Background and project initiation
1. The rodent – farmland conflict:
Agriculture has always dealt with various kinds of pests, including rodents, that inflict large losses and cause severe destruction of crops. As modern agriculture increased crop production and quality, easy access to large quantities of food also increased the prevalence of pests. Rodent populations have gotten out of control, and international studies assess rodent damage at around 35% of global production (seeds, fruits, vegetables, etc.). Farmers usually deal with rodent pests by applying highly toxic pesticides that severely damage the ecological system. Some of the pesticides affect non-target animals, and some seep into the groundwater, impairing their quality and putting consumers at risk. Some pesticides stick to plants, fruits, or vegetables, harming those who eat them, both directly and indirectly (cow-feed crops sprayed with pesticides, like alfalfa, are fed to cows and pesticides enter the milk!). Some substances don’t degrade fast enough, and when a predator eats the poisoned organism, that predator may also be poisoned by high levels of residual pesticide in the prey. In many places, these secondary poisonings have caused raptor (both day and night) populations to crash, and these (mainly Barn Owls) are the major natural enemies of many types of pests
2. Chemical pest management and its destructive outcomes:
The use of anti-rodent pesticides in Israel became widespread during the 1950s with bleak consequences. Rodent damage persisted while raptors, their natural enemy, rapidly declined. Many species that once nested in northern Israel became extinct, and others are still under serious threat today. Many raptors met their demise in alfalfa fields, a perennial crop preferred by voles. When fields are plowed the voles’ habitat is destroyed and their population shrinks. But alfalfa is only plowed once every 3-4 years, during which voles breed uncontrollably. Voles became the main pests in alfalfa agriculture, and farmers declared war. Control was done by baiting animals using wheat grains covered with Thallium sulfide. The poisonous bait was used in quantities far greater than necessary to control the rodents, which ended up consuming much more than the lethal dose. Thallium sulfide is a slow-acting poison, and its effect on the body starts with paralysis. Poisoned rodents move slowly across the field and are unable to reach their burrows, making them easy prey for raptors flying overhead and picking an easy meal. The raptors themselves are then paralyzed and die from secondary poisoning. Professor Heinrich Mendelson assessed that the majority of Israel’s wintering raptor population was wiped out by secondary poisoning of Thallium sulfide between 1950-1956. “The frequent use of large quantities of Thallium bait has selectively affected the predators of field mice, destroying the ancient natural balance between mouse and predator populations.” (Mendelson, 1969). Non-migratory rodent predators were also brought to the brink of extinction in the years that followed.
3. Biological pest control in the Hula Valley – “The failed attempt”:
In 1981, researchers from Tel Aviv University and the Hebrew University in Jerusalem joined the Society for the Protection of Nature in Israel (SNPI) and Israel Nature and Parks Authority (NPA) personnel to end the horrible situation. They set out to offer a reasonable pesticide substitute to alfalfa farmers in the Hula Valley: vole control using Barn Owls. A vole-infested field in Neot Mordechai was chosen as a test site. After obtaining approval from the local farmers, wooden nest boxes were installed on 2.5-meter poles, and four Barn Owl pairs were brought for acclimatization.
The local farmers agreed to make any effort needed to avoid using pesticides in and around the field, and emergency aid by flooding was promised in case of emergency, with help from NPA youth groups. Introduced Barn Owls were released following a short acclimatization period, but four individuals were found dead nearby shortly after. A subsequent trial was performed the following year (March 1982), but this time Barn Owls were released after a longer acclimatization period which lasted three weeks. Some of these remained in the field and other nest boxes were populated by local pairs. During Passover that year, the field was treated with a forbidden substance called Azodrin which killed mammals, storks, and many raptors, including four of the introduced Barn Owls. After this poisoning, two populated nest boxes disappeared, and another was knocked down – the experiment failed! (Hotter, 1983).
4. Biological pest control in Sde Eliyahu – Beginning in the orchards:
Following the above-mentioned unfortunate events, Professor Yossi Leshem, then manager of the NPA’s Raptor Information Center, contacted members of Kibbutz Sde Eliyahu in 1983 and asked them to take control of the experiment. Sde Eliyahu maintains a relatively large (2000 acres) block of bio-organic agriculture. Back then it contained 300 acres of date plantations, about 100 acres of pomegranate orchards, a similar area of grape vines, 1,100 acres of field crops and vegetables, and 400 acres of the Kibbutz settlement itself. Researchers hoped that the local pesticide-free agricultural environment would reduce the chances of Barn Owl death by secondary poisoning. At that time farmers in Sde Eliyahu were dealing with different rodent infestations in vegetable areas and serious mouse and rat damage in date plantations and pomegranate orchards. Farmers responded positively and in that same year 14 nest boxes, populated by 14 Barn Owl pairs brought from the zoological garden at Tel Aviv University, were installed around the orchards and plantations. Barn Owls were freed after a period of acclimatization but surprisingly did not succeed in nesting during the first year (Kobliner, 1984). Luckily, local, “natural” Barn Owls came to populate the nest boxes in the following year.
