The steroid environment encountered by developing vertebrates has important organizational effects on physiology and behaviour that persist throughout an organism's lifetime. Optimal allocation of maternal steroids to zygotes may be difficult to achieve because of the sexually antagonistic effects of steroids; thus, for example, a hormone environment beneficial to a developing male may be much less beneficial to a developing female. Research into the important topic of how mothers might adaptively adjust steroid titres experienced by particular young has been constrained by the difficulty of measuring the steroid environment experienced by the embryo at critical times in development. A potential approach to this problem has been suggested by research on variation in digit ratios in humans, where the ratio of the length of the second and fourth digits reflects the steroid environment experienced by the foetus; notably, digit 4 lengthens in response to androgens. In light of the conservative nature of homeobox genes regulating early development in tetrapods, we questioned whether a sex difference in digit ratio exists in a passerine bird, the zebra finch, Taeniopygia guttata castanotis, and whether observed variation in the ratio is consistent with the previously reported pattern that androgen allocation to zebra finch egg yolk declines across laying order. We established an aviary population of outbred, wild-type zebra finches, and allowed them to breed freely. Hatchlings were marked to correspond to their egg order, and their digit ratios were measured after birds reached adulthood. We found that digit ratio increased across egg order, which is consistent with a pattern of decreasing androgen allocation. Moreover, digit ratios differed between the sexes. We also investigated whether variation in digit ratio among adult females predicted variation in their performance in mate-choice tests. Digit ratio accounted for almost 50% of the variance in strength of female preference for an attractive male trait: specifically, females with higher (presumably less 'androgenized') ratios had stronger preferences for attractive males. Digit ratio may prove to be an extremely useful tool for addressing a wide range of questions about vertebrate differentiation and behaviour.

No abstract

Parrots are unusual among birds and animals in general in the extent of their ability to learn new vocalizations throughout life and irrespective of season. The budgerigar (Melopsittacus undulatus), a small parrot that is well suited for laboratory studies, has been the subject of numerous studies investigating the neurobiology of vocal learning. To date, few studies have focused on the function of vocal imitation by parrots. Previous work from our research group has shown that vocal imitation in budgerigars is sex-biased, as males paired with females learn vocalizations from their new mates, but not vice versa. This bias led us to hypothesize that vocal learning has a reproductive function. To test this hypothesis, we conducted two experiments. In the first experiment, we tutored males so that they could produce a call similar to one shared by a group of experimental females. The experimental females were then presented with one of the tutored males and another, equally unfamiliar, male that had not been tutored. We found that the females spent a greater proportion of time in proximity of, and made more affiliative displays toward, the tutored males. In the second experiment, seven males received small bilateral brain lesions that disrupt vocal learning. These males and an equal number of control males were then released into an aviary containing females and reproductive resources. We found that lesioned and control males were equally successful in obtaining social mates, but females mated to lesioned males were more likely to engage in extra-pair activities. These experiments indicate that a male's ability to imitate a female's call can influence the sexual behavior of the female even though lack of imitation ability does not appear to influence social pairing. We hypothesize that mate choice in budgerigars has multiple stages. Upon meeting a strange male, a female quickly assesses its ability for social acquisition of calls by the presence or absence of a call type similar to its own in its repertoire. As courtship proceeds into pair formation, the female assesses the ability of male to learn more directly by the extent of the male's perfection of imitation. Ethology 111, 901-923 (2005)

Safety training should be provided before YWs start work and in media other than school. Seatbelt use should be addressed.

While behavioral ecologists have studied sex allocation for 30 yr, almost nothing is known about the roles of male vs. female parents in making secondary allocation decisions in species with bi‐parental care. To investigate possible sex differences in tactics in zebra finches, we manipulated the condition of one cohort of females by trimming their flight feathers; a second cohort of females and all males were left intact. Focal observations of feeding behavior revealed that manipulated females did not reduce their feeding time, but rather focused their efforts on rearing sons, while control females allocated effort to rearing daughters. Males mated to manipulated females tended to focus effort to daughters, while control males showed no consistent response. Manipulated females experienced a lower reproductive rate, primarily because of a low daughter rate, relative to control females. Manipulated females also laid smaller clutches and had longer inter‐clutch intervals, which suggest that their ability to metabolize and allocate essential proteins from pectoral muscle mass during the egg‐laying period was impaired. To our knowledge, this study is the first to show that parents of both sexes make active sex allocation decisions when the physiological condition of one parent is manipulated; males do not simply adopt female allocation patterns, but make complementary adjustments. Our results have implications for interpretation of handicapping studies that seek to understand the dynamics of inter‐sexual negotiations of care‐giving. Investigation of sex differences in sex allocation tactics in species with limited dietary protein, such as granivorous birds, is a potentially important direction for future research.