Food supply fluctuations constrain group sizes of kangaroos and in turn shape their vigilance and feeding strategies

Seasonal variation in food resources and predation risk imposes major constraints on herbivores, which must adjust their behaviour to maximize their energy intake and survival. In seasonally driven landscapes, it is not yet clear what the primary drivers are that shape seasonal variation in vigilance and feeding rates. These rates have been shown to vary in relation to various environmental, social and individual factors, but many of these factors also vary through the year, due to variation in food supply. We studied wild female eastern grey kangaroos, Macropus giganteus, under low predation risk over a year to investigate whether vigilance and feeding rates varied seasonally and whether this variation was mainly driven by food quantity or quality, group size or individuals\u27 reproductive states. Both vigilance and feeding rates varied seasonally, as did food quantity and quality and group size. Vigilance, including antipredator (head orientation away from the group) and exclusive (i.e. vigilance without chewing) vigilance, decreased and feeding rate increased with increasing group size. However, because group size increased with food quality and quantity, food resources emerged as the primary driver of variation in behavioural strategies. These results suggest that the observed effects of group size on the trade-off between food acquisition and safety are in fact corollaries of the seasonal variation in food supply in our study system, in which the risk of predation on adults is low, and hence are by-products of the foraging choices made by kangaroos in response to the dynamics of the quantity and quality of food

Songs of male humpback whales, Megaptera novaeangliae, are involved in intersexual interactions

Male humpback whales produce complex songs during the breeding season, yet the singing behaviour of males and whether songs function in male contests and/or through female choice are still poorly understood. We investigated song function by obtaining simultaneous observations of the positions and movements of singing and nonsinging whales in real time during their migration off the east coast of Australia. We collected movement data by acoustic tracking using a hydrophone array, land-based visual tracking and observations from a small boat. Of the 114 singers analysed, 66 (58%) associated with conspecifics. Singers were significantly more likely to join groups containing a mother-calf pair than other groups. Males started to sing after joining groups only if they consisted of a mother-calf pair not escorted by another male. Singers also associated longer and sang for a significantly greater proportion of time with mother-calf pairs than any other group type. Associating with mother-calf pairs has been shown to be a reproductively successful strategy for males. In contrast, whales that joined singers were usually lone males; these associations were brief and singers typically stopped singing in the presence of other males. This is the highest reported incidence in humpback whales of males singing when escorting females and supports an intersexual function of song in humpback whales. We suggest that males joining singers are prospecting for females rather than engaging in male social ordering and that singing may incur the cost of attracting competing male

Structured association patterns and their energetic benefits in female eastern grey kangaroos, Macropus giganteus

Abstract not availableAlecia J. Carter, Stewart L. Macdonald, Vicki A. Thomson, Anne W. Goldize

Supplementary Material for: The Evolution of Relative Brain Size in Marsupials Is Energetically Constrained but Not Driven by Behavioral Complexity

<p>Evolutionary increases in mammalian brain size relative to body size are energetically costly but are also thought to confer selective advantages by permitting the evolution of cognitively complex behaviors. However, many suggested associations between brain size and specific behaviors - particularly related to social complexity - are possibly confounded by the reproductive diversity of placental mammals, whose brain size evolution is the most frequently studied. Based on a phylogenetic generalized least squares analysis of a data set on the reproductively homogenous clade of marsupials, we provide the first quantitative comparison of two hypotheses based on energetic constraints (maternal investment and seasonality) with two hypotheses that posit behavioral selection on relative brain size (social complexity and environmental interactions). We show that the two behavioral hypotheses have far less support than the constraint hypotheses. The only unambiguous associates of brain size are the constraint variables of litter size and seasonality. We also found no association between brain size and specific behavioral complexity categories within kangaroos, dasyurids, and possums. The largest-brained marsupials after phylogenetic correction are from low-seasonality New Guinea, supporting the notion that low seasonality represents greater nutrition safety for brain maintenance. Alternatively, low seasonality might improve the maternal support of offspring brain growth. The lack of behavioral brain size associates, found here and elsewhere, supports the general ‘cognitive buffer hypothesis' as the best explanatory framework of mammalian brain size evolution. However, it is possible that brain size alone simply does not provide sufficient resolution on the question of how brain morphology and cognitive capacities coevolve.</p

Population structure of humpback whales in the western and central South Pacific Ocean as determined by vocal exchange among populations

For cetaceans, population structure is traditionally determined by molecular genetics or photographically identified individuals. Acoustic data, however, has provided information on movement and population structure with less effort and cost than traditional methods in an array of taxa. Male humpback whales (Megaptera novaeangliae) produce a continually evolving vocal sexual display, or song, that is similar among all males in a population. The rapid cultural transmission (the transfer of information or behavior between conspecifics through social learning) of different versions of this display between distinct but interconnected populations in the western and central South Pacific region presents a unique way to investigate population structure based on the movement dynamics of a song (acoustic) display. Using 11 years of data, we investigated an acoustically based population structure for the region by comparing stereotyped song sequences among populations and years. We used the Levenshtein distance technique to group previously defined populations into (vocally based) clusters based on the overall similarity of their song display in space and time. We identified the following distinct vocal clusters: western cluster, 1 population off eastern Australia; central cluster, populations around New Caledonia, Tonga, and American Samoa; and eastern region, either a single cluster or 2 clusters, one around the Cook Islands and the other off French Polynesia. These results are consistent with the hypothesis that each breeding aggregation represents a distinct population (each occupied a single, terminal node) in a metapopulation, similar to the current understanding of population structure based on genetic and photo-identification studies. However, the central vocal cluster had higher levels of song-sharing among populations than the other clusters, indicating that levels of vocal connectivity varied within the region. Our results demonstrate the utility and value of using culturally transmitted vocal patterns as a way of defining connectivity to infer population structure. We suggest vocal patterns be incorporated by the International Whaling Commission in conjunction with traditional methods in the assessment of structure