DOI: 10.5061/dryad.mpg4f4rdm
title: Oklahoma Black-capped Vireo dispersal study

description: Mechanisms driving breeding dispersal are complex but are of high interest
 because dispersal strongly links individual fitness to population
 dynamics. We examine the relative importance of personal information,
 neighborhood effects, and structural habitat characteristics in
 determining an individual’s propensity for breeding dispersal. We
 attempted to identify relevant cues for breeding dispersal of a North
 American territorial migratory bird species, the Black-capped Vireo. We
 color marked and radio-tagged males in Southwestern Oklahoma and used a
 conditional inference tree analysis to evaluate 11 variables that
 individuals could use as predictors of emigration. We used the correlation
 between arrival date and habitat structure to determine habitat
 preference. Breeding dispersal propensity among Black-capped Vireos
 depended mostly on their personal breeding experience, but also on
 reproductive information gleaned from their neighbors. Older and younger
 age classes that reproduced successfully did not disperse, but younger age
 class individuals that failed to reproduce were more likely to disperse
 than older individuals within the breeding season. Dispersal events among
 young males were significantly related to the proportion of their
 neighbors that successfully reproduced with more dispersal from
 neighborhoods of fewer, less successful neighbors. Vegetation structure
 within a territory was not identified as a significant cue.
description: We conducted our study on the Fort Sill Military Installation in
 Southwest Oklahoma, USA, from April to September in 2017 and 2018. The
 Fort Sill Military Installation, roughly 38,000 ha, with adjacent Wichita
 Mountain National Wildlife Refuge adding 23,885 ha total, with about
 10,000 ha suitable vireo habitat (Diamond and Elliot 2015), forms a
 contiguous track of the Wichita Mountain ecoregion in Oklahoma. Two common
 vegetation structures in vireo habitat included patches of short stature
 (one to three meters in height) black-jack and post oaks
 (<em>Quercus marilandica, Quercus stellata,</em>
 respectively), skunkbush (<em>Rhus triolobata</em>),
 flame-leaf sumac (<em>Rhus lanceolata</em>), and tall stature
 oak woodland (3 to 10 meters in height) with hackberry (<em>Celtis
 occidentalis</em>) common in the understory (Diamond and Elliot
 2015). During the two years of this study, Fort Sill and the wildlife
 refuge controlled for Brown-headed cowbirds, a frequent nest parasite of
 black-capped vireos, by removal through trapping in the spring and
 summer. We selected two main study sites that
 represented these two dominant vegetation structures used by Black-capped
 Vireos. The 49-hectare Quanah study site consisted predominantly of tall
 stature oak woodland habitat. The Sherman study site was 42 hectares and
 located in the central parcel of Fort Sill and was predominantly short
 stature oak habitat. We attempted to monitor breeding activities all
 territorial males within the boundaries of the study sites during the
 breeding period from April to July. To achieve sufficient sample sizes of
 vireo age classes, we also monitored selected territorial males of a
 certain age class in the area adjacent to the Sherman study area
 boundary. <strong>Field
 Methods</strong> We attempted to capture and mark
 all territorial males within the monitored study areas with a USGS issued
 aluminum numerical band and unique combination of colored leg bands. We
 captured Black-capped Vireos using six-meter length, 30mm mesh mist-nets
 while broadcasting Black-capped Vireo songs, scolds, heterospecific
 scolds, and Eastern Screech Owl calls. We determined sex, age, wing
 length, and mass. Age is most accurately determined by feather wear
 between the greater and primary coverts, but there are a high proportion
 of SY males with gray napes compared to black napes typical of ASY males
 (Pyle 1997, Cimprich 2018). Plumage characteristics are also diagnostic
 for sex as Black-capped Vireos are the only members in their family that
 are sexually dimorphic, but we also checked for full brood patches for
 females. Males that we could not catch were aged as after hatching year
 (AHY), though we note that most of these males had fully black
 napes. From the first week of April to the first week
 in May, we recorded arrival dates for territorial males by surveying the
 study sites at least four days in each seven-day period to detect new
 individuals. Observers spent 20 minutes in areas to detect individuals. We
 either visited both study sites in a single day or regularly alternated
 visiting sites to reduce effort bias. We gathered
 presence/absence and location data of monitored males from April to July
 by visiting their territories once at least every three days. A male was
 considered territorial if we found the same individual within 25 meters of
 a previous location where it had been singing or displaying other acts of
 area defense for three consecutive visits. We followed territorial males
 and recorded their locations using GPS (Garmin Rhino 650). Observers
 followed individuals only as closely needed to sight leg bands; usually no
 closer than 10 meters. We marked the GPS location of the vireo only after
 the vireo had moved voluntarily to avoid biasing movements based on the
 observer. GPS locations were taken no less than five minutes apart with no
 more than five locations per day to capture the full size of the breeding
 territory while the vireos were actively nesting. We
 monitored a total of 130 males in 2017 (Sherman n = 38, Quanah n = 36) and
 2018 (Sherman n = 30, Quanah n = 26) within the study sites. This count
 includes birds of three age classes: SY, ASY, and AHY. We excluded the age
 class of AHY from our analyses because these birds could be either SY or
 ASY but had not been captured to confirm their age. Within the study
