SummaryIn many bird monitoring surveys, no attempt is made to estimate bird densities or abundance. Instead, counts of one form or another are made, and these are assumed to correlate with bird density. Unless complete counts on sample plots are feasible, this approach can easily lead to false conclusions, because detectability of birds varies by species, habitat, observer and many other factors. Trends in time of counts often reflect trends in detectability, rather than trends in abundance. Conclusions are further compromised when surveys are conducted at unrepresentative sites. We consider how to avoid these problems. We give a brief description of distance sampling methods, which allow detectability to be estimated. We consider strategies to ease their implementation, to enhance their reliability, to adapt the methods for difficult species, and to deal with circumstances in which representative sampling is problematic. We also consider some of the common problems encountered, and suggest solutions.

The suitability of point count distance methods for estimating densities of tropical parrots and hornbills was assessed during surveys in Indonesia. The methods will perform well, so long as the following are considered. (1) Enough bird records must be accumulated to model species' detection curves precisely. For some species, around 2000 point counts may be needed and, in very rare species, the method may not be appropriate. Pooling data across habitats, species or years may increase precision in cases of small sample size. (2) Point counts are likely to be less biased than line transects because bird detection rates close to the recorder may be higher and there may be less chance of double‐counting birds. Distances greater than 400 m between census points are unnecessary. (3) Count periods lasting ten minutes may be needed to ensure that most birds close to the recorder are detected. Controlled flushing of concealed birds after the main count period may also be appropriate. (4) The best time of day for census is the period when bird detectability is high but bird mobility low. For many large avian frugivores, this corresponds to the period between one hour after dawn and 10.30 h. (5) Records of flying birds must be excluded from density calculations. In the species studied, between 2% and 20% should be added to density estimates to compensate for the exclusion of flying birds.

SUMMARYAlthough small-scale agroforestry systems (swiddens, complex and single-crop-dominated agroforests, and homegardens) form a diverse and important tropical land use, there has been no attempt to collate information on their value for biodiversity. This paper reviews 52 published studies that compared species richness and/or abundance between agroforests and primary forest, and 27 studies that compared biodiversity parameters across agroforests. The former covered a broad range of taxa and geographical areas, but few focused on homegardens, while those comparing across agroforestry systems were biased towards studies of plants (21 studies) and homegardens (13 of 27). Of 43 studies comparing species richness or diversity across habitats, 34 reported lower richness in agroforests than in adjacent forest. There was also high β diversity between primary forests and agroforests. Patterns of abundance shifts were less straightforward, with many species traits (for example diets) being generally poor indicators of response to agricultural disturbance. Among the few trends identified, restricted-range or rare species, and terrestrial and some understorey vertebrates tended to decline most, and open country species, granivores and generalists increased most in agroforests. Variability in biodiversity retention across systems has been linked most strongly to economic function, management intensity and extent of remnant forest within the landscape, as well as more subtle cultural influences. Species richness and abundance generally decrease with increasing prevalence of crop species, more intensive management, decreasing stratum richness and shortening of cultivation cycles. Increasing holding size did not necessarily reduce α diversity. Knowledge of the general effects of small-scale agroforestry on biodiversity is substantial, but the great diversity of systems and species responses mean that it is difficult to accurately predict biodiversity losses and gains at a local level. Further work is required on the influence of spatial and temporal structure of agricultural holdings on biodiversity retention across agriculture/succession/forest mosaics, how β diversity across individual holdings influences biodiversity across landscapes, and ultimately on how agricultural intensification can be best managed to minimize future losses of biodiversity from tropical landscapes.

We estimated densities of parrot and hornbill species in primary and selectively logged forest and forest gardens at two lowland sites on New Britain, PNG. We related differences in abundance to food and nest‐site availability in the different habitats and determined whether nest‐site availability might limit local breeding populations. Blue‐eyed Cockatoo Cacatua ophthalmica and Blyth's Hornbill Rhyticeros plicatus were usually rarer in forest gardens than in primary forest, but both fared well in logged forest. Eclectus Parrot Eclectus roratus was more common in all human‐altered forests than in primary forest, and Eastern Black‐capped Lory Lorius hypoinochrous was reasonably common throughout but extremely abundant in forest gardens at one site. Parrots and hornbills were recorded eating fruits of 15 tree species and flowers of nine species. Densities of these fruiting and flowering trees were highest in logged forest and forest gardens, respectively, indicating the importance of these anthropogenic habitats as feeding grounds for the assemblage. Active nest cavities were found in large individuals of 12 tree species. Densities of potential nest cavities were highest in primary forest and lowest in forest gardens. At both sites, estimates of potential nest‐site density were significantly lower than estimates of the density of pairs of all species of parrots and hornbills: there may be 10–20 parrot/hornbill individuals per nest‐hole. Continuing forest alteration, whilst further reducing nest‐site availability, may allow large populations of parrots and hornbills to persist due to increased availability of food in some anthropogenic habitats. However, current abundance of such bird species may be a poor correlate of future extinction risk as long‐lived taxa may remain common for some period even when annual recruitment has declined to critically low levels.

Many South-East Asian bird species are in rapid decline due to offtake for the cage-bird trade, a phenomenon driven largely by consumption in Indonesia and labelled the 'Asian Songbird Crisis'.Interventions aimed at reducing this offtake require an understanding of the spatial and temporal dynamics of the trade. We surveyed the bird-keeping habits of over 3,000 households from 92 urban and rural communities across six provinces on Java, Indonesia, and compared prevalence and patterns of bird keeping with those from surveys undertaken a decade ago. We estimate that one-third of Java's 36 million households keep 66-84 million cage-birds. Despite over half of all birds owned being non-native species, predominantly lovebirds (Agapornis spp.), the majority of bird-keepers (76%) owned native species.Ownership levels were significantly higher in urban than rural areas, and were particularly high in the eastern provinces of the island. Overall levels of bird ownership have increased over the past decade, and species composition has changed. Notably, lovebirds showed a seven-fold increase in popularity while ownership of genera including groups with globally threatened species such as leafbirds (Chloropsis spp.) and white-eyes (Zosterops spp.) also rose sharply. The volume of some locally threatened birds estimated to be in ownership (e.g., >3 million White-rumped Shama Kittacincla malabarica) cannot have been supplied from Java's forests and research on supply from other islands and Java's growing commercial breeding industry is a priority. Determining temporal and spatial patterns of ownership is a crucial first step towards finding solutions to this persistent, pervasive and adaptive threat to the regional avifauna.