paired available locations, we deployed a
 DS1921G-F50 Thermochron® iButton® (Maxim Integrated Products, Inc.,
 Sunnyvale, CA) temperature sensor within the center of the roost disk and
 at a site 15 m in a random azimuth (determined by spinning a pencil). At
 15 m from the roost site, the observer tossed the pencil in the air above
 and the point of its landing served as the precise random location.
 Sensors were glued to a 5-cm, 11-gauge roofing nail which secured its
 position flush with the ground surrounding it. Sensors were calibrated to
 collect a temperature reading every 20 minutes from 2100 hrs to 0600 hours
 (28 readings). The sensor operated under conditions ranging from -40° C to
 85° C at 0.5°C increments. Accuracy of temperature readings within this
 range is 1 °C (Maxim Integrated Products, Inc., Sunnyvale, CA).
 Authors characterizing
 temperatures by bobwhite in the literature commonly report estimates of
 operative temperature by using temperature loggers fixed inside black,
 steel spheres (Carroll et al. 2015, Carroll et al. 2016, Carroll et al.
 2018, Olsen et al. 2018, Kline et al. 2019). Operative temperatures
 represent the temperature experienced by an animal by accounting for solar
 radiation and convection. However, ambient temperature and operative
 temperature should be similar at night (i.e., given lack of solar
 radiation) assuming a constant wind speed (Guthery 2002). Thus, we did not
 adjust temperatures recorded by the iButtons and assumed constant
 convection. <i>Vegetation
 Sampling</i> We collected
 measurements of vegetation during the same age intervals and mornings
 temperature sensors were deployed. At the roost site, we estimated visual
 obscurity (%) using a 1-m<sup>2</sup> cover board and
 vegetation composition (%) for 5 functional groups within a
 1-m<sup>2 </sup>quadrat frame. Functional groups which
 comprised vegetation composition included grasses, forbs, bare ground,
 litter, and woody/shrub cover. Species such as greenbriar and sand
 blackberry were categorized as woody/shrub cover, when present, due to
 their suffruticose or frutescent growth habits in the region. We pooled
 the estimates of bare ground (i.e., exposed soil) and litter (e.g., pine
 needles) to an index called bareness. Pooled, they effectively represent
 traversability and lack of vertical vegetation structure. 
  Visual obscurity and vegetation composition were estimated using
 an image classification system. Images (3,024 x 4,032 pixel resolution)
 were classified using the point sampling software SamplePoint to
 standardize estimation among observers (Booth et al. 2006). Photos were
 taken nadir (facing the quadrat, 1 m above) for estimates of vegetation
 composition. Photos were taken 4 m south of the roost at a height of 1 m
 to estimate visual obscurity. The images were then cropped to size of the
 cover board and quadrat and imported into SamplePoint. A systematic grid
 of 225 points was generated across the image and observers assigned a
 functional group to each point.
description: See ReadME file.