CHAPTER 3 AN ANALYSIS OF MORTALITIES INVOLVING THE VULNERABLE AFRICAN GRASS OWL (TYTO CAPENSIS) AS WELL AS IN THE MARSH OWL (ASIO CAPENSIS), BARN OWL (TYTO ALBA) AND THE SPOTTED EAGLE OWL (BUBO AFRICANUS) RELATED TO VEHICLE COLLISIONS IN GAUTENG. “Owls face many natural hazards anyway, but piled on top of these are the growing perils of living in an environment increasingly modified by man” (Tarboton & Erasmus, 1998). 209 CHAPTER 3.1: INTRODUCTION 3.1. INTRODUCTION Human advancements have had a major impact on nature in numerous and various ways. Most species extinctions are anthropogenically induced. This has been achieved mainly as a result of the expansion of major towns, industries and agriculture into natural habitats. Other factors include fragmentation as well as destruction of forests and pollution of rivers, which, according to Whitford (1985) have together resulted in a changed world. Little is known about the mortality of raptors in relation to other aspects of their ecology. This is because the actual deaths are seldom witnessed (unless at the hand of man) and because no known method of study gives unbiased information on the ages at death, or on the causes of death. Mortality estimates are important in understanding population turnover and in pinpointing vulnerable age groups or populations (Newton, 1979). Causes of death to owls vary from starvation during harsh winters, entrapment in man-made structures, and collision with obstacles. Drowning, being deliberately killed, and poisoning by pesticide have also rooted many deaths. The majority of these are a result of human interference with fairly few owls dieing from natural causes (Newton, 1979). One important impact on owl mortality, which relates to this study, is the prevalence and advancement of roads in developed as well as developing countries throughout the world. This contributes to the great loss and fragmentation of their habitats and placing them in direct threat of being knocked over by a vehicle. In an extensive study of the Barn Owl (De Bruijn, 1994), found that the majority of these owls (56%), 210 CHAPTER 3.1: INTRODUCTION from ring recoveries, died as road victims, starvation in harsh winters accounted for 15%, being locked up unintentionally (8%), collision with obstacles such as walls, windows and power lines (6%), 2% were found to be killed deliberately and 13% making up other causes not mentioned. Although roads are required to meet various demands of the public and hence also form a part of human progress, they represent one of the commonest and most extensive intrusions of man into natural areas (Whitford, 1985). Roads have also been known to have direct and detrimental effects on wildlife itself and the threat of traffic on wildlife have long been recognised. There are many examples in the international literature on road mortalities of wildlife and birds throughout the world. There are a number of studies involving general wildlife being killed by traffic, e.g. wildlife destruction by automobile traffic (Dickerson, 1939); vertebrate road mortality (Hodson, 1960); animal victims on Nebraska’s highways (McClure, 1951); and wildlife mortalities in New South Wales (Vestjens, 1973). Studies relating specifically to bird mortalities are reflected in papers by (roadside birds in Punjab) Dhindsa, Sandhu, & Sandhu, (1988) (Wiltshire) Dunthorn & Errington (1964), (roadside birds) Finnis (1956), road casualties particularly among House Sparrows, Blackbird and Song Thrush birds are discussed by Finnis (1960) and Govett (1960), vertebrate road mortality were discussed by Barnes (1936); Harrison (1954); Hodson (1960); Hodson (1962); Schorger (1954) and White (1927). There are only a few published records of road-killed owls, throughout the world and their relationship with roads. These limited studies have been 211 CHAPTER 3.1: INTRODUCTION conducted on T. alba and A. otus (Baudvin 1997); T. alba, Tyto capensis, Tyto novaehollandiae, Ninox novaeseelandiae and Ninox strenua (Clancy 2002-in press); T. alba (De Bruijn 1994, Newton, Wyllie & Dale 1997, Shawyer and Dixon 1999); A. noctua (Fajardo, Pividal, Trigo & Jimenez 1998; Hernandez 1988); and Westphalian Owls (Illner 1992). A survey in East Germany recorded 51 Barn Owl road kills on a 2.5 km stretch of freeway over a seven day period (Uhlenhaut 1976) and the main cause of Barn Owl deaths in Great Britain (N>1000) were starvation and collision, mostly with road traffic (Newton et al., 1997). Owls and diurnal raptors accounted for 81.5% of all birds killed by vehicles in a study in France (Baudvin, 1997). In far North Queensland 13 road killed Southern Boobooks were recorded between Mount Garntt and Georgetown on one day (Emmerson, 1999). A study conducted on mortalities from vehicles on the Little Owl (Athene noctua) in Spain represents 82% of non-natural deaths of A. noctua (Hernandez 1988) Within South Africa there is reference to the subject of vertebrate mortalities by Siegfried (1965,1966) for the