Andrew J. Pierce

A Field Test of Distance Sampling Methods for a Tropical Forest Bird Community

ABSTRACT. Distance sampling is usually preferred over uncorrected point counts for surveys of forest birds, but rarely has its accuracy been assessed against known numbers, particularly in tropical forests. We compared density estimates of eight species of breeding bird—Black-naped Monarch (Hypothymis azurea), Hill Blue Flycatcher (Cyornis banyumas), White-rumped Shama (Copsychus malabaricus), Puff-throated Bulbul (Alophoixus pallidus), Abbotts Babbler (Malacocincla abbotti), Puff-throated Babbler (Pellorneum ruficeps), White-browed Scimitar Babbler (Pomatorhinus schisticeps), and White-bellied Yuhina (Yuhina zantholeuca)—obtained through color-banding, nest finding, and territory mapping with those derived from distance methods in evergreen forest in northeastern Thailand. We also assessed the availability of birds to be detected using a closed-capture model and incorporated this with point-transect distance sampling. Abundance estimates from territory mapping and distance sampling were highly correlated, but biased for two species using line transects and five species using point transects. Six of the seven biased estimates were biased low. Probabilities of detection were not significantly different between lines and points, and there was no significant difference in the overall accuracy between methods. Accounting for observer differences improved density estimates but reduced precision. The variance in accuracy was mostly related to the behavior of the different species. Adjusting for availability did not improve the overall accuracy of the estimates, because of the low singing rates of tropical birds. Nonetheless, distance sampling provided relatively robust estimates despite the near total dependence on aural cues. Violations of distance-sampling assumptions may be frequent in heavily forested habitats, where both availability for detection and probability of detection on the transect line (or point) are likely to be <1.

Plant-frugivore interactions in an intact tropical forest in north-east Thailand

Fleshy-fruited plants in tropical forests largely rely on vertebrate frugivores to disperse their seeds. Although this plant-animal interaction is typically considered a diffuse mutualism, it is fundamental as it provides the template on which tropical forest communities are structured. We applied a mutualistic network approach to investigate the relationship between small-fruited fleshy plant species and the fruit-eating bird community in an intact evergreen forest in northeast Thailand. A minimum of 53 bird species consumed fruits of 136 plant species. Plant-avian frugivore networks were highly asymmetrical, with observed networks filling 30% of all potential links. Whereas some of the missing links in the present study might be due to undersampling, forbidden links can be attributed to size constraints, accessibility and phenological uncoupling, and although the majority of missing links were unknown (58.2%), many were probably due to a given bird species being either rare or only a very occasional fruit eater. The most common frugivores were bulbuls, barbets and fairy-bluebirds, which were responsible for the majority of fruit removal from small fleshy fruited species in our system. Migratory birds seemed to be a minor component of the plant-frugivore networks, accounting for only 3% of feeding visits to fruiting trees; they filled 2% of the overall potential networks. The majority of interactions were generalized unspecific; however, Saurauia roxburghii Wall. appeared to be dependent on flowerpeckers for dispersal, while Thick-billed Pigeons were only seen to eat figs.

Plastic colour rings and the incidence of leg injury in flycatchers (Muscicapidae, Monarchidae)

Studies of birds involving colour ringing can provide much detailed information concerning bird movements and behaviour without the need for recapture. However, a fundamental premise of colour ringing, and indeed all ringing studies, is that the rings applied should neither cause harm to the birds concerned nor alter their behaviour or survival. Colour rings have been used safely for many studies on a wide range of species, and problems are rarely reported. Here, we report on problems associated with colour‐ringing several species of flycatcher, and discuss the nature and extent of the issue. Unacceptable levels of leg injury were reported when flycatchers were ringed using either celluloid or PVC colour rings, particularly when the colour ring was proximal to the foot. In the light of our evidence, we would urge those considering embarking upon colour‐ringing projects involving flycatchers to consider using anodised aluminium colour rings and to avoid the use of plastic colour rings.

Observations and Predation of a Coral-billed Ground Cuckoo (Carpococcyx renauldi) Nest in Northeastern Thailand

Abstract We found the first documented wild nest of a Coral-billed Ground Cuckoo (Carpococcyx renauldi) at Khao Yai National Park, Thailand in June 2007. The large stick nest was monitored for 24 days including 1095 hrs of video footage; it contained two eggs and was in dense vegetation 4.85 m above the ground. Nest attentiveness of adults was almost constant with both birds taking turns to incubate or brood. Food delivered to nestlings included lizards, nestlings, a snake, frogs, earthworms, and other invertebrates. Nest defense was observed against several known nest predators but the nest ultimately failed due to predation by a pig-tailed macaque (Macaca nemistrina). These observations provide insight into the breeding ecology of the only two congeners, C. viridis and C. radiceus, for which little is known of their ecology and both are endangered.

Breeding Ecology and Nesting Success of Abbott's Babbler (Malacocincla abbotti)

Abstract Baseline demographic data are lacking for most tropical forest birds, particularly from undisturbed habitats. During the 2003 breeding season, we documented the productivity of Abbotts Babbler (Malacocincla abbotti), a sedentary insectivorous passerine, on a 30-ha permanent forest plot in northeastern Thailand. We found 17 active nests of 13 breeding pairs, for which the Mayfield estimate for overall nesting success was 0.36 ± 0.13 SE. Breeding started in mid-January, a month earlier than previously recorded. Despite a relatively long period of post-fledging parental care, at least five pairs were double-brooded.

Diet and Breeding Biology of Asian Golden Weaver (Ploceus hypoxanthus)

The Asian Golden Weaver ( Ploceus hypoxanthus ) occurs in Myanmar, Thailand, Laos, Vietnam, Cambodia, and Indonesia and inhabits marshes, grasslands, reeds and rice fields close to water in the lowlands (Robson 2000) and natural waterholes in lowland dry dipterocarp forest (Round 1998). It is globally ‘Near-threatened’ due to habitat loss through the conversion of wetlands to agricultural and settlement areas (BirdLife International 2007). In Thailand it is local and uncommon in the north, north-east and central regions (Lekagul and Round 1991, Robson 2000). However, no quantitative data are available regarding its ecological requirements. Our objectives were to collect basic ecological data on: i) population structure, ii) nesting habitat characteristics, iii) food selection and foraging behaviour, and iv) parental care at the nest.