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1 June 2007 BREEDING SUCCESS OF THE EURASIAN KESTREL (FALCO TINNUNCULUS) NESTING ON BUILDINGS IN ISRAEL
Motti Charter, Ido Izhaki, Amos Bouskila, Yossi Leshem
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Urbanization has changed the landscape in many countries in the world, particularly so in Israel since the establishment of the State (Yom-Tov and Mendelssohn 1988, Mendelssohn and Yom-Tov 1999). Urbanized areas have become more widespread, destroying natural habitats, decreasing animal diversity, and to a lesser extent, also creating new habitats for some species. Most raptors live in natural habitats away from humans, but some species, such as Eurasian Kestrels (Falco tinnunculus; hereafter “kestrel”) also inhabit urban areas.

Kestrels are one of the most studied raptors in the world, but research has generally focused on breeding parameters of kestrels inhabiting rural environments in Europe (Cavé 1968, Village 1990, Plesník and Dusík 1994, Kostrzewa and Kostrzewa 1997, Fargallo et al. 2001), and only a few studies have addressed kestrel breeding success in urban habitats (Pikula et al. 1984, Plesník 1985, 1990, 1991, Rejt 2001, Salvati 2002, Kübler et al. 2005). Most of the latter studies found that urban-breeding kestrels have a higher reproductive rates than those in rural areas, with the exception of Kübler et al. (2005), who found no difference. Compared to rural kestrels, urban populations may be ecologically, ethologically, and even genetically different (Rejt et al. 2004). For example, urban pairs use different nest types and prey on more species of birds than do rural pairs (Salvati et al. 1999, Kübler et al. 2005).

Kestrels do not build nests, but, unlike many raptors, they breed in both open-type nests (e.g., abandoned nests of other birds, date palms, cliff edges) and closed-type nests (e.g., cavities in trees and cliffs; Village 1990). In contrast to populations studied in the Czech Republic, Italy, and Poland, where urban kestrels nest primarily in closed-type nests on buildings, the majority of kestrels found breeding in urban sites in Israel used open-type nests, especially flower pots on windowsills (Leshem 1984, Charter et al. 2005).

The higher breeding success reported for urban kestrels (e.g., Pikula et al. 1984, Plesník 1985, 1990, 1991, Rejt 2001, Salvati 2002) may be due to the mainly closed-nest types used by urban birds, in contrast with rural nests, which are located primarily in abandoned corvid nests in trees and, to a lesser extent, in artificial nest boxes (Village 1990). In rural habitats, kestrels breeding in cavity-type nests have higher breeding success than those in open-type nests (Kostrzewa and Kostrzewa 1997, Fargallo et al. 2001, M. Charter unpubl. data), most likely due to decreased predation and increased protection from weather.

In this study we investigated kestrels in Israel, which breed mainly on the windowsills of buildings in cities (urban), towns (suburban), and villages (rural). Because kestrels use the same nest types in the three locations, any differences found in breeding success and reproductive rate would most likely be due to the difference in habitat. We hypothesized that the breeding success of kestrels in rural areas (villages) would be higher than that in both dense urban areas and moderately populated suburban areas, due to the closer proximity of hunting sites and greater mammalian prey availability in the rural areas. In addition, we investigated how nest orientation may affect breeding success in the above-cited different nest habitats.

Methods

Study Area

Our study was conducted throughout the country of Israel. We defined cities, towns, and villages as follows. Cities were highly developed and densely populated by humans (>100 000 people), and kestrels there lacked both trees and bushes and open landscape (i.e., favorable hunting territories) near their nests. Towns had smaller human populations (11 000–25 000 people), and smaller buildings that were more widely spaced than in cities but more dense than in villages. Towns also had moderate amounts of trees and bushes, and, due to their comparatively small size, had open landscapes relatively close to the kestrel nests. Villages had very small populations (fewer than 700 people), few buildings, many trees, bushes and fields, and open landscapes (i.e., agricultural areas). In cities, kestrels have to fly great distances in order to hunt in open landscapes, whereas those breeding in villages nest only a few hundred meters from fields.

Nesting Survey

A nationwide survey on the breeding biology of kestrels in Israel was conducted from 2003–2006. A standardized questionnaire on kestrel breeding success was placed on the website of the International Center for Study of Bird Migration (Latrun), and the Israel Ornithology Center ( http://www.birds.org.il). Participants were asked to fill in as many of the following fields as possible: participant's name, address, telephone number; laying date of kestrel's first egg, laying date of last egg, clutch size, total number of young hatched (i.e., brood size during first week), date that the first young fledged, number of young that died, number of young that fledged (approx. 23–27 d old), and the nest orientation, grouped in four categories: N-NE, E-SE, S-SW, W-NW. All participants were contacted by phone at least three times to verify data reliability. Questionnaires with no contact information were eliminated from the survey. During the study, about 40% of participants sent pictures, and a third of the homes were visited at least twice yearly.

Reproductive Parameters

At nests for which the time of laying was unknown, the date was estimated by subtracting the incubation period (28 d; Cramp 1985) from the hatching date. Breeding data were recorded for each laying pair and for each successful nest. We defined (1) hatching success as the percentage of eggs that hatched within each clutch, (2) the percentage of young that fledged from each brood as the percentage of hatched young that reached fledging age, (3) egg productivity as the percentage of eggs per nest that hatched, (4) brood size as the number of young hatched, and (5) a successful nest as one that fledged at least one young. Egg laying date (N  =  9) and hatching interval order (N  =  12) were provided by participants who observed the nest in their home daily. Partial nest failure was recorded when a pair fledged some but not all of their hatched young. Eight nests were used for more than one breeding season; for these nests with multiple records, we randomly selected one year of data, to avoid pseudoreplication. Data from two pairs breeding in cities and one pair in a village that laid second clutches after successfully raising first broods during the 2004 breeding season (Charter at al. 2005) were not included in this analysis.

Statistical Analyses

All statistical tests were two-tailed and all tests were nonparametric. Descriptive breeding data were analyzed using Kruskal-Wallis ANOVA and Kruskal-Wallis Multiple Comparisons. Spearman test was used to analyze correlations among breeding parameters, and chi-square and Fisher's Exact Test were used for comparing nest success between locations. Levels of significance were set at P < 0.05. Statistical analyses were performed using Statistica 7.1 software.

Results

One hundred and twenty-four pairs of laying kestrels were monitored during the 2003–2006 breeding seasons. No differences in breeding parameters were found among the four years (24 Kruskal-Wallis tests, P > 0.05) and the data were therefore pooled. Seventy-nine pairs nested in cities (Tel Aviv region, Netanya, and Haifa), 19 pairs in towns (11 towns, mostly located in the West Bank), and 26 pairs in villages (13 villages