DOI: 10.5061/dryad.cc2fqz69z
title: Data for: Experimental variation of perceived predation risk does not influence coordination of parental care in the long-tailed tit

description: To maximise fitness, parents should optimise their investment in each
 breeding attempt. When there are multiple carers, the fitness of each
 individual may also depend on the relative timing of their investment,
 with coordination of care hypothesised to maximise its efficiency and
 reduce predation risk. The aim of this study was to test the hypothesis
 that carers coordinate provisioning as an antipredator measure that
 reduces the time that a brood’s location is advertised to predators
 (‘predation hypothesis’). We presented predatory and non-predatory model
 birds to provisioning long-tailed tit Aegithalos caudatus parents and
 helpers, predicting that coordination would increase, and carer activity
 near the nest would decrease following predator presentation, relative to
 controls. First, carers reduced provisioning rates and took longer to
 resume provisioning following the predator presentation. Second, contrary
 to predictions, we found no significant change in any metric of
 coordination following predator presentations, relative to controls.
 Moreover, following predator presentation carers spent more time near the
 nest, resulting in greater near-nest activity compared to controls. In
 conclusion, although provisioning long-tailed tits are sensitive to
 perceived predation risk, our findings do not support the prediction of
 the predation hypothesis that carers adjust coordination behaviour in
 response to that threat.
description: <strong>Study
 system and general field protocol</strong>
 Data were collected
 during the breeding seasons (March–June) of 2021 and 2022 from a
 population of long-tailed tits in a ~3km<sup>2</sup> field
 site in the Rivelin Valley, Sheffield, UK (<em>53°23′N,
 1°34′W</em>). Nests were located by following adult birds during
 nest building, and once located, were monitored at 1–3 day intervals to
 record lay dates and the start of incubation, with daily checks to record
 hatch date within 24 h. Brood size was recorded on day 11 (d11) after
 hatching (d0) when chicks were ringed. Long-tailed tits typically build
 their nests in low vegetation (&lt;3 m) or tree forks (&gt;3 m).
 Our experimental protocol required model presentation within 2 m of the
 nest, so we conducted experiments only on nests within reach of an
 observer (&lt;3 m) (<em>N</em> = 22). All birds in our
 study were individually identifiable after being ringed with a British
 Trust for Ornithology ring and a unique combination of two colour rings
 either as nestlings in our field site or during nest building if
 immigrants. In total, 21 breeding females, 20 breeding males and 11
 helpers (10 males, 1 female) were observed at 22 nests. It was not
 possible to record data blind because our study involved focal animals in
 the field. <strong>Experimental
 protocol</strong> Long-tailed tits provision
 their brood in the nest from hatching (d0) until failure or fledging
 (d16–18). Breeding females brood the chicks until around d5, during which
 time males provide most food, but from d6 onwards brooding ceases and
 carers provision chicks directly. We conducted experiments on d8–10 at 22
 nests (d8: <em>N</em> = 12; d9: <em>N</em> = 6;
 d10: <em>N</em> = 4) in April–May 2021 and 2022. At each nest,
 we performed an experiment comprising a series of provisioning watches
 with intermittent periods of model presentation (Fig. 1). First, an
 observer (CH) set up a wooden pole (1.2 m tall) for model presentations
 and a video camera on a tripod ~2 m from the nest to record the time, to
 the nearest second, that each carer fed the brood, before retreating to an
 observation position &gt;20 m from the nest. The first watch was a
 control provisioning period of 1h which commenced upon the first feed
 observed after an initial 10-minute acclimation period. The observer
 recorded the time, to the nearest second, that a carer arrived within 15 m
 of the nest, so that the time between arrival and feeding, termed the
 ‘loitering period’, could be calculated. If two or more carers arrived
 simultaneously, they were recorded as arriving at the same time, but the
 observer noted the order in which they were identified. Some arrivals did
 not result in feeds (4.69%, <em>N</em> = 1,561), so were
 omitted from our final analysis. In addition, some arrivals (4.03%,
 <em>N</em> = 1,491) were missed, in which case the time of
 arrival was assumed to be the time first seen on camera; the longer a
 carer loitered the lower the chance that their arrival was missed, so we
 reasoned that missed arrivals would typically occur with short loitering
 periods. Watches were performed for one hour after the first observed
 feed, and watch duration was calculated as the time between first arrival
 and final feed. Following the control period,
 the observer fixed the first taxidermic model atop the pole before
 retreating to the same observation position. The model was either a
 non-predatory (rock dove, <em>Columba livia</em>) or predatory
 (Eurasian jay) bird; jays commonly depredate long-tailed tit eggs and
 chicks, but not adults. The first model was presented for ~15 minutes
 (dove mean (±SE): 15 mins 19s ± 6s, <em>N</em> = 22; jay mean
 (±SE): 15 mins 22s ± 8s, <em>N</em> = 22), while the observer
 and video camera recorded arrival and feed times to the nearest second.
