Birds and the Fire Cycle in a Resilient Mediterranean Forest: Is There Any Baseline?

This study investigates the effects of recurrent wildfires on the resilience of a typical Mediterranean ecosystem. It is based on uninterrupted monitoring over 42 years of the avifauna in a cork oak forest that burned three times during this time interval. The monitoring involved two line-transect counts in spring accompanied by the simultaneous and independent estimation of the vegetation cover profile. One of the two transects was initially designed to serve as an unburned control before it also burned during the second fire. Many forest bird species were already present from the first spring postfire due to the rapid regeneration of the canopy. Some open-habitat bird species colonized the burned area during the first 2–4 years after the fire, resulting in an initial phase of high diversity. The postfire bird succession was mainly driven by sedentary species that recolonized the burned area after the first winter, whereas most migratory species present before the fire resettled as early as the first postfire spring, probably because of site tenacity. It was found that the impact of the second fire on avifauna was lower than that of the first or third fire. The return to an avifauna and forest structure successionally equivalent to the prefire control was achieved in about 15 years, which can be considered as the recovery time. Afterwards, both vegetation and avifauna in the burned areas tended to take on more forest characteristics than in the prefire control. These findings suggest that: (i) the recurrence of fire does not necessarily result in the cumulative degradation of the ecosystem at each repetition; (ii) the asymptotic resilience model is not adapted to the case of disturbances in non-mature environments; (iii) the notion of returning to an original undisturbed baseline is illusive in an area that has been under continuous human influence since ancient times.

Airborne environmental DNA metabarcoding for the monitoring of terrestrial insects - a proof of concept

Biodiversity is in decline due to human land use, exploitation, and climate change. To be able to counteract this alarming trend it is paramount to closely monitor biodiversity at global scales. Because this is practically impossible with traditional methods, the last decade has seen a strong push for solutions. In aquatic ecosystems the monitoring of species from environmental DNA (eDNA) has emerged as one of the most powerful tools at our disposal but in terrestrial ecosystems the power of eDNA for monitoring has so far been hampered by the local scale of the samples. In this study we report the first attempt to detect insects from airborne eDNA. We compare our results to two traditional insect monitoring projects (1) using light trapping for moth monitoring and (2) transect counts for the monitoring of butterflies and wild bees. While we failed to detect many of the same species monitored with the traditional methods, airborne eDNA metabarcoding revealed DNA from from six classes of Arthropods, and twelve order of Insects - including representatives from all of the four largest orders: Diptera (flies), Lepidoptera (butterflies and moths), Coleoptera (beetles) and Hymenoptera (bees, wasps and ants). We also recovered DNA from nine species of vertebrates, including frogs, birds and mammals as well as from 12 other phyla. We suggest that airborne eDNA has the potential to become a powerful tool for terrestrial biodiversity monitoring, with many impactful applications including the monitoring of pests, invasive or endangered species or disease vectors.

Seasonality and landscape characteristics impact species community structure and temporal dynamics of East African butterflies

Species community structures respond strongly to habitat changes. These are either driven by nature or human activities. The biota of East African drylands responds highly sensitively to natural and anthropogenic impacts. Thus, seasonality strongly influences resource availability in a cyclic manner during the year, with cyclic appearance of the different developmental stages of invertebrates, while man-made landscape transformations profoundly and permanently modify habitat structures and, as a consequence, species communities. Butterflies are an excellent model group for the study of the effects of seasonality, and to test for biodiversity responses to anthropogenic activities such as habitat modification, degradation and destruction. We performed transect counts of adult butterflies in riparian forests and their adjoining areas, either dry savannahs with occasional pasturing (i.e. near-natural status) or farmland areas with fields, gardens and settlements (i.e. highly degraded status with lack of original vegetation). Transects were set along the river beds as well as at 250 m and 500 m distances parallel to these rivers, with eight transects per distance class and site (i.e. 48 transects in total). We recorded habitat structures for each transect. Counts were conducted during the dry and the rainy season, with 16 repetitions for each single transect, i.e. eight per season and transect. We compiled trait data on morphology, geographic distribution, ecology, behaviour, and life-history for all butterfly species encountered. Our results show higher species richness and numbers of individuals in farmland transects compared with the savannah region. Seasonal fluctuations of the detectable species abundances between the rainy and dry season were severe. These fluctuations were much more pronounced for the savannah than the farmland area, i.e. was buffered by human activities. Farmland and savannah support two distinct butterfly communities, with generalist species being more common in the farmland communities. Strict habitat associations were comparatively weak and typical dry savannah and riparian forest species were not clearly restricted to the near natural landscape.

