Wintering Black Storks (Ciconia nigra) cause severe damage to transmission lines in Israel A study on the risk and mitigation possibilities

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1 Wintering Black Storks (Ciconia nigra) cause severe damage to transmission lines in Israel A study on the risk and mitigation possibilities EDM International Conference on Overhead lines, Fort-Collins, CO, March 31-April 3, 2008 Dr. Ofer Bahat 1 Seminar Hakibutzim College, Tel-Aviv, Israel; Indianapolis University Branch, Galilee, Israel; BirdsVision Ltd. Summary The Black Stork (Ciconia nigra), a large bird with cm wingspan, has the widest geographical range of any stork species, nesting from Spain in the west to China in the east. A small population of storks winters in the north of Israel and is responsible for severe damage to a 161 KV transmission lines, which may account for up to 90% of the overall bird damage to transmission lines in Israel. The wintering Black Storks are responsible for events of severe outages every winter in the study area alone, which are made while the birds roost on the transmission line poles. The direct damage for a single event may be over 400K $ US. Although the Israel Electric Corporation developed and implemented various mitigation devices to prevent the outages, these devices proved to be insufficient and the situation remained very severe. The current study investigated the causes of the outages, their correlation with the Black Storks activity and different ecological factors in the study area and possible measures to reduce the damage. A major result of the study show that the Black Storks feed solely on fish in fish ponds which are in close vicinity of the transmission line. The Black Storks are the only bird species that regularly use the transmission line for roost. The study area provides the storks with a combination of high food availability and safe roost. However, implementation of newly developed management measures may be useful to reduce the number of outages. 1 bahat@shani.net 1

2 Key words: Black Stork, Ciconia nigra, wintering population, transmission lines, roosting, foraging, outages, bird streamers, flashovers. 2

3 Introduction The Black Stork (Ciconia nigra) is a monotypic species and a member of the Stork order (Ciconiiformes), and the family of storks (Ciconidae). It is a large bird with a 3 kg body mass, cm body length and cm wingspan. Adult Black Storks have a black body with varying green and purple gloss on the feathers and white areas on the breast and belly. The bill and legs are deep red, intensifying their red color during mating season and turn more brown during winter months. Young black storks do not have the adult s colorful feathers, and these colors appear when they are one year old. The sexes are alike, although males are larger than females (21, 25, 27). The Black Stork is one of the stork species that has been little studied and many aspects of its ecology, physiology and behaviour are not known or only partly investigated. Even detailed information on the populations of this species throughout its distribution range is neglected, mainly because Black Storks breed in dense wood areas where accurate nesting surveys are difficult to carry out (5). However, during the last decade, several research groups made substantial advancement in the study of Black Storks, including several radio tracking projects with the use of satellites as well as counts and surveys in their breeding, migration and wintering areas, and studies related to conservation risks in different parts of their distribution range mainly in Europe (10, 14, 18, 19, 22). The Black Stork has the widest geographical range of any stork species (21, 25). It is widely distributed in Europe, Asia and also found in Africa. It nests from Spain and France in the west through central Europe and the Balkans, east across Asia into Mongolia, China and South Korea (27). A separate resident population is found in Zambia and South-Africa. Apart from few resident populations in Europe (e.g. in Spain and Bulgaria) most of the Palearctic populations of the Black Stork migrate to southern winter quarters. The European populations migrate across Gibraltar or the Bosporus south. Some storks find their wintering grounds in the Middle-East, although most of the populations migrate to Africa and winter in the Sahel area in West Africa or in East Africa (21, 25, 27). 3

