ESM: Thompson et al. Blackmail by fledgling location
Electronic supplementary material
The influence of fledgling location on adult provisioning: a test of the blackmail hypothesis
Alex M. Thompson, Nichola J. Raihani, Philip A.R. Hockey, Fiona M. Finch, Adam Britton and Amanda
R. Ridley
PREDATORS
There are a variety of predators at the study site: the main aerial predators are raptors (gabar
goshawk Micronisus gabar, pale chanting goshawk Melierax canorus) [1] and the main terrestrial
predators are mammals (yellow mongoose Cynictis penicillata, slender mongoose Galerella
sanguinea, meerkat Suricata suricatta) [1,2]. Reptiles (rock monitor Varanus albigularis, Cape cobra
Naja nivea, puff adder Bitis arietans,) pose a lesser threat.
METHODS
a) Additional information about focals
Focal observations were not carried out during inter-group-interactions or immediately after major
predator alarms, and focals were terminated if one of these events occurred after the focal had
started. Focal data collection was paused when the bird was obscured from view and resumed when
the bird was again in clear view. If the break in observation was longer than 5 minutes the focal
observation was aborted.
b) Equipment
All sound was recorded using a RØDE™ NTG-2 shotgun microphone onto a Microtrack II digital sound
recorder. All playbacks were group-specific to avoid the group responding to the playback as if it
were a neighbouring group. Playbacks were created using Raven Pro 1.3© (Cornell Lab of
Ornithology, Ithaca, NY, USA) and normalized to levels appropriate for the experiment.
c) Statistical analyses
We created a series of linear mixed models (LMMs) with normal distributions and identity link
functions to investigate the response terms of interest. The effects of fixed terms were considered
using maximum-likelihood estimation, and random terms were included to account for the potential
influence of repeated measures. We used the Akaike’s Information Criterion for small datasets (AICc)
[3] as our model selection criteria [4,5]. We created a set of models to investigate a priori
hypotheses and a basic model that contained only the constant, random terms and residual
variance. Co-linearity was checked for all explanatory terms and correlated terms were never
included in the same model. We then ranked the models in order of their AICc values: models with
lower AICc values were considered to have more explanatory power. Overall the model with the
highest Akaike weight (wi) and lowest AICc value was considered the best model, but all models
within ΔAICc <5 were considered to have at least some support [4]. When more than one model
appeared to have some support (i.e. ΔAICc <5), the importance of explanatory terms was evaluated
by calculating the predictor weight [6] for each term.
RESULTS
a) Candidate models tested
For tables S1-S3: Deviance = -2 log-likelihood output of each model; K = number of parameters
tested in each model; AICc = Akaike information criterion for a small data sets; ΔAICc = the models
AICc minus the minimum AICc among candidate models. For each candidate model: Basic = basic
model with no predictor terms, only constant, the random terms and residual variance (σ²); Fage =
ESM: Thompson et al. Blackmail by fledgling location
fledgling age (days post hatching); Anum = adult number (individuals >1 year old); Fnum = fledgling
number; ADFL = adult:fledgling ratio; dCov = distance to cover (m); trPrv = provision rate while in
tree (g/min); grPrv = provisioning rate while on the ground (g/min); toPrv = total provisioning rate
(g/min); Loc = fledgling location (ground or tree).
Table S1. Difference in response time to alarm calls
N=68
Explanatory terms
Fage + Anum
Fage
Fage + Anum +
Fnum
Basic
Fage + Anum + dCov
Anum
Fage + Fnum
Fage + ADFL
Fage + dCov
Fnum
ADFL
Anum + Fnum
dCov
Anum + dCov
Fage + dCov + Fnum
Fage + dCov + ADFL
dCov + Fnum
dCov + ADFL
Fage + Fnum + dCov
Deviance
-40.53
-37.04
-36.07
K
4
3
5
AICc
-35.90
-32.67
-31.10
ΔAICc
0.00
3.23
4.79
-34.23
-33.51
-32.85
-32.64
-32.19
-29.84
-29.08
-28.89
-27.9
-27.28
-26.01
-25.41
-25.04
-22.13
-22.02
-21.14
2
5
3
4
4
4
3
3
4
3
4
5
5
4
4
5
-30.05
-28.54
-28.48
-28.01
-27.56
-25.21
-24.71
-24.52
-23.27
-22.91
-21.38
-20.44
-20.07
-17.50
-17.39
-16.17
5.85
7.35
7.42
7.89
8.34
10.69
11.19
11.38
12.63
12.99
14.52
15.45
15.82
18.40
18.51
19.72
All LMMs were fitted with a normal distributions and identity link functions, individual identity
was included as a random term to account for repeated measures.
