- Email: [email protected]
Bird nesting on electric power supports in northwestern Spain
Ecological Engineering 20 (2003) 321 /326 www.elsevier.com/locate/ecoleng
Short communication
Bird nesting on electric power supports in northwestern Spain O. Infante, S. Peris * Dpto. Zoologı´a, Fac. de Biologı´a, Universidad de Salamanca, 37071 Salamanca, Spain Received 2 July 2002; received in revised form 25 February 2003; accepted 3 March 2003
Abstract Use of electric power poles as nesting supports by birds was surveyed in the northern Spanish plateau, a deforested and nest-site sparse area. A total of 4336 poles of five different designs was sampled and the nesting rate was 4.99%. White stork (Ciconia ciconia ) is the most frequent nesting species using the structures with 79.2% of the total bird nest. Crows and ravens (Corvus corax and Corvus corone ) have 15.7% of the nests, and raptors have 4.6%. Pole types A and E are favorite supports for nesting and those near irrigation croplands or wooded-grasslands are preferred by all bird species. # 2003 Elsevier B.V. All rights reserved. Keywords: Power-poles; Nest support; Birds; Spanish plateau
1. Introduction In applied biodiversity conservation, any knowledge about human impact and its importance on the ecosystems and/or animals has an increasing role (Meffe and Carroll, 1997). Over the past 50 years, electric power-lines have been a conspicuous part of the landscape of industrialized countries. From their very beginnings, it was known that these lines and support structures would cause wildlife mortality, especially in birds, and in recent decades this has been increasingly well documented throughout the world (Bevanger, 1994; Brown and Drewien, 1995; Ferrer et al., 1991; Ferrer and
* Corresponding author. E-mail address: [email protected] (S. Peris).
Hiraldo, 1992; O’Neil, 1988; Ferrer and Janss, 1999; Janss and Ferrer, 2001 among others). The deforestation of many landscapes and the actual characteristics of the power-line poles make them prone to being used as nests by several avian species (Nelson, 1982; Negro, 1987), and in fact, some authors have argued that such supports may well be responsible for the population increases in some species such as the white stork (Ciconia ciconia ) in treeless landscapes of the Iberian Peninsula (Navazo and Roig, 1996; Navazo and Lazo, 1999) or raptors and ravens in NorthAmerican plains (Steenhof et al., 1993). However, data on the utilization of these structures as nest supports by birds are not as abundant (Negro, 1999). Since nest-building material increases the weight placed on the supports and since the excreta of nestling and adult birds deposited on pylons can
0925-8574/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0925-8574(03)00013-2
322
O. Infante, S. Peris / Ecological Engineering 20 (2003) 321 /326
cause short-circuits on the line, most nests constructed on electric power line supports constitute an important economic and operational problem for power companies (Negro, 1999).
2. Objectives The present study is an effort to document the degree of bird utilization of power-line supports as nest-sites in an extensive and almost deforested landscape on the central Spanish plateau, assessing type poles, nesting species and habitat characteristics.
3. Material and methods Five provinces on the northwestern side of the Spanish plateau (600 /1000 m.a.s.l.) were sampled; namely, Avila, Palencia, Salamanca, Valladolid, and Zamora, with a total of nearly 38 000 km2
sampled (Fig. 1). Temperatures in the basin range from /6 8C in winter to /40 8C in summer (annual mean 12 8C). Rain averages 350 /550 mm/year and the human population density is 26.5 inhabitants/km. Essentially, five large landscapes can be defined on the plateau: (1) Traditional cultures of cereal with 39.1% of the range, although a 1% annual decrease has been reported (Anonymous, 2000). (2) Irrigated land with 4.9% of the area, but with an increase per year ranging from 1 to 40%. (3) Grasslands and shrubs with 20.4% of the surface and currently increasing. (4) A savannah-type landscape of grassland interspersed with oak trees (Quercus ilex and Q. pyrenaica ), known locally as ‘‘dehesa’’, which covers about 12.7% of the rangeland. (5) Surrounding the basin are mountainous areas */ 1500/2500 m.a.s.l. */with forests, mainly of Pinus spp. and to a lesser extent, Q. pyrenaica and Castanea sativa , which account for 23% of the remaining area. For the present work, this remaining landscape was not prospected.