Evaluation of counting methods for monitoring populations of a cryptic alpine passerine, the rock wren (Passeriformes, Acanthisittidae, Xenicus gilviventris)

Developing and validating methods to determine trends in populations of threatened species is essential for evaluating the effectiveness of conservation interventions. For cryptic species inhabiting remote environments, this can be particularly challenging. Rock wrens, Xenicus gilviventris, are small passerines endemic to the alpine zone of southern New Zealand. They are highly vulnerable to predation by introduced mammalian predators. Establishing a robust, cost-effective monitoring tool to evaluate population trends in rock wrens is a priority for conservation of both the species and, more broadly, as part of a suite of indicators for evaluating effectiveness of management in New Zealand’s alpine ecosystems. We assessed the relative accuracy and precision of three population estimation techniques (mark-resight, distance sampling and simple counts on line transects) for two populations of rock wrens in the Southern Alps over six breeding seasons (2012–2018). The performance of these population estimators was compared to known rock wren population size derived from simultaneous territory mapping. Indices of abundance derived from counts on transects were correlated with territory mapping at both study areas, and performed better than either mark-resight methods or distance sampling. Simple counts on standardised line transects are a highly cost-effective method of monitoring birds because they do not require banding a population. As such, we recommend that line transect counts using the design outlined in this paper be adopted as a standard method for long-term monitoring of rock wren populations. Although species-specific testing is required to validate use of low-cost population indices, our results may have utility for the monitoring of other cryptic passerines in relatively open habitats.

Environmental pollution and arthropod community change: Impact of quarry activities on invertebrate biodiversity in Ghana.

Quarry operations can have a negative impact on invertebrate biodiversity and threaten local species through a variety of factors, such as habitat loss and pollution. Quarrying is a common practice in Ghana, but little is known about its effects on local insect diversity and abundance. In this study, the relationship between quarry operations and insect communities on an active quarry site, the Mowire quarry site in the Ashanti region of Ghana was assessed. Transect counts, aerial nets, pitfall traps, Flight interception traps (FIT) and fruit baiting (Charaxes) traps were employed to assess arthropod assemblage, specifically insects as a surrogate for arthropod communities. A total of 2,902 individual insects belonging to 56 families and eleven orders were recorded in all transect points across the three sampling zones. Quarry operations had little impact on the relative abundance (N = 974) of insects at Transect point (TP) 400m in the Eastern Zone (EZ), species richness (S = 49) and the highest abundance (N = 302) corresponding with high diversity of flowering plants at this site that are a food source for pollinators and herbivorous insects. Quarry operations negatively affected the relative abundance (N= 541) and richness (S = 37) of insects in the Western zone (WZ), significantly affecting TP 400m in the WZ, corresponding to the low abundance of food plant as well as volumes of dust that settle at the WZ after every blast, as dust travels in the direction of this zone. It is recommended that interventions to prevent biodiversity habitat loss in and around the quarry operational site should focus on policies that ensure and enforce the establishment of a dust control mechanism system in the extractive industry.

How reliable is the use of transect counts to assess the population of the New Forest Burnet moth (Zygaena vicae [D. & S.], 1775) (Lepidoptera: Zygaenidae) at its only British site in western Scotland

The population of the New Forest burnet moth, Zygaena viciae, at its only UK site in western Scotland, was assessed between 1990 and 2019, using direct counts, standard transect counts and Mark/Release/Recapture (MRR). Data from eleven of these years, when reliable comparative transect counts and MRR population estimates were available, were analysed to answer the question as to whether the more economical transect counts provided a reliable estimate of the population size. Lin's Concordance Coefficient showed conclusively that transect counts do have a consistent relationship with the MRR population estimates. However, it was found that transect counts consistently under-estimate the MRR derived population estimates and that the scaling factor between them is best valued at ×5 (see Results). It can be concluded that, when resources are too limited to allow a full MRR population analysis, the more economical transect counts can trusted to indicate the relative size of the moth population.

