ABSTRACT. Automated sound recording devices have become an important monitoring tool used to estimate species richness and abundance of birds in a variety of ecological and conservation studies. The prevalence of calls detected in a specific time period can be used as an index of relative abundance, to compare between populations. However, the statistical power to infer true differences in abundance between populations is low when detections are highly aggregated in time leading to high variance between samples from the same population. Here, we used two different sampling methods, and used the data from each to calculate species richness and acoustic prevalence of nine bird taxa from a total of 50 sound recordings. The first method simulated typical monitoring techniques used by observers in the field by using a continuous five-minute section of the recording. The second method used the first 10 seconds of each minute to create a composite recording, also of five minutes total duration. There was no difference in the mean prevalence index between methods. The intermittent samples, however, produced prevalence indices with a lower standard deviation (mean difference = 19 %), detected 26% more species per five-minute sample and required 60% less total listening time to detect as many species as the continuous method. The only cost of subsampling from a long recording is the extra digital memory and battery life required to obtain the recordings in the first place. Given that these costs are minor, the intermittent method holds much promise because it detects species more efficiently and provides greater power to detect differences in a species' relative abundance, which in turn should allow for better-informed management regarding population status and trends.Échantillonnage efficace d'enregistrements d'oiseaux : le sous-échantillonnage intermittent améliore les estimations d'occurrence pour une espèce et de la richesse spécifique totale RÉSUMÉ. Les appareils d'enregistrement automatiques sont devenus des outils de suivi importants pour estimer la richessse spécifique et le nombre d'oiseaux dans le cadre de diverses recherches en écologie et conservation. La fréquence des chants détectés dans une période spécifique peut servir d'indice d'abondance relative, afin de comparer des populations. Toutefois, la puissance statistique à révéler les vraies différences d'abondance entre des populations est faible lorsque les détections sont très rapprochées dans le temps, ce qui engendre une grande variance entre les échantillons d'une même population. Dans la présente étude, nous avons utilisé deux méthodes différentes d'échantillonnage et les données provenant de celles-ci pour calculer la richesse spécifique et l'occurrence de neuf taxons d'oiseaux à partir de 50 enregistrements. La première méthode simulait la technique habituellement utilisée par les observateurs sur le terrain, soit l'écoute d'une section de 5 minutes continues de l'enregistrement. La seconde méthode reposait sur les 10 premières secondes de chaque mi...

Woody plants in arid and semi-arid environments may enhance soil nutrient status, the so-called 'fertile island' effect, but this mechanism has never been tested in the drylands of New Zealand. In this study I investigated effects of Kunzea serotina, Discaria toumatou, Rosa rubiginosa, and Coprosma propinqua on soil properties in the drylands of central Otago, New Zealand. Soils had significantly higher organic matter under C. propinqua and significantly higher nitrate and phosphorus concentrations under K. serotina than soils in the adjacent open grassland. A bioassay using oat (Avena sativa) growth indicated higher fertility in soils from under K. serotina than from under grassland. A review of 28 other studies revealed that fertile island effects of woody plant species on soil nitrogen and phosphorus concentrations decreased significantly with increases in annual precipitation. The occurrence of fertile islands under only two of the four shrub species in the current study in a dry sub-humid environment is consistent with this trend of decreased fertile island effect with increased annual precipitation. The higher concentration of nitrogen in soils under woody plants such as C. propinqua may be explained by the plants depositing organic matter on the surface, but some species such as K. serotina, D. toumatou, R. rubiginosa and C. propinqua, may also preferentially establish in areas of high soil phosphorus availability. I conclude that the occurrence of fertile islands under woody plants may be due to both effects of the woody plant canopy, and the plants preferentially establishing in areas of high soil fertility.

No abstract

No abstract

<p>Electronic bioacoustic techniques are providing new and effective ways of monitoring birds and have a number of advantages over other traditional monitoring methods. Given the increasing popularity of bioacoustic methods, and the difficulties associated with automated analyses (e.g. high Type I error rates), it is important that the most effective ways of scoring audio recordings are investigated. In Chapter Two I describe a novel sub-sampling and scoring technique (the ‘10 in 60 sec’ method) which estimates the vocal conspicuousness of bird species through the use of repeated presence-absence counts and compare its performance with a current manual method. The ‘10 in 60 sec’ approach reduced variability in estimates of vocal conspicuousness, significantly increased the number of species detected per count and reduced temporal autocorrelation. I propose that the ‘10 in 60 sec’ method will have greater overall ability to detect changes in underlying birdsong parameters and hence provide more informative data to scientists and conservation managers.  It is often anecdotally suggested that forests ‘fall silent’ and are devoid of birdsong following aerial 1080 operations. However, it is difficult to objectively assess the validity of this claim without quantitative information that addresses the claim specifically. Therefore in Chapter Three I applied the methodological framework outlined in Chapter Two to answer a controversial conservation question: Do New Zealand forests ‘fall silent’ after aerial 1080 operations? At the community level I found no evidence for a reduction in birdsong after the 1080 operation and eight out of the nine bird taxa showed no evidence for a decline in vocal conspicuousness. Only one species, tomtit (Petroica macrocephala), showed evidence for a decline in vocal conspicuousness, though this effect was non-significant after applying a correction for multiple tests.  In Chapter Four I used tomtits as a case study species to compare manual and automated approaches to: (1) estimating vocal conspicuousness and (2) determine the feasibility of using an automated detector on a New Zealand passerine. I found that data from the automated method were significantly positively correlated with the manual method although the relationship was not particularly strong (Pearson’s r = 0.62, P < 0.0001). The automated method suffered from a relatively high false negative rate and the data it produced did not reveal a decline in tomtit call rates following the 1080 drop. Given the relatively poor performance of the automated method, I propose that the automatic detector developed in this thesis requires further refinement before it is suitable for answering management-level questions for tomtit populations. However, as pattern recognition technology continues to improve automated methods are likely to become more viable in the future.</p>