After several years of Barn Owl activity in and around plantations and orchards, the damage to the dates and pomegranates subsided significantly. Farmers asked for additional nest boxes to be installed and in 1990 nine additional nest boxes were placed in and around the plantations.
5. Biological pest control in Sde Eliyahu – Moving to the fields:
Rodent pest management in the orchard and plantation proved satisfactory, but vegetables, mostly carrots and potatoes, were still heavily infested. A request came to place nest boxes around the fields. The terrain encompassed 1000 acres of flat, treeless fields, and its suitability for Barn Owl nesting was not certain. Despite the doubts and in the absence of other options (the area was bio-organically managed), 24 new nest boxes were placed in and around the area in 1993. Initially, no activity was observed. During the second year, a few Barn Owls got acquainted with the nest boxes, and pellets were even found in some. Three years after placing nest boxes in the exposed field, nesting began, and vegetable damages were reduced to a minimum.
6. Biological pest control in Sde Eliyahu – The alfalfa problem:
Sde Eliyahu was left with a single area where the pest situation was still a problem in alfalfa fields. Vole damage was so vast, and bald patches in the fields were so large that very little was left to harvest. Farmers had to renew the crop every 18 months instead of every 3-4 years. A large group of Barn Owls (up to 11 individuals per night over 110 acres) was feeding off the plot but could not control the voles due to their high breeding rates. Alfalfa farming in Sde Eliyahu was on the brink of collapse. Meanwhile, nest boxes were being populated and chicks were constantly hatching, and it was decided to add more nest boxes to the system. 15 nest boxes were installed in 1997, and this time some were placed outside the bio-organic plots, where standard farming practices are used, to test the method on this type of system. In addition to nest boxes, alfalfa fields were also fitted with observation and resting posts to assist the general raptor population in hunting. Results were already evident in autumn that year, as increasing predation pressure reduced the damage to new alfalfa plots to a minimum (this positive outcome still holds at the time these lines are written, spring 2003).
Due to the active predator-prey balance between Barn Owls and voles and the rapid decline of vole populations, nest box occupancy was very low during 1999. Those involved in the project feared that the shrinking Barn Owl population would be unable to contain an unavoidable future increase in the vole population. We were surprised to see the Barn Owls changing tactics and hunting birds in nearby orchards and plantations. When vole populations resurfaced in the autumn of 2002, Barn Owls responded quickly, doubling the number of nests, and the resulting predation pressure successfully contained the new infestation and ensured crop safety.
7. The Beit She'an Valley conflict:
Beit She’an Valley is home to almost 7000 acres of alfalfa fields. It plays an important role in the crop cycle and is more resilient to the harsh conditions in the southeastern part of the valley, making it very valuable to farmers in the area. During October and early November of 1997, farmers in the Beit She’an Valley sprayed vole-infested alfalfa fields with Monophos (of which the active agent is Monocrotophos, an organophosphate), a substance that is not approved for use against rodents and specifically against voles in alfalfa fields. The substance, sprayed in two distant plots, caused heavy environmental damage. Dozens of raptors, mainly kites and barn owls, as well as hundreds of passerines, were affected by secondary poisoning. The event symbolized the height of the agriculture (or farmer) nature conflict in the field. Following an uprising brought on by the catastrophe, all sides sat down to work out solutions and prevent something similar from happening again. In March 1998, a debate was held in the Beit She’an Valley led by the Minister of Agriculture and the Environment Raphael Eitan (Raful), the Ministry of Agriculture, the National Parks Authority, the Beit She’an Valley Regional Council, Tel Aviv University, the Hebrew University of Jerusalem, the Society for the Protection of Nature in Israel, alfalfa growers of the inner valleys, and other organizations involved. The representatives of the farmers claimed that without the use of the harsh poisons, it is not possible to overcome the plague of voles in the valley. The representatives of the academy and the other participants in the discussion explained how dangerous and destructive the use of these substances is to the environment and humans. The Sde Eliyahu representative explained the model according to which he operates on his farm. The suggestion was made to try the “Sde Eliyahu model” with improvements, as presented by various speakers. Since that meeting, the farmers have indeed changed the alfalfa growing interface in the area, adding nest boxes and making further adjustments to the situation. The poisoning in the valley has stopped and no environmental damage has been caused from this direction. In the spring of 2002, with the growth of the vole population, it became clear that in certain areas, where there was a sufficient density of active nest boxes, rodent control was reasonable. In other plots, however, the alfalfa suffered serious damage. The conclusion was that nest boxes should be added in areas where there is still a lot of damage, and in that environment the occupancy of the nest boxes was maximum. It was proof that there was a lack of nesting sites there and that the addition of boxes would improve the situation. As a general rule, it can be said that maximum occupancy of nest boxes (over 80% or so) does not herald success, but the opposite. Maximum occupancy signifies a situation where the food (the rodents) is so abundant that the nesting sites in the area are not sufficient for the number of barn owls attracted to the place in its wake, and therefore damage should be expected. In such a case, additional nest boxes should be immediately placed in the area.
