A Morphometric Assessment of the Intended Function of Cached Clovis Points

A number of functions have been proposed for cached Clovis points. The least complicated hypothesis is that they were intended to arm hunting weapons. It has also been argued that they were produced for use in rituals or in connection with costly signaling displays. Lastly, it has been suggested that some cached Clovis points may have been used as saws. Here we report a study in which we morphometrically compared Clovis points from caches with Clovis points recovered from kill and camp sites to test two predictions of the hypothesis that cached Clovis points were intended to arm hunting weapons: 1) cached points should be the same shape as, but generally larger than, points from kill/camp sites, and 2) cached points and points from kill/camp sites should follow the same allometric trajectory. The results of the analyses are consistent with both predictions and therefore support the hypothesis. A follow-up review of the fit between the results of the analyses and the predictions of the other hypotheses indicates that the analyses support only the hunting equipment hypothesis. We conclude from this that cached Clovis points were likely produced with the intention of using them to arm hunting weapons

Unexpected diversity in socially synchronized rhythms of shorebirds

The behavioural rhythms of organisms are thought to be under strong selection, influenced by the rhythmicity of the environment1, 2, 3, 4. Such behavioural rhythms are well studied in isolated individuals under laboratory conditions1, 5, but free-living individuals have to temporally synchronize their activities with those of others, including potential mates, competitors, prey and predators6, 7, 8, 9, 10. Individuals can temporally segregate their daily activities (for example, prey avoiding predators, subordinates avoiding dominants) or synchronize their activities (for example, group foraging, communal defence, pairs reproducing or caring for offspring)6, 7, 8, 9, 11. The behavioural rhythms that emerge from such social synchronization and the underlying evolutionary and ecological drivers that shape them remain poorly understood5, 6, 7, 9. Here we investigate these rhythms in the context of biparental care, a particularly sensitive phase of social synchronization12 where pair members potentially compromise their individual rhythms. Using data from 729 nests of 91 populations of 32 biparentally incubating shorebird species, where parents synchronize to achieve continuous coverage of developing eggs, we report remarkable within- and between-species diversity in incubation rhythms. Between species, the median length of one parent’s incubation bout varied from 1–19 h, whereas period length—the time in which a parent’s probability to incubate cycles once between its highest and lowest value—varied from 6–43 h. The length of incubation bouts was unrelated to variables reflecting energetic demands, but species relying on crypsis (the ability to avoid detection by other animals) had longer incubation bouts than those that are readily visible or who actively protect their nest against predators. Rhythms entrainable to the 24-h light–dark cycle were less prevalent at high latitudes and absent in 18 species. Our results indicate that even under similar environmental conditions and despite 24-h environmental cues, social synchronization can generate far more diverse behavioural rhythms than expected from studies of individuals in captivity5, 6, 7, 9. The risk of predation, not the risk of starvation, may be a key factor underlying the diversity in these rhythms

Do female zebra finches (Taeniopygia guttata) copy each other\u27s mate preferences?

We investigated whether female zebra finches (Taeniopygia guttata) would alter their mate preferences after observing the choices of other females. Experimental trials consisted of four 30-min stages: (A) acclimation, (B) observer female chooses between two males, (C) observer female watches a model female interact with her nonpreferred male from stage B, and (D) observer female again chooses between the two males. Control trials were identical except that there was no model female in stage C. Females in both experimental and control trials spent significantly more time with the nonpreferred male in stage D than they had in stage B; thus, our experiment appeared to reveal no evidence of mate choice copying. There was, however, a significant positive relationship between the increase in the time that an observer female in experimental trials spent with her nonpreferred male in stage D and the number of interactions that she had previously observed between the model female and that male in stage C. A second..., Le but de notre recherche est d\u27examiner si les femelles du diamant mandarin (Taeniopygia guttata) modifient leur choix de parternaire en fonction de celui d\u27autres femelles. La procédure expérimentale consiste en quatre étapes de 30 min : (A) période d\u27acclimatation, (B) une femelle observatrice choisit entre deux mâles, (C) cette même femelle observe une femelle modèle en interaction avec le mâle non choisi de l\u27étape B et (D) la femelle observatrice choisit à nouveau entre les deux mâles. Les procédures témoins sont semblables, sauf qu\u27il n\u27y a pas de femelle modèle présente à l\u27étape C. Les femelles expérimentales et témoins ont toutes deux passé significativement plus de temps avec le mâle non retenu à l\u27étape D qu\u27à l\u27étape B. Notre expérience ne semble donc pas démontrer clairement que le choix de partenaire chez le diamant mandarin se fait en imitant le choix d\u27autres femelles. Cependant, il y a une relation positive significative entre l\u27augmentation du temps que les femelles observatrices passen..

Brood sex ratio in the Kentish plover

How and why do the mating opportunities of males and females differ in natural population of animals? Previously we showed that females have higher mating opportunities than males in the Kentish plover Charadrius alexandrinus. Both parents incubate the eggs, and males provide more brood care than females; thus it is not obvious why the females find new mates sooner than the males. In this study we investigated whether the sex-biased mating opportunities stem from biased offspring sex ratios. We determined the sex of newly hatched, precocial chicks using CHD gene markers. Among fully sexed broods, 0.461 � 0.024 (SE) of chicks (454 chicks in 158 broods) were male, and this sex ratio was not significantly different from unity. The proportion of males at hatching decreased significantly over the breeding season, which occurred consistently in all 3 years of the study. Large chicks were more likely to be males than females. Neither parental age nor body size of male and female parents was related to brood sex ratio. We also sexed a number of chicks that were caught after they left their nest (range of estimated ages 0--17 days) and found that the proportion of males increased with brood age. This relationship remained highly significant when controlling statistically for hatching date. As brood size decreased due to mortality after the chicks left their nest, these results suggest that the mortality of daughters was higher than that of the sons shortly after hatching. Taken together, our results show that the female-biased mating opportunities in the Kentish plover are not due to biased brood sex ratio at hatching but, at least in part, are due to female-biased chick mortality soon after hatching. Copyright 2004.Charadrius alexandrinus; Kentish plover; mating opportunities; parental care; seasonal trends; sex allocation; sex ratio

Extra-pair mating, male plumage coloration and sexual selection in yellow warblers (Dendroica petechia)

Extra-pair mating has been proposed as a source of sexual selection responsible for secondary sexual traits that are common among socially monogamous birds, although supporting evidence is scant. In the socially monogamous yellow warbler, males are larger than females, and unlike females, have extensive reddish streaking on their breasts. Using DNA fingerprinting we show that within-pair parentage was positively related to male size, and that extra-pair mating success was positively related to the amount of streaking on the breast. To our knowledge, this is the first intraspecific evidence of an association between a male plumage ornament and gains of extra-pair paternity that is apparently independent of age. This study confirms that extra-pair mating can be an important mechanism of sexual selection even when the most successful sires are commonly cuckolded, and refutes a previous hypothesis that the variation in plumage and behaviour among male yellow warblers is an example of alternative, equally successful, evolutionarily stable strategies (ESS). More generally, the demonstrated independence of within-pair and extra-pair success and their associated traits indicates that where animals have multiple secondary sexual traits, different traits may be selected by different mechanisms that contribute to total reproductive success