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Local and Global Climate Effects on Storm Petrel Demography
Table 4. Results of the GOF test for the single-state model.
Test component X2 d.f. P
Global test 233.82 61 0
162.40 10 0
Test 3.SR (test for transience) 9.23 9 0.42
71.42 51 0.03
Test 2.CT (test for trap-dependence)
Considering single and additive effects of group (sex) and
Global test (corrected for transience) individual covariates (local climatic descriptive indexes) we found
that recruitment differed between sexes with males recruiting
doi:10.1371/journal.pone.0094526.t004 earlier. Pre-breeding season conditions with colder springs was
negatively affecting recruitment (Table 7), whereas survival in first
sexing. There were no ethics committee approval requirements to year after fledging and adults was affected positively by warm
carry out this project due to the minimum handling of the breeding-period conditions and negatively by abundant rainfall
individuals that was carried out according to Italian and Sicilian explaining the correspondence of the drops in figure S3b with
region legislation (LN 157/92, LR 105/99 and LR 74/2012) by higher B and WSR and lower PB values in figure S3a.
certified ringers authorized by the Institute for Research and
Environmental Protection (ISPRA) to handle adults and chicks. After defining environmental covariates as SST and CHL PCA
factors (Table 8) we obtained cues on their effects on adults
Results survival and encounter probability. We obtained that SST and
CHL, are not correlated (Spearman R = 20.336, p = 0.321, figure
Individual covariates were defined and we made sure that the S4a) giving strength to the models involving them both. We can
covariates used as integrative climatic indexes were not inter- confirm that SST and CHL may influence storm petrels ecology
correlated (Table 5). WSR is represented by the first principal during winter time [39]. A higher sea surface temperature and
component explaining 86,49% of the total variance (figure S2a). lower chlorophyll concentration were associated with lower
PB is represented by principal components 1 and 2 (PC1PB and encounter rates during the subsequent breeding period (figure
PC2PB hereafter). The first factor, explaining 42.57% of the total S4b) and a higher encounter rate after favourable years. Winter
variance, is correlated positively with temperature and negatively sea conditions in different areas of the Mediterranean affected the
with rainfall, whereas factor 2, explaining 32.19% of the total survival of the Marettimo birds. In particular, we found that
variance, is positively correlated with the NAO (figure S2b). periods of low productivity (high SST and low CHL) in the
During the pre-breeding period, warm and dry conditions are Alboran Sea negatively influenced adult survival (Table 9). In fact
associated with a high NAO, whereas cold and wet conditions are we found a significant effect of Alboran Sea conditions
associated with a low NAO. B is represented by the first principal (AIC = 4175.04 and compared to time effect: DAIC = 1.37, AIC
component (PC1B hereafter, explaining 45.97% of the total weight 0.335, F2,15 = 14.385, p = 0.004), with 62% of the temporal
variance), which is positively correlated with rainfall and the NAO. variance in adult survival explained by the Alboran sea-surface
B is also represented by the second principal component (PC2B temperature and chlorophyll variation. When considering neigh-
hereafter, explaining 33.42% of the total variance; figure S2c), bouring models (SST and CHL covariates considered separately)
which is positively correlated with temperature. These results we obtained that SST has a stronger effect (AIC = 4175.04 and
indicate that during the breeding period (i.e., the chick-rearing compared to time effect: DAIC = 1.37, AIC weight 0.335,
period), warm and dry conditions are associated with a low NAO, F2,15 = 14.385, p = 0.004, R2 = 62%) than CHL (AIC = 4183.76
and cold and wet conditions are associated with a high NAO. and compared to time effect: DAIC = 10.09, AIC weight 0.001,
Trends of individual and environmental covariates are summa- F2,15 = 5.560, p = 0.040, R2 = 38%). Thus SST alone explains a
rised in figures S3a and S4a. large percentage of the total variation on adult survival. This
finding suggested that the Alboran Sea was the most probable
By fixing to 1 the potential age of becoming a breeder (full wintering site, and that environmental conditions there affect
recruitment) or the age at which all the birds of the colony may be overwintering conditions in the Mediterranean storm petrel
considered breeders, we found that the 2nd year is the age at which population of Marettimo.
most birds start to recruit with a small difference with the 3rd year
of age (AIC = 3176.14 and AIC weight = 0.342; DAIC = 1.60 and Discussion
AIC weight = 0.154 for 3rd year of age, but see Table 6 for more
details) suggesting that at the 2nd and, in smaller proportion, at the Recruitment age determination
3rd year of age are Marettimo’s storm petrels are becoming Petrels are long-lived organisms with delayed sexual maturity. A
breeders. In table 6 both the results of full recruitment age
identification and of sex effect on recruitment age are reported. prolonged pre-recruitment period and extended lifespan provide
The best model considered constant annual survival trends, seabirds with sufficient time to explore marine habitats and to
whereas recruitment was affected by sex, with males recruiting gather crucial information about prey patches and the spatio-
earlier than females (see also figure S5). Recruitment probability in temporal variability in their availability [5]. Although we found
males is slightly higher than in females during the first 3 years of survival values similar to those reported by a previous study [32],
age (in average 4.8%), this difference is no more perceivable from the recruitment age for the Marettimo colony was lower, perhaps
the 4th year. Full breeding age in the Marettimo colony is at the 6th due to the greater number of individuals located in this colony and
year of age (Table 3). the much greater intra-individual variation that resulted. Mar-
We found high mortality in juveniles. The average first year
survival after fledging was 0.222 (60.093) and adults survival was
0.923 (60.060). Survival was highly variable (figure S3b),
especially for juveniles.
PLOS ONE | www.plosone.org 5 April 2014 | Volume 9 | Issue 4 | e94526
