Male snakes generally approached the diver, whereas few females did so (approaches recorded in 39 of 58 encounters with males vs. 35 of 100 encounters with females; Fisher Exact Test P < 0.001; see Fig. 1 and Table 1). Males were rarely observed outside the breeding season (12 of 58). The proportion of females that approached the diver did not differ significantly between breeding and non-breeding seasons (respectively, 10 of 36 encounters vs. 25 of 64 encounters; P = 0.28). Removing data for snakes that were inactive did not change these inferences (male vs. female, P < 0.001; breeding vs. non-breeding females, P = 0.08).
Approaches to divers by Olive sea snakes (Aipysurus laevis) as a function of snake sex. The graph shows the total frequency of approaches per 30-min observation period recorded over the duration of the study, divided based on whether all snakes are included (a) or only snakes that were active during the focal observation period (b).
Of snakes that approached the diver, males were more likely to do so repeatedly during the 30-min focal observation period, whereas most females only did so once (using data on mean number of approaches per individual [20 males, 34 females] to avoid pseudoreplication: Z = 3.274, P < 0.001; Fig. 2a). Hence, males cumulatively spent longer interacting with the diver over the course of the 30-min observation period than did females (using mean values per individual, Z = 3.07, P < 0.0025; Fig. 2b). The median time for each individual interaction was also higher for males than for females (excluding one outlier female, Z = 2.99, P < 0.003).
Approach frequency and duration by Olive sea snakes (Aipysurus laevis) during focal observation periods. The upper panel (a) shows the number of repeat approaches by the same individual within a 30-min focal observation session (data for snakes that did not approach are not included in the lower panels), and the lower panels show the duration of time for which snakes interacted with divers as a function of snake sex and season (breeding vs. non-breeding). Panel (b) provides data on cumulative time spent with the diver, whereas panel (c) shows mean times per approach. Boldface horizontal line shows median, box shows 25th to 75th percentile, lines are 95% confidence limits, and points show outliers. Focal animal observations: males N = 58, females N = 100, non-breeding season females N = 64, breeding season females N = 36.
For female snakes, the season (breeding vs. non-breeding) did not significantly affect the number of approaches per observation session (Z = 1.312, P = 0.19 ; Fig. 2a), the cumulative duration of interactions (Z = 1.42, P = 0.15; Fig. 2b) or the mean duration per interaction (Z = 1.06, P = 0.29; see Fig. 2c).
Males were also more likely to tongue-flick the diver (proportion of encounters per individual that included tongue-flicking: Z = 2.71, P < 0.007). Male snakes typically also tongue-flicked rapidly near the diver’s body, but only 15 males and 2 females actually tongue-flicked the diver’s wetsuit, fins or exposed skin.
Most approaches to divers were slow, and appeared to be investigatory; in contrast, some approaches involved higher speeds and substantial agitation (see Table 1 for sample sizes).
Males chased females during four focal animal observations, and 12 other non-focal males (i.e., males that were not the focus of specific observation periods) were also observed to do so. No focal females were chased (Table 1), reflecting the fact that most observations of females occurred during the non-breeding season when few males were present (above). The duration of the chase was similar in all focal observations, being 150, 160, 120 and 120 s. When chased, females swam fast, changed direction erratically and then entered crevices within the reef. They usually soon re-emerged, using a different exit, and swam above the coral for a short distance before re-entering crevices. In 10 chases the females eluded males by using this tactic. In two cases the females did not reappear, while the males reappeared 15 and 17 min later. On one occasion (23 June 1993), a group of six males chased two females (counted as a single non-focal animal observation). When more than one male chased a female, the males showed no overt reaction to each other.
Charging towards divers only occurred during the breeding season with three focal animals (1 male, 2 females) and 10 non-focal animals (6 males, 4 females) exhibiting this behaviour (Table 1). All charges by males were immediately preceded by either male-male rivalry (apparently, misdirected courtship) or after an unsuccessful chase of a female. For the two female focal animals, one charge occurred after the female had been lost from observation before re-approaching the diver. In the other case, a male was chasing the female. The other four examples of charges by females (i.e., outside focal animal observations) all involved females being chased by males.
Copulation was never observed, but on three occasions non-focal pairs were seen intertwined in a pre-copulatory position. The male positioned himself above and behind the female before quickly throwing two and a half coils around the female to hold her firmly. In each case the coils were positioned along the rear half of the female’s body. In one case the female appeared to be compliant, but the animals disengaged when disturbed by the observer. In the other two cases, the female actively dislodged the male by slithering into a crevice in the coral. Tongue-flicking to the back of the other snake was evident during pre-copulation behaviour.
Female snakes generally ignored each other, but when males sighted each other on the reef they engaged in intense interactions (except for one case after the breeding season had ended, when two males ignored each other). Three male-rivalry focal animal observations were recorded, as were 10 other non-focal rivalry events (Table 1). Duration of the interactions between males was variable, with two long bouts (130 and 135 s) and one brief bout (5 s). In each case, male snakes charged towards each other before pausing in the last 1–2 m of the approach and slowly moving into contact and commencing to tongue-flick each other intensely. This interaction would escalate into an extremely fast and highly excited contest, with each animal apparently trying to position itself above and behind the other. At the conclusion of the interaction one of the males would abruptly turn and swim slowly away.
Male snakes were observed to coil around the diver’s fin, and to strike at their reflections in camera lenses, but no bites to divers were recorded during these interactions. Even after charging, unprovoked bites never occurred during underwater observations. However, snakes readily tried to bite when harassed during capture, or (especially) when handled on the boat after capture. Male snakes can be highly persistent in their attempts to approach divers. On one occasion the diver attempted to flee from a snake by swimming vigorously for 20 min but was unable to outpace his follower. When the diver finally stopped, the snake tongue-flicked him for a minute and then left.
Source: Ecology - nature.com