 Although we did not systematically quantify other behaviours during this
 period, carers usually responded to the jay by intensely alarm-calling and
 mobbing the model before retreating from the nest area. In contrast,
 during the dove presentation, carers alarm-called less and rarely mobbed
 the model, often resuming provisioning within 2 minutes of the
 presentation. After 15 minutes the observer retrieved and concealed the
 model before returning to the same observation position to perform another
 1h provisioning watch. The observer then repeated the presentation
 procedure and subsequent observation period for the other model. All
 watches at a focal nest were performed on the same day, back-to-back, with
 minimal breaks between watch periods and the next model presentation. Each
 experiment typically lasted 4–5 h. The order of model presentations was
 stratified to minimise confounding order effects with model treatment
 (dove first: N = 10 trials; jay first: N = 12 trials). Nevertheless, we
 tested the effect of presentation order on all measures of coordination,
 finding that it was not statistically significant in any case and no other
 result qualitatively changed with its inclusion (Table S1). Therefore, we
 did not include presentation order in our final
 analyses. <strong>Calculating
 coordination</strong> <strong>Effect of
 experimental treatments on provisioning
 behaviour</strong> To establish whether model
 presentations disturbed regular provisioning behaviour, we first
 calculated the time between the removal of each model (dove or jay) and
 the first feed by any carer during the subsequent watch, termed the ‘Lag
 time’ (Fig. 1). Secondly, we calculated the ‘Number of feeds’ by all
 carers during control watches, during model presentation periods (dove or
 jay present) and in watches following model removal (post-dove and
 post-jay). This was analysed as the total number of feeds per watch, which
 functioned as a measure of provisioning rate when watch duration was
 included in the model. <strong>Does predation
 threat increase coordination?</strong> To test the prediction that
 carers increase their coordination in response to elevated predation risk,
 we calculated provisioning and coordination metrics by all carers during
 control watches and post-dove and post-jay watches, as follows.
 ‘Alternation’ – the number of alternated feeds, defined as the number of
 feeds that occurred following the feed of another carer,
 <em>i.e.</em> non-consecutive feeds (<em>e.g.</em>
 A-B-A-C-B) (median = 16, range = 3–37, <em>N</em> = 66 watches
 at 22 nests). ‘Arrival synchrony’ – the number of synchronised arrivals,
 defined as the number of arrivals that occurred within a time window of 2
 minutes following an arrival by another carer (as in: Bebbington and
 Hatchwell 2016; Halliwell et al 2022, 2023) (median = 10, range = 1–30,
 <em>N</em> = 66). ‘Feed synchrony’ – the number of
 synchronised feeds, defined as the number of feeds that occurred within a
 2 minute time window of a feed by another carer (median = 10, range =
 1–30, <em>N</em> = 66). ‘Present upon arrival’ – the number of
 feeds where the focal carer arrived back within 15 m of the nest with
 another carer loitering nearby (median = 6, range = 0–24,
 <em>N</em> = 66). ‘Present upon feed’ – the number of feeds
 where the focal carer fed whilst another carer loitered nearby (median =
 5, range = 0–24, <em>N</em> = 66). ‘Loitering time’ – the mean
 loitering period duration by all carers who provisioned the brood during a
 watch (mean (±SE) = 45.8s ± 3.8s, <em>N</em> = 66) and
 ‘Duration of time with carer(s) nearby’ – the total time during each watch
