DOI: 10.5061/dryad.hmgqnk9dv
title: Least tern disturbance and productivity data

description: Disturbance from human activity can cause reduced productivity of coastal
 birds that nest on sandy beaches. A common method to protect coastal birds
 from human disturbance is the use of signs and fencing to close off a
 section of beach used for breeding. This management action requires public
 compliance and might require enforcement, such as in the use of volunteer
 stewards stationed at protected colonies that provide education and
 enforcement. I assessed the effectiveness of active stewardship as a
 conservation measure to protect nesting Least Terns (Sternula antillarum)
 in coastal Mississippi by determining if colony-level productivity
 (fledglings produced per nest) was correlated with stewardship effort
 (hours that stewards protected each colony), the rate of disturbance from
 human and natural sources, and additional factors. Observers surveyed 24
 Least Tern colonies in Harrison County, Mississippi, twice weekly during
 the 2017–2019 breeding seasons to record number of nests present, fate of
 marked nests, predator tracks within the colony, and number of fledglings
 produced per colony. Concurrently, stewards recorded during their work
 shifts all sources and durations of disturbance events that caused the
 terns to flush or respond with defense. Least Tern daily nest survival
 increased with colony size and stewardship effort, and was lower during
 intervals that included weekends and evidence of owl presence. Total
 productivity was negatively associated with avian predator disturbance
 rate and total time adults spent flushed, but was not associated with
 stewardship effort. The results of this study demonstrate that active
 stewardship can have a positive effect on Least Tern productivity by
 increasing nest success, whereas current stewardship practices were not
 sufficient to increase chick survival, even in a system with a paucity of
 ground predators.
description: Colony Survey Data: Audubon Mississippi
 staff conducted surveys at tern colonies throughout the breeding seasons,
 visiting at least once per week until all adults and fledglings had
 dispersed. Staff counted the number of active nests, flightless chicks,
 and fledglings using either an exterior or interior survey protocol. Staff
 conducted exterior surveys by standing outside the symbolic fencing at one
 corner of the colony and scanning the interior with binoculars (8x42) and
 scope (60x power). Birds seen in incubation posture provided a nest count.
 Fledglings often congregated on the shoreline and were easily counted from
 outside the colony. At large colonies (&gt;250 pairs) or colonies that
 contained visual obstructions such as dunes, staff conducted the exterior
 survey by visiting multiple viewpoints. Staff conducted interior surveys
 by walking systematically through the entire colony, keeping a count of
 all nests, chicks, and fledglings observed, and by noting and identifying
 any predator or human tracks within the colony. All colonies were surveyed
 using a combination of interior and exterior protocols throughout the
 season. The exterior protocol was employed whenever an interior survey
 would cause excessive disturbance (though staff would enter these colonies
 at other times for the purpose of checking nest plots), such as in the
 case of large colonies, colonies with a large number of flightless but
 mobile chicks, days with high winds or other inclement weather, hot and
 sunny days, or when time and logistics otherwise necessitated an exterior
 survey. Disturbance Data: The
 stewards recorded all interactions they had with the public and conducted
 continuous disturbance and behavior observations throughout their work
 shifts. When recording public interactions, stewards classified the
 interaction as an intervention if they prevented or interrupted a
 disturbance (such as somebody entering the colony, approaching with an
 off-leash dog, or setting off fireworks near the colony boundary), or as
 education if the interaction only involved answering questions or teaching
 the public about the birds. Interventions were often accompanied by
 education efforts that were not tallied under that category. In addition,
 stewards assessed the reaction of the person to the intervention or
 education, and classified the reaction as positive if the person appeared
 receptive, interested, or apologetic, or negative if the person appeared
 dismissive, disinterested, or combative. For the disturbance observations,
 anytime a portion of the tern colony flushed or reacted defensively (e.g.
 by dive-bombing a potential threat), the stewards recorded the source of
 disturbance, duration of the disturbance event to the nearest minute
 (using a watch or cell phone), and the maximum proportions of the colony
 that reacted by flushing, engaging in defensive behavior, or failing to
 react. Proportions for these reactions totaled one. The disturbance event
 was considered over once all terns had returned to pre-disturbance
 behavior. Any subsequent flush or defensive behavior was recorded as a new
 disturbance event. Simultaneous and sequential disturbance events were
 rare, but in cases of simultaneous disturbance events, stewards
 categorized the source as which source was present during the majority of
 the time that terns spent reacting. For sequential disturbance events
 caused by different sources, events were assigned separate durations and
 sources accordingly. Stewards categorized disturbance sources as
 pedestrian (any human approaching or entering the colony on foot,
 including staff entering for research purposes), dog (off-leash or
 on-leash), avian predator of eggs and chicks (gull, crow, Gull-billed
 Tern), avian non-predator (primarily Osprey [<i>Pandion
 haliaetus</i>] but also herons, egrets, shorebirds, passerines, and
 near-passerines), vehicle, aircraft, other (miscellaneous and infrequent
 sources such as kites flown nearby and beach balls or trash blowing into
 the colony), and unknown (source could not be determined).
 Nest Survival Data: Each year, I selected up
 to 6 colonies where individual nests were marked for nest survival
 estimation. I selected colonies systematically in an attempt to include a
 range of colony sizes and geographic locations. I attempted to mark all
 nests in selected colonies in 2017 but used nest plots in subsequent
 years. Nest plots (3–6 per colony) were 10- x 10-m in extent and placed
 randomly throughout each colony. I placed a 20-cm wooden stick marked with
 the nest number ~5–20 cm to the north of each nest; densely-spaced nests
 at many colonies prevented me from placing the stick any farther from a
 nest. Audubon staff visited each nest plot 2–3 times per week, marking all
 new nests that appeared within the plot boundaries and checking the status
 of existing nests. Staff estimated the nest initiation date based on
 laying sequence for nests found prior to clutch completion and assumed a
 21-day incubation period (Thompson et al. 1997) ±3 days to determine the
 range of expected hatch dates. For nests discovered after clutch
 completion, staff estimated a range of possible nest initiation dates
 based on the date of nest discovery within the nest plot and date of the
 previous visit to the plot. Expected hatch dates were not calculated for
 nests that had complete clutches on the day that plots were established.
 During each visit, staff assigned each nest one of the following fates:
 active with eggs, hatched, failed, or unknown. Nests were assigned as
 hatched if at least one downy chick was present, or if the nest scrape was
 empty and an appropriately-aged chick was &lt; 1 m from the nest that
 could not have come from any other nest within that radius. Nests were
 assigned as failed if there were signs of depredation (yolk or punctured
 egg), the scrape was empty but there were fresh predator tracks leading to
 the scrape, or if the scrape was empty and the date did not fall within
 the expected hatch window. If eggs were present but appeared abandoned as
 evidenced by partial burial or bleaching of the shell, then staff assigned
 the fate as unknown but checked the nest again during subsequent visits.
 If the nest continued to appear untended during the next visit, it was
 assigned as failed. Staff also assigned nests as failed if there was
 evidence of tidal overwash or washout due to heavy rain (nest and scrape
 gone and sand freshly washed over). Staff assigned fate for nests as
 unknown if the nest was empty but evidence did not meet any of the
 previous criteria, or if the nest was empty with no evidence of hatch or
 failure and staff had not been able to determine an expected hatch
 window.
description: Data files are unprocessed except for QA/QC that occurred at the
 ends of each season. I have included the R script used to process the data
 for analysis.