Variations in pest bird density in Argentinean agroecosystems in relation to land use and/or cover, vegetation productivity and climate

Context Changes in environmental conditions may influence bird populations, including pest bird species, and their distribution. In Argentina, particularly in the Pampas region, agricultural expansion has resulted in important changes in agroecosystems, with impacts on bird species. Aims This study analysed the relationship between pest bird densities and the environmental variables associated with land use and/or cover, vegetation productivity and climate. The study focused on the most important pest bird species to grain crops in Argentina and Uruguay: the eared dove (Zenaida auriculata) and the monk parakeet (Myiopsitta monachus). Methods An area in Central Argentina was divided into three agro-productive regions, one predominantly agricultural and two with mixed production activities: agricultural rangeland and agricultural forested rangeland. Bird populations were sampled on a yearly basis between 2003 and 2011 in point-transects located along secondary roads (47 routes in total). Linear mixed models and a multi-model inference approach were used to compare the effects of individual predictive variables on bird densities. Key results Mean estimated density for the eared dove was 0.39 individuals per ha (±0.02), almost three times the density of the monk parakeet (0.10 individuals per ha±0.02). The spatial distribution of changes in density of the eared dove and monk parakeet showed irregular patterns across the study area. Density of eared dove was directly related to cover of native and exotic woodlots and inversely related to cover of fallow and weedy fields, and to temperature and rainfall. Monk parakeet density, in turn, was directly related to cover of woodlots. Conclusions The density of eared doves and monk parakeets changed mostly in relation to land use and/or cover and, to a lesser extent, to climatic conditions. Information of pest bird populations in a long-term period allowed us to understand spatial patterns in bird population distribution and to identify the main environmental factors explaining them. Implications The consideration of land use and/or cover, vegetation productivity and climate variables at regional scale, measured during a long-term period, would be critical for anticipating population increases and, possibly, increases in crop damage.

Impact of the insecticide Alphacypermetrine and herbicide Oxadiazon, used singly or in combination, on the most abundant frog in French rice fields, Pelophylax perezi

The potential impact of agricultural pesticides is a major concern with regard to biodiversity conservation. Pesticides are considered as one of the main causes of the worldwide decline of Amphibians. They are rarely used singly, but their cumulative impact and interaction are often neglected, as is the importance of the age or stage of the animal on which the impact of the molecules is assessed. We therefore tested the potential cumulative impact of the only authorized insecticide (Alphacypermetrine) and the main herbicide (Oxadiazon) used in French rice fields on four replicates of 25 eggs, young larvae and prometamorphosis tadpoles of the most abundant frog in paddies (Pelophylax perezi). We found no significant effect of the insecticide and herbicide, used singly or in combination, on hatching and young tadpoles. However, we found a strong impact of insecticide and herbicide used singly and a highly deleterious impact of their combined use on prometamorphosis tadpoles. Among the four replicates, only one of the prometamorphosis tadpoles did not reach this adult stage in the control against 9, 9, 6, 4 and 13, 9, 8, 7 with the herbicide and insecticide, respectively. But when the two pesticides were used in combination, only two prometamorphosis tapdoles reached the adult stage. Our results emphasize the potential impact on amphibians of pesticides used in agriculture and highlight the necessity of testing their role as cocktails. They also stress the importance of the age and/or stage of the target organism, the choice of which can lead to contrasting conclusions. Finally, our results suggest a possible underestimation of the impact of pesticides on non-targeted fauna in the rice fields in particular, and on living organisms in general.

Modelling hen harrier dynamics to inform human-wildlife conflict resolution: a spatially-realistic, individual-based approach

Individual-based models have gained popularity in ecology, and enable simultaneous incorporation of spatial explicitness and population dynamic processes to understand spatio-temporal patterns of populations. We introduce an individual-based model for understanding and predicting spatial hen harrier (Circus cyaneus) population dynamics in Great Britain. The model uses a landscape with habitat, prey and game management indices. The hen harrier population was initialised according to empirical census estimates for 1988/89 and simulated until 2030, and predictions for 1998, 2004 and 2010 were compared to empirical census estimates for respective years. The model produced a good qualitative match to overall trends between 1989 and 2010. Parameter explorations revealed relatively high elasticity in particular to demographic parameters such as juvenile male mortality. This highlights the need for robust parameter estimates from empirical research. There are clearly challenges for replication of real-world population trends, but this model provides a useful tool for increasing understanding of drivers of hen harrier dynamics and focusing research efforts in order to inform conflict management decisions.

