Supplementary material
Appendix S1: Summary of nest recording methodology
Appendix S2: Location of the three African zones used in the analysis.
Appendix S3: The effect of varying the time window used to calculate spring temperature.
Appendix S4: Species-specific responses of first egg date and clutch size to wintering ground
precipitation.
Appendix S5: Modelled changes in first egg date for species wintering in the arid zone.
Appendix S1: Summary of nest recording methodology
Nests monitored by NRS volunteers can be found at any stage of the nesting cycle and visit
regimes are not standardised between recorders. The laying date of the first egg (FED) is
therefore seldom known with certainty but estimates of the earliest and latest possible FED can
be generated by back-calculation. Such calculations are based on observations of clutch size and
the age or stage of the nest contents on each visit, with reference to information on typical egglaying interval, length of incubation and nestling periods and synchronicity of hatching as
extracted from the literature [1]. For the purposes of the analyses presented here, and previous
published studies that use NRS data to derive laying dates [2][3], the mid-point in the FED range
is used as the phenological metric, with nests excluded if the range exceeds 10 days.
Clutch size is defined as the maximum number of eggs recorded during any visit to the nest. It is
important to ensure that the clutch is complete on counting and nests were therefore omitted
from the analyses if they were only visited on a single occasion, if the maximum chick count on
any subsequent visit exceeded the maximum egg count or if there was any evidence of egg
dumping or brood parasitism [1]. Nests that had already failed at the time of the first visit were
also excluded.
Although variation in observer effort is not standardised (see [1] for discussion of this issue),
this should not vary systematically with either temperature or precipitation and therefore
should not affect our results. The close correlation between modelled and observed FED
(Figure 1), suggest the magnitude of potential bias is indeed small.
1
Crick, H. Q. P., Baillie, S. R. & Leech, D. I. 2003 The UK Nest Record Scheme: its value
for science and conservation. Bird Study 50, 254–270.
(doi:10.1080/00063650309461318)
2
Crick, H.Q.P., Dudley, C., Glue, D.E. & Thomson, D.L. 1997 UK birds are laying eggs
earlier. Nature 338, 526.
3
Thackeray, S.J. et al. 2010 Trophic level asynchrony in rates of phenological change for
marine, freshwater and terrestrial environments. Glob. Ch. Biol. 16, 3304–3313
(DOI: 10.1111/j.1365-2486.2010.02165.x)
Appendix S2: Location of the three African zones used in the analysis.
Figure S1: Map of Africa showing the location of the three wintering zones within which
wet-season precipitation was summarised.
Appendix S3: The effect of varying the time window used to calculate spring
temperature
Spring temperature may be defined in a number of different ways. In the paper we calculated
specific spring temperature measures for each species based upon the laying period. In order
to test the resilience of our results to how this was defined, we repeated our analysis for FED,
but with spring temperature calculated using three alternative time-periods applied across all
species (April-May, April-June and March-June). Importantly, all of the model parameter
estimates fall within the 95% confidence intervals of those presented in the paper (Table S1).
Table S1. Model outputs for FED are similar, irrespective of how spring temperature was
calculated.
Months used to
Variable significance
Parameter estimates (s.e.)
Temperature: F1,18 =139, p<0.001
-3.14 (0.27)
Precipitation: F1,18 =26.4, p<0.001
-11.09 (2.16)
Temperature : F1,18 =180, p<0.001
-3.73 (0.278)
Precipitation : F1,18 =15.1, p=0.001
-8.65 (2.23)
Temperature : F1,18 =174, p<0.001
-3.98 (0.30)
Precipitation : F1,18 =23.6, p<0.001
-10.38 (2.14)
define spring
temperature
April-May
April-June
March-June
Appendix S4: Species-specific responses of first egg date and clutch size to wintering
ground precipitation and breeding season temperature.
Species-specific responses of first egg date and clutch size to both wintering ground
precipitation and breeding season temperature were derived from a GLM in which the
dependent variable was modelled with a species-specific intercept and two interaction terms:
species identity and breeding season temperature, and species identify and wintering ground
precipitation. The species-specific responses to temperature and precipitation are shown in Table
S2a for first egg date and S2b for clutch size.
Table S2a. Species-specific slopes of first egg date in response to temperature on breeding
grounds (days/˚C) and precipitation on wintering grounds in the arid and humid zones of West
Africa (days/m). Standard errors are in parentheses. The temperature relationships presented are
derived from the model with arid zone precipitation only.