 sites, 15 of 130 (11.5 %) of the males were SY males. Eighteen additional
 territorial SY males were located and monitored outside of the main study
 sites. We sought out these additional 18 territories of SY males to
 increase our sample size of SY males. Males were
 monitored for two weeks after nesting activity ceased in that territory,
 which included actively building nests or incubating behavior. Nests were
 located using behavioral cues. We considered a male successful if it
 produced at least one fledgling. Reproductive success differed between the
 sites, with 13.8 % more territories producing offspring on the Sherman
 site than on the Quanah site across both years (Table 1). Both Sherman and
 Quanah males experienced more success in 2017 than 2018. Compared to 2017,
 27 % fewer males were successful at Sherman and 17 % fewer males were
 successful at Quanah in 2018. An early April frost in 2018 likely explains
 the difference in success between years. Budding oak leaves were killed
 and did not fully redevelop until late April, which, delayed nesting and
 also likely reduced time for subsequent nesting following failed attempts
 (PMC unpubs. data). We monitored 73 nests in 2017 and 83 nests in 2018
 that had at least one egg. Nest failure was mainly due to predation, where
 all eggs or nestlings would be absent with the nest intact likely due to
 snake depredation (82 nests), or nests that had been removed from the
 shrub likely due to a mammalian predator (11 nests). Eight nests were
 abandoned with eggs while five nests had eggs destroyed by having holes
 poked in them. Cowbirds were controlled through trapping at Fort Sill and
 the Wichita Mountain Wildlife Refuge in both years, and we only found one
 nest parasitized on the study sites. We chose ordinal date 181 (June 30)
 as a cut off for the primary breeding season because our nest data
 indicate 98% (n = 172, includes nests in building stages) of nests were
 completed either as successful or failed, and territories were not
 initiating new nests. Dispersal of territorial males
 during the breeding season was determined in two ways. First, we resighted
 color-banded males by searching territories at least once every three days
 to determine presence or absence. Second, we radio-tagged (JDJC corps, 260
 mg) individuals (2017 n = 38: 7 ASY and 31 SY, 2018 n = 45: 11 ASY and 34
 SY) beginning mid-May through July using a modified leg-loop harness
 method with an elastic thread degradable within 30 to 60 days (Rappole and
 Tipton 1991) in addition to colored leg bands and a USGS band. Not all
 transmitted males were territorial when initially caught. We located
 radio-tagged males using a hand-held three-element Yagi antenna and
 receiver (Model R4000, Advanced Telemetry Systems, Inc., Isanti, MN) and
 employed the homing method. Transmitters weighed &lt; 4 % of an
 individual’s body mass and had a battery life that ranged from 28 to 50
 days for radio-tagged males that we were able to relocate for the first
 three days. We checked for radio-tagged males every day until they
 disappeared, the radio tag fell off and was recovered, or the tag battery
 died. If the male was territorial, we mapped their territory with up to
 five locations in one that were no less than five minutes apart. If the
 male abandoned their territory , we attempted to relocate the radio-tagged
 bird at least twice to get a location point no less than two hours apart
 to determine if they returned, settled elsewhere, or kept
 moving.
description: # Oklahoma Black-capped Vireo dispersal study Dataset DOI:
 [10.5061/dryad.mpg4f4rdm](https://doi.org/10.5061/dryad.mpg4f4rdm) ##
 Description of the data and file structure These data are Black-capped
 Vireo *Vireo atricapilla* reproductive and movement data from 2017 and
 2018 collected on the Fort Sill Military Installation in Lawton, Oklahoma.
 They were used in a decision tree that analyzed within season dispersal
 and territory abandonment of adult males. ### Files and variables ####
 File: ForParty_breeding_2022_updated.csv **Description:** Data for
 decision tree to determine dispersal correlates ##### Variables * TerrNo:
 Individual Territory Number of the individual bird * Move_behavior:
 Categorical what did the bird do (stayed put: stationary;Explored but came
 back to territory = forayed; Disappeared = disappeared from territory, no
 resight afterwards; Left territory permanently but I was able to keep
 track of them through telemetry = Wandered; Relocated = Left territory
 permanently and resettled elsewhere) * NoNest: How many nests did this
 territory have * S_N: Number of successful neighbors did this territory
 have * Total_Neighbor: How many neighbors did this territory have *
 Neighbor_success_prop: what is the proportion of successful neighbors *
 Neighbor_Success: Categorical was at least one neighbor successful * Move:
 Did the individual bird disperse during the breeding season * Site_start:
 What study site did the bird start out on * Site_end: What study site did
 the bird start end at * Female: Did the male pair with a female (y = yes,
 n = no, t = transitory) * Foliage_mean: Mean foliage density of the
 territory, percent * Canopy_mean: Mean canopy cover of the territory,
 percent * Shrub_mean: Mean shrub cover of the territory, percent * HA: How
 many hectares was the territory size (calculated from Hull convex), ha *
 Success: did the individual produce a fledgling yes or no * Mass: what did
 the individual weigh in grams * Wing: wind cord in mm * Tarsus: tarsus
 length in mm * massWingratio: mass divided by tarsus length * Cap: Cap
 color category. 5 is completely black, 0 is all gray * Age: ASY
 (after-second year) or SY (second-year) * Period: what time period was
 this territory monitored ### ## Code/software R and R studio version 4.2.0
 or above. Packages were: party partykit tidyverse ggparty 
 
 I made a model using ctree() with Move as the root, mincriterion = 0.5,
 and ctree_control "Bonferroni". Then I remade the figures using
 ggparty.