8. Research development:
In 1988, it was decided that the project would be accompanied by continuous research to obtain an accurate picture of the situation as well as to draw lessons that would allow it to be expanded. At this point, Dr. Gila Kahila Bar-Gal from the Hebrew University of Jerusalem entered the picture, doing her master’s research work under the supervision of Prof. Eitan Tchernov. Dr. Kahila Bar-Gal’s research on the Barn Owl as a biological control of the rodent population in agricultural areas focused on three areas:
- Studying the reproductive biology and dynamics of the Barn Owl population.
- Studying the habitat of the Barn Owl population and their patterns of habitat use.
- Studying the diet of the Barn Owl population and its predation pressure.
The first issue is investigated through systematic monitoring of what happens in the nesting boxes. The Barn Owls’ living area and habitat are determined using two methods of marking individuals and tracking them: ringing and radio-telemetry. The diet of the Barn Owls that nested in the investigated plot was studied based on the examination of the contents of the pellets systematically collected from the nesting boxes and their surroundings. From the analysis of these data, we also get a clear idea about the predation pressure created. While we were enriched with knowledge about the ecology of Barn Owls, we were aware of the fact that we lacked quantitative data about what happens “on the other side” – with the rodents. From 1996 to 1998, a study was conducted on the dynamics of rodent populations in agricultural areas, both within and at some distance from the network of nesting boxes (which had increased to 60). The research was done by Eitan Aram from the Hebrew University of Jerusalem, as a master’s thesis under the supervision of Prof. Eitan Tchernov. The purpose of the study was to examine ecological and agricultural factors that affect the rodent population. The indicators that were examined were the size of the population, the size of the habitat, relationships between the individuals and recapture of the rodents. Additionally, the impact of Barn Owls that established themselves in the nesting boxes on the rodent population was tested. The research method involved placing 250 traps for three consecutive nights each month, over a period of 32 months, at several fixed sites. This was done to compare captures in plantation plots and field crops with nesting boxes to captures in identical plots without nesting boxes.
From 1999, the project was accompanied by Dr. Yoav Motro, during his PhD studies at the Hebrew University of Jerusalem, under the guidance of Prof. Uriel Safriel, who replaced Prof. Tchernov who had passed away, and also under the guidance of Prof. Yoram Yom-Tov. Dr. Yoav Motro researched the influence of various factors on the home range and food composition of Barn Owls in the agricultural habitat. As part of the research, Yoav Motro conducted radio-telemetry tracking of Barn Owls equipped with lightweight transmitters. Their spatial movements, nesting sites, roosting sites, and hunting areas were recorded. The monitoring was conducted from a distance to minimize any impact on the Barn Owls’ natural behavior. This took place during the nesting season and the months following it. Additionally, the composition of the Barn Owls’ diet was analyzed by identifying the contents of pellets and food remains found in the nesting boxes in the laboratory.
In 2001, Amalia (Mali) Torres from Tel-Aviv University joined the project for her master’s thesis under the guidance of Prof. Yoram Yom-Tov and Prof. Uzi Motro. She examined the food remains from various nesting boxes. In her research, she compared the food compositions from different nesting boxes that year with those from the same boxes in previous years. In addition to identifying the skulls, different body parts of species were also examined to understand selectivity in the eating method. This work was done in the laboratory at Tel Aviv University, using the comparative collections of both Hebrew University and Tel Aviv University for identification.
In 2001, Moti Charter from Tel Aviv University joined the research team to pursue a master’s degree under the guidance of Dr. Yossi Leshem and Dr. Amos Buskila. His aim was to study the biology of the Common Kestrel, which also played a role in rodent control in agricultural fields. As part of his research, Moti Charter examined the biological characteristics of the Common Kestrel to compare his findings with those from other studies worldwide