Cape Province and Stellenbosch as well as a few others limited to the grey literature mostly reporting on general observations and a number of letters published in newspapers, mentioning species involved, the number of mortalities, their localities and mileage travelled by the observer. There is a particular paucity of published data regarding the limit of use of road verges by raptors, with few references to the nature of verges, the 212 CHAPTER 3.1: INTRODUCTION surrounding habitats or the effect of seasons (Knight & Kawashima, 1993; Meunier, Corbin, Verheyden & Jouventin, 1999; Meunier, Verheyden & Jouventin, 2000). Yet, the potential importance of roadsides is indicated by the literature on raptors’ associations with other linear man-made habitats like power lines (review in Williams & Colson, 1989). Not many birds have been known to be killed on roads in the past and is relatively new for developing countries (Dhindsa et al., 1988),. This could probably be attributed to unsophisticated infrastructure of roads and vehicles. Most vehicles usually did not exceed the speed of 80 kilometers per hour or perhaps vehicles were extremely expensive to own. Further more roads were in exceptionally poor condition and were not maintained as they are today, using more resilient road surface materials. Thus the advancement of technology today has resulted in faster moving vehicles in conjunction with reconditioned and improved surfaces facilitating faster traveling and resulted in higher volumes of birds being killed in this manner. This does not seem to be the case for South Africa, where few reports of bird counts are also due to the lack of mortalities not being formerly reported and such extensive studies have not been scientifically conducted. While traffic on the N17 highway is not as intense as that on more heavily used motorways, such as the N1 and M1 highways of Gauteng, highway loses to wildlife are greater (pers. obs.). Perhaps owing to the fact that the N17 is a fairly new highway, may have caused an increase in owl mortalities in the area that was previously not threatened. This implication is a major concern. It 213 CHAPTER 3.1: INTRODUCTION was Paul Jooste’s5 (pers. comm.) experience of traveling along this road and observing high numbers of owls found on or alongside this road that led to the present study. Moreover, the present study draw’s attention to this important ecological aspect that roads have on our wildlife, which has largely been neglected throughout southern Africa. Considerable losses of birds that are of valuable concern have attracted comments by many observers. For this reason the high numbers of the scarce Grass Owl initiated the grounds to investigate the cause of such an obstacle that adds to the many other anthropogenic factors causing them to decline. This chapter reports on how many owls were recorded as road casualties due to vehicle collisions along the N17 and R550 roads, and of which species in particular, would frequent roads and may be prone to mortality from fast- moving vehicles. Additional information on other problem areas throughout South Africa is also presented. As far as could be ascertained, no such account has been published on owl mortalities in the South African region especially in the Gauteng Province. This chapter gives the results of the first study of its kind during a two-year period in the East Rand Highveld, including important information in addition to mere mortality counts. 5 Mr. P. Jooste, Endangered Wildlife Trust, Devon, South Africa. 214 CHAPTER 3.2 MATERIALS AND METHODS 3.2. MATERIALS AND METHODS 3.2.1 Study area The section of the N17 between Springs and Devon (Figure 3.1) was surveyed daily, for two official years (2002 to 2003) and three unofficial years, to determine owl mortality attributable to collisions with motor vehicles. Both the N17 and the adjacent R550, which runs parallel to the N17, were surveyed for a total length of 30 km of fairly flat roadway. Both road surfaces consist of dark tarmac. The N17 is flanked throughout its entire length by grassy verges of 10 to 30 m up to a boundary line, which consists of a 1.2 m, five-stranded barbed wire fence. These verges are interrupted by ditches for the purpose of road drainage, as well as access bridges adjoining farms. The R550 is less complex, with smaller road verges up to 10 m. The north and south of the N17 roadway, adjoining the R550, are flanked by predominately-cultivated fields such as Erogrostis curvula, maize, sunflowers as well as Cosmos bipinnatus with some sections of grassy grazing paddocks used by cattle, similar to the adjacent land of the R550. Small farm dams, connected by small streams undulate through the area. The road verges vary in gradient from being completely flat to 60° angled slopes to accommodate farm bridges. The R550 is flattened throughout. The road connecting Springs to Devon is generally a single-lane national freeway with one lane approximately five meters in width both ways.