Spatial-temporal variation in sex ratio and group size of ostriches (Struthio namelus) in the Serengeti National Park and environs in Northern Tanzania

A study was conducted on variation in sex ratio and group size of ostriches (Struthio camelus) in Serengeti National Park and adjacent partially protected areas in northern Tanzania. Data were collected for two years (2005- 2006), along 388 km of roads. The two areas were compared with respect to ostrich sex ratio (male: female) and group size. Seasonal variation of these variables (sex ratio and group size) was also determined. Repetitive sampling showed an overall femaleskewed sex ratio, which was significantly different from unity. The sex ratio inside the National Park was also significantly skewed towards females, whereas that in the partially protected areas was skewed in favour of the males. There was a significant difference in sex ratios between the two areas (Chi square: !2 = 48.041, DF = 2, p<0.001). The grand median group size was 3 birds and the same median group size was obtained both in the National Park and partially protected areas, and there was no significant difference in group sizes between the areas (Median test: !2 = 1.861, DF = 1, p = 0.173) although bigger groups were observed in the park than in the partially protected areas. In addition, there was a tendency for ostriches to form significantly larger groups in the wet season than dry season in both areas (p<0.05). Natural predators of ostrich were found to be significantly higher inside the National Park than outside it (p<0.05). The presence of natural predators and seasonal variations may have influenced the present results.Keywords: group size – ostrich – Serengeti – sex ratio – Struthio camelu

A Comparative Study of Species Diversity of Migrant Birds Between Protected and Unprotected Areas of the Hadejia-Nguru Wetlands, Nigeria

Among the most complex and fascinating behaviour in birds is their long, non-stop migration. Despite Hadejia-Nguru Wetlands (Ramsar site) being an important wintering ground for migratory birds, little is known about the diversity while density is completely lacking. This study assessed the status of migratory birds in the wetland’s Protected Areas (PAs) and Unprotected Areas (UPAs). A total of 99 census points spaced 400 m apart with radius of 100 m were surveyed from 14 wetlands (48 point count stations in the PAs and 51 in the UPAs). A total of 54 migrant bird species belonging to 13 orders and 25 families were recorded. Of the 54 species, 20 were Intra-African migrants and 34 Palearctic winters including two globally threatened species; the European Turtle Dove Streptopelia turtur and Pallid Harrier Circus macrourus. Results showed that Protected wetlands had significantly higher species diversity (H' = 1.39) than Unprotected ones (H' = 1.28) (p = 0.0064), however, there was no significant difference in the density of birds between the two areas (p = 0.9246). The two areas were similar in species composition by 81%. Both Palearctic and Intra-Africa migrant birds were recorded in the wetland, thus revealing the importance of the Hadejia-Nguru as wintering sites for migratory birds. The Nigerian government has obligation to protect these migratory birds because it is a signatory to several international treaties aimed at conserving these birds. Key words: Circus macrourus, Hadejia-Nguru Wetlands, Threats to migratory birds, Palearctic and Intra-Africa Migrant birds, Streptopelia turtu

Using social network analysis of mixed-species groups in African savanna herbivores to assess how community structure responds to environmental change

The dynamics of wildlife populations often depend heavily on interspecific interactions and understanding the underlying principles can be an important step in designing conservation strategies. Behavioural ecological studies can here provide useful insights into the structure and function of communities and their likely response to environmental changes. In this study of the Masai Mara herbivore community, we use a social network approach to investigate social affinities between species and how these change over the year in response to seasonal changes in ecological conditions. We find that even though social networks were correlated across different ecological conditions, for half the species dyads in the community, the strength of social affinities responded to changes in rainfall and/or the presence of migratory wildebeest. Several species consequentially adopted more or less central positions in the network depending on ecological conditions. The findings point out interspecific social links that are likely to be attenuated or strengthened as a consequence of human-induced environmental changes, and therefore call for particular attention of conservation managers. The eco-evolutionary ramifications of the perturbations of social affinities still require further stud

Background matching in the brown shrimp Crangon crangon : adaptive camouflage and behavioural-plasticity

A combination of burrowing behaviour and very efficient background matching makes the brown shrimp Crangon crangon almost invisible to potential predators and preys. This raises questions on how shrimp succeed in concealing themselves in the heterogeneous and dynamic estuarine habitats they inhabit and what type of environmental variables and behavioural factors affect their colour change abilities. Using a series of behavioural experiments, we show that the brown shrimp is capable of repeated fast colour adaptations (20% change in dark pigment cover within one hour) and that its background matching ability is mainly influenced by illumination and sediment colour. Novel insights are provided on the occurrence of non-adaptive (possibly stress) responses to background changes after long-time exposure to a constant background colour or during unfavourable conditions for burying. Shrimp showed high levels of intra- and inter-individual variation, demonstrating a complex balance between behavioural-plasticity and environmental adaptation. As such, the study of crustacean colour changes represents a valuable opportunity to investigate colour adaptations in dynamic habitats and can help us to identify the mayor environmental and behavioural factors influencing the evolution of animal background matching