4 In Israel, the Black Stork is mostly a migrant species during spring and autumn, but a small population winters in the northern part of the country. There has been no study so far on the biology of this species in Israel and the existing data is based on counts of migrating birds: these counts show that the total number of migrating Black Storks does not exceed 40,000 individuals (17, Dan Alon - pers. comm.). The number of wintering Black Storks all over Israel was estimated between individual birds during the 1980 s and 1990 s (25), but more recent surveys during the early 2000 s indicate a substantial increase in the wintering population which was estimated at 1,450 birds throughout the country, including 800 individuals in the study area Beit-Shean Valley (Willem Van Den Bossche - pers. comm.). The wintering population of Black Storks starts to settle in its wintering quarters in Israel from mid September and the wintering period usually ends by mid March. However, although there is very limited data on the population dynamics during the winter, it is most probable that individual birds continue to arrive to the wintering areas until early November or maybe even December. First individual storks leave the wintering areas from mid February. Accordingly, the wintering population reaches its peak probably during January, and birds probably winter in these areas during an average period of 4 months. However, wintering period may probably be from 2 months only up to 6 months (25, Willem Van Den Bossche - pers. comm.). Since the mid 1990 s, Black Storks have been observed roosting on steel poles of transmission lines (161 KV) at the northern valleys in the north of Israel, and questions were raised concerning the possible correlation between roosting activity of the storks and failures and electrocutions that started to become more and more obvious in the transmission lines (Bahat pers. Comm.). It gradually became clear that this species regularly use transmission lines for roosting in northern Israel. As some electrocuted birds were found ( , Bahat pers. observations) and the number of outages unexplained by any other factor, and thus related to bird activity, increased, the connection between the stork activity and the transmission line failures became more and more obvious. Moreover, the 4

5 magnitude of power outages which was in probable relation to roosting Black Storks augmented up to 90% of the overall annual outages on transmission lines in Israel (Bahat pers. comm. based on IEC unpublished material). Inspection of the failures in the transmission lines showed that Black Storks are electrocuted on a very small scale (few individual birds every winter) while roosting on the middle or lower arms of the 161 KV steel poles. However, it has been suggested that the storks usually roost on the upper arms - where they are not susceptible to electrocutions and thus most outages are probably the result of the bird s streamers of semi-conductive effluent that bridge the gap between the pole arms and wires, pollute the insulators below and eventually cause flashovers (Bahat - pers. comm.). The Israel Electric Corporation (IEC) together with Raychem Ltd., started during late 1996 to develop new mitigation solutions based on insulation of the wires and use of "umbrellas" to avoid flashovers. These were implemented in the last several years, and in some cases substantially decreased the number of outages. Nonetheless, the problem is still severe and the damage to the transmission lines is still substantial (Bahat - pers. comm. based on IEC unpublished material). Accordingly, the IEC initiated the present study during winter 2006, in order to achieve the following goals: 1. Examine the areas where damage is caused to transmission lines by wintering Black Storks, and identify possible patterns in the outages occurrence. 2. Carry out day and night observations during the winter on transmission lines to identify the bird species that roost on the poles, analyze their activity and behaviour and identify any change in the use of the line along the winter in relation to power outages. 3. Examine the pattern of use of the transmission poles the by roosting birds, their exact location on the pole during day and night, and the possible effect of ecological factors on the use of the line by the storks. 5

6 4. Examine Outages events and their mechanisms, the efficiency of the mitigation devices that were implemented by the IEC and the possible use of other mitigation measures. Materials and methods A literature survey has been done at the beginning of the study in order to collect any relevant biological data on the Black Storks that may have an effect on the transmission line outages. A statistical examination of outages data from previous years ( ) was carried out in order to assess any patterns related to the Black Stork roosting activity. During winter 2006, starting from the beginning of November 2005 to the end of March 2006, observations on the Black Storks were conducted at the Beit-Shean Valley in northern Israel. The night observations were made from a 4x4 car, in order to prevent disturbance to the birds, at a specific location approximately 150 meters from the transmission poles. Daytime observations were also conducted from the car for the same reason. Night observations started 2 hours before sunset (at approximately 15:00) and ended after the last stork left the poles (at approximately 07:00). These were conducted twice every week during the 2006 winter. Daytime observations started immediately after the Black Storks left their roost on the transmission line (at approximately 07:00 in the morning) and ended at 15:00 in the afternoon. These were conducted twice every week during the 2006 winter. One a week a day and night observations were conducted continuously to obtain 24 hours documentation of the Black Storks activity. Daytime activity observation covered the foraging behaviour of the storks, as well as other activities such as aggregations after feeding and before roost. Foraging was investigated by direct observations of storks feeding and by analysing pellets and prey remains that were systematically collected near the feeding places and under the transmission line poles where the storks roosted. Counts of the Black Storks throughout the entire Beit Shean Valley, in an area of 70 sq. km., were conducted with the help of local ornithologists. 6