Fig. 1. Location of the study area, showing the five sampled provinces and range of the principal habitats (AV, Avila; P, Palencia; SA, Salamanca, VA, Valladolid; ZA, Zamora). B, a comparative sampled area in south-western Spain.
O. Infante, S. Peris / Ecological Engineering 20 (2003) 321 /326
Only active nests on powerline supports were surveyed in the months of March /July coinciding with the birds’ breeding season-during 1999, 2000 and 2001. Based on a map about existing powerlines supplied by the utility company in the region, transects were made on those lines which represent the five most common (/3% of the total) pole configurations in the region (Fig. 2). An attempt was made to cover 90/95 km on each defined landscape, except forest. Sampling of power line supports with bird nests was done with binoculars from vehicles and on foot, and about 370 km of electric lines were sampled. Supports with nests were drawn on maps at a scale of 1:100 000 checking the habitat within a 3 km radius */ looking for a balance among the most abundant bird nesting species and range from the nest when feeding chicks (Holyoak, 1967; Alonso et al., 1991). Each nest was noted on the basis of the above-defined habitat categories. Statistical analysis followed the methodology of Fowler and Cohen (1999).
4. Results A total of 4366 different supports were surveyed. 218 of them contained 230 nests of five species, i.e. structure occupation rate of 4.99%. The white stork (C. ciconia) is by a large margin the species that uses such structures the most, with 79.2% of the total bird nests and 83.6% of the occupied supports. It is also the only species that two or more breeding pair will nest on the same support. Crows and ravens (Corvus corax and Corvus corone ), occupy 15.7% of nests, and raptor accounted for 4.6% of the power-line support nests on the plateau (Table 1). A statistically significant association was observed between power-line support design and a preference for nesting on them (test-G /196.1, 4 df, P B/0.01). Thus, the tallest electric utility structures (type E) were more used by storks and corvids; whereas the smaller although similar in shape, type A, was selected by all the encountered bird species (Tables 1 and 2). No statistically significant differences were observed between ravens and crows in the use of supports (U /0.2;
323
P B/0.5 Mann/Whitney U -test) and neither as regards the habitat (x2 /1.93, P B/0.01 with Yate’s correction). Power supports near irrigated croplands as well as in wooded grasslands were the most selected by all bird species studied and this selection was statistically significant (x2 /23.67, 4 df, P B/0.01).
5. Discussion The use by birds of power poles as nesting supports in the deforested northern plateau is only 5% but is greater than the percentages of 2.9 /4.3% reported in the more forested areas of southern Spain (Navazo and Roig, 1996; Sa´nchez et al., 1996). Three species observed to nest on powerline supports in northern Spain are the same as those described by the latter authors for southern Spain. However, the common buzzard and the crow were also common in northern Spain. In any case, the nesting percentages differ considerably among regions. Thus, the most common species breeding in the north*/the white stork, with up to 82% of the total bird nests found*/accounts for only 26% of the nests in the south (Navazo and Lazo, 1999). By contrast, the raven has 77% of the total nests observed in the south, as compared with only 13.9% in northern regions. Kestrel nests are a higher proportion in the south (5.8%) than in the north (3.4%). Two buzzard nests were observed in wooded-grassland on the plateau, whereas only one nest of Bonelli’s Eagle (Hieraaetus fasciatus ) has been detected in the south (Navazo and Lazo, 1999). The white stork makes the greatest use of power-line supports in northern Spain, 79.13% of all supports harboring bird nests as compared with only 17% in southern Spain (Navazo et al., 1996). These differences could be due to the absence of large trees in the cropland landscape of the north. By contrast, southern Spain maintains more extensive wooded grasslands. Probably because of the relative lack of tall trees on the plateau, the stork in northern Spain is an ubiquitous species which breeds in all managed landscapes, including power line supports. Also, up to three pairs of white stork had been observed to nest on the same
324
O. Infante, S. Peris / Ecological Engineering 20 (2003) 321 /326
Fig. 2. Pole designs of the most frequent power support in the study area. H, average height in meters; W, average wide in meters. Nesting locations are indicate by arrows.
