The impact of roads on the densities of four bird species in an open field habitat—evidence of a long-distance effect

Roads may effect animal communities in various ways. One such way is ‘di sturbance’, i.e. emission of stimuli to which animals may respond by avoiding the vicinity of the road. The extent, intensity and mechanism of this effect is almost entirely unknown. Veen (1973), studying the bird species lapwing Vanellus vanellus, black-tailed godwit Limosa limosa, oystercatcher Haematopus ostralegus, redshank Tringa totanus and ruff Philomachus pugnax in open grassland areas, found disturbance over surprisingly long distances, ranging from 500–600 m for a quiet rural road to 1600–1800m for a busy highway. However, his approach has met with serious methodological criticism.The validity of Veen's conclusions was tested by critically reanalysing bird distribution in one of his study plots. It is inferred that his conclusions do hold for the lapwing, the godwit and possibly the redshank, though not for the oystercatcher. An additional field study in four areas yielded similar results, with comparable disturbance distances. The total population loss over this distance may amount to 60%. Rough indications were obtained that the distance-density graph is a logistic one, while the relation between traffic volume and total population loss is possibly logarithmic. In addition confirmation was obtained of the general impression that, apart from roads, disturbance may also be caused by farms, other buildings and plantations, suggesting that disturbance caused by a road is not easily eliminated by planting trees alongside.It is recommended that extra care be taken in planning new roads, while impact statements concerning roads which disregard disturbance and other long-distance effects on the fauna should be rejected.     

Post-fledging dispersal, habitat use, and survival of Sprague’s pipits: Are planted grasslands a good substitute for native?

Loss and degradation of native grasslands on the North American landscape are some of the key factors influencing population declines of grassland songbirds. It is unclear what role anthropogenic grasslands play in the conservation of grassland specialists and whether demographic parameters of grassland songbirds differ between anthropogenic and native grasslands. Furthermore, there has been little research examining the overlap (or lack thereof) between nesting and post-fledging habitat. We initiated a radio-telemetry study from 2004 to 2008 on dispersal, microhabitat use, and survival of juvenile Sprague’s pipits (Anthus spragueii), a threatened grassland-obligate songbird, in native pastures and fields planted with exotic species (planted grasslands). Dispersal distance was greater in planted compared to native grasslands, but appeared to be constrained to natal fields up to 26-d post-fledging. Pipits used microhabitats in planted grasslands with vegetation that was on average 11 cm taller than used locations in native pastures, possibly due to the rapid growth of planted vegetation by the time individuals fledged. Individuals that were reared in planted grasslands had consistently lower daily survival rates compared to those in native pastures. Our observation that young birds rarely left their natal field suggests that conserving nesting habitat in native pastures would be an effective management strategy for this species. However, our results suggest that planted grasslands may act as population sinks given the lower survival of juvenile pipits reared in planted fields in our region. Demographic studies during the post-fledging period are essential to determine the conservation value of anthropogenic grasslands for North American songbirds.     

Introduced house mice Mus musculus: a significant predator of threatened and endemic birds on Gough Island, South Atlantic Ocean?

House mice Mus musculus have successfully colonized many temperate and sub-Antarctic islands that are the location for breeding colonies of millions of seabirds. Unlike other introduced mammals, the impact of house mice on seabirds and endemic birds is believed to have been negligible. The breeding ecology of seabirds breeding on Gough Island, central South Atlantic Ocean, was studied for the first time during September 2000 to September 2001. Breeding success of the endangered Tristan albatross Diomedea (exulans) dabbenena and endangered Atlantic Petrel Pterodroma incerta were 27.3 and 19.9% respectively. Mortality of large Tristan albatross and Atlantic petrel chicks was observed, and the pattern of wounds and observations of feeding indicate that introduced mice were responsible for this predation. Breeding numbers of the endemic Gough bunting Rowettia goughensis are mostly found in upland areas of Gough Island where mice are scarce and are restricted to inaccessible cliffs in the lowlands where mice are abundant. This pattern, together with the high predation rates of artificial-eggs in lowland habitats in comparison to the uplands, strongly suggests that mice constrain the distribution of Gough buntings. The results of this study provide the first evidence for the role of house mice as a significant predator of endangered and endemic birds. Further research is required to determine if the observed levels of mice predation are a regular occurrence.