7 The observation gear included 8x42 Leica binoculars and 15-60x70 Kowa telescope, in addition to 22x Canon 750i DV camera. Night observations were made with the use of a Cyclop 1081 Star Light Scope (SLS), and FLIR Systems (Indigo) Photon 75 mm thermal imaging camera. Data was analysed using SPSS package and statistics were made with the support of Prof. Uzi Motro from the Hebrew University in Jerusalem. Results 1. Analysis of previous outages in the transmission line: During the 2003 winter, a total of 14 bird-made outages affected the transmission line in the study area. All these outages were carefully examined by the utility experts together with the researcher and were unquestionably categorized as bird made outages. They were recorded from the 8 th of October 2002, until the 23 rd of February All theses events happened during night from 21:20 in the evening until 06:14 in the morning. However, the highest event number (79%) occurred from midnight until 07:00 in the morning. During the 2004 winter, a total of 34 outages that were considered as bird-made, were recorded in the study area. These outages took place from the 17 th of September 2003, until the 6 th of March All theses events happened during night from 17:50 in the evening until 05:36 in the morning, and were evenly distributed along the dark hours. During the 2005 winter, a total of 31 outages that were considered as bird-made, were recorded in the study area. These outages took place from the 6 th of October 2004, until the 4th of April All theses events happened during night, and were evenly distributed along the dark hours, apart from one birdmade outage that happened at 12:30 in mid day. There is no record of the bird species that is responsible for this exceptional outage. Examination of the pool of events of these 3 years samples of outages (n=78) did not reveal any statistical difference in the distribution of events during the different months of the winter, due to the high variability of the events occurrence. 7

8 Nevertheless, the data clearly show that the outages numbers are highest from November to February, as is demonstrated in the following figure: Black Stork made outages per Month Beit-Shean Valley, Israel Number of outages September October November December January Month February March April Fig. 1: Number of outages made by wintering Black Storks per month Analysis of the 3 years data pool was also made to examine a possible statistical difference between outage events in different hours. In this case, similarly to the analysis of outages events per hour, due to the very high variability of the data, no statistical difference was found. However, although it not significant, but there is a tendency for high number of outage events in between 21:00-23:00 at night and between 03:00-05:00 in the early morning, as is shown in the next figure: 8

9 12 Number of Voltage Dips per Hour at Beit- Shean Valley Number of Voltage Dips Hour Fig. 2: Number of outages made by wintering Black Storks per hour during 24 hr period No statistical difference was found between the outage numbers in different circuits, on the same transmission line, therefore the susceptibility of the circuits on the two sides of the poles to the bird-made outages was even. 2. Examination of the occurrence of outage by electric phase: Previous data contained no record concerning the phase on which the outage took place. However, the present study observations definitely show that the Black Storks hardly ever use the middle or lower arms of the poles, and nearly always use the upper arms and the central top of the pole for roosting, as is clearly shown in the following figure: 9

10 Fig. 3: Black Storks land for roost on a 161 KV pole. Note the mitigation devices on top of the pole and its centre (perches), on the upper right arm (unstable metal cables), on the tip of the upper arms (metal thorns), on the insulators ( umbrellas on top and bottom) and on the wire attached to the insulators ( sleeves ) (photo: Ofer Bahat ). The observation data show that although the upper arms of specific poles that suffered heavily from outages are equipped with the listed above serious of protective and deterring devices, most of the Black Stork eventually found their own appropriate perching position. The number of individual birds roosting on one pole is usually between 8-12 birds, but may be up to 18 birds. The Black Storks nearly always roost on the transmission lines in groups that contain at least 4 individual birds, but in some atypical cases, single birds or birds in groups of 2-3 individuals, were also observed. Once the Black Storks sit on the upper arms, there is an immediate and concrete risk of an outage due to flash over by the birds' streamers. 10

11 Fig. 4: A Black Stork perches for roost on the upper arm of a 161 KV pole, despite the different deterrent devices (photo: Ofer Bahat ). Fig. 5: A Black Stork (on the right) produces a streamer (white string indicated by the red arrow) from its roosting position on the upper arm of a 161 KV pole (a pole with protective devices) (photo: Ofer Bahat ). 11