On the Reproducibility of Bird and Mammal Transect Counts in Polar Seas

In order to make comparisons between seabird and marine mammal data collected at sea, a first step consists in evaluating their reproducibility. The same transects counted during years show huge variations up to one or two orders of magnitude. In this paper, I compare return transects followed in a short period. Out of important heterogeneities such as local hotpot concentrations, results obtained along the same return transect seem to vary by a factor of two to four. Within a same transect, data simultaneously collected by two observers on both sides of the bridge show ratios of mean values (numbers per 30 min counts) remaining below a factor two, with a mean variation by a factor1.4.

Seabird and Marine Mammal at-sea Distribution in the Norwegian, Greenland and Wandel Seas, 2018

Quantitative seabird and marine mammal at-sea distribution was determined in the Norwegian, Greenland and Wandel seas in August 2018 on board the icebreaking RV Polarstern. A total of 7,380 seabirds belonging to 25 species were tallied during 380 transect counts lasting 30 minute each, i.e. a mean value of 19 per count. Cetaceans were represented by seven species (mean of 0.1 per count) and pinnipeds by four species (0.1 per count). Numbers of seabird species and of individuals were low in the Norwegian Sea and the Greenland Sea (12 and 14 species, 4 and 8 individuals per count). They were especially low in the Wandel Sea off North Greenland: seven seabird species (2 individuals per count), mainly ivory gull Pagophila eburnea and fulmar Fulmarus glacialis. Cetaceans were absent and pinnipeds represented by three species only (0.3 per count). These concentrations are extremely low even when compared to other areas of the high Arctic Ocean.

Behaviourally mediated biases in transect surveys: a predation risk sensitivity approach

Variation in the behaviour of individuals or species, particularly their propensity to avoid or approach human observers, their conveyances (e.g., cars), or their proxy devices (e.g., drones) has been recognized as a source of bias in transect counts. However, there has been little attempt to predict the likelihood or magnitude of such biases. Behavioural ecology provides a rich source of theory to develop a general framework for doing so. For example, if animals perceive observers as predators, then the extensive body of research on responses of prey to their predators may be applied to this issue. Here we survey the literature on flight initiation distance (the distance from a predator or disturbance stimulus at which prey flee) for a variety of taxa to suggest which characteristics of the animal, the observer, and the environment may create negatively biased counts. We also consider factors that might cause prey to approach observers, creating positive bias, and discuss when and why motivation for both approach and avoidance might occur simultaneously and how animals may resolve such trade-offs. Finally, we discuss the potential for predicting the extent of the behaviourally mediated biases that may be expected in transect counts and consider ways of dealing with them.

Bird and Mammal at-sea Distribution Along the North-East Passage off Siberia

Quantitative seabird and marine mammal at-sea distribution was determined along the North-East Passage, off Siberia, in August 2017. A total of 18,400 seabirds were tallied during 340 transect counts, belonging to 31 species. Some bird species were numerically dominant: fulmar Fulmarus glacialis, Brünnich’s guillemot Uria lomvia, shorttailed shearwater Puffinus tenuirostris and crested auklet Aethia cristatellea representing more than 90 % of the total. Humpback Megaptera novaeangliae and bowhead whales Balaena mysticetus formed the bulk of the 100 large whales, as well as 40 white-beaked dolphins Lagenorhynchus albirostris, concentrated in a major hotspot. Two species represented 97 % of the 910 identified pinnipeds: harp seal Phoca goenlandica and walrus Odobenus rosmarus. Polar bear Ursus maritimus was detected as 75 individuals, while more than 3,500 were noted on Wrangel Island, out of effort. The major factors affecting top predators’ quantitative distribution were the geographic differences between seas, and the importance of a major hotspot for humpback whales and harp seals.