Data analysis model selection for estimating local population size of the Risso’s dolphin (Grampus griseus) in the Azores

27th Annual Conference of the European Cetacean Society. Setúbal, Portugal, 8-10 April 2013.Different models estimating cetacean population size require making assumptions about the marking and recapturing of individuals, and on the structure of the population. Crucial in selecting the most appropriate model is a critical assessment of these assumptions. In this study we applied the robust parameterization of the open Jolly-Seber (JS) model (POPAN), using the software program MARK. This model was applied to data collected on the Risso’s dolphin (Grampus griseus). Between 2004 – 2007, photo-identification was used as a Capture-Mark-Recapture technique to identify 670 unique individuals off Pico Island, Azores. For this model, it was assessed what assumptions are supported or violated. The aim of this study was improving our understanding of how to select the most appropriate population size model

Movement Patterns of African Elephants (Loxodonta africana) in a Semi-arid Savanna Suggest That They Have Information on the Location of Dispersed Water Sources

Water is a scarce resource in semi-arid savannas where over half of the African elephants (Loxodonta africana) populations occur and may therefore influence their movement pattern. A random search is expected for an animal with no information on the location of the target resource, else, a direction-oriented walk is expected. We hypothesized that elephants movement patterns show a stronger directional orientation toward water sources in the dry season compared to the wet season. We investigated the movement paths of four male and four female elephants with hourly GPS fixes in Tsavo National Park, Kenya in 2012–2013. Consistent with our predictions, the movement paths of elephants had longer step lengths, longer squared net displacements, and were directed toward water sources in the dry season as compared to the wet season. We argue that African elephants know the location of dispersed water resources, enabling them to survive with scarce resources in dry savannas. These results can be used in conservation and management of wildlife, through for instance, protection of preferred water sources

Breeding performance of the grasshopper buzzard (<i>Butastur rufipennis</i>) in a natural and a human-modified West African savanna

Few studies have examined raptor reproduction in response to land-use change in sub-Saharan Africa, hampering conservation efforts to address regional declines. To further our understanding of mechanisms underlying the dramatic declines of West African raptors, we examined the relationship between environmental conditions, nest density, and measures of reproduction in the Grasshopper Buzzard (Butastur rufipennis). Analyses were based on 244 nest sites divided between transformed and natural habitat in northern Cameroon. At the landscape scale, nest density increased with the density of preferred nest trees. Nests were more widely spaced in transformed than in natural habitat. Dispersion was adjusted to differences in availability of small mammals, which was negatively associated with distance to nearest neighbor, and in the area under cultivation, which was positively associated with distance to nearest neighbor. Productivity was positively associated with rainfall, canopy shielding the nest, availability of grasshoppers, and the nest's visibility from ground level; canopy shielding, grass cover, rainfall, and distance to nearest neighbor were positively associated with nest success. In natural habitat, losses of eggs and nestlings to natural predators were greater than in transformed habitats, while losses through human predation were small. Productivity and nest success were unaffected by land use because of the opposing effects of greater predation pressure, closer spacing of nests, and more food in natural habitat than in transformed habitat. Thus transformed habitat may provide adequate breeding habitat for the Grasshopper Buzzard, but declining rainfall and intensifying anthropogenic land use are likely to affect future reproductive output

Large herbivores may alter vegetation structure of semi-arid savannas through soil nutrient mediation