12 3. Examination of major outages areas: The analysis of the outages events clearly demonstrate that their majority (78%) are concentrated in specific limited areas and not randomly distributed, as shown in the following figure: 2 Ein- Harod Beit- Hashita Gidona 6 1 Heftziba Nir-David Beit- Shean 1 km Fig. 6: Map of the major Outages events in the Black Stork research area, marked in black circles and numbered from 1 to 6. The corresponding fish ponds where the storks forage are marked in red circles. Names of major town and villages are added. Details on the outage occurrences in each geographical area: a) 47% of all the outages in the study area took place in area no. 1. The average distance of the outages from the nearest transformation station was 9.0±0.9 km. This area is located km south of a large concentration of fish ponds. Most of the night observations in the present study took place in this area. b) 16% of all the outages in the study area took place in area no. 2. The average distance of the outages from the nearest transformation station was 18.7±0.9 km. This area is located km west of a large concentration of fish ponds. 12

13 c) 13% of all the outages in the study area took place in area no. 3. The average distance of the outages from the nearest transformation station was 1.5±0.5 km. This area is located km north-east and 3 km west of a large concentration of fish ponds and water reservoirs. d) 8% of all the outages in the study area took place in area no. 4. The average distance of the outages from the nearest transformation station was 3.4±0.3 km. This area is located in the middle of a large concentration of fish ponds and water reservoirs. e) 8% of all the outages in the study area took place in area no. 5. The average distance of the outages from the nearest transformation station was 2.3±0.2 km. This area is located approximately 1 km from three different concentrations of fish ponds. f) 7% of all the outages in the study area took place in area no. 6. The average distance of the outages from the nearest transformation station was 12.4±1.5 km. This area is located km south and west of two large concentrations of fish ponds and water reservoirs. 4. Quantification of the damage: As the number of outages differs in between years, and the damage accounted by each event varies considerably, it is impossible to give accurate quantification of the damage. However, based on previous data, it is possible to give a general estimation: the direct repair damages costs for the utility are approximately 70K $ US for one event. Total damages estimated for a single event may reach 400K $ US (including costs of unsupplied electricity, excluding possible compensations to factories and other possible indirect costs) (Bahat - pers. comm. based on IEC unpublished material). Accordingly, as each winter a minimum number of 20 outage events takes place in the study area, the damage to the utility, (excluding potential indirect costs) is in the magnitude of 8 million $ US in this area alone. 13

14 5. The Black Storks population size: The number of Black Stork individuals in the study area varied along the winter period, as a result of local changes in the distribution of the birds and possibly also due to movements in between different wintering grounds in northern Israel. Accordingly, the size of the Black Stork population varied along the winter period and the data presented here is the peak count which was conducted in mid winter during daytime, on the A total of 1,730 individual Black Storks were counted throughout the study area, although only 435 birds were observed in close vicinity to the 161 KV line. The other birds were foraging in fish ponds further away from the transmission line or, on some occasions, concentrating in large aggregations, in open fields or near fish ponds and water reservoirs on the open ground, after completing their foraging, as shown in the next figure: Fig. 7: Aggregation of approximately 150 Black Storks near fish ponds where they forage together with egrets and herons (photo courtesy: Kobi Merom ) Concentrations in large numbers also occurred in the afternoon when the birds assembled in high numbers (usually several hundred individuals together) at preroost sites. These sites, where usually in a close vicinity to the transmission line 14

15 which was used by the storks for roosting. However, in some cases the birds aggregated in pre-roost concentrations at areas further away from the transmission line, up to 5 km. 6. Food and foraging: Both direct observations and analysis of prey remains and droppings/pellets definitely show that fish are the only food resource of the wintering Black Storks in the study area, and no other food resource was found. Birds were observed foraging in fish ponds where different fish species were cultivated, including carp (Cyprinus carpio), St. Peter's fish (Oreochromis sp.) and grey mullet (Mugil cephalus). Birds were observed foraging in all the fish ponds in the study area, moving from pond to pond according to the fishermen s activity and fish availability: The birds did not forage in deep water but rather used shallow water near the edge of the ponds. Fig. 8: Fish remains and droppings of Black Storks found on the ground under a 161 KV roosting pole (photo: Ofer Bahat ). 15