 where one or more carers loitered within 15 m of a nest (mean (±SE) = 11
 mins 54s ± 36s, <em>N</em> = 66); when watch duration was
 included as a covariate this measure functioned as an analysis of the
 proportion of a watch where at least one carer was loitering
 nearby. To further test the dynamics of
 any potential response to predation threats, we compared several metrics
 of carer behaviour between sub-sections of control watches and post-dove
 and post-jay watches, each split into thirds by watch duration (mean third
 duration (±SE) = 18 mins 47s ± 8s, <em>N</em> = 198); response
 variables were: ‘Number of feeds’ (provisioning rate), ‘Loitering time’,
 and the levels of each coordination metric (‘Arrival synchrony’, ‘Present
 upon arrival’, ‘Present upon feed’, ‘Feed synchrony’, ‘Alternation’). This
 analysis attempted to determine the time frame on which carers adjusted
 their provisioning behaviour in response to elevated predation
 risk. <strong>Statistical
 analysis</strong> All statistical analyses were
 performed in R version 4.2.1 (R Core Team 2022). All models were built
 using lme4 (Bates et al 2015) and <em>P</em> values were
 extracted using lmerTest (Kuznetsova et al 2017). Where appropriate, we
 used the package emmeans (Lenth et al 2019) to perform <em>post
 hoc</em> testing. Figures were produced using the packages ggplot2
 (Wickham 2016), cowplot (Wilke 2020) and ggsignif (Ahlmann-Eltze and Patil
 2021). Our general approach to analyses was to use full mixed effects
 models with all biologically relevant fixed and random effects. To confirm
 that our findings were not influenced by overparameterisation of these
 models, we also conducted analyses of the same dataset using stepwise
 elimination of non-significant terms and an information theoretic (AIC)
 approach, but results were very consistent between these methods (see
 online resource details, table S3). Therefore, here we present only the
 results of full mixed-effect models. <strong>Effect of
 experimental treatments on provisioning
 behaviour</strong> To determine whether model
 presentation treatments affected provisioning behaviour, we first built a
 normally distributed linear mixed effects model (LMM) to compare the lag
 time between model removal and the first subsequent feed for dove and jay
 treatments. The response variable was log-transformed ‘Lag time’ because
 the assumption of normality was met only when the response variable was
 appropriately transformed. This model’s term of interest was ‘Treatment’
 (post-dove or post-jay), with the fixed effects covariates as follows.
 ‘Provisioning rate’ – the total number of feeds by all carers per hour in
 the watch following model removal (in this case: mean (±SE) = 25.09
 feeds/h ± 1.33, range = 7.94–46.42, <em>N</em> = 44) ‘Carer
 number’ – the number of unique carers which provisioned during each watch
 following model removal (in this case: 2: 70.5%, 3: 20.5%, 4: 2.3% and 5:
 6.8%; <em>N</em> = 44). ‘Brood size’ – the number of live
 chicks recorded in the nest on d11 (median = 9, range = 2–11, <em>N
 </em>= 22). ‘Watch start time’ – the time of day each experiment
 started (mean = 08:30 BST, range = 07:20–12:40, <em>N </em>=
 22). ‘Brood age’ – the number of days since hatching upon which a watch
 was performed (d8: <em>N</em> = 12; d9: <em>N</em>
 = 6; d10: <em>N</em> = 4). Finally, ‘Hatch date’ – the number
 of days since March 1 of each year on which each brood hatched (median =
 April 30, range = April 19 – May 29, <em>N </em>= 22). Random
 effects were ‘Year’ and ‘Nest ID’ – a unique identifier for each nest.