pole, aggregation smaller than the observed by Janns (2001) in southern Spain. Most of the nests were found on power line supports in irrigated fields (42.6%). Storks forage
on wet pastures and grasslands (Melendro et al., 1987) but also in garbage dumps and near towns where they find habitat also for breeding (Alonso et al., 1991). Owing to the lack of natural nesting
O. Infante, S. Peris / Ecological Engineering 20 (2003) 321 /326
325
Table 1 Nesting species on power-lines according to type of electric support Type of pole
Number of poles sampled
Number of poles with nests
Number of total nests
%
Nesting species CC FT CO BB
A B C D E
420 418 1130 1164 1224
38 22 12 3 142
41 22 12 3 181
9 5.3 1.1 0.3 11.6
14 8 20 / 10 2 3 / 165 /
17 2 / / 16
2 / / / /
CC, C. ciconia ; FT, Falco tinnunculus ; CO, Corvids (C. corone and C. corax ); BB, Buteo buteo .
substrate on the croplands, power poles are the only alternative. Poles in wooded-grasslands have the second most nests, but corvids are the main species involved. The relative low degree of pole nesting (12.2%) in cereal croplands, as is also observed in other Iberian regions (Navazo and Roig, 1996), can be attributed to the birds preference for forage on wetter and/or semiwooded habitats. Nearly 30 bird species are involved in mortality due to electrocution and/or collision with powerlines in Spain, and the white stork accounts for about 13.8% of the total casualties on the plateau (Lopez et al., 2001). This percentage is lower than the use that the species makes of the electric-line supports as nesting sites. In fact, the increase in Spain’s stork population*/from 6753 breeding pairs in 1990 to 16 643 in 1994 (Ortega, 1997), with a major increase on most of the cultivated northern regions */is suggestive of the adaptation of the species to these relatively new structures in the landscape. Power structures could help to
increase the numbers of this species, in spite of the actual mortality on the poles. Since many of the power lines cross croplands and grasslands, which offer better quality forage than urban source, the nestling productivity on these nests could be greater than that of birds nesting on town and city buildings where food sources has lower quality (Janns and Sanchez, 1997). This latter hypothesis needs more field research. Stork nests with an average height of 1/2 m and diameter of 0.8 /1.5 m (Cramp and Simmons, 1977), and a weight ranging from 60 to 250 kg, render these structures incompatible with a properly run electricity service, especially on type A supports which are for low tension delivery (Negro, 1999). These lines are more prone to short-circuits and electric companies */in an effort to control the problem */usually remove voluminous nests from the supports, installing artificial nest platforms as alternatives in the surroundings of the old nests. However, to date no practical success has been reported (Janns, 1998; own data).
Table 2 Nests on power-line supports according to nearby habitat Habitat
Cereal cropland Irrigated land Grasslands Wooded-grasslands
Type of pole
% Nesting on electric supports (n/259)
A
B
C
D
E
1 / 14 26
/ 20 2 /
/ 10 / 2
/ 1 2 /
32 81 13 55
12.8 43.2 12.0 32.1
CC, C. ciconia ; FT, F. tinnunculus ; CO, Corvids; BB, B. buteo .
Species CC
FT
CO
BB
28 112 20 52
/ / 4 6
5 / 7 23
/ / / 2
326
O. Infante, S. Peris / Ecological Engineering 20 (2003) 321 /326
Acknowledgements One author (O. Infante) had a grant from the company IBERDROLA. Fieldwork was financed by the project 1FD97-1468. The manuscript was improved by suggestions of the editor and two anonymous reviewers.