16 Fig. 9: Pellets of fish remains and droppings of Black Storks found on the ground under a 161 KV roosting pole (photo: Ofer Bahat ). The Black Storks were particularly attracted to ponds that were emptied by the fishermen who harvested the fish while pumping the water out of the pond. Such events were highly profitable to the Black Storks that aggregated in their dozens or even hundreds in such ponds, to consume the remaining fish that were left by the fishermen. In addition, the Black Storks were also greatly attracted to special pits that were dug by the fishermen in the fishponds areas, and were used to dump unusable fish of poor quality. These pits, although only about 2x3 meters in size and 2 meters deep, contained sometimes thousands of fish and once filled by the fishermen, were readily used by the foraging Black Storks, as well as other fish eating birds, mostly White Storks (Ciconia ciconia) and Grey Heron (Ardea cinerea). Some of these pits were located in a close vicinity to the transmission line. As the pit dumps were filled only occasionally, once they contained fish, the Black Storks used to fly in the early morning straight from the electric poles to feed in them, sometimes concentrating in numbers over 400 individuals at one pit. The birds used to stay near the full pits the whole day, moved their pre-roost aggregation to nearby fields, and flew in the evening from the area of the pits straight back to the electric poles. 16

17 Discussion The present study investigated the impact of the wintering of a single species, the Black Stork, on numerous outages that took place in a single area in northern Israel. The results of the present study clearly demonstrate that the combination of highly available ecological resources in a concentrated area, together with birds that are attracted to a transmission line as their favourable roost, is very destructive. The attractiveness of the transmission line as a safe roost, with the high food availability to the Black Storks is well reflected in the increasing numbers of storks in the study area, as shown earlier. These numbers are currently greater than the estimated number of all the wintering population of Black Storks in Israel, in the early 2000 s. A question of major biological interest is related to the fact that the Black Stork is the only bird species that regularly use the transmission line as a roosting site, although during the daytime, the poles are frequently used by raptors, mostly European Kestrels (Falco tinnunculus) and occasionally Long-legged Buzzards (Buteo rufinus) as perches while hunting (Bahat pers. observations). This may be related to the fact that Black Storks are typical tree nesting species and are used to nest on high trees near water with food (18, 19, 22, 27). The 161 KV transmission line poles, 30m tall on average in the study area, are probably a good replacement to the trees the storks are used to, and provide the storks with a safe shelter and a good vantage point looking over the feeding area for next day foraging. The fact that the wintering population of the Black Storks feeds solely on fish, and the fact that fish are highly available in the study area, make this area very attractive to Black Storks. In their breeding grounds, during spring and summer, Black Storks feed on a variety of food items, including fish, amphibians, insects and rodents (5, 10, 27). As fish are most likely to be the only food available for Black Storks in the study area during winter, they use this resource very extensively. The potential conflict between the storks and the fishermen is insignificant, because the birds are unable to feed in deep water and take few fish from the full ponds. In addition, the birds consume extra fish that are left in 17

18 the ponds after harvest, and intensively use the pit dumps where the fishermen throw away the unusable fish of poor quality. The fishermen regard the Black Storks as sanitarians that provide them with cleaning service and make no attempt to chase them away (Bahat pers. observations). Previous studies have clearly demonstrated that bird streamers are the cause for flashovers and consequent outages in different countries, involving various birds species (1, 3, 26, 28, 29). The present study observations on the behaviour of the roosting Black Storks on the electric poles, yielded several possible explanations for the mechanism of outage formation in relation to the storks behaviour: a) The aggregation of many birds on one pole when they come to roost, leads to competition on high priority roosting points, thus increases tension and the possibility of a streamers secretion followed by a flashover. b) As the Black Storks are extremely sensitive to human activity near the electric line while they roost, and as streamers secretion is a typical fright and flight behavior of these birds (Bahat pers. Observations), the night outages are related to human interference near the transmission line. c) The outages are related to the storks taking-off flights in the early morning, which are preceded by streamers secretion. d) The Black Storks streamers secretion takes place throughout the night, and is predominantly determined by the internal digestion of food by the storks, and not by external factors. The results of the present study disagree with the first and third explanations because the outage events are evenly spread throughout the night and not concentrated in the evening or early morning. On the contrary, they are much more likely to happen in the middle or late night, between 21:00-23:00 and 03:00-05:00. The third explanation also does not explain the results, as human disturbances were documented in very few cases, and no outage was documented subsequently. Consequently, it seems most likely that the birds streamers production is timed by the birds digestion process. Although fish digestion process by Black Storks 18

