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Conservation Physiology • Volume 3 2015 Research article

Figure 1: Experiment 1. Individual stress response: comparison of corticosterone (CORT) concentrations in the same individual of disturbed and Downloaded from http://conphys.oxfordjournals.org/ by guest on March 12, 2016
not-disturbed groups at 0 and 30 min in 2011 (a) and in 2012 (b), considering the control group of experiment 3. The white boxplots and circles
refer to the inner colony, while red boxplots and triangles refer to the outer colony.

Experiment 2: population stress response factors treatment and sub-colony. This analysis showed no
effect of either treatment (F2,39 = 1.567, P = 0.390) or sub-
In both the outer and the inner sub-colonies, the stress colony (F1,39 = 0.113, P = 0.768) but a significant interaction
response did not change over time (time, F8,53 = 0.669, effect (F2,39 = 3.963, P = 0.027), showing that the effect of
P = 0.072; Fig. 2), but the curve was lower in the disturbed treatment was different between the two sub-colonies
sub-colony (sub-colony, F1,53 = 13.4, P < 0.001), while the (Fig. 3). Therefore, we ran an analysis of variance for the two
interaction between time and sub-colony was not significant sub-colonies separately, with treatment as the only factor.
(time × sub-colony, F8, 53 = 0.909, P = 0.52). There was no significant effect of treatment on CORT in the
non-disturbed sub-colony (treatment, F2,19 = 0.161,
The non-disturbed sub-colony showed an increasing trend P = 0.852; Fig. 3a), whereas there was a highly significant
in the stress response after 25 min of human disturbance, with effect of treatment in the sub-colony exposed to tourists
a peak of 50.49 ng/ml CORT concentration. In contrast to the (treatment, F2,20 = 9.53, P = 0.001). A post hoc analysis with
non-disturbed sub-colony, the disturbed sub-colony did not Dunnet’s test showed that ACTH-treated birds tended to
show any fluctuation in stress response across time. have a higher CORT compared with control birds (P = 0.06;
Fig. 3b), whereas DEX-treated animals had lower CORT
Experiment 3: adrenocorticotrophic than control birds (P = 0.029; Fig. 3b). Overall, DEX-treated
­hormone and dexamethasone birds showed lower levels of CORT, but in the non-disturbed
challenge test group there was no suppression of the stress response,
whereas this is evident in the disturbed group.
We first ran a global full-factorial GLM analysis, including
time as a within-subjects factor and treatment, sub-colony Discussion
and sex as between-subjects factors, and included all interac-
tion effects. Only time (F1,33 = 23.092, P < 0.001), treatment Human presence can be stressful to breeding populations
(F2,33 = 5.502, P < 0.01) and treatment × sub-colony because it can be perceived as potential predation, which in turn
(F2,33 = 3.303, P < 0.05) provided significant results. In addi- may have dramatic consequences (Lishman, 1985; Culik et al.
tion, Student’s paired t-test showed no difference for CORT 1990; Culik and Wilson, 1991; Ellenberg et al., 2007; Seddon
at time 0 (t29 = 1.8, P = 0.075) and 30 min (t19 = 1.1, P = 0.28) and Ellenberg, 2008). However, storm petrels (Hydrobatidae)
between uninjected birds and those injected with saline; apparently lack anti-predator behaviour, making them particu-
therefore, we pooled the latter two groups. As already larly defenceless to predators (Burger and Gochfeld, 1993; Sirot,
reported above, we observed no significant differences in the 2006). In this study, we investigated whether storm petrels
individual stress response of control and saline-injected birds breeding in a cave that is regularly disturbed by tourist boats
between disturbed and non-disturbed colonies. We ran a sec- during the breeding season are chronically stressed.
ond analysis for CORT at time 30 min including only the

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