Dataset: Winter mixed-species flock and point count surveys in NC Florida upland hardwood forest habitat Harrison H. Jones1,2*, Mitchell J. Walters1,2, and Scott K. Robinson1,2

1 Department of Biology, University of Florida, Bartram Hall, 876 Newell Dr. Gainesville, FL 32611 2 Florida Museum of Natural History, University of Florida, Dickinson Hall, 1659 Museum Rd. Gainesville, FL 32611

*Correspondence address: [email protected]

INTRODUCTION In order to characterize the winter avifauna of a hardwood forest community and determine the proportion of time each species spent in mixed-species foraging flocks, we conducted paired mixed-species flock and point count surveys. Surveys were carried out between November 2018 and January 2019 at five field sites in North-Central Florida. In this data set we describe abundances of species detected by site or sound in each survey type. Field methods used and variable descriptions are stated below.

METHODS Study sites and flocking system Bird surveys were conducted on wildlands near Gainesville, Florida, USA in the North- central portion of the Florida peninsula. Study sites included San Felasco Hammock Preserve State Park (29.7191ºN, 82.4531ºW), Paynes Prairie State Park (29.5588ºN, 82.3261ºW), and Split Rock Conservation Area (29.6331ºN, 82.4103ºW). To standardize the habitat types sampled, we selected only field sites in broadleaf forest, which has the most species-rich forest bird community in winter (Engstrom 1993). This habitat is known as upland hardwood forest and grows near lakes and spring-fed steams where and the leaf mulch conserves soil moisture, leading to mesic conditions (Florida Natural Areas Inventory 2010). The closed canopy of the forest is structurally-diverse and dominated by an assemblage of deciduous and evergreen trees. Near Gainesville, this mesic forest type is primarily composed of American sweetgum (Liquidambar styraciflua), spruce pine (Pinus glabra), southern magnolia (Magnolia grandiflora), swamp chestnut oak (Quercus michauxii), diamondleaf oak (Quercus laurifolia), bluff oak (Quercus austrina), sugarberry (Celtis laevigata), and pignut hickory (Carya glabra). Common understory trees include American holly (Ilex opaca), Eastern hophornbeam (Ostrya virginiana), southern sugar maple (Acer floridanum), and flowering dogwood (Cornus florida). Florida is home to one of the most complex and diverse mixed-species flocking systems in North America due to the presence of overwintering migratory species. In this system, the Tufted Titmouse (Baeolophus bicolor) is an abundant, year-round-resident that acts as a nuclear species for other forest passerines along with the Carolina Chickadee (Poecile carolinensis; Farley et al. 2008). These species are considered passive nuclear species, because flocks form around and follow small family groups of 2-5 individuals that hold stable winter territories (Brawn and Samson 1983; Pravosudova and Grubb 2000). The movement of the flock is directly correlated with the movement of the leader species (Contreras and Sieving 2011), who give alarm calls in the presence of Accipiter hawks (Morse 1970; Gaddis 1980; Sieving et al. 2004). These flocks are joined by many species of small forest passerines (Gaddis 1983; Farley et al. 2008); common flock-following species include Black-and-white Warbler (Mniotilta varia), Blue-gray Gnatcatcher (Polioptila caerulea), Blue-headed Vireo (Vireo solitarius), Downy Woodpecker (Picoides pubescens), Orange-crowned Warbler (Oreothlypis celata), Ruby- crowned Kinglet (Regulus calendula), and Yellow-throated Warbler (Setophaga dominica).

Mixed flock surveys with paired point counts During the winter of 2018 (November-February), we conducted surveys to determine the composition of mixed-species foraging flocks in mesic hardwood forest. We rotated between survey sites to ensure that the air temperature during a survey was not correlated with any given set of field sites. Surveys were conducted from ~0730 to ~1200, and only one site was sampled per day. At least two observers familiar with the local avifauna walked trails or transects through suitable habitat until a flock was encountered, at which point the flock was followed for a minimum of 10 minutes to accurately characterize the composition and the abundance of all participating species. Bird species were identified by sight (using 10x binoculars) and sound; inter-observer bias was minimized by having one of the same two observers (HHJ and MJW) for each survey. For each flock, we recorded the Julian date on which it was observed, as well as the number of observers and start and end time of the survey to account for survey effort. We also recorded the average air temperature (°C) using a hand-portable weather meter (Kestrel 2500; Kestrel Meters) and the canopy height in meters using a laser rangefinder (Nikon 8397 Aculon AL11; Nikon Corporation) at the start of each survey. We did not record canopy height for the point count surveys. We recorded canopy height as a proxy for vegetation structure, which has been shown to influence mixed flock composition (Lee et al. 2005; Zhang et al. 2013; Mokross et al. 2014). In order to calculate the flocking propensity of species in our winter community, we paired 50-meter radius point counts with each of our flock surveys, following the methodology of Farley et al. (2008). After characterizing the flock composition, we waited until the flock had moved at least 100 meters away before conducting a point count at the last point at which the flock was observed. This allowed us to account for species that joined the flock temporarily before dropping out as the flock moved on, as well as species that do not join foraging flocks. We conducted a 10-minute point count during which we characterized all species seen or heard, excluding fly-overs. To determine a flocking propensity for each species for the survey period, we calculated a proportion by dividing the total number of individuals observed in a flock by the total number of individuals observed in both flocks and point counts.