ESM: Thompson et al. Blackmail by fledgling location
Table S2. Provisioning rate
N=472
Explanatory terms
Loc + Fage
Loc + Fage + Anum
Loc + Fage + Fnum
Loc + Fage + ADFL
Loc*Fage
Loc*Fage + Fnum
Loc*Fage + ADFL
Loc
Loc*Fage + Anum +
Fnum
Loc + Anum
Loc + Fage
Loc + ADFL
Loc + Anum +
Fnum
Fage + Anum
Fage + Fnum
Fage + ADFL
Fage + Anum +
Fnum
Basic
Anum
Fnum
ADFL
Anum + Fnum
Deviance
-1324.58
-1318.35
-1315.58
-1314.79
-1313.13
-1304.13
-1303.34
-1297.74
-1297.85
K
6
7
7
7
6
7
7
5
8
AICc
-1318.40
-1312.11
-1309.34
-1308.55
-1306.95
-1297.89
-1297.10
-1291.61
-1291.54
ΔAICc
0.00
6.29
9.06
9.85
11.45
20.51
21.30
26.79
26.86
-1292.7
-1289.07
-1288.33
-1283.97
6
6
6
7
-1286.52
-1282.89
-1282.15
-1277.73
31.88
35.51
36.25
40.67
-1225.53
-1222.54
-1221.64
-1216.44
5
5
5
6
-1219.40
-1216.41
-1215.51
-1210.26
99.00
101.99
102.89
108.14
-1210.44
-1205.17
-1201.73
-1200.92
-1196.39
3
4
4
4
5
-1204.39
-1199.08
-1195.64
-1194.83
-1190.26
114.01
119.32
122.76
123.57
128.14
All LMMs were fitted with a normal distributions and identity link functions, individual and
group identity were included as random terms to account for repeated measures.
ESM: Thompson et al. Blackmail by fledgling location
Table S3. Proportion of time fledglings spent on the ground
N=307
Explanatory terms
Fage + Anum
Fage + Anum +
Fnum
Fage + ADFL
Fage
Fage + Fnum
trPrv
trPrv + ADFL
trPrv + Fnum
Anum
grPrv
Basic
toPrv
grPrv + ADFL
adfl
grPrv + Fnum
Fnum
Deviance
-609.78
-603.65
K
5
6
AICc
-603.58
-597.37
ΔAICc
0.00
6.21
-602.67
-601.44
-596.12
-432.56
-426.2
-425.35
-398.93
-385.31
-383.93
-382.72
-380.34
-378.86
-378.74
-377.43
5
4
5
4
5
5
4
4
3
4
5
4
5
4
-596.47
-595.31
-589.92
-426.43
-420.00
-419.15
-392.80
-379.18
-377.85
-376.59
-374.14
-372.73
-372.54
-371.30
7.12
8.27
13.66
177.15
183.58
184.43
210.78
224.40
225.73
226.99
229.44
230.85
231.04
232.28
b) Best models from each candidate model set
Table S4: Factors affecting the difference in response times between adults and fledglings to alarm
calls.
Explanatory terms
a) Fledgling age (days) + adult
number
b) Fledgling age (days)
c) Fledgling age (days) + adult
number + Fledgling number
χ²
25.65
10.57
22.47
26.21
9.99
0.79
wi
0.69
0.14
0.06
Effect ± standard error
Fage:
-0.013 ± 0.003
Anum:
0.167 ± 0.051
-0.013 ± 0.003
Fage:
-0.013 ± 0.003
Anum:
0.200 ± 0.063
Fnum
-0.064 ± 0.073
Results for the best LMMs (n=68) in table S1 with normal distributions and identity link
functions. The response term was the log10 of the difference in response time between adults and
fledglings, the random term was individual identity (n=21 individuals).
