R.P.B. Foppen

The effects of car traffic on breeding bird populations in woodland. Ill. Reduction of density in relation to the proximity of main roads

1. This study investigated the effect of car traffic on the breeding density of birds in deciduous and coniferous woodland, and the importance of noise and visibility of cars as possible factors affecting density. 2. Of the 43 species analysed in both woodland types, 26 species (60%) showed evidence of reduced density adjacent to roads (based on analysis with Wilcoxon signed-ranks test and regression). 3. Regression models with noise load as the only independent variable gave the best overall results. Calculated «effect distances» (the distance from the road up to where a reduced density was present) based on these regressions varied between species from 40-1500 m for a road with 10 000 cars per day to 70-2800 m for a road with 60 000 cars per day (120 km h −1 and 70% amount of woodland along the road). For a zone of 250 m from the road the reduction of the density varied from 20 to 98%. 4. When visibility of cars was controlled for, the number of species showing density reductions was much higher on plots with a high noise load than on ones with a low noise load. When noise conditions were held constant, however, there was no difference in bird densities between plots with high and low visibility of cars. 5. It is argued that noise load is probably the most important cause of the reduced densities. Visibility of cars, direct mortality and pollution are considered unimportant. 6. The results of this study stress the importance of considering the effect of car traffic on the breeding density of birds in planning and constructing main roads

Avian population consequences of climate change are most severe for long-distance migrants in seasonal habitats

One consequence of climate change is an increasing mismatch between timing of food requirements and food availability. Such a mismatch is primarily expected in avian long-distance migrants because of their complex annual cycle, and in habitats with a seasonal food peak. Here we show that insectivorous long-distance migrant species in The Netherlands declined strongly (1984–2004) in forests, a habitat characterized by a short spring food peak, but that they did not decline in less seasonal marshes. Also, within generalist long-distance migrant species, populations declined more strongly in forests than in marshes. Forest-inhabiting migrant species arriving latest in spring declined most sharply, probably because their mismatch with the peak in food supply is greatest. Residents and short-distance migrants had non-declining populations in both habitats, suggesting that habitat quality did not deteriorate. Habitat-related differences in trends were most probably caused by climate change because at a European scale, long-distance migrants in forests declined more severely in western Europe, where springs have become considerably warmer, when compared with northern Europe, where temperatures during spring arrival and breeding have increased less. Our results suggest that trophic mismatches may have become a major cause for population declines in long-distance migrants in highly seasonal habitats.

Declines in insectivorous birds are associated with high neonicotinoid concentrations

Recent studies have shown that neonicotinoid insecticides have adverse effects on non-target invertebrate species. Invertebrates constitute a substantial part of the diet of many bird species during the breeding season and are indispensable for raising offspring. We investigated the hypothesis that the most widely used neonicotinoid insecticide, imidacloprid, has a negative impact on insectivorous bird populations. Here we show that, in the Netherlands, local population trends were significantly more negative in areas with higher surface-water concentrations of imidacloprid. At imidacloprid concentrations of more than 20 nanograms per litre, bird populations tended to decline by 3.5 per cent on average annually. Additional analyses revealed that this spatial pattern of decline appeared only after the introduction of imidacloprid to the Netherlands, in the mid-1990s. We further show that the recent negative relationship remains after correcting for spatial differences in land-use changes that are known to affect bird populations in farmland. Our results suggest that the impact of neonicotinoids on the natural environment is even more substantial than has recently been reported and is reminiscent of the effects of persistent insecticides in the past. Future legislation should take into account the potential cascading effects of neonicotinoids on ecosystems.

The effects of traffic on the density of breeding birds in Dutch agricultural grasslands

Abstract The effect of traffic on the breeding density of grassland birds was studied in 1989 in 15 transects along main roads in The Netherlands. Out of 12 species that could be analysed, 7 showed a reduced density adjacent to the road. There was also a strong effect on the summed densities of all species. Disturbance distances varied between species, ranging from 20 to 1700 m from the road at 5000 cars a day and from 65 to 3530 m at 50,000 cars a day (car speed 120 km/h). At 5000 cars a day most species had an estimated population loss of 12–56% within 100 m of roads, but beyond 100 m > 10% loss only occurred in black-tailed godwit Limosa limosa (22% for 0–500 m zone) and oystercatcher Haematopus ostralegus (44% up to 500 m and 36% for 0–1500 m zone). At 50,000 cars a day all species had estimated losses of 12–52% up to 500 m while lapwing Vanellus vanellus, shoveler Anas clypeata, skylark Alauda arvensis, blacktailed godwit and oystercatcher populations were reduced by 14–44% up to 1500 m. In The Netherlands, with a dense network of extremely crowded motorways, traffic should be considered a serious threat to breeding bird populations in grasslands. Greater care should be taken in planning new roads, and it is important to explore how the present effects can be reduced.