VARIABLE DESCRIPTIONS Survey ID- Each set of paired flock and point count surveys was assigned a survey ID number.

Date and Julian Date- We recorded the date of the survey to account for time of year effects. This date was converted to a Julian (ordinal) date for ease of analysis.

Site- Indicates the field site at which the survey took place. We performed field work at three field sites (see above), though at the San Felasco site we performed surveys in three distinct areas which represented separate trail networks. Only one site was sampled per day, and each sampling occasion represents approximately a half day of sampling.

Survey Type- Indicates whether the survey in question was a flock or point count survey. Point count surveys represent standard ten-minute, 50 meter fixed-radius counts where species were detected by sight and sound. We did not record fly-overs of species (e.g. soaring raptors) because we were only interested in species present at the study site. Flock surveys consisted of ten minute or longer surveys during which we followed foraging flocks and recorded the abundances of all species seen or heard.

Start Time and Minute- Start time corresponds to the time at which the flock was first encountered, in order to account for possible time of day effects on flock size. For ease of analysis we converted this value to a number, corresponding to the minute of the day. In this scheme, midnight would correspond to minute 1, with each minute receiving an increasing value.

Survey Duration- The duration, in minutes, of the survey. This value was always ten minutes for the point count survey type, and always at least ten minutes for the flock survey type, where possible. Flock size was variable, and for larger flocks more time was necessary to completely survey the number of species and individuals present.

Number of Observers- The number of observers present for the survey to account for survey effort. This value ranged from one to three observers.

Temperature- The air temperature, in degrees Celsius, was recorded using a hand-portable weather meter (Kestrel 2500; Kestrel Meters) when the flock was first encountered and at the beginning of the point count, such that each survey has an associated temperature. Measurements do not account for wind chill factor; we allowed the instrument several minutes to equilibrate before taking a reading in each case.

Canopy Height- This is a measure in meters, to the nearest meter, of canopy height at the site where the flock was first encountered. We used a laser rangefinder to target the tallest visible foliage (or branches if leaves absent) while standing directly underneath. We made only one measurement per flock, but generally flocks moved short distances and canopy heights did not vary greatly during the observation period.

Northing and Easting- These correspond to northing and easting values for the point count point, as recorded using the Universal Transverse Mercator projection. This point also represents a location in which the mixed-species foraging flock was observed. The grid zone designation for these coordinates is 17R.

Number of Species- The total species richness detected by sight or sound in either the mixed- species foraging flock over the course of the observation period or during the ten-minute point count. The values were calculated by totaling all species with a least one individual detected during the relevant survey type.

Number of Individuals- Total number of individual birds observed in either the mixed-species foraging flock over the course of the observation period or during the ten-minute point count. These represent ‘raw’ values calculated by adding the abundances of each species detected during the relevant survey type.

Species abundance values- Number of individuals detected for each of 45 bird species detected at least once in one survey type. Each individual species has a column, which is labeled with the four-letter Alpha Code. Full English and Latin binomial names for each species are made available in Table 1, listed in phylogenetic order.