19 has not been investigated, the scientific data concerning this process in large sized fish-eating birds (e.g. penguins and albatrosses), show that fish retention time in the digestive tract of these birds is between hours for the liquid components of the food, and hours for the solid components (15, 16, 20). It would be most likely to assume that Black Storks have a digestion rate of similar magnitude. As the results of the present study show that the birds feed only on fish, therefore a bird that feeds in 08:00 in the morning will end the digestion of the liquid parts from 12:00 onwards. The digestion of the solid parts, however, will end up only from 23:00 at night onwards. Accordingly, the production of bird streamers will be made during the late night from this hour onwards. These assumptions correspond well with the outage data of the present study. An evidence for the occurrence of this process is given by the documentation of the streamers production by the birds, but moreover, by the enormous amounts of fresh white wash which is found every morning under transmission line poles that hosted roosting storks the previous night. It has been shown that stork species are highly susceptible to electrocution hazards due to their large body size and long wingspan (8, 9, 23) Satellite tracking of breeding Black Storks has shown that birds migrate through extensive areas where they are exposed to various hazards, including powerlines (14). Mitigation measures to prevent birds electrocutions on power lines are widely and successfully implemented worldwide and saved many endangered bird lives, e.g. raptors (11, 13). In addition, intensive and important work has been done in different countries and also in the study area, to implement mitigation solutions to prevent the problem of birds streamers on transmission line (3, 4, 7, 12, 28). However, the existing measures to prevent flashovers on transmission lines, give only partial solution to the problem, as this case is far more complicated due to the very high voltage and the limited possibilities to insulate the wires. This is a severe problem for the utilities but also is in many cases a severe threat to bird populations, including populations of highly endangered species (2). In addition, the presence of birds on very high tension poles (e.g. for breeding) may be a 19

20 hazard to the birds also because of electromagnetic fields that negatively affect the birds reproduction and physiology (6). Accordingly, diminishing the damage of birds streamers to transmission lines should include mitigation measures, but it should be also be based on immediate management actions, which are aimed to reduce the carrying capacity of the area in focus, thus make it less attractive to the birds. In the case of the present study, the following recommendations are made: a) Completely ban the use of pit dumps by the fishermen and find alternative ways to get rid of the unusable fish. b) Check the possibility to feed the storks (e.g. by using these unusable fish in feeding stations) in certain remote areas, to attract them to areas that are far away from the transmission lines. c) Continue to develop and implement mitigation solutions on the poles, but also check the possibility to build artificial perches which are attractive to the birds and are far away from the transmission line. d) Conduct experiments of Black Storks detection and deterrence with different technologies. Acknowledgements I thank Kobi Merom, an expert local ornithologist, who took part in the field work and made an invaluable contribution to the study. I also am grateful to Hezi Samoha, Head of Transmission Lines Department, Israel Electric Corporation, for the important support to the study and the development of mitigation solutions. I also thank Amir Balzam, Israel Electric Corporation North district transmission lines maintenance department, for the support in the field and for providing substantial information. 20

