DOI: 10.5061/dryad.p2ngf1vvq
title: Mockingbird flush distances when approached by humans of differing threat levels

description: These data show flush distances of incubating female mockingbirds on the
 University of Florida campus (Gainesville, FL) when approached by four
 different humans, each posing a different level of threat to the
 bird.  Column A (Nest Location) describes the location of each
 nest. Multiple rows for the same nest indicate approaches by different
 humans and/or on different days.  Column B (Visitor Type)
 indicates the classification (experimental treatment) of the human. The
 threat level of that human is provided in Column J (Threat Ranking, which
 ranges from 2 [high] to 5 [low]).  An “Intruder” approached the
 nest on 4 sequential days and placed one hand on the rim of the nest for
 15 seconds before retreating.  Mockingbirds quickly learned to
 recognize them and thus Intruders have the highest threat ranking
 (2).  An “Associate” approached the nest alongside the Intruder
 but stopped 3m from the nest and waited there until the Intruder returned
 from the nest. The Associate and Intruder stood facing each other for 15
 sec before departing from the nest. Associates had a medium threat ranking
 (3).  A “Bystander” approached alone on four consecutive days,
 stopped 3m from the nest and stood quietly without looking at the female
 for 10 min before departing. Females did not flush during these trial
 sessions and hence flush data and behavioral data are not provided.
 However, the Bystander approached the nest and placed one hand on the lip
 of the nest for 15 seconds on the last day of trials, forcing the female
 to flush; results from those trials (one per female) are shown. Bystanders
 had a low threat ranking (4) because they typically didn’t threaten the
 nest.  Finally, a Control individual who the female had never
 seen approached the nest on the last day of trials and placed one hand on
 the lip of the nest for 15 seconds.  Control individuals had the
 lowest threat ranking (5). Column C indicates the human’s distance from
 the nest when the female flushed upon approach.  All humans
 started to approach the nest from ~30m and walked towards it at a speed of
 ~1m/sec. Columns D through I provide behavioral data of the female and her
 mate (who sometimes wasn’t present; see column M). Female and male
 mockingbirds cannot be distinguished. Hence data in columns D through I
 are summed for whatever bird or birds were responding.  Column D
 shows the number of times birds hovered over the head of the human. Hovers
 were brief, typically &lt;3 sec, and often ended in a “swoop” (Column
 E) or an “attack” (Column G). An attack was defined as a downward flight
 to within 1m of the human. A swoop was a downward flight toward the human
 but not to within 1m.  Column F (“indirect flights”) shows the
 number of flights over or around and within 5m from the human, typically
 from one perch to another.  Column H shows the time of the first
 alarm call in minutes and seconds from the time the human started to
 approach the nest.  Column I shows the total number of alarm
 calls from the start to finish of the trial. Column K provides an estimate
 of human activity near the nest (the number of humans who walked within 5m
 of the nest in a 10 min period). Column L indicates an irregularity with a
 trial (0 = protocol tightly followed; 1 = protocol not tightly followed or
 a problem outside of investigators’ control). Column M provides
 miscellaneous notes. Data on presence of the male was inconsistently
 taken.
description: Our study took place in Gainesville,
 Florida on the ~800-ha campus of the University of Florida. Northern
 mockingbirds commonly nest in isolated shrubs or small trees in open areas
 frequented by thousands of students daily. They are highly acclimated to
 the presence of humans, typically showing no response unless approached
 within 2–3 m. Pairs are socially monogamous and territorial. Territory
 size is 1–2 ha on campus. Only the female incubates the eggs, which
 allowed us to tightly control a given bird’s exposure to different humans.
 Because much of the population was individually color banded and the study
 occurred during a single breeding season on widely separated territories,
 we are confident that each female was included only once in our
 sample. When the nest of an incubating female
 was discovered, we first established three 30m paths along which an
 approaching human could be seen from the nest. In some cases, a person not
 participating in the trials removed a small number of leaves or twigs near
 the nest to assure equal visibility of approaching humans along all paths.
 The purpose of multiple approach paths was to minimize the possibility
 that the bird might respond to the direction of approach rather than (or
 in addition to) the identity of the human. On the day that trials at a
 given nest were initiated, one approach path was randomly selected for
 use. On the second day, one of the remaining two paths was randomly
 selected and on the third day, the last path was used. On subsequent days
 and trials, path use was randomized in the same
 manner.   Trials on a given nest occurred over
 five consecutive days. On the first three days (training period) the nest
 was visited by High and Medium Threat individuals together and at least
 3hr before or after by the Low Threat individual. The goal of these trials
 was to establish the three treatments – i.e., to familiarize the female
 with each type of human and their threat level. Prior work using a similar
 protocol established that mockingbirds significantly increase their
 response to threatening humans after 2 visits to a nest. On the last two
 days (test period), we measured the female’s response to approaches by a
 single individual of the four threat levels, including the No Threat
 individual who had not previously approached the nest. The order and paths
 of these approaches were randomized. On the last two days, two trials
 occurred per day, separated by &gt;6 h. In these four trials, all
 humans behaved identically, except for the approach path used. They
 approached the nest from 30 m at a rate of 1 m/s, paused ~1 m from the
 nest for 15 s, touched the rim of the nest for 15 s, and walked away at
 the same rate and along the same path as they had arrived. None paused 3 m
 from the nest.   Our experimental design did not employ
 distinctive clothing or masks with exaggerated features that the birds
 could associate with treatments. All participants were instructed to wear
 their normal clothing, regardless of the trial; the only restriction was
 no hats or sunglasses. Except for the first author, all participants in
 trials were university students, presumably indistinguishable at the start
 of trials from the other ~50,000 students on campus at the time. (The
 study occurred before the COVID pandemic.) Our goal was to mimic as
 closely as possible the natural variety of humans near each bird’s nest.
   Because all trials were conducted during
 incubation, our experimental design also controlled for the well-known
 association between nest defense behavior and stage of the breeding cycle.
 If any eggs hatched or disappeared, we discontinued trials on the impacted
 nest.   Data have been quality checked but not
 otherwise processed.   Our experimental protocol was reviewed
 and approved by the University of Florida Institutional Animal Care and
 Use Committee (protocol #D884-007).