Yoshihisa Mori

Diving Performance of Adelie Penguins in Relation to Food Availability in Fast Sea-Ice Areas: Comparison between Years

Between-year variation in adelie penguin Pygoscelis adeliae foraging behaviour was studied using time-depth recorders at a colony in Lutzow-Holm Bay, Antarctica in the summers of 1990 and 1991 in areas where fast sea-ice remained. Poor chick survival and growth, long foraging trip duration and low meal delivery rate indicate that food availability was poor in 1991 when compared to 1990. However, mass of food brought to chicks per shore visit and rate of decrease of parental mass did not differ between these years. In 1991, the penguins on average dived deeper (12.3 ± 4.2m) and for longer durations (1.9 ± 0.2 min) than they did in 1990 (7.1 ± 1.6 m depth and 1.5 ± 0.2 min duration)

Urban noise and male density affect songs in the great tit Parus major

Since ambient noise interferes with sound transmission, urban noise can affect the acoustic structure of birdsong. Previous studies have examined song features (e.g. high minimum frequency) in urbanised areas; however, these studies did not exclude the effects of other factors. For example, the intensity of male–male competition is known to affect song structure. In 22 urban parks in Tokyo, Japan, we measured the effects of noise level and male density, an indicator of the intensity of competition among males, and examined the relationship between these factors (noise and male density) and song structure of the great tit, Parus major. We found that males in noisier parks sang songs with higher minimum frequencies, more phrases and longer durations. The frequency shift appeared to mitigate the acoustic masking of songs by low-frequency background noise, as has been shown in previous studies. Songs with repeated phrases and of longer duration are likely to be more detectable for receivers under noisy conditions. In addition, we found that male density tended to affect the minimum frequency and the number of phrases in, but not the lengths of, their songs. Overall, both noise and male density affected the song structure of great tits in urban habitats.

DEFINING DIVE BOUTS USING A SEQUENTIAL DIFFERENCES ANALYSIS

Bout analysis searches for a bout-ending criterion (BEC) to determine whether successive events are part of the same bout. Methods widely used for finding the BEC are logsurvivorship, log-frequency, and log-normal analyses. These analyses are based on the assumption that frequency distributions of event intervals can be described by two or three random distributions, and that the mean interval within a bout is common to all other bouts. Diving typically occurs in bouts. Since a dive bout is a sequence of complex behaviours in which the duration, depth, and interval between dives may all be adapted for optimal foraging, it is unreasonable to assume that the mean dive interval within a bout is common to all other dive bouts. Furthermore, one should not assume that dives might be split into bouts based only on dive interval without considering other characteristics, such as dive depth. Here we propose a new method, the sequential differences analysis, to find the BEC for dive bout analysis. This method has two features: (1) the frequency of differences in dive characteristics between two successive dives is used instead of the frequency of dive intervals, and (2) along with the dive interval, other characteristics are used to determine the BEC. Compared with the log-frequency analysis using dive intervals, the sequential differences analysis results in bouts with less variation (i.e. a smaller coefficient of variation) in dive characteristics, and a smaller number of dives within a bout. This suggests that our method splits dive sequences into bouts at a finer scale than the existing method. The sequential differences analysis is useful for dividing a sequence of complex behaviours with several characteristics into more meaningful bouts.

Seasonal Activity Pattern of a Nocturnal Fossorial Snake, Achalinus spinalis (Serpentes: Xenodermidae)

Abstract: Ecological information on inconspicuous, small, fossorial, and nocturnal snakes is very limited. We investigated seasonal activity patterns of Achalinus spinalis, a small, nocturnal, and fossorial snake endemic to East Asia. We also examined factors that affect its activity pattern above the ground. The seasonal activity of the snake showed a bimodal pattern, which peaked in early summer and autumn. Males were more active than females in early summer. Gravid females were captured in May and July, but we did not find any gravid females in June. Effect of temperature on the snake activity was found in autumn, and a positive relationship between snake activity and prey (earthworms) abundance was detected in early summer. The prey items were confirmed from eight snakes, and half of the diet records were obtained in June. The annual activity pattern of A. spinalis was concordant with that in other species of temperate snakes. However, the activity of juvenile snakes is considerably different from that of temperate snakes: hatchlings of A. spinalis remained underground and did not actively move after hatching until emergence from their first hibernation early the following summer.

Cost of complex behaviour and its implications in antipredator defence in orb-web spiders

Complex behaviour may incur a cost. We assumed here that web-building behaviour for two species of orb-web spider, Cyclosa argenteoalba and Eriophora sagana, was more complex when their webs were asymmetric from top to bottom than when their webs were symmetric. The rationale for this assumption was that, while spiders have to adjust their spiral building behaviour in different web sectors to build asymmetric webs, they do not have to make these adjustments for symmetric webs. To estimate the costs involved in building more asymmetric webs, we measured the time taken for spiders to build orb-webs with various up-down size asymmetries and used this as a measure of the complexity of web-building behaviour. The results showed that the spiders required more time to lay the spiral threads as their webs became more asymmetric even when the length of spiral threads was the same, suggesting a time cost of processing complex information. Furthermore, we found that spiders built more symmetric webs when they perceived a risk of predation, perhaps to reduce the web-building time during which they are more vulnerable. This suggests that the cost of behavioural complexity may mediate the outcome of interspecific interactions and thus may be ecologically important.

Natural History of the Oriental Odd-Tooth Snake (Dinodon orientale) in Yamanashi, Japan: Seasonal Activity and Body Condition Associated with Sex

Abstract The natural history of an animal provides crucial information for more focused studies in areas such as ecology, ethology, and evolution. Dinodon orientale is a small, nocturnal, and rather rare endemic species in Japan. Here we provide information on the natural history of D. orientale including information on seasonal activity pattern, body size, body mass, and body condition index associated with sex, based on 110 individuals captured in Yamanashi Prefecture, central Japan. Both sexes demonstrated a similar trend in the seasonal activity pattern and body condition. The seasonal activity peak of both sexes was in September, probably because hatchlings appeared in September. Body condition was high at the beginning and end of the active season and low in summer. We did not observe sexual dimorphism in snout-vent length (SVL) or body mass. The seasonal trend in the body size distribution of captured snakes suggests that hatchlings of D. orientale (of around 180 mm SVL) appear in September, grow to an SVL of about 250 mm by late October, and begin hibernation in November. Juveniles emerge in April or May and grow to an SVL of around 350 mm by late September.

An observation of between-mates feeding behaviour in chick-guarding chinstrap penguins

Courtship feeding has not been reported for chinstrap penguins (Pygoscelis antarctica). However, we observed a male chinstrap penguin fed to his mate during the guard stage of chick. After being fed, the female regurgitated the food to her chick. Our observation suggests that the chicks’ behaviour of begging for food may be retained in adults, but it is usually restrained.