 Detailed descriptions of all fixed and random effects are available in
 Table S2 (online resource). Secondly, we built a Poisson-distributed
 generalised linear mixed effects model (GLMM) to compare provisioning
 rates during control watches, model presentations, and watches following
 model removal (post-dove and post-jay). The response variable was ‘Number
 of feeds’ and the term of interest was ‘Treatment’ (control, dove present,
 jay present, post-dove or post-jay) with fixed effect covariates as
 follows: ‘Carer number’ – for provisioning watches, this was the number of
 carers that provisioned during each watch (2: 69.7%, 3: 21.2%, 4: 3.0% and
 5: 6.1%; <em>N</em> = 66); for presentation periods, this was
 the maximum number of carers observed provisioning the nest at any point
 during the experiment (2: 68.2%, 3: 22.7%, 4: 0.0%, 5: 9.1%; N = 44),
 ‘Watch duration’ – the time, in minutes, between first arrival and last
 feed of each watch (including display periods: mean (±SE) = 41 mins 18s ±
 125s, N = 110), ‘Brood size’, ‘Watch start time’, ‘Brood age’ and ‘Hatch
 date’, as above. Random effects were ‘Year’, ‘Nest ID’ and ‘Rowref’, which
 was an observation level random effect providing a unique identifier for
 each provisioning watch; included throughout to account for overdispersion
 in Poisson-distributed models. <strong>Does predation
 threat increase coordination?</strong> To test the prediction that
 carers increased coordination in response to a perceived predation threat,
 we first produced a series of Poisson-distributed GLMMs to compare
 coordination metrics between control watches and watches following model
 presentations. The response variables were as follows: ‘Arrival
 synchrony’, ‘Present upon arrival’, ‘Present upon feed’, ‘Feed synchrony’
 and ‘Alternation’, as described above, with ‘Treatment’ (control,
 post-dove or post-jay) being the term of interest in each model. Fixed
 effect covariates for these models were: ‘Provisioning rate’ (in this
 case: mean (±SE) = 22.94 feeds/h ± 1.06, range =
 7.94–46.42, <em>N</em> = 66), ‘Carer number’, ‘Watch duration’
 (in this case: mean (±SE) = 58 mins 36s ± 48s, <em>N</em> =
 66), ‘Brood size’, ‘Watch start time’, ‘Brood age’, ‘Hatch date’ and
 ‘Maximum possible alternation’ – a variable that reflects the disparity in
 provisioning rate within groups of carers, <em>e.g.</em> if
 two carers feed at the same rate, all feeds (except the first) are
 potentially alternated, but if one carer feeds more than all others
 combined there exist several feeds which cannot be alternated (mean (±SE)
 = 87.80% ± 1.34%). Therefore, this variable represents the percentage of
 visits performed during a watch which could theoretically be alternated
 (or synchronised) given the relative number of feeds by all carers during
 that watch (see Table S2 for further details). Random effects were ‘Year’,
 ‘Nest ID’ and ‘Rowref’. Secondly, to test whether
 treatment influenced loitering times and consequently, the total time that
 carers were nearby the nest, we built two normally distributed LMMs. The
 response variables were log-transformed ‘Loitering time’ and ‘Duration of
 time with carer(s) nearby’, with the term of interest being ‘Treatment’
 (control, post-dove or post-jay). Fixed effect covariates were:
 ‘Provisioning rate’, ‘Carer number’, ‘Watch duration’, ‘Brood size’,
 ‘Watch start time’, ‘Brood age’ and ‘Hatch date’. Additionally, to further
 investigate the time during a watch with carer(s) nearby we re-ran the
 original model with mean loitering time included as a covariate to account
 for the effect of potentially different loitering times during different
 watches; we report both model outputs. Random effects were ‘Year’, ‘Nest
 ID’ and ‘Rowref’. As the final test of this
 hypothesis, we used a series of Poisson-distributed GLMMs to compare
 ‘Provisioning rate’ and coordination metrics between successive sections
 (1<sup>st</sup>, 2<sup>nd</sup> and
 3<sup>rd</sup>) of control watches and watches following model
 removal. The response variables were: ‘Number of feeds’, ‘Arrival
 synchrony’, ‘Present upon arrival’, ‘Present upon feed’, ‘Feed synchrony’,
 ‘Alternation’ and ‘Loitering time’, with the terms of interest being
 ‘Section’ and its interaction term with ‘Treatment’, which measures
 whether watches exposed to different treatments varied in their subsequent
 coordination through time. Fixed effect covariates were: ‘Provisioning
 rate’, ‘Carer number’, ‘Watch duration’, ‘Brood size’, ‘Watch start time’,
 ‘Brood age’, ‘Hatch date’ and ‘Maximum possible alternation’ (except the
 provisioning rate and loitering time models), which was calculated for
 each individual section of the watch, <em>i.e.</em> ‘Maximum
 possible alternation’ for 1<sup>st</sup>,
 2<sup>nd</sup> and 3<sup>rd</sup> sections
 separately. Random effects were ‘Year’, ‘Nest ID’, ‘Rowref’ and ‘Watch ID’
 – a unique identifier for each watch from which a section was
 sampled.
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