Rajarathinavelu Nagarajan

Oystercatchers use colour preference to achieve longer-term optimality

The optimal diet model entails that foragers look beyond the individual prey encounter, to at least the level of intake rate across a bout of foraging, but optimization over a longer time remains controversial. In this paper, we show how oystercatchers increase their intake over the longer term using mussel colour as a cue. Wintering oystercatchers Haematopus ostralegus feed extensively on mussels Mytilus edulis in the estuaries of southern Britain. They show a marked preference for brown–shelled mussels over the commoner black–shelled morph, and we show that this enables them to maximize their rate of energy gain over a longer period than a single foraging bout. The brown and black mussels did not differ in ventral thickness and energy content, which are the main criteria for mussel selection and most important for short–term optimization. The brown mussels contained significantly less moisture, so by selecting them, oystercatchers could pack more mussel flesh into their limited oesophageal storage capacity. This enables them to increase their overall consumption during a feeding bout and increases their long–run energy gain rate, to an extent that is large enough to be significant for survival, especially during the short exposure of the mussel beds in winter.

PATTERNS OF GROWTH IN NESTLING INDIAN BARN-OWLS

Abstract We examined nestling growth patterns of the Indian Barn-Owl (Tyto alba stertens) in Tamilnadu, Southern India, with reference to body mass, body length, bill length, bill width, wing length, wingspan, tail length, tarsus length, and middle claw length. Body mass reached an asymptote of 447.0 ± 6.8 g during week 7, which was 10% higher than the adult mass. Then it significantly declined to 437.0 ± 10.9 g at fledging. At the end of week 4, the body length, bill length, bill width, tarsus length, and middle toe length had surpassed 50% of adult sizes. The wingspan and tarsus length reached almost adult size by the time of fledging. A logistic growth curve was found to be a good fit for all the growth variables and explained between 71% (wing length) and 86% (body length) of the variance. Patrones de Crecimiento en Polluelos de Tyto alba stertens Resumen. Examinamos los patrones de crecimiento de polluelos de Tyto alba stertens en Tamilnadu, sudoeste de India, en relación al peso y el largo del cuerpo, el largo y el ancho del pico, el largo del ala y su envergadura, y el largo de la cola, los tarsos y de la garra mediana. El peso corporal alcanzó una asíntota de 447.0 ± 6.8 g durante la séptima semana, el cual fue un 10% mayor que el peso de los adultos. Posteriormente, durante el período de volantones, el peso corporal disminuyó hasta 437.0 ± 10.9 g. Al final de la cuarta semana, el largo del cuerpo, el largo y el ancho del pico, y los largos del tarso y del dedo mediano habían sobrepasado el 50% de los tamaños adultos. La envergadura del ala y el largo del tarso casi alcanzaron tamaños adultos durante el período de volantones. Se encontró que una curva de crecimiento logístico se ajustó bien a todas las variables de crecimiento y explicó un 71% (largo del ala) y un 86% (largo del cuerpo) de la varianza.

Biology, Ecology, and Conservation of Golden Langur, Trachypithecus geei

The Golden Langur Trachypithecus geei is a rare colobine monkey with a very restricted range being confined to Western Assam in India and Bhutan. In Assam, at least 19 fragmented areas now hold the species, which was originally a single habitat. The langur distributed from the subtropical forests of Western Assam to the broadleaf forests of Bhutan. The individuals of Golden Langur in Manas, Ripu, and to some extent Chirang have link among themselves and also with Bhutanese populations, and the remaining populations found in fragmented areas have no link and became isolated. The estimated total population in India is 5600 individuals, and most of the information on this species was available in the form of short-term studies; most of them are about the status and distribution. None of the population was monitored for longer period of time, and the population inhabited both in India and Bhutan are declining. Golden Langur is folivorous in nature and feeds on a variety of food plants. Activity pattern showed a bimodal diurnal activity pattern in feeding with peaks in the morning and evening hours. Golden Langur is threatened by habitat fragmentation. In fragmented areas, they cause considerable damages to food crops. To maintain its populations for the future, long-term and large-scale planning is necessary.