References Alonso, J.C., Alonso, J.A., Carrascal, L.M., 1991. Habitat selection by foraging White Storks, Ciconia ciconia , during the breeding season. Can. J. Zool. 69, 1957 /1962. Anonymous, 2000. Medio Ambiente en Castilla y Leo´n; Informe 2000. Junta de Castilla y Leo´n. Valladolid. Bevanger, K., 1994. Birds interactions with utility structures: collision and electrocution, causes and mitigating measures. Can. J. Zool. 136, 412 /425. Brown, W.M., Drewien, R.C., 1995. Evaluation of two power line markers to reduce crane and waterfowl collision mortality. Wildl. Soc. Bull. 3 (2), 217 /227. Cramp, S., Simmons, K.E.L. (Eds.), The Birds of the Western Palearctic, vol. I. Oxford University Press, Oxford 1977. Ferrer, M., Hiraldo, F., 1992. Man-induced sex-biased mortality in the Spanish Imperial Eagle. Biol. Conserv. 60, 57 /60. Ferrer, M., Janss, G. (coord.), 1999. Aves y lı´neas ele´ctricas. Colisio´n, electrocucio´n y nidificacio´n. Quercus, Madrid. Ferrer, M., de la Riva, M., Castroviejo, J., 1991. Electrocution of raptors on power lines in Southern Spain. J. Field Ornithol. 62 (2), 54 /69. Fowler, J., Cohen, L., 1999. Estadı´stica ba´sica en ornitologı´a. SEO/BirdLife. Madrid. Holyoak, D., 1967. Breeding biology of the Corvidae. Bird Study 14, 153 /168. Janns, G.F.E., 1998. Nests of white storks on electric utility towers. Wildl. Soc. Bull. 26 (2), 274 /278. Janns, G.F.E., 2001. Birds and power lines: a field of tension. Ph.D., Utrecht University, 175 pp. Janss, G.F.E., Ferrer, M., 2001. Avian electrocution mortality in relation to pole design and adjacent habitat in Spain. Bird Cons. Int. 11, 3 /12.
Janns, G.F.E., Sanchez, I., 1997. Productivity of White Stork at different nest sites. Ardeola 44 (1), 101 /104. Lopez, V., Cuadrado, M., Diez, F., Peris, S., 2001. Aves y tendidos ele´ctricos en las provincias de Salamanca y Avila. Salamanca, Rev. Est. 46, 201 /233. Meffe, G.K., Carroll, C.R., 1997. Principles of Conservation Biology, second ed. Sinauer Association, Sunderland. Melendro, J., Gisbert, J., Rodriguez, A., 1987. Datos sobre la alimentacio´n de Ciconia ciconia . Ardeola 24, 207 /209. Navazo, V., Lazo, A., 1999. La nidificacio´n de aves en la red de transporte de electricidad de Espan˜a: evaluacio´n, prevencio´n y correccio´n de la problema´tica asociada. In: Ferrer, M., Janss, G. (coord.), Aves y lı´neas ele´ctricas. Colisio´n, electrocucio´n y nidificacio´n, Quercus, Madrid, pp. 187 /216. Navazo, V., Roig, J., 1996. Estudio sobre la nidificacio´n de aves en apoyos de lı´neas de transporte de electricidad. In: Segundas jornadas sobre lı´neas ele´ctricas y medio ambiente. REE, Red Ele´ctrica Espan˜ola, Madrid, pp. 223 /231. Navazo, V., Roig, J., Lazo, A., 1996. Caracterı´sticas generales de las especies nidificantes en lı´neas de alta tensio´n. Datos para un manejo apropiado. In: Segundas jornadas sobre lı´neas ele´ctricas y medio ambiente. REE, Red Ele´ctrica, Madrid, pp. 433 /439. Negro, J.J., 1987. Adaptacio´n de los tendidos ele´ctricos al entorno. Monografı´as de Alytes no. 1. Adenex, Me´rida. Negro, J.J., 1999. Pasado y futuro de la investigacio´n sobre interacciones entre la fauna y las lı´neas ele´ctricas. In: Ferrer, M., Janss, G. (coord.), Aves y lı´neas ele´ctricas. Colisio´n, electrocucio´n y nidificacio´n. Quercus, Madrid, pp. 21 /29. Nelson, M.W., 1982. Human impacts on Golden Eagles: positive outlook for the 1980s and 1990s. J. Raptor Res. 16, 97 /103. O’Neil, T.A., 1988. An analysis of bird electrocutions in Montana. J. Raptor Res. 22 (1), 27 /28. Ortega, A., 1997. Cigu¨en˜a Blanca. In: Atlas de las Aves de Espan˜a (1975 /1995). SEO/BirdLife (Purroy, F. coord.), Lynx, Barcelona, pp. 58 /59. ´ lvarez, Sa´nchez, A., Bueno, A., Rodrı´guez, J., Gonza´lez, F., .A A., Ramos, V., Caldera, J., 1996. Nidificacio´n de aves en lı´neas ele´ctricas en Extremadura: problema´tica y manejo de conservacio´n. In: Segundas jornadas sobre lı´neas ele´ctricas y medio ambiente. REE, Red Ele´ctrica, Madrid, pp. 207 /213. Steenhof, K.M., Kochert, N., Roppe, J.A., 1993. Nesting by raptors and Common Ravens on electric transmission line towers. J. Wildl. Manage. 57, 271 /281.
