Douglas W. Bird

The hunting handicap: costly signaling in human foraging strategies

Abstract. Humans sometimes forage or distribute the products of foraging in ways that do not maximize individual energetic return rates. As an alternative to hypotheses that rely on reciprocal altruism to counter the costs of inefficiency, we suggest that the cost itself could be recouped through signal benefit. Costly signaling theory predicts that signals can provide fitness benefits when costs are honestly linked to signaler quality, and this information is broadcast to potential mates and competitors. Here, we test some predictions of costly signaling theory against empirical data on human food acquisition and sharing patterns. We show that at least two types of marine foraging, turtle hunting and spearfishing, as practiced among the Meriam (a Melanesian people of Torres Strait, Australia) meet key criteria for costly signaling: signal traits are (1) differentially costly or beneficial in ways that are (2) honestly linked to signaler quality, and (3) designed to effectively broadcast the signal. We conclude that relatively inefficient hunting or sharing choices may be maintained in a population if they serve as costly and reliable signals designed to reveal the signalers qualities to observers.

The “fire stick farming” hypothesis: Australian Aboriginal foraging strategies, biodiversity, and anthropogenic fire mosaics

Aboriginal burning in Australia has long been assumed to be a “resource management” strategy, but no quantitative tests of this hypothesis have ever been conducted. We combine ethnographic observations of contemporary Aboriginal hunting and burning with satellite image analysis of anthropogenic and natural landscape structure to demonstrate the processes through which Aboriginal burning shapes arid-zone vegetational diversity. Anthropogenic landscapes contain a greater diversity of successional stages than landscapes under a lightning fire regime, and differences are of scale, not of kind. Landscape scale is directly linked to foraging for small, burrowed prey (monitor lizards), which is a specialty of Aboriginal women. The maintenance of small-scale habitat mosaics increases small-animal hunting productivity. These results have implications for understanding the unique biodiversity of the Australian continent, through time and space. In particular, anthropogenic influences on the habitat structure of paleolandscapes are likely to be spatially localized and linked to less mobile, “broad-spectrum” foraging economies.

Hunting and nuclear families: some lessons from the Hadza about men's work

Hadza hunter-gatherers display economic and social features usually assumed to indicate the dependence of wives and children on provisioning husbands and fathers. The wives and children of better Hadza hunters have been found to be better-nourished, consistent with the assumption that men hunt to provision their families. Yet, as is common among foragers, the Hadza share meat widely. Analyses of meat-sharing data confirm that little of the meat from large prey went to the hunters own household. These analyses also show that neither a mans hunting success nor the time he spent hunting made any difference in how much meat his family got from the kills of others. Here we address questions posed by this set of observations. What explains the better nutrition of the children of better hunters if they did not get differential rations of meat? If better hunters got no more meat for their effort and poorer hunters were not punished with less, what incentive could account for the continuing disproportionate contribution that some men made to the groups nutrition? If women were not dependent on their husbands hunting success for meat, an obvious incentive for women to marry hunters disappears. We briefly consider the implications of these patterns for the evolution of marriage and nuclear families.

IN PURSUIT OF MOBILE PREY : MARTU HUNTING STRATEGIES AND ARCHAEOFAUNAL INTERPRETATION

By integrating foraging models developed in behavioral ecology with measures of variability in faunal remains, zooarchaeological studies have made important contributions toward understanding prehistoric resource use and the dynamic interactions between humans and their prey. However, where archaeological studies are unable to quantify the costs and benefits associated with prey acquisition, they often rely on proxy measures such as prey body size, assuming it to be positively correlated with return rate. To examine this hypothesis, we analyze the results of 1,347 adult foraging bouts and 649 focal follows of contemporary Martu foragers in Australias Western Desert. The data show that prey mobility is highly correlated with prey body size and is inversely related to pursuit success—meaning that prey body size is often an inappropriate proxy measure of prey rank. This has broad implications for future studies that rely on taxonomic measures of prey abundance to examine prehistoric human ecology, including but not limited to economic intensification, socioeconomic complexity, resource sustainability, and overexploitation.

Constraints of knowing or constraints of growing

Recent theoretical models suggest that the difference between human and nonhuman primate life-history patterns may be due to a reliance on complex foraging strategies requiring extensive learning. These models predict that children should reach adult levels of efficiency faster when foraging is cognitively simple. We test this prediction with data on Meriam fishing, spearfishing, and shellfishing efficiency. For fishing and spearfishing, which are cognitively difficult, we can find no significant amount of variability in return rates because of experiential factors correlated with age. However, for shellfish collecting, which is relatively easy to learn, there are strong age-related effects on efficiency. Children reach adult efficiency more quickly in fishing as compared to shellfish collecting, probably owing to the size and strength constraints of the latter.

