Electronic Supplementary Material for:
Vögeli, M. et al. “Predation of experimental nests is linked to local population
dynamics in a fragmented bird population”
Characteristics of artificial and natural nests
Acknowledging the methodological shortcomings of artificial nest experiments, we
minimized them as much as possible with an accurate experimental design. Orientation
and visibility of nests are the most important microhabitat cues for larks in semiarid
shrub steppe related to predation pressure (Yanes et al. 1996; Suárez et al. 2009).
Hence, both artificial and natural nests (Supplementary Figure 1) were characterized by
measuring these two characters (Supplementary Table 1). We recorded their orientation,
divided into eight classes (North 0°, Northeast 45°, East 90°, Southeast 135°, South
180°, Southwest 225°, West 270°, and Northwest 315°), whereas their visibility was
estimated as the proportion of the nest area that could be seen by sight from ca. 1.5 m
straight above the nest (in %, steps of 10%).
The natural Dupont’s lark nests (N = 27) were found at the base of a shrub or a
perennial grass tussock, with a visibility between 0 and 100% (mean = 46%), and NE, E
and SE were the main orientation classes (67% of all surveyed nests). The nests’
internal diameter ranged between 7 and 8 cm, whereas the nest cup depth was between 5
and 6.5 cm.
The artificial nests were made of Lygeum spartum, one of the most abundant
plant species in the study area. Their internal diameter and cup depth were within the
range of the values of natural Dupont’s lark nests. For the artificial nest experiment,
they were placed with a visibility from 0 to 100% (mean = 40%), and 267 of them
(60%) were NE, E, and SE oriented. The visibility and orientation did not differ
between artificial and natural nests (Mann-Whitney tests, N = 361, both P not
significant). The nests were aired outside, and included exposure to sunlight and rain,
for at least three weeks before being placed and baited with a fresh quail (Coturnix
japonica) egg. Nests and eggs were manipulated with gloves to avoid human olfactory
cues that might be used by predators. The whole artificial nest experiment was carried
out by M.V. to minimize any investigator effect.
Survival and population viability analyses
Dupont’s lark population growth rates (λ) of each local population were calculated with
VORTEX (Miller & Lacy 2005). We included life history parameter values (see below)
derived directly from each local population, acknowledging its spatial context as
described in Laiolo et al. (2008). Very conservative simulations were set up, supposing
no catastrophes nor inbreeding depression occurring, and all males reproducing. We run
simulations 100 times with a time frame of 100 years, whereas extinction was defined
as only one sex remaining in the population.
Apparent survival probabilities were estimated with MARK 4.3 (White &
Burnham 1999), based on acoustic mark-recapture data of 208 male individuals (see
Vögeli et al. 2008 for more details). We started the survival analysis from the fully time
dependent Cormack-Jolly-Seber model for open populations (Lebreton et al. 1992),
where apparent survival () and reencounter probabilities (p) were time-specific for
each population size (classes of <10, 10-30, >30 occupied territories). After testing the
goodness of fit of this global model with U-CARE 2.3.2 (Choquet et al. 2009; global
test, one-tailed directional test for transience, and signed test for trap-dependence: all P
> 0.05), we implemented constant and time dependent model structures in MARK. The
survival estimate of the most parsimonious model using the Akaike’s Information
Criterion corrected by sample size (AICc) for model selection (Burnham & Anderson
2002) did not vary among population size classes (=0.46 ± 0.08SE). Hence, we
employed identical mortality rates (54%) for all local populations.
The Dupont’s lark is monogamous, both sexes breed from the first year on, and
we set the maximum age of reproduction of 15 years with 10 offspring as a maximum
number of progeny and a 50:50 birth sex-ratio (Cramp 1988).
