SummaryThe breeding biology of Hill Mynah Gracula religiosa was studied in eight provinces of Thailand from 1991 to 1998 to evaluate how breeding behaviour has evolved to enhance reproductive success in the face of human interference. The northern race G. r. intermedia bred mostly during February to April whereas the southern race G. r. religiosa bred mostly later during April to June. Both races were cavity-nesting, non-excavating, monogamous and similar in breeding activities except for differences in body size. They nested at the bottom of deep cavities with a long entrance (mean 45 cm), in tall trees. Average nest height was 23 m. Nests were sometimes abandoned (10% of nests) during nest-building or incubation. Most Hill Mynahs (70%) had clutches of three eggs. Both parents shared incubation and feeding of young. The most detrimental factor to the reproductive success of this species was human theft of the young, rather than any natural factors. During 1991 to 1998, 80% of eggs laid were hatched, but 88% of all eggs hatched were lost before fledgling. Those illegally stolen by humans amounted to 61% of eggs hatched. Only 37 of 308 nestlings or 12% of eggs hatched survived to independence. In 1999, nests were experimentally guarded to prevent human interference, and fledgling success increased to 75% of eggs hatched. The remaining 25% of nestlings were lost to predators and unknown causes, close to the 27% lost to these causes in unguarded nests during 1991 to 1998. Although the breeding pattern of this species has evolved to promote survival of young, it does not seem to have evolved adaptations to human predation. The continuing decrease of wild Hill Mynah populations has prompted attempts at captive breeding. Data on breeding biology from this study should enhance its success.

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Hill Mynah Gracula religiosa is one of the most popular bird pets worldwide due to its ability to mimic diverse sounds, especially human speech. However, Mynahs have rarely been bred in captivity, so nestlings from natural populations are in large demand, resulting in many populations being threatened with extinction. Both subspecies in Thailand, intermedia and religiosa, are costly and desired in the pet market. Captive breeding is one of the most practical strategies to solve a conservation problem of this nature and this report describes a success in breeding Hill Mynahs in captivity. Mated pairs were given free access to food, nest-cavities and nest materials. Reproductive behaviour in captivity was not different from that in the wild, with the exception that breeding occurred throughout the year, even during the non-breeding season for wild populations. Although there are doubts concerning the reintroduction of captive-bred birds and whether successful Hill Mynah breeding in captivity is an economically competitive alternative to poaching, it ensures species survival in captivity as the risk of extinction increases.

To investigate the effects of familiarity with opponents on the activation of aggression and dominance by testosterone (T) in white-throated sparrows Zonotrichia albicollis, we studied birds in groups of five or six in outdoor aviaries and in a free-living population. Experiments were conducted between January and April, when plasma levels of endogenous gonadal hormones were low. Previously published experiments (ARCHAWARANON & WILEY, 1988) showed that when subjects were given subcutaneous implants of T, held individually in cages for one week, and then grouped with unfamiliar opponents, they established dominance over controls with empty implants. In contracts, the present study showed that low-ranking birds given subcutaneous implants of T and returned to their original groups and aviaries did not change in dominance rank nor in aggression scores over a period of two weeks. When these birds were regrouped with unfamiliar opponents in new aviaries, their dominance ranks and aggression scores increased. This rise in dominance rankings and aggression scores did not result from any effects of regrouping in the absence of hormonal treatments. The sexes did not differ in their responses to these treatments. In the field, T implants markedly increased some individuals' frequencies of aggression but had little or no effect on dominance relationships. The absence of behavioral changes in stable groupings after hormonal treatment, called social inertia, indicates that birds recognize the relative dominance of previous opponents, at least when encountered in familiar locations. Results from the field experiment thus suggest that white-throated sparrows can recognize at least 20 opponents. Hormonal state has more influence on dominance relationships of strangers than on those of opponents familiar with each other in familiar locations.

This study aimed to discover whether the Hill Mynah Gracula religiosa forms pairs for a single breeding season or engages in long-term pair bonding, and to investigate the role of female aggression in maintaining pair bonds. Experiments were conducted on captive birds in Thailand between 2006 and 2013, and pair behaviours such as allopreening and aggression were observed four times every day. In the first experiment, when each breeding pair was preparing to rear a new clutch, pairs were placed in a new aviary with unfamiliar males and females with which they could potentially form relationships. Results indicated that breeding pairs stayed with the same mates over four continuous breeding seasons (2006–2009) without changing partners or taking additional mates. In a second experiment, the role of female aggression in maintaining long-term pair bonding was examined. Each breeding pair, when preparing to rear a new clutch, was placed in a new aviary with three unfamiliar females. The results showed that female breeders displayed vigorous aggression towards the other three females, forcing them to retreat from the pair; this behaviour was sustained over four continuous breeding seasons (2010–2013). Thus, it is suggested that the Hill Mynah engages in long-term pair bonding and that the aggression of the breeding female is an essential component in the maintenance of pair-bonds.