UK
Arid zone
Humid zone
Temperature
precipitation
precipitation
Species
European Turtle Dove
-4.71 (1.90)
2.06 (18.08)
7.14 (9.35)
Sand Martin
-1.81 (1.48)
-26.05 (13.33)
Barn Swallow
-2.18 (1.26)
-24.11 (10.71)
Wood Warbler
-3.52 (1.02)
-5.23 (9.61)
Common Chiffchaff
-6.37 (1.15)
-3.13 (10.98)
Willow Warbler
-3.18 (0.80)
0.43 (7.99)
Eurasian Blackcap
-5.91 (1.15)
-16.77 (11.25)
Garden Warbler
-3.29 (1.21)
-10.71 (11.53)
Lesser Whitethroat
-0.37 (1.56)
-10.00 (13.52)
Common Whitethroat
-4.01 (1.45)
-19.53 (13.29)
Sedge Warbler
-3.04 (1.27)
-13.39 (11.03)
Eurasian Reed Warbler
-4.64 (0.92)
-25.08 (8.22)
-9.25 (4.47)
Spotted Flycatcher
-1.42 (1.08)
-0.53 (9.68)
-4.71 (5.38)
Pied Flycatcher
-4.54 (0.47)
-3.28 (4.58)
-0.021 (2.50)
Common Redstart
-5.47 (0.82)
-17.32 (7.68)
Whinchat
-1.98 (1.11)
-6.73 (10.35)
Wheatear
-3.89 (1.28)
-36.4 (13.65)
Yellow Wagtail
-5.41 (1.26)
-8.96 (12.57)
Tree Pipit
-2.00 (1.54)
-12.03 (13.59)
1.56 (5.30)
0.44 (4.36)
7.56 (6.64)
-9.79 (5.40)
5.30 (7.34)
Table S2b. Species-specific slopes of clutch size in response to temperature on the breeding
grounds (eggs/˚C) and precipitation on wintering grounds in the arid and humid zones of West
Africa (eggs/m). Standard errors are in parentheses. The temperature relationships presented are
derived from the model with arid zone precipitation only.
UK
Arid zone
Humid zone
Temperature
precipitation
precipitation
Species
European Turtle Dove
-0.0070 (0.048)
0.41 (0.47)
-0.15 (0.15)
2.92 (0.79)
Barn Swallow
-0.023 (0.030)
-0.15 (0.25)
Wood Warbler
0.036 (0.054)
-0.53 (0.53)
0.0024 (0.047)
-0.23 (0.45)
Willow Warbler
0.034 (0.047)
-0.0018 (0.46)
Eurasian Blackcap
0.029 (0.041)
-0.10 (0.41)
Garden Warbler
0.017 (0.050)
0.028 (0.49)
-0.011 (0.065)
0.49 (0.54)
0.078 (0.045)
-0.36 (0.41)
-0.0036 (0.049)
-0.71 (0.40)
0.020 (0.032)
0.17 (0.29)
0.17 (0.17)
-0.036 (0.038)
0.021 (0.35)
-0.016 (0.21)
Pied Flycatcher
0.21 (0.031)
-0.55 (0.30)
-0.45 (0.18)
Common Redstart
0.20 (0.046)
-1.15 (0.43)
Whinchat
0.021 (0.076)
0.21 (0.63)
Wheatear
0.079 (0.066)
1.18 (0.67)
Yellow Wagtail
-0.19 (0.077)
-0.81 (0.80)
Tree Pipit
0.057 (0.061)
1.48 (0.57)
Sand Martin
Common Chiffchaff
Lesser Whitethroat
Common Whitethroat
Sedge Warbler
Eurasian Reed Warbler
Spotted Flycatcher
0.083 (0.23)
-0.34 (0.31)
-0.40 (0.27)
-0.22 (0.28)
0.35 (0.31)
0.63 (0.34)
Appendix S5: Modelled changes in first egg date for species wintering in the arid zone.
a)
b)
Figure S2. Observed and modelled changes in first egg date across nine arid zone migrant
species between 1966-2011. Plot shows predictions from models containing a) arid zone
rainfall or b) UK spring temperature alone, plus a full model containing both terms that is
identical across both panels.