Exploring the effects of spatial autocorrelation when identifying key drivers of wildlife crop-raiding

Few universal trends in spatial patterns of wildlife crop-raiding have been found. Variations in wildlife ecology and movements, and human spatial use have been identified as causes of this apparent unpredictability. However, varying spatial patterns of spatial autocorrelation (SA) in human–wildlife conflict (HWC) data could also contribute. We explicitly explore the effects of SA on wildlife crop-raiding data in order to facilitate the design of future HWC studies. We conducted a comparative survey of raided and nonraided fields to determine key drivers of crop-raiding. Data were subsampled at different spatial scales to select independent raiding data points. The model derived from all data was fitted to subsample data sets. Model parameters from these models were compared to determine the effect of SA. Most methods used to account for SA in data attempt to correct for the change in P-values; yet, by subsampling data at broader spatial scales, we identified changes in regression estimates. We consequently advocate reporting both model parameters across a range of spatial scales to help biological interpretation. Patterns of SA vary spatially in our crop-raiding data. Spatial distribution of fields should therefore be considered when choosing the spatial scale for analyses of HWC studies. Robust key drivers of elephant crop-raiding included raiding history of a field and distance of field to a main elephant pathway. Understanding spatial patterns and determining reliable socio-ecological drivers of wildlife crop-raiding is paramount for designing mitigation and land-use planning strategies to reduce HWC. Spatial patterns of HWC are complex, determined by multiple factors acting at more than one scale; therefore, studies need to be designed with an understanding of the effects of SA. Our methods are accessible to a variety of practitioners to assess the effects of SA, thereby improving the reliability of conservation management actions.

Non-linear feeding functional responses in the Greater Flamingo (Phoenicopterus roseus) predict immediate negative impact of wetland degradation on this flagship species

Accurate knowledge of the functional response of predators to prey density is essential for understanding food web dynamics, to parameterize mechanistic models of animal responses to environmental change, and for designing appropriate conservation measures. Greater flamingos (Phoenicopterus roseus), a flagship species of Mediterranean wetlands, primarily feed on Artemias (Artemia spp.) in commercial salt pans, an industry which may collapse for economic reasons. Flamingos also feed on alternative prey such as Chironomid larvae (e.g., Chironomid spp.) and rice seeds (Oryza sativa). However, the profitability of these food items for flamingos remains unknown. We determined the functional responses of flamingos feeding on Artemias, Chironomids, or rice. Experiments were conducted on 11 captive flamingos. For each food item, we offered different ranges of food densities, up to 13 times natural abundance. Video footage allowed estimating intake rates. Contrary to theoretical predictions for filter feeders, intake rates did not increase linearly with increasing food density (type I). Intake rates rather increased asymptotically with increasing food density (type II) or followed a sigmoid shape (type III). Hence, flamingos were not able to ingest food in direct proportion to their abundance, possibly because of unique bill structure resulting in limited filtering capabilities. Overall, flamingos foraged more efficiently on Artemias. When feeding on Chironomids, birds had lower instantaneous rates of food discovery and required more time to extract food from the sediment and ingest it, than when filtering Artemias from the water column. However, feeding on rice was energetically more profitable for flamingos than feeding on Artemias or Chironomids, explaining their attraction for rice fields. Crucially, we found that food densities required for flamingos to reach asymptotic intake rates are rarely met under natural conditions. This allows us to predict an immediate negative effect of any decrease in prey density upon flamingo foraging performance.

Lead poisoning in wild birds from southern Spain: a comparative study of wetland areas and species affected, and trends over time

We studied lead (Pb) shot contamination in sediments from the Guadalquivir marshes and six other closed-basin lagoons in Southern Spain that are of major importance for threatened species of waterbirds. Shot densities were relatively low in Doñana, ranging from 0 to 25 shot/m(2) in the top 10 cm of sediments. The density at Medina lagoon (Ramsar site) was 148 shot/m(2), making it the most contaminated wetland known in Europe. Densities in the other five lagoons ranged from 9 to 59 shot/m(2). We studied the prevalence of ingested Pb shot in waterbirds from Doñana and found a lower prevalence in ducks than previously recorded in other Spanish wetlands. Lead shot were also found embedded in tissues of some waterbirds, proving that protected species such as the greater flamingo (Phoenicopterus ruber) and the glossy ibis (Plegadis falcinellus) are subjected to illegal hunting. The prevalence of embedded shot for geese was especially high (44% for trapped birds). Lead shot were detected in 2.8% of the pellets of the Spanish imperial eagle (Aquila adalberti) which usually preys on geese. We found that the prevalence of ingested Pb shot in geese and in Spanish imperial eagles has significantly decreased in recent years, possibly due to restrictions on hunting activity, efforts to remove shot from a sand dune used by geese to obtain grit, and to the high rainfall in Doñana during the last years that permitted waterfowl to stay more within the protected areas.