Short communication
Bird nesting on electric power supports in northwestern Spain O. Infante, S. Peris * Dpto. Zoologı´a, Fac. de Biologı´a, Universidad de Salamanca, 37071 Salamanca, Spain Received 2 July 2002; received in revised form 25 February 2003; accepted 3 March 2003
Abstract Use of electric power poles as nesting supports by birds was surveyed in the northern Spanish plateau, a deforested and nest-site sparse area. A total of 4336 poles of five different designs was sampled and the nesting rate was 4.99%. White stork (Ciconia ciconia ) is the most frequent nesting species using the structures with 79.2% of the total bird nest. Crows and ravens (Corvus corax and Corvus corone ) have 15.7% of the nests, and raptors have 4.6%. Pole types A and E are favorite supports for nesting and those near irrigation croplands or wooded-grasslands are preferred by all bird species. # 2003 Elsevier B.V. All rights reserved. Keywords: Power-poles; Nest support; Birds; Spanish plateau
1. Introduction In applied biodiversity conservation, any knowledge about human impact and its importance on the ecosystems and/or animals has an increasing role (Meffe and Carroll, 1997). Over the past 50 years, electric power-lines have been a conspicuous part of the landscape of industrialized countries. From their very beginnings, it was known that these lines and support structures would cause wildlife mortality, especially in birds, and in recent decades this has been increasingly well documented throughout the world (Bevanger, 1994; Brown and Drewien, 1995; Ferrer et al., 1991; Ferrer and
* Corresponding author. E-mail address: [email protected] (S. Peris).
Hiraldo, 1992; O’Neil, 1988; Ferrer and Janss, 1999; Janss and Ferrer, 2001 among others). The deforestation of many landscapes and the actual characteristics of the power-line poles make them prone to being used as nests by several avian species (Nelson, 1982; Negro, 1987), and in fact, some authors have argued that such supports may well be responsible for the population increases in some species such as the white stork (Ciconia ciconia ) in treeless landscapes of the Iberian Peninsula (Navazo and Roig, 1996; Navazo and Lazo, 1999) or raptors and ravens in NorthAmerican plains (Steenhof et al., 1993). However, data on the utilization of these structures as nest supports by birds are not as abundant (Negro, 1999). Since nest-building material increases the weight placed on the supports and since the excreta of nestling and adult birds deposited on pylons can
0925-8574/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0925-8574(03)00013-2
322
O. Infante, S. Peris / Ecological Engineering 20 (2003) 321 /326
cause short-circuits on the line, most nests constructed on electric power line supports constitute an important economic and operational problem for power companies (Negro, 1999).
2. Objectives The present study is an effort to document the degree of bird utilization of power-line supports as nest-sites in an extensive and almost deforested landscape on the central Spanish plateau, assessing type poles, nesting species and habitat characteristics.
3. Material and methods Five provinces on the northwestern side of the Spanish plateau (600 /1000 m.a.s.l.) were sampled; namely, Avila, Palencia, Salamanca, Valladolid, and Zamora, with a total of nearly 38 000 km2
sampled (Fig. 1). Temperatures in the basin range from /6 8C in winter to /40 8C in summer (annual mean 12 8C). Rain averages 350 /550 mm/year and the human population density is 26.5 inhabitants/km. Essentially, five large landscapes can be defined on the plateau: (1) Traditional cultures of cereal with 39.1% of the range, although a 1% annual decrease has been reported (Anonymous, 2000). (2) Irrigated land with 4.9% of the area, but with an increase per year ranging from 1 to 40%. (3) Grasslands and shrubs with 20.4% of the surface and currently increasing. (4) A savannah-type landscape of grassland interspersed with oak trees (Quercus ilex and Q. pyrenaica ), known locally as ‘‘dehesa’’, which covers about 12.7% of the rangeland. (5) Surrounding the basin are mountainous areas */ 1500/2500 m.a.s.l. */with forests, mainly of Pinus spp. and to a lesser extent, Q. pyrenaica and Castanea sativa , which account for 23% of the remaining area. For the present work, this remaining landscape was not prospected.
Fig. 1. Location of the study area, showing the five sampled provinces and range of the principal habitats (AV, Avila; P, Palencia; SA, Salamanca, VA, Valladolid; ZA, Zamora). B, a comparative sampled area in south-western Spain.