Variability in Avian Eggshell Colour: A Comparative Study of Museum Eggshells

Background: The exceptional diversity of coloration found in avian eggshells has long fascinated biologists and inspired a broad range of adaptive hypotheses to explain its evolution. Three main impediments to understanding the variability of eggshell appearance are: (1) the reliable quantification of the variation in eggshell colours; (2) its perception by birds themselves, and (3) its relation to avian phylogeny. Here we use an extensive museum collection to address these problems directly, and to test how diversity in eggshell coloration is distributed among different phylogenetic levels of the class Aves. Methodology and Results: Spectrophotometric data on eggshell coloration were collected from a taxonomically representative sample of 251 bird species to determine the change in reflectance across different wavelengths and the taxonomic level where the variation resides. As many hypotheses for the evolution of eggshell coloration assume that egg colours provide a communication signal for an avian receiver, we also modelled reflectance spectra of shell coloration for the avian visual system. We found that a majority of species have eggs with similar background colour (long wavelengths) but that striking differences are just as likely to occur between congeners as between members of different families. The region of greatest variability in eggshell colour among closely related species coincided with the medium-wavelength sensitive region around 500 nm. Conclusions: The majority of bird species share similar background eggshell colours, while the greatest variability among species aligns with differences along a red-brown to blue axis that most likely corresponds with variation in the presence and concentration of two tetrapyrrole pigments responsible for eggshell coloration. Additionally, our results confirm previous findings of temporal changes in museum collections, and this will be of particular concern for studies testing intraspecific hypotheses relating temporal patterns to adaptation of eggshell colour. We suggest that future studies investigating the phylogenetic association between the composition and concentration of eggshell pigments, and between the evolutionary drivers and functional impacts of eggshell colour variability will be most rewarding.Phillip Cassey, Steven J. Portugal, Golo Maurer, John G. Ewen, Rebecca L. Boulton, Mark E. Hauber and Tim M. Blackbur

Buses, cars, bicycles and walkers the influence of the type of human transport on the flight responses of waterbirds

One way to manage disturbance to waterbirds in natural areas where humans require access is to promote the occurrence of stimuli for which birds tolerate closer approaches, and so cause fewer responses. We conducted 730 experimental approaches to 39 species of waterbird, using five stimulus types (single walker, three walkers, bicycle, car and bus) selected to mimic different human management options available for a controlled access, Ramsar-listed wetland. Across species, where differences existed (56% of 25 cases), motor vehicles always evoked shorter flight-initiation distances (FID) than humans on foot. The influence of stimulus type on FID varied across four species for which enough data were available for complete cross-stimulus analysis. All four varied FID in relation to stimuli, differing in 4 to 7 of 10 possible comparisons. Where differences occurred, the effect size was generally modest, suggesting that managing stimulus type (e.g. by requiring people to use vehicles) may have species-specific, modest benefits, at least for the waterbirds we studied. However, different stimulus types have different capacities to reduce the frequency of disturbance (i.e. by carrying more people) and vary in their capacity to travel around important habita

Parents, predators, parasites, and the evolution of eggshell colour in open nesting birds

The colourful surface of birds’ eggshells varies dramatically between species, but the selective pressures driving this variation remain poorly understood. We used a large comparative dataset to test several hypotheses proposed to explain the evolution of eggshell colouration. We tested the hypothesis that predation pressure might select for cryptic eggshells by examining the relationship between predation rate and egg colouration. We found that predation rates were positively related to eggshell brightness. The blackmail hypothesis suggests that females lay colourful eggshells to coerce males into providing additional care during incubation to keep colourful eggs covered. According to this hypothesis, conspicuous eggs should be found in situations with high risk of visual detection from predators or brood parasites. In support of this hypothesis, proportional blue-green chroma was positively related to parasitism risk, and eggs with higher proportional blue-green chroma or higher ultraviolet chroma received higher combined parental nest attendance during the incubation period. The sexual signalling hypothesis states that blue-green colour indicates female quality; however, we did not find that blue-green eggshell colour was greater in species where males participate in any form of parental care, and relative male provisioning was unrelated to blue-green eggshell chroma. We found some support for the hypothesis that brood parasitism may select for high inter-clutch variation in eggshell colour to facilitate egg recognition. In our dataset, parasitism risk was negatively related to inter-clutch repeatability of blue-green chroma. Our study highlights the diversity of selection pressures acting on the evolution of eggshell colour in birds and provides suggestions for novel areas of future key research direction.Daniel Hanley, Phillip Cassey, Stéphanie M. Douce