The Effects of Car Traffic on Breeding Bird Populations in Woodland. I. Evidence of Reduced Habitat Quality for Willow Warblers (Phylloscopus trochilus) Breeding Close to a Highway

This study investigated the effect of a highway with dense traffic on the quality of adjacent habitats for the willow warbler Phylloscopus trochilus. In the zone of 0-200 m from the highway (road zone) the density of territorial males was much lower (2.1 ha −1 ) than in zones with a comparable habitat at a greater distance (3.3 ha −1 ). The lower density in the road zone was due to a low presence of older males. As a consequence, the proportion of yearling males in the road zone was about 50% higher than in the other zones. Yearling males occupied their territories in the road zone later than in the other zones. In the road zone the proportion of successful yearling males was about 50% lower than in the other zones. No difference was observed in the number of nestlings per male

Disturbance by traffic of breeding birds: evaluation of the effect and considerations in planning and managing road corridors

In wildlife considerations in planning and managing road corridors little attention has been given to the effects of disturbance by traffic on populations of breeding birds. Recent studies, however, show evidence of strongly reduced densities of many species of woodland and open habitat in broad zones adjacent to busy roads. The density reduction is related to a reduced habitat quality, and traffic noise is probably the most critical factor. Because density can underestimate the habitat quality, the effects on breeding populations are probably larger than have been established. In consequence, species that did not show an effect on the density might still be affected by traffic noise. On the basis of this recent knowledge, methods have been developed that can be used in spatial planning procedures related to main roads, and in road management practice, and some practical points are discussed. An example of application shows that the effects are probably very important in The Netherlands with a dense network of extremely crowded main roads. For ‘meadow birds’, which are of international importance, the decrease in population in the West of The Netherlands may amount to 16%. Because breeding birds suffer from many other environmental influences there is also a great risk of an important cumulation of effects.

The Effects of Car Traffic on Breeding Bird Populations in Woodland. II. Breeding Dispersal of Male Willow Warblers (Phylloscopus trochilus) in Relation to the Proximity of a Highway

1. In this study the dispersal activity of male willow warblers Phylloscopus trochilus breeding next to a highway carrying heavy traffic was investigated. 2. Breeding dispersal distances of yearling males along the road were larger than at further distances and were in the same order of magnitude as natal dispersal distances (medians being 303 and 515 m, respectively). 3. A simulation of dispersal directions, adjusted for actual landscape features, indicated that breeding dispersal was actively directed away from the road. 4. There appeared to be a relation between dispersal and breeding performance for yearling males, unsuccessful males moving more frequently and further (median 294 m) than successful males (median 120 m)

The effects of car traffic on breeding bird populations in woodland. IV: Influence of population size on the reduction of density close to a highway

1. This study tested the assumption that in years with a low overall population size the density-depressing effect of roads on breeding birds will be more important than in years with a high overall population size. 2. The effect on the density was investigated in 1984, 1986 and 1988. Of the 23 species that could be analysed each year, 17 species had a lowered density close to the road in at least 1 year. In 1984 and 1986 the number of affected species was much higher (10 and 14, respectively) than in 1988 (4). 3. The number of affected species, as well as the effect size for all species combined and for most individual species, was negatively correlated with the overall population size. 4. It is concluded that in years with a high-overall population size, the use of density as a response variable will cause a considerable underestimation of the reduction of the habitat quality close to roads. This has not been recognized well in impact studies concerning road traffic, nor in other impact studies.

Consistent response of bird populations to climate change on two continents.

Birds populations allied in abundance Changes in climate can cause populations of species to decline, to increase, or to remain steady. Stephens et al. looked across species of common birds in Europe and the United States. Despite many differences between the two regions, expectations about how a species might respond to climate change did predict actual responses. Species predicted to benefit from increasing temperatures, or their associated effects, tended to increase, whereas those predicted to be negatively affected declined. Thus, even across widely varying ecological conditions and communities, climate change can be expected to alter population sizes. Science, this issue p. 84 The impact of climate change on population sizes of birds across continents can be predicted. Global climate change is a major threat to biodiversity. Large-scale analyses have generally focused on the impacts of climate change on the geographic ranges of species and on phenology, the timing of ecological phenomena. We used long-term monitoring of the abundance of breeding birds across Europe and the United States to produce, for both regions, composite population indices for two groups of species: those for which climate suitability has been either improving or declining since 1980. The ratio of these composite indices, the climate impact indicator (CII), reflects the divergent fates of species favored or disadvantaged by climate change. The trend in CII is positive and similar in the two regions. On both continents, interspecific and spatial variation in population abundance trends are well predicted by climate suitability trends.

Impact of road traffic on breeding bird populations

This chapter deals with the direct effect that highway and roads have on animal populations. Notwithstanding change of habitat conditions at the side of the road, many wildlife species are less common or absent near roads. Because these road-avoidance zones can extend to more than 1000m, this could effectively result in the loss of a particular population. Potential causes of these zones include all relevant influences of traffic, such as visual disturbance, vehicle pollution, road-kills, traffic noise and soil vibration. Railway traffic may also be an important source of disturbance for animal populations. Several potential causes are similar to those of road traffic, such as visual disturbance, noise and collisions. However, such available data is scarce. This chapter focuses on breeding birds along roads because this species group has been the most extensively studied during the last decade and they show strong effects.