O. Infante, S. Peris / Ecological Engineering 20 (2003) 321 /326
Only active nests on powerline supports were surveyed in the months of March /July coinciding with the birds’ breeding season-during 1999, 2000 and 2001. Based on a map about existing powerlines supplied by the utility company in the region, transects were made on those lines which represent the five most common (/3% of the total) pole configurations in the region (Fig. 2). An attempt was made to cover 90/95 km on each defined landscape, except forest. Sampling of power line supports with bird nests was done with binoculars from vehicles and on foot, and about 370 km of electric lines were sampled. Supports with nests were drawn on maps at a scale of 1:100 000 checking the habitat within a 3 km radius */ looking for a balance among the most abundant bird nesting species and range from the nest when feeding chicks (Holyoak, 1967; Alonso et al., 1991). Each nest was noted on the basis of the above-defined habitat categories. Statistical analysis followed the methodology of Fowler and Cohen (1999).
4. Results A total of 4366 different supports were surveyed. 218 of them contained 230 nests of five species, i.e. structure occupation rate of 4.99%. The white stork (C. ciconia) is by a large margin the species that uses such structures the most, with 79.2% of the total bird nests and 83.6% of the occupied supports. It is also the only species that two or more breeding pair will nest on the same support. Crows and ravens (Corvus corax and Corvus corone ), occupy 15.7% of nests, and raptor accounted for 4.6% of the power-line support nests on the plateau (Table 1). A statistically significant association was observed between power-line support design and a preference for nesting on them (test-G /196.1, 4 df, P B/0.01). Thus, the tallest electric utility structures (type E) were more used by storks and corvids; whereas the smaller although similar in shape, type A, was selected by all the encountered bird species (Tables 1 and 2). No statistically significant differences were observed between ravens and crows in the use of supports (U /0.2;
323
P B/0.5 Mann/Whitney U -test) and neither as regards the habitat (x2 /1.93, P B/0.01 with Yate’s correction). Power supports near irrigated croplands as well as in wooded grasslands were the most selected by all bird species studied and this selection was statistically significant (x2 /23.67, 4 df, P B/0.01).
5. Discussion The use by birds of power poles as nesting supports in the deforested northern plateau is only 5% but is greater than the percentages of 2.9 /4.3% reported in the more forested areas of southern Spain (Navazo and Roig, 1996; Sa´nchez et al., 1996). Three species observed to nest on powerline supports in northern Spain are the same as those described by the latter authors for southern Spain. However, the common buzzard and the crow were also common in northern Spain. In any case, the nesting percentages differ considerably among regions. Thus, the most common species breeding in the north*/the white stork, with up to 82% of the total bird nests found*/accounts for only 26% of the nests in the south (Navazo and Lazo, 1999). By contrast, the raven has 77% of the total nests observed in the south, as compared with only 13.9% in northern regions. Kestrel nests are a higher proportion in the south (5.8%) than in the north (3.4%). Two buzzard nests were observed in wooded-grassland on the plateau, whereas only one nest of Bonelli’s Eagle (Hieraaetus fasciatus ) has been detected in the south (Navazo and Lazo, 1999). The white stork makes the greatest use of power-line supports in northern Spain, 79.13% of all supports harboring bird nests as compared with only 17% in southern Spain (Navazo et al., 1996). These differences could be due to the absence of large trees in the cropland landscape of the north. By contrast, southern Spain maintains more extensive wooded grasslands. Probably because of the relative lack of tall trees on the plateau, the stork in northern Spain is an ubiquitous species which breeds in all managed landscapes, including power line supports. Also, up to three pairs of white stork had been observed to nest on the same
324
O. Infante, S. Peris / Ecological Engineering 20 (2003) 321 /326
Fig. 2. Pole designs of the most frequent power support in the study area. H, average height in meters; W, average wide in meters. Nesting locations are indicate by arrows.