Why Women Hunt Risk and Contemporary Foraging in a Western Desert Aboriginal Community

An old anthropological theory ascribes gender differences in hunter‐gatherer subsistence to an economy of scale in household economic production: women pursue child‐care‐compatible tasks and men, of necessity, provision wives and offspring with hunted meat. This theory explains little about the division of labor among the Australian Martu, where women hunt extensively and gendered asymmetry in foraging decisions is linked to men’s and women’s different social strategies. Women hunt primarily small, predictable game (lizards) to provision small kin networks, to feed children, and to maintain their cooperative relationships with other women. They trade off large harvests against greater certainty. Men hunt as a political strategy, using a form of “competitive magnanimity” to rise in the ritual hierarchy and demonstrate their capacity to keep sacred knowledge. Resources that can provision the most people with the most meat best fit this strategy, resulting in an emphasis on kangaroo. Men trade off reliable consumption benefits to the hunter’s family for more unpredictable benefits in social standing for the individual hunter. Gender differences in the costs and benefits of engaging in competitive magnanimity structure men’s more risk‐prone and women’s more risk‐averse foraging decisions.

Risk and reciprocity in Meriam food sharing

Abstract Foragers who do not practice food storage might adapt to fluctuating food supplies by sharing surplus resources in times of plenty with the expectation of receiving in times of shortfall. In this paper, we derive a number of predictions from this perspective, which we term the risk reduction reciprocity (RRR) model, and test these with ethnographic data on foraging (fishing, shellfish collecting, and turtle hunting) among the Meriam (Torres Strait, Australia). While the size of a harvest strongly predicts that a portion will be shared beyond the household of the acquirer, the effects of key measures of foraging risk (e.g., failure rate) are comparatively weak: Harvests from high-risk hunt types are usually shared more often than those from low-risk hunt types in the same macropatch, but increases in risk overall do not accurately predict increases in the probability of sharing. In addition, free-riders (those who take shares but do not reciprocate) are not discriminated against, those who share more often and more generously do not predictably receive more, and most sharing relationships between households (over 80%) involve one-way flows.

Children on the reef

Meriam children are active reef-flat collectors. We demonstrate that while foraging on the reef, children are significantly less selective than adults. This difference and the precise nature of children’s selectivity while reef-flat collecting are consistent with a hypothesis that both children and adults attempt to maximize their rate of return while foraging, but in so doing they face different constraints relative to differences in walking speeds while searching. Implications of these results for general arguments about factors that shape differences between child and adult behavior and human life-histories are explored.

Aboriginal hunting buffers climate-driven fire-size variability in Australia’s spinifex grasslands

Across diverse ecosystems, greater climatic variability tends to increase wildfire size, particularly in Australia, where alternating wet–dry cycles increase vegetation growth, only to leave a dry overgrown landscape highly susceptible to fire spread. Aboriginal Australian hunting fires have been hypothesized to buffer such variability, mitigating mortality on small-mammal populations, which have suffered declines and extinctions in the arid zone coincident with Aboriginal depopulation. We test the hypothesis that the relationship between climate and fire size is buffered through the maintenance of an anthropogenic, fine-grained fire regime by comparing the effect of climatic variability on landscapes dominated by Martu Aboriginal hunting fires with those dominated by lightning fires. We show that Aboriginal fires are smaller, more tightly clustered, and remain small even when climate variation causes huge fires in the lightning region. As these effects likely benefit threatened small-mammal species, Aboriginal hunters should be considered trophic facilitators, and policies aimed at reducing the risk of large fires should promote land-management strategies consistent with Aboriginal burning regimes.

Provisioning offspring and others: risk–energy trade-offs and gender differences in hunter–gatherer foraging strategies

Offspring provisioning is commonly referenced as the most important influence on mens and womens foraging decisions. However, the provisioning of other adults may be equally important in determining gender differences in resource choice, particularly when the goals of provisioning offspring versus others cannot be met with the acquisition of the same resources. Here, we examine how resources vary in their expected daily energetic returns and in the variance or risk around those returns. We predict that when available resources impose no trade-off between risk and energy, the targets of mens and womens foraging will converge on high-energy, low-risk resources that allow for the simultaneous provisioning of offspring and others. However, when minimizing risk and maximizing energy trade-off with one another, we expect mens foraging to focus on provisioning others through the unreliable acquisition of large harvests, while women focus on reliably acquiring smaller harvests to feed offspring. We test these predictions with foraging data from three populations (Aché, Martu and Meriam). The results uphold the predictions, suggesting that mens and womens foraging interests converge when high-energy resources can be reliably acquired, but diverge when higher-energy resources are associated with higher levels of risk. Social factors, particularly the availability of alloparental support, may also play a major role.