LITERATURE CITED Brawn, J. D., and F. B. Samson (1983). Winter behavior of Tufted Titmice. Wilson Bulletin 95:222-232. Contreras, T. A., and K. E. Sieving (2011). Leadership of winter mixed-species flocks by Tufted Titmice (Baeolophus bicolor): are titmice passive nuclear species? International Journal of Zoology 2011:1-11. Engstrom, T. (1993). Avian Communities in Florida Habitats: Analysis and Review. Florida Game and Fresh-water Fish Commission, Tallahassee, FL. Farley, E. A., K. E. Sieving, and T. A. Contreras (2008). Characterizing complex mixed-species bird flocks using an objective method for determining species participation. Journal of Ornithology 149:451-468. Florida Natural Areas Initiative (2010) Guide to the Natural Communities of Florida. https://fnai.org/PDF/FNAI-Natural-Community-Classification-Guide- 2010_20150218.pdf Accessed 6 February 2019. Gaddis, P. K. (1980). Mixed flocks, Accipiters, and antipredator behavior. Condor 82:348-349. Gaddis, P. K. (1983). Composition and behaviour of mixed-species flocks of forest birds in north-central Florida. Florida Field Naturalist 11:25-34. Lee, T. M., M. C. K. Soh, N. Sodhi, L. P. Koh, and S. L. H. Lim (2005). Effects of habitat disturbance on mixed species bird flocks in a tropical sub-montane rainforest. Biological Conservation 122:193-204. Mokross, K., T. B. Ryder, M. C. Cortes, J. D. Wolfe, and P. C. Stouffer (2014). Decay of interspecific avian flock networks along a disturbance gradient in Amazonia. Proceedings of the Royal Society B-Biological Sciences 281. Morse, D. H. (1970). Ecological aspects of some mixed-species foraging flocks of birds. Ecological Monographs 40:119-168. Pravosudova, E. V., and T. C. Grubb (2000). An experimental test of the prolonged brood care model in the tufted titmouse (Baeolophus bicolor). Behavioral Ecology 11:309-314. Sieving, K. E., T. A. Contreras, and K. L. Maute (2004). Heterospecific facilitation of forest- boundary crossing by mobbing understory birds in North-Central Florida. Auk 121:738- 751. Zhang, Q., R. C. Han, Z. L. Huang, and F. S. Zou (2013). Linking vegetation structure and bird organization: response of mixed-species bird flocks to forest succession in subtropical China. Biodiversity and Conservation 22:1965-1989.

TABLES Table 1. Species names and alpha codes of species detected during mixed-species flock and point count surveys. English Name Latin Name Alpha Code Family Wood Duck Aix sponsa WODU Anatidae Red-shouldered Hawk Buteo lineatus RSHA Accipitridae Sharp-shinned Hawk Accipiter striatus SSHA Accipitridae Cooper's Hawk Accipiter cooperii COHA Accipitridae Barred Owl Strix varia BAOW Strigidae Belted Kingfisher Megaceryle alcyon BEKI Alcedinidae Red-bellied Woodpecker Melanerpes carolinus RBWO Picidae Yellow-bellied Sapsucker Sphyrapicus varius YBSA Picidae Downy Woodpecker Picoides pubescens DOWO Picidae Northern Flicker Colaptes auratus NOFL Picidae Pileated Woodpecker Dryocopus pileatus PIWO Picidae Eastern Phoebe Sayornis phoebe EAPH Tyrannidae White-eyed Vireo Vireo griseus WEVI Vireonidae Blue-headed Vireo Vireo solitarius BHVI Vireonidae American Crow Corvus brachyrynchos AMCR Corvidae Blue Jay Cyanocitta cristata BLJA Corvidae Carolina Chickadee Poecile carolinensis CACH Paridae Tufted Titmouse Baeolophus bicolor TUTI Paridae Carolina Wren Thryothorus ludovicianus CAWR Troglodytidae House Wren Troglodytes aedon HOWR Troglodytidae Blue-gray Gnatcatcher Polioptila caerulea BGGN Polioptilidae Ruby-crowned Kinglet Regulus calendula RCKI Regulidae Golden-crowned Kinglet Regulus satrapa GCKI Regulidae Hermit Thrush Catharus guttatus HETH Turdidae Eastern Bluebird Sialia sialis EABL Turdidae American Robin Turdus migratorius AMRO Turdidae Gray Catbird Dumetella carolinensis GRCA Mimidae Cedar Waxwing Bombycilla cedrorum CEWA Bombycillidae Black-and-white Warbler Mniotilta varia BAWW Parulidae Yellow-rumped Warbler Setophaga coronata MYWA Parulidae Orange-crowned Warbler Leiothlypis celata OCWA Parulidae Ovenbird Seiurus aurocapilla OVEN Parulidae Pine Warbler Setophaga pinus PIWA Parulidae Prairie Warbler Setophaga discolor PRWA Parulidae Palm Warbler Setophaga palmarum PAWA Parulidae Yellow-throated Warbler Setophaga dominica YTWA Parulidae

Table 1. Continued. Northern Parula Parula americana NOPA Parulidae American Redstart Setophaga ruticilla AMRE Parulidae Bay-breasted Warbler Setophaga castanea BBWA Parulidae Northern Cardinal Cardinalis cardinalis NOCA Cardinalidae American Goldfinch Spinus tristis AMGO Fringillidae Purple Finch Haemorhous purpureus PUFI Fringillidae Pine Siskin Spinus pinus PISI Fringillidae Baltimore Oriole Icterus galbula BAOR Icteridae Red-winged Blackbird Agelaius phoeniceus RWBB Icteridae