pole, aggregation smaller than the observed by Janns (2001) in southern Spain. Most of the nests were found on power line supports in irrigated fields (42.6%). Storks forage
on wet pastures and grasslands (Melendro et al., 1987) but also in garbage dumps and near towns where they find habitat also for breeding (Alonso et al., 1991). Owing to the lack of natural nesting
O. Infante, S. Peris / Ecological Engineering 20 (2003) 321 /326
325
Table 1 Nesting species on power-lines according to type of electric support Type of pole
Number of poles sampled
Number of poles with nests
Number of total nests
%
Nesting species CC FT CO BB
A B C D E
420 418 1130 1164 1224
38 22 12 3 142
41 22 12 3 181
9 5.3 1.1 0.3 11.6
14 8 20 / 10 2 3 / 165 /
17 2 / / 16
2 / / / /
CC, C. ciconia ; FT, Falco tinnunculus ; CO, Corvids (C. corone and C. corax ); BB, Buteo buteo .
substrate on the croplands, power poles are the only alternative. Poles in wooded-grasslands have the second most nests, but corvids are the main species involved. The relative low degree of pole nesting (12.2%) in cereal croplands, as is also observed in other Iberian regions (Navazo and Roig, 1996), can be attributed to the birds preference for forage on wetter and/or semiwooded habitats. Nearly 30 bird species are involved in mortality due to electrocution and/or collision with powerlines in Spain, and the white stork accounts for about 13.8% of the total casualties on the plateau (Lopez et al., 2001). This percentage is lower than the use that the species makes of the electric-line supports as nesting sites. In fact, the increase in Spain’s stork population*/from 6753 breeding pairs in 1990 to 16 643 in 1994 (Ortega, 1997), with a major increase on most of the cultivated northern regions */is suggestive of the adaptation of the species to these relatively new structures in the landscape. Power structures could help to
increase the numbers of this species, in spite of the actual mortality on the poles. Since many of the power lines cross croplands and grasslands, which offer better quality forage than urban source, the nestling productivity on these nests could be greater than that of birds nesting on town and city buildings where food sources has lower quality (Janns and Sanchez, 1997). This latter hypothesis needs more field research. Stork nests with an average height of 1/2 m and diameter of 0.8 /1.5 m (Cramp and Simmons, 1977), and a weight ranging from 60 to 250 kg, render these structures incompatible with a properly run electricity service, especially on type A supports which are for low tension delivery (Negro, 1999). These lines are more prone to short-circuits and electric companies */in an effort to control the problem */usually remove voluminous nests from the supports, installing artificial nest platforms as alternatives in the surroundings of the old nests. However, to date no practical success has been reported (Janns, 1998; own data).
Table 2 Nests on power-line supports according to nearby habitat Habitat
Cereal cropland Irrigated land Grasslands Wooded-grasslands
Type of pole
% Nesting on electric supports (n/259)
A
B
C
D
E
1 / 14 26
/ 20 2 /
/ 10 / 2
/ 1 2 /
32 81 13 55
12.8 43.2 12.0 32.1
CC, C. ciconia ; FT, F. tinnunculus ; CO, Corvids; BB, B. buteo .
Species CC
FT
CO
BB
28 112 20 52
/ / 4 6
5 / 7 23
/ / / 2
326
O. Infante, S. Peris / Ecological Engineering 20 (2003) 321 /326
Acknowledgements One author (O. Infante) had a grant from the company IBERDROLA. Fieldwork was financed by the project 1FD97-1468. The manuscript was improved by suggestions of the editor and two anonymous reviewers.
References Alonso, J.C., Alonso, J.A., Carrascal, L.M., 1991. Habitat selection by foraging White Storks, Ciconia ciconia , during the breeding season. Can. J. Zool. 69, 1957 /1962. Anonymous, 2000. Medio Ambiente en Castilla y Leo´n; Informe 2000. Junta de Castilla y Leo´n. Valladolid. Bevanger, K., 1994. Birds interactions with utility structures: collision and electrocution, causes and mitigating measures. Can. J. Zool. 136, 412 /425. Brown, W.M., Drewien, R.C., 1995. Evaluation of two power line markers to reduce crane and waterfowl collision mortality. Wildl. Soc. Bull. 3 (2), 217 /227. Cramp, S., Simmons, K.E.L. (Eds.), The Birds of the Western Palearctic, vol. I. Oxford University Press, Oxford 1977. Ferrer, M., Hiraldo, F., 1992. Man-induced sex-biased mortality in the Spanish Imperial Eagle. Biol. Conserv. 60, 57 /60. Ferrer, M., Janss, G. (coord.), 1999. Aves y lı´neas ele´ctricas. Colisio´n, electrocucio´n y nidificacio´n. Quercus, Madrid. Ferrer, M., de la Riva, M., Castroviejo, J., 1991. Electrocution of raptors on power lines in Southern Spain. J. Field Ornithol. 62 (2), 54 /69. Fowler, J., Cohen, L., 1999. Estadı´stica ba´sica en ornitologı´a. SEO/BirdLife. Madrid. Holyoak, D., 1967. Breeding biology of the Corvidae. Bird Study 14, 153 /168. Janns, G.F.E., 1998. Nests of white storks on electric utility towers. Wildl. Soc. Bull. 26 (2), 274 /278. Janns, G.F.E., 2001. Birds and power lines: a field of tension. Ph.D., Utrecht University, 175 pp. Janss, G.F.E., Ferrer, M., 2001. Avian electrocution mortality in relation to pole design and adjacent habitat in Spain. Bird Cons. Int. 11, 3 /12.