ESM: Thompson et al. Blackmail by fledgling location
Table S5: Factors affecting provisioning rate (g/min) to fledglings
Explanatory terms
Location + Fledgling age (days)
χ²
116.2
wi
0.939
44.19
Effect ± standard error
gr:
0.000 ± 0.000
tr:
-0.139 ± 0.013
Fage:
-0.004 ± 0.001
Results for the best LMM (n=472) in table S2 with normal distributions and identity link
functions. The response term was the square root of provisioning rate (g/min), the random terms
were individual (n=82 individuals) and group identity (n=15 groups).
Table S6: Factors affecting the proportion of observation time that fledglings spend on the ground
Explanatory terms
Fledgling age (days) + adult
number
χ²
374.27
19.84
wi
0.96
Effect ± standard error
Fage:
0.022 ± 0.001
Anum:
-0.039 ± 0.009
Results for the best LMM (n=307) in table S3 with normal distributions and identity link
functions. The response term was the arcsine-square-root of the proportion of time that fledglings
spend on the ground, the random terms were individual (n=93) and group identity (n=15 groups).
c) Predictor weights for each candidate model set
Table S7: Predictor weights for all variables investigated in each candidate model set
Model
Predictor terms
Weight
a) Fledgling response Fledgling age (days)
0.975
to alarm calls
Adult number
0.791
Fledgling number
0.081
Adult:fledgling ratio
0.013
Distance to cover (m)
0.023
b) Provisioning rate
Location (ground or tree)
1.000
(g/m)
Fledgling age (days)
1.000
Adult number
0.040
Fledgling number
0.010
Adult:fledgling ratio
0.007
c) Proportion of time Fledgling age (days)
1.000
on the ground
Adult number
0.958
Fledgling number
0.042
Adult:fledgling ratio
0.026
Tree prov. rate (g/min)
3.33x10-39
Total prov. rate (g/min)
4.69x10-50
Ground prov. rate (g/min)
2.00x10-50
Predictor weights for the all variables investigated in LMMs. Predictor weights for each variable were
calculated by summing the Akaike weights for each model that contained that variable [6]. Variables
that appear in all the top models will have weights that tend towards 1 and if variables only appear
in unlikely models their weight will tend towards 0 [6]. All variables deemed to be important are in
bold.
ESM: Thompson et al. Blackmail by fledgling location
Table S8: Results from paired analyses investigating the effects of increasing perceived predation
risk
Variables
Time on ground (%)
Terrestrial prov. (g/min)
Arboreal prov. (g/min)
Lead calls (s)
Before
33.59 ± 4.73
0.13 ± 0.02
0.017 ± 0.003
3.03 ± 0.78
Control
During
41.98 ± 4.82
0.12 ± 0.02
0.025 ± 0.007
1.76 ± 0.47
p-value
0.286
0.378
0.869*
0.120
Experimental
Before
During
44.90 ± 4.26
27.51 ± 3.12
0.14 ± 0.02
0.27 ± 0.06
0.022 ± 0.007
0.030 ± 0.009
1.98 ± 0.30
7.07 ± 1.06
Table S8 gives the means and standard errors for the behaviours investigated: time that fledglings
spent on the ground (%); terrestrial provisioning rate (g/min) to fledglings; arboreal provisioning rate
(g/min) to fledglings; and time that adults spent giving lead calls to terrestrial fledglings (%). Two
treatments: control, with heterospecific contact calls; experimental, with heterospecific alarm calls.
All paired analyses were conducted using paired t-tests, except for those labelled with * which were
conducted using Wilcoxon Matched-pairs tests. All significant results (p<0.05) are in bold. N=24
pairs.
Table S9: Results from paired analyses investigating the difference in provisioning behaviour
Control
Variables
Experimental
Before
During
p-value
Before
During
p-value
Biomass (%)
39.92 ± 8.32
52.96 ± 7.14
0.064
34.40 ± 6.84
45.17 ± 7.51
0.112
Feeds (%)
37.28 ± 8.03
47.19 ± 6.81
0.166
30.90 ± 6.34
41.11 ± 7.25
0.116
Table S9 gives the means and standard errors for the proportion of biomass fed to fledglings by
dominants and the proportion of feeds to fledglings by dominant individuals. All p-values were
generated by conducting using paired t-tests to compare feeding behaviours before and after
control and experimental playbacks.
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(doi:10.1098/rsbl.2007.0325)
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Behavioral Ecology and Sociobiology 65, 23–35. (doi:10.1007/s00265-010-1029-6)
p-value
<0.001
0.002*
0.564*
<0.001
ESM: Thompson et al. Blackmail by fledgling location
6
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