When measuring reproductive success is difficult and invasive, as it is the case of
the secretive and imperilled Dupont’s Lark (Laiolo & Tella 2006), the yearling to adult
male ratio is usually used as a surrogate of productivity (Vaughan et al. 2005; De Leo et
al. 2007). The territorial calls of Dupont’s lark yearlings can be distinguished during
summer and early autumn from those of adults by the presence of quavering harmonics,
and relatively amorphous notes revealed by spectrograms (Laiolo & Tella 2005; Laiolo
et al. 2007; Laiolo et al. 2008). The call learning process in Dupont’s lark yearlings lasts
approximately 30 days, and leads to a gradual improvement of their call quality. Hence,
we quantified the relative proportion of yearlings calling in the whole population of
vocalizing males in the summer-autumn period, and thus obtained an estimate of
yearling to adult male ratio (Laiolo & Tella 2007; Laiolo et al. 2008). We assumed all
recorded yearlings to be born in the same local population. Only very few immigration
events were effectively detected, and discarded since we were able to identify males
uttering a territorial call typical of a different local population (Laiolo & Tella 2007).
Eventually, these proportions were used to adjust the maximum, theoretic productivity
values: Productivity was calculated as twice the species’ average clutch size (2.76 eggs
per clutch, two clutches per breeding season are laid; Cramp 1988) corrected by the
proportion of juveniles to adults detected over three consecutive breeding seasons (20042006) in each local population. Given the poor information available on breeding
success of this species (Cramp 1988), we built different scenarios varying the
percentages of successful breeding females with 10%-steps from 40 to 100%.
Dispersal probabilities were set at 10% among populations separated by less
than 20 km (Vögeli et al. 2010). The initial size of local populations was determined by
mapping of male territories (Vögeli et al. 2010), and the carrying capacity was obtained
by multiplying the maximum density observed in the metapopulation (4.8
territories/10ha) with the respective size of the local populations (Vögeli et al. 2010).
We used λ to characterize population viability as it covaried with other
population viability indices, such as the exponential rate of increase, the median
extinction time and the mean extinction time (r > 0.53, all P < 0.05). We employed in
subsequent analyses the average annual rate of population change λ calculated in the
seven different simulation scenarios (from 40 to 100% females breeding successfully).
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Supplementary Figure 1. In situ comparison of a natural Dupont’s lark nesting site
(A.1) and nest (A.2) with a nesting site (B.1) and nest (B.2) employed in the artificial
nest experiment.
Supplementary Table 1. Characteristics of the nests employed for the artificial nest
experiment and the natural Dupont’s lark nests found in our study area.
Population
Sample
size
Orientation (in degrees)
Visibility (in percents)
Min.
0
90
0
0
90
0
0
0
0
0
0
90
0
0
45
45
Max.
270
135
315
315
225
270
315
270
315
315
270
270
315
225
270
315
Mean
33
34
46
42
35
43
35
30
35
30
36
45
39
43
38
53
Min.
0
0
0
0
10
0
0
0
0
0
0
20
0
20
10
20
Max.
80
70
90
90
80
90
80
70
80
60
100
90
90
70
70
90
0
315
46
0
100
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
30
6
42
24
18
29
36
12
23
18
12
6
48
6
12
12
Mean
138
120
113
118
145
144
181
116
106
162
116
158
121
128
135
173
Natural nests
27
108
Supplementary Table 2. Detailed characteristics – including population growth rates
(λ) – of the 16 local populations where artificial nest predation experiments were
conducted (circled patches in Fig. 1). The information on nests set out/predated refers to
the artificial nests used for the experiment.
Population
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Total
Territories
25
6
40
50
12
30
42
2
30
7
6
5
36
7
2
2
302
Size (ha)
158.7
38.2
510.1
771.6
260.8
240.0
486.4
27.0
126.7
42.1
19.4
23.4
370.2
14.6
20.8
46.6
3156.6
λ
0.95
0.90
1.03
0.95
0.64
0.86
0.90
0.63
0.95
0.68
0.98
0.97
1.07
0.73
0.00
0.00
Nests set out
30
6
42
24
18
29
36
12
23
18
12
6
48
6
12
12
334
Nests predated
20
3
36
10
15
24
15
7
4
5
4
3
26
5
7
12
196
%
66.7
50.0
85.7
41.7
83.3
82.8
41.7
58.3
17.4
27.8
33.3
50.0
54.2
83.3
58.3
100.0
58.7