Scurfield Memorial Bursary Report 2014 - Luke Nelson

Luke Nelson

This summer, thanks to the Scurfield Memorial Bursary, I had the opportunity to be a research assistant for Dr Dave Edwards, working on a project looking at avian community responses to logging of tropical rainforests.

Background rationale of the project

Biodiversity is declining, and habitat loss and degradation are a major driver of this decline. Tropical rainforests are the most biodiverse ecosystems on Earth, yet are under increasing threat from deforestation and logging. Continued logging results in an increasingly degraded and often fragmented landscape. Nevertheless, work based at the Danum Valley and Ulu Segama-Malua Forest Reserve in Sabah, Borneo suggests that logged-over forests retain much biodiversity in the short term. However, there are negative impacts of logging on some species, and the key issues are whether overall levels of biodiversity and, in particular, species that have been negatively impacted by logging will remain after longer time periods.

The project which I have been involved in focuses on avian community responses to logging. To do so a network of long-term research plots have been created, which will allow us to answer two broad questions.

First, by comparing vital rates and population parameters of primary forest understory bird communities to those in logged forest stands, the project will reveal whether there are long-term impacts of logging on populations and their ecology. Specifically, this will allow us: (i) to determine the extent to which logged forests will retain species populations and diversity over long time periods; (ii) to determine relationships between avian population parameters and variation in microhabitat structure and composition resulting from different local intensities of logging; and (iii) to determine impacts of logging on site- and landscape-level ecological parameters, including dispersal, site fidelity, foraging range, and source/sink dynamics.

Second, focusing on reproduction, we will determine whether logging impacts species at the physiological level. Most accumulated information regarding how birds time reproduction has been collected in mid and high latitudes of the northern hemisphere. Forces determining reproductive timing in these environments may include environmental factors like resource availability, temperature, and photoperiod; these may act as proximate cues to physiological activities regulating reproduction. Because tropical species are exposed to less pronounced seasonal environmental changes than those in temperate zones, results observed in temperate zones should not be extrapolated to tropical birds. Still, many tropical bird species show pronounced breeding seasons. While the ultimate factors driving reproduction timing in tropical species may be similar to those in temperate zones (e.g. resource availability, predation pressure, other cyclic energetic expenditures), little is known about proximate factors. This study will thus determine the impacts of logging on reproductive hormones during the 2014 field season. This component of the research will also help to answer the more general scientific question of whether and to what extent the temperate model of hormone production in territorial birds applies to territorial tropical birds.


The study was carried out in the 1 million hectare Yayasan Sabah logging concession in Sabah, Malaysia. To carry out the study, standardised mist netting was carried out in primary rainforest, and twice logged forest. Six sites were established with three in unlogged forest, and three in twice logged forest. Sites within each habitat were located more than or equal to 2km apart. Within each site there were two transects 200m long and consisting of 15 12m long mist nets each, allowing for a spare 20m for gaps due to fallen tree trunks, precipitous gullies, etc.. Each transect was split into 5 zones consisting of three nets each. The approximate distance between the midpoints of each zone was 50m, so that distances of 50m, 100m, 150m, and 200m coulf be calculated by comparing the zone a bird was retrapped in with zones it was previously caught in. In addition the transects were placed 250m apart to capture any movement of birds over further distances. Nets were opened from 06.00-12.00 on two consecutive days, with each transect being visited three time over the course of the field season, with the aim of re-trapping birds to measure distance moved. Each bird was marked with a uniquely numbered metal leg-ring, and species and zone caught in were recorded. Morphometric measurements were taken of flattened wing chord, tail length, tarsus length, bill length and bill depth. Birds were processed and released in the zone which they were caught in, to prevent any measurements of distance moved to be due to sampling effects.

Luke Nelson Figure 1

Personal Experience

Having had previous mist-netting experience, after 2 weeks supervision and guidance in species identification, specific practice for the study and the idiosyncrasies of rainforest mist-netting, I was made team leader of one of two mist netting teams. I was always accompanied by another research assistant, but being team leader meant I was responsible for ensuring best practice and the birds' welfare. I believe this greatly improved my ringing, as I was reliant on myself to make decisions, such as which size ring to put on birds, where to place the nets, and when to stop ringing due to rain.

Luke Nelson Figure 2

In addition to ringing the birds and taking morphometric measurements, data related to vital rates was also collected where possible, including age and sex. Previously I had had experience of ageing and sexing birds in the UK, where you know what features to look out for depending on species and time of year, and there are guides that you can refer to. Features include plumage, feather condition, brood patch and cloacal condition. In Borneo however there is no guide, which means you have to have a more detailed knowledge of moult to work out the ages of the birds. This is further confounded by the fact that in temperate regions most birds follow a similar annual cycle of breeding in the spring, and having well known times of moult. However as tropical avifauna have been understudied compared to temperate regions it is not known what time of year birds breed, or if they follow a general pattern: it may be different for each individual species. I learnt more back to basics understanding of moult, by being taught by Suzanne Tomassi, the project manager who is an experienced ringer from the USA. As Suzanne is going to be involved with the project for the next decade, she has decided to write a book about ageing and sexing the birds of Borneo, which I hope to remain involved in. Together we worked out how to sex Little Spiderhunters based on bill length (Fig. 3) and that Pittas seem to both have brood patches, suggesting they share parental duties. Over the ten years further research will be done, including analysing all the morphometric data and photos from this first year of data collection.

Luke Nelson Figure 3

Personal conclusions

In total 1453 birds were caught with a total of 90 species. For an example of the diversity see figure 4. As this was year one, little useful analysis can be done on the data, only within year movement. After next year both within year and between year movements can be analysed, and a better picture of how logging is affecting bird movement can be made. In addition the data from this first year can be used as pilot data to apply for funding to carry the project onwards, as this year all contributions of time were voluntary.

Not only did I learn a lot of specific skills (mist-netting, ageing birds etc.) during my time as a research assistant, I also learned lots about life in academia (for a tropical scientist). Firstly tropical fieldwork is extremely hard work! The heat, humidity, biting insects, hilly and muddy jungle, long days and heavy equipment all add up to the toughest work I've ever done. It is definitely not for everyone, but it definitely confirmed with me that this is what I want to do in the future. The joys of seeing so much biodiversity and learning and seeing something new every time you enter the forest far outweigh all the physical discomforts. Although if you asked me on day one I may have replied differently. I absolutely loved my time as a research assistant and am really grateful having the opportunity to spend a significant amount of time working in the rainforest. I also learned teamwork skills, as for the mist-netting we had a core team of 5 with several others who helped. I learnt the importance of good communication, and how to work well with people you don't necessarily get on with. In addition, working at a field centre I learnt a lot about what academic life is like for tropical researchers.

Thanks are given to the Scurfield Family for awarding me the Scurfield Memorial Bursary allowing me this opportunity to gain tropical field experience. The bursary helped to cover transport and accommodation costs.

Luke Nelson Figure 4