21 Bibliography 1. Bekker, H.J.J. and Hoch, D.A Analysis of factors contributing to unexplained transmission line faults on a high voltage transmission network. Pp in: Proceedings of the 6 th Africon Conference in Africa, University of Natal, S.A. 2. Bevanger, K Biological and conservation aspects of bird mortality caused by electricity power lines: A review. Biol. Conservation 86(1): Burnham, J.T Bird streamer flashovers on FPL transmission lines. Power Delivery 10(2): Burnham, J., Carlton, R., Cherney, E.A., Couret, G., Eldridge, K.T., Farzaneh, M., Frazier, S.D., Gorur, R.S., Harness, R., Shaffner, D., Siegel, S., and Varner, J Preventive measures to reduce bird-related power Outagespart I: electrocution and collision. Power Delivery vol. 19(4): delhoyo, J., Elliot, A. and Sargatal, J Handbook of Birds of the World. Lynx Edicions, Barcelona. 6. Fernie, K.J. and Reynolds, J.S The effects of electromagnetic fields from power lines on avian reproductive biology and physiology: A review. Journal of Toxicology and Environmental Health B 8(2): Frazier, S.D. and Bonham, C Suggested practices for reducing animalcaused outages. Industry Applications Magazine 2(4): Garrido, H.R. and Fernández-Cruz, M Effects of power lines on a White Stork Ciconia ciconia population in central Spain. Ardeola 50(2): Guyonne F. and Janss, E Avian mortality from power lines: a morphologic approach of a species-specific mortality. Biol. Conservation 95(3): Hampl, R., Bureš, S., Baláž, P., Bobek, M. and Pojer, F Food provisioning and nestling diet of the black stork in the Czech Republic. Waterbirds 28(1): Harness, R. E. and Wilson, K. R Raptor electrocutions and outages - a review of rural utility records spanning Pp in: Chancellor, 21

22 R.D. and Meyburg, B.U. (eds.) Raptors at Risk. Proceedings of the V World Conference on Birds of Prey and Owls, Midrand, Johannesburg, SA, Hancock House, Berlin, Germany. 12.Harness, R.E. and Carlton, R New solutions for bird collision and electrocution outage problems. Power Engineering Society Winter Meeting, 2001, Vol. 1: Harness, R. E. and Wilson, K. R Electric utility structures associated with raptor electrocutions in rural areas. Wildlife Society Bull. 29: Jiguet, F. and Villarubias, S Satellite tracking of breeding black storks Ciconia nigra: new incomes for spatial conservation issues. Biol. Conservation 120(2): Karasov, W.H. and J.M. Diamond A simple method for measuring intestinal uptake in vitro. J. Comparative Physiology 152: Karasov, W.H. and J.M. Diamond Interplay between physiology and ecology in digestion. BioScience 38: Leshem, Y. and Bahat, O Flying With the Birds. Yediot Ahronot Publishing House and the Society for the Protection of Nature in Israel, Tel- Aviv. 18.Lõhmus, A. and Sellis, U Nest trees a limiting factor for the the Black Stork (Ciconia nigra) population in Estonia. Aves 40(1-4): Lõhmus, A., Sellis, U. and Rosenvald, R Have recent changes in forest structure reduced the Estonian black stork Ciconia nigra population? Biodiversity and Conservation 14(6): Martı nez del Rio C., H.G. Baker, and I. Baker Ecological and evolutionary implications of digestive processes: bird preferences and the sugar constituents of floral nectar and pulp. Experientia 48: Perring, C. and Middleton, A The Encyclopedia of Birds. Equinox, Oxford. 22.Rosenvald, R. and Lõhmus, A Nesting of the black stork (Ciconia nigra) and white-tailed eagle (Haliaeetus albicilla) in relation to forest management. Forest Ecology and Management 185(3):

23 23.Rubolini, D., Gustin, M., Bogliani, G. and Garavaglia, R Birds and powerlines in Italy: an assessment. Bird Conservation International 15: Shirihai, H The Birds of Israel. Academic Press, London. 25.Sibley, C. and Monroe, B Distribution and Taxonomy of Birds of the World. Yale University Press, New Haven. 26.Smallie, J. and van Rooyen, C Impact of bird streamers on quality of supply on transmission lines: A case study. Proceedings of European Power and Energy Systems conference, Benalmádena, Spain. 27.Snow, D.W. and Perrins, C.M The Birds of the Western Palearctic, Concise Edition. Vol. 1: Non-Passerines. Oxford University Press, Oxford. 28.van Rooyen, C., Vosloo, H. and Harness, R Eliminating bird streamers as a cause of faulting on transmission lines. Proceedings of Rural Electric Power Conference, Colorado Springs, CO, USA. 29.van Rooyen, C., Vosloo, H. and Harness, R Watch the birdie! [overhead line faults]. Industry Applications Magazine 9(5):