Rien Reijnen

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.

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.

Effect of road traffic on the breeding site-tenacity of male Willow Warblers (Phylloscopus trochilus)

The breeding site-tenacity of colour-ringed male Willow Warblers (Phylloscopus trochilus) was studied in an homogenous area of 154 ha, which is crossed by a heavily travelled road (45 000 cars per day). Close to the road (<200 m) the dispersal of the males is much higher than for birds further away. There is also some evidence that most of the near-to-the-road males are yearlings. The differences indicate that adjacent to the road the habitat is less favourable for the Willow Warbler and can be considered as marginal. Untersucht wurde die Brutortstreue von individuell fabrberingter Männchen des Fitis (Phylloscopus trochilus) in einem 154 ha großen Gebiet, das von einer Autobahn mit regem Verkehr (45 000 Fahrzeuge pro Tag) durchschnitten wird. In der Nähe der Autobahn (<200 m) zeigten die Reviermännchen eine viel größere Dismigration als die Revierinhaber in größerem Abstand von der Verkehrstraße. Auch gab es Hinweise, daß in der Nähe der Autobahn überwiegend einjährige Männchen die Reviere besetzten. Für den Fitis kann man Habitate entlang der Autobahn als marginal betrachten.