Janns, G.F.E., Sanchez, I., 1997. Productivity of White Stork at different nest sites. Ardeola 44 (1), 101 /104. Lopez, V., Cuadrado, M., Diez, F., Peris, S., 2001. Aves y tendidos ele´ctricos en las provincias de Salamanca y Avila. Salamanca, Rev. Est. 46, 201 /233. Meffe, G.K., Carroll, C.R., 1997. Principles of Conservation Biology, second ed. Sinauer Association, Sunderland. Melendro, J., Gisbert, J., Rodriguez, A., 1987. Datos sobre la alimentacio´n de Ciconia ciconia . Ardeola 24, 207 /209. Navazo, V., Lazo, A., 1999. La nidificacio´n de aves en la red de transporte de electricidad de Espan˜a: evaluacio´n, prevencio´n y correccio´n de la problema´tica asociada. In: Ferrer, M., Janss, G. (coord.), Aves y lı´neas ele´ctricas. Colisio´n, electrocucio´n y nidificacio´n, Quercus, Madrid, pp. 187 /216. Navazo, V., Roig, J., 1996. Estudio sobre la nidificacio´n de aves en apoyos de lı´neas de transporte de electricidad. In: Segundas jornadas sobre lı´neas ele´ctricas y medio ambiente. REE, Red Ele´ctrica Espan˜ola, Madrid, pp. 223 /231. Navazo, V., Roig, J., Lazo, A., 1996. Caracterı´sticas generales de las especies nidificantes en lı´neas de alta tensio´n. Datos para un manejo apropiado. In: Segundas jornadas sobre lı´neas ele´ctricas y medio ambiente. REE, Red Ele´ctrica, Madrid, pp. 433 /439. Negro, J.J., 1987. Adaptacio´n de los tendidos ele´ctricos al entorno. Monografı´as de Alytes no. 1. Adenex, Me´rida. Negro, J.J., 1999. Pasado y futuro de la investigacio´n sobre interacciones entre la fauna y las lı´neas ele´ctricas. In: Ferrer, M., Janss, G. (coord.), Aves y lı´neas ele´ctricas. Colisio´n, electrocucio´n y nidificacio´n. Quercus, Madrid, pp. 21 /29. Nelson, M.W., 1982. Human impacts on Golden Eagles: positive outlook for the 1980s and 1990s. J. Raptor Res. 16, 97 /103. O’Neil, T.A., 1988. An analysis of bird electrocutions in Montana. J. Raptor Res. 22 (1), 27 /28. Ortega, A., 1997. Cigu¨en˜a Blanca. In: Atlas de las Aves de Espan˜a (1975 /1995). SEO/BirdLife (Purroy, F. coord.), Lynx, Barcelona, pp. 58 /59. ´ lvarez, Sa´nchez, A., Bueno, A., Rodrı´guez, J., Gonza´lez, F., .A A., Ramos, V., Caldera, J., 1996. Nidificacio´n de aves en lı´neas ele´ctricas en Extremadura: problema´tica y manejo de conservacio´n. In: Segundas jornadas sobre lı´neas ele´ctricas y medio ambiente. REE, Red Ele´ctrica, Madrid, pp. 207 /213. Steenhof, K.M., Kochert, N., Roppe, J.A., 1993. Nesting by raptors and Common Ravens on electric transmission line towers. J. Wildl. Manage. 57, 271 /281.