In a series of 6 experimental studies, the means by which a chick recognises its mother, and the reversibility of filial attachments were examined using bantam hens and their chicks. In a simultaneous discrimination test it was determined that the chick could discriminate between own and alien hens by means of the hens' cluck vocalizations, on the 4th and 8th days post hatching, (Experiment 1). The chicks could make this discrimination more efficiently when live hens were presented (Experiment 2). On separating the hen and chicks for 4 h on the 4th day, the chicks could no longer discriminate between own and an alien live hen (Experiment 3) while they would accept an alien hen, (Experiment 4). These findings suggest that maternal-filial bonds may be reversed with little difficulty. Thus Experiment 5 was designed to examine the stability of these later maternal filial bonds. Chicks spent the first 3 days post hatching, with the hen who incubated the eggs. Then they spent 3 days with an alien hen, after which 3 days isolation followed. It was found that chicks could discriminate in favour of their own hen after the first period of exposure, and in favour of the alien hen after the second period of exposure. Following 3 days isolation they showed no preference for either hen. Experiment 6 was essentially a replication of Experiment 5, but included a control for familiarity. Only one test took place after the 3 days isolation. The chicks were presented with the 1st 2nd and an unfamiliar alien hen. The chicks did not discriminate in favour of any particular hen. It is concluded that after 4 h or 3 days isolation, the chicks did not discriminate between the hens presented, yet they remained responsive to hens.

The birth sex ratio of a commercial flock of Suffolk x sheep, Ovis aries, were studied over six consecutive lambing seasons. In all, data from 1820 lambs were recorded and analysed. The overall birth sex ratio was 49.56% male lambs. Significantly more males (56.23%) were born to ewes with single lambs than to ewes with like-sex twins (47.73%). Significantly more female lambs were born to ewes with triplet births (41.79% male). A significant difference in the birth sex ratio was observed between the first and second half of the lambing season, among like-sex pairs of twin lambs. More males were born in the first half (51.43%) and significantly more females (43.59% male) in the second half of the lambing season. The results are discussed with reference to the theory of Trivers and Willard (1973).

The predominant frequency, rate of clucking and intensity of the maternal cluck vocalization of the broody hen (Gallus gallus) are described. The frequency, rate of clucking, and level of intensity of the cluck vocalizations were altered independently of each other. Three-day-old chicks were given a simultaneous choice test between the normal and an altered cluck or between the two altered clucks in a 'T' shaped simultaneous choice test apparatus. No significant preferences were found when the frequency was increased or decreased by 25% (Experiment 1A) but the chicks significantly prefer the normal cluck over a cluck with a 33% increase in frequency. The preference for the normal cluck over the 33% decrease in frequency was nearly significant (Experiment 1B). Thus, there exists an optimal frequency range for the maternal cluck vocalization of the domestic hen. When the rate of clucking was increased or decreased by 25% the chicks preferred the higher rate of clucking in all conditions (Experiment 2). However, the highest rate of clucking used in this experiment was close to that of the normal cluck. When the intensity was increased or decreased by 100% no significant preferences were found in any choice test (Experiment 3). This contrasts with earlier findings possibly due to a methodological difference.

This study examines the socioeconomic and familial background of Irish Catholic priests born between 1867 and 1911. Previous research has hypothesized that lack of marriage opportunities may influence adoption of celibacy as part of a religious institution. The present study traced data from Irish seminary registries for 46 Catholic priests born in County Limerick, Ireland, using 1901 Irish Census returns and Land Valuation records. Priests were more likely to originate from landholding backgrounds, and with landholdings greater in size and wealth than the local average. Priests were found to originate from families with more sons than the national average, but with similar numbers of daughters. These findings are discussed in relation to competition for resources and lineage survival strategies.

Herein we examined the effects of yolk size and ovulation order on the fertilisation of yolks within double-yolked (DY) duck eggs. Single-yolked (SY) duck eggs had high fertility (89.98%), whereas in DY duck eggs fertility was low (51.9% yolks). The yolks closer to the airspace (Yolk 1) in DY eggs had higher fertility (68.82% vs 34.98% for Yolk 2; P<0.001). When only one of the two yolks was fertilised, Yolk 1 was fertilised in 99.12% of those eggs. Yolk 1 is presumed to be the first ovulated. The higher fertility of Yolk 1 is consistent with a primacy effect where the first ovulation has a higher probability of achieving fertilisation. Small DY eggs within the normal SY egg weight range (75-104.9g) had significantly lower yolk fertility (47.91%; n=550) compared with large (≥105g) DY eggs (54.56%; n=768; P<0.001). Yolk 1 fertility was lower in small compared with large DY eggs (64.18% vs 72.14%, respectively; P=0.003). Although Yolk 2 fertility was low, it was not affected by egg size. DY eggs with zero fertilised yolks were significantly lighter than DY eggs with one (P=0.007) or two (P<0.001) fertilised yolks (i.e. larger DY eggs were more likely to have fertilised yolks). Larger eggs (≥105g) have larger yolks and the evidence here shows that an optimal yolk size is a significant positive factor in achieving fertilization by dislodging spermatozoa, after ovulation, from their storage sites.

Testosterone (T) concentrations in many species are sensitive to seasonal changes and to changes in social conditions. However, the effect of the natural or endogenous T increase in the juvenile on their social behaviour is not well understood. In this study, T and behaviour were measured from the pro-social juvenile to the adult stage in semi-feral domestic fowl. During the pro-social phase T levels and the distance chicks maintained between each other, i.e. inter-individual distance (IID) were low. Then, as T increased, a corresponding increase in IID occurred and continued in males until dispersal to individual adult male territories. In the new and initially stable adult social structure, T declined and IID remained high, indicating a new behavioural mechanism was in place. Males first mated as T levels were declining. They were then challenged; then T increased, and then IID increased again. Adult male T levels fluctuate, being low or declining in a socially stable environment and increasing following a challenge, suggesting a regulatory or modulating role for T. The results are consistent with T having an endogenous role: in the juvenile, driving behavioural change towards adulthood, and in adulthood, a modulating role regulating social organisation.

The relationship between the cow and calf develops over time after birth. The behavioural mechanisms underlying its development are important and comparisons with other species may increase our understanding. In nature the cow will separate herself from the herd to give birth and then the cow–calf relationship will develop with the ability to recognise each other. While twinning levels are low in cows, they do rear their twin calves. If the calf is lost at or after birth the cow can be responsive towards other calves and in specific circumstances the cow can develop a maternal bond with an alien calf, i.e. foster. In this Research Reflection a distinction is made between the development of, on the one hand, maternal responsiveness (the tendency of the cow to care for a calf which occurs before birth) and, on the other hand, the development of the maternal–filial bond or relationship which is reciprocal, occurs after birth and is characterised by the ability to discriminate the mother's own calf from alien calves. These processes can overlap and the relationship between cow and calf in this ‘hider’ species is more plastic than in some other mammals. For example, a cow might form an attachment with an alien calf before she gives birth. After the cow has given birth the loss of her own calf may result in the state of maternal responsiveness being maintained, such that developing a maternal bond with one or several appropriate alien calves is possible. Viable fostering techniques are possible. If a maternal relationship to the mother's own calf has developed then fostering will be more difficult. If the cow's relationship with her own calf is not exclusive, and she is in a state of maternal responsiveness then fostering of calves of an appropriate age and status can be achieved.

No abstract