In savannas, the tree–grass balance is governed by water, nutrients, fire and herbivory, and their interactions. We studied the hypothesis that herbivores indirectly affect vegetation structure by changing the availability of soil nutrients, which, in turn, alters the competition between trees and grasses. Nine abandoned livestock holding-pen areas (kraals), enriched by dung and urine, were contrasted with nearby control sites in a semi-arid savanna. About 40 years after abandonment, kraal sites still showed high soil concentrations of inorganic N, extractable P, K, Ca and Mg compared to controls. Kraals also had a high plant production potential and offered high quality forage. The intense grazing and high herbivore dung and urine deposition rates in kraals fit the accelerated nutrient cycling model described for fertile systems elsewhere. Data of a concurrent experiment also showed that bush-cleared patches resulted in an increase in impala dung deposition, probably because impala preferred open sites to avoid predation. Kraal sites had very low tree densities compared to control sites, thus the high impala dung deposition rates here may be in part driven by the open structure of kraal sites, which may explain the persistence of nutrients in kraals. Experiments indicated that tree seedlings were increasingly constrained when competing with grasses under fertile conditions, which might explain the low tree recruitment observed in kraals. In conclusion, large herbivores may indirectly keep existing nutrient hotspots such as abandoned kraals structurally open by maintaining a high local soil fertility, which, in turn, constrains woody recruitment in a negative feedback loop. The maintenance of nutrient hotspots such as abandoned kraals by herbivores contributes to the structural heterogeneity of nutrient-poor savanna vegetation

Results of the bootstrap analysis on cattle with or without a magnet attached.

<p>The mean cow direction is given in degrees (+/- standard deviation). The “Rayleigh north” is the mean result of the Rayleigh test (+/- standard deviation), testing for a deviation from north. “Rayleigh random” is the mean result of the Rayleigh test (+/- standard deviation), testing for a deviation from random distribution.</p

Results of the bootstrap analysis of correlation between cow compass direction and wind direction or sun direction while wearing or not wearing a magnet.

<p>The mean correlations are shown +/- standard deviation and represent the correlation between cow compass orientation and wind direction or sun direction, respectively. The mean test statistic and the mean P-value are also given (+/- standard deviation).</p

An experimental approach in revisiting the magnetic orientation of cattle

<div><p>In response to the increasing number of observational studies on an apparent south-north orientation in non-homing, non-migrating terrestrial mammals, we experimentally tested the alignment hypothesis using strong neodymium magnets on the resting orientation of individual cattle in Portugal. Contrary to the hypothesis, the 34 cows in the experiment showed no directional preference, neither with, nor without a strong neodymium magnet fixed to their collar. The concurrently performed 2,428 daytime observations—excluding the hottest part of the day—of 659 resting individual cattle did not show a south-north alignment when at rest either. The preferred compass orientation of these cows was on average 130 degrees from the magnetic north (i.e., south east). Cow compass orientation correlated significantly with sun direction, but not with wind direction. In as far as we can determine, this is the first experimental test on magnetic orientation in larger, non-homing, non-migrating mammals. These experimental and observational findings do not support previously published suggestions on the magnetic south-north alignment in these mammals.</p></div

Results of the analysis of correlation between cow compass direction and wind direction or sun direction, on bootstrapped data.

<p>“Correlation wind” and “correlation sun” represent the correlation between cow direction and wind direction or sun direction, respectively. “Test stat wind” and “Test stat sun” represent the respective test statistics. The “P-value” represents the significance of the correlation between cow compass orientation and wind direction or sun direction, respectively.</p

Large herbivore dynamics in northern Gonarezhou National Park, Zimbabwe

We compared densities and distribution of wild ungulates and domestic livestock based on aerial surveys conducted during 1991 - 2010 in northern parts of Gonarezhou National Park (GNP), Zimbabwe. The sampled area covered approximately 320 km2 (Chipinda Pools area) representing ca. 27 % of the GNP, which was colonized by a few herder families along with their cattle in the year 2000. We hypothesized that (1) human and livestock encroachment in the park would lead to decline in densities of native ungulates, and (2) wild ungulates would avoid habitats influenced by humans. The results show that cattle densities significantly increased after the year 2000 whereas the densities of the native ungulates did not differ significantly after 2000. The ‘no change’ situation in herbivore populations is attributed to strict anti-poaching measures and restriction of human activities within small portion (4 %) of the park. However, the aerial survey does suggest that human and livestock presence in the northern GNP did influence the distribution of wild ungulates. Repeat observations during various seasons would be necessary to understand the spatio-temporal segregation among cattle and wild ungulates