Author's personal copy Author's personal copy Author's personal copy Author's personal copy 50 O. Keynan, R. Yosef / Behavioural Processes 85 (2010) 47–51 Fig. 3. The chances (%) of a meal worm to be impaled and cached for a series of 1–10 worms given for males (N = 9) and females (N = 4) during the non-breeding season (A), during courtship (N = 17 pairs, B), during incubation (N = 13 pairs, C) and during the rearing of nestlings (N = 18 pairs, D). sexes fed the nestlings with most of the meal worms—males usually Although we did not find evidence that male shrikes left impaled fed the females that then fed the nestlings (males—R2 = 0.26, N = 18, prey uneaten as a signal for quality, the impaling of mice near df = 9, f = 3.03, p = 0.12; females—R2 = 0.001, N = 18, df = 9, f = 0.007, the territory borders implies that it certainly served a communi- p = 0.98, Fig. 3D) the same trend continued during the fledgling cation purpose. Shrikes left the mouse uneaten for a relatively long period and both sexes engaged in feeding the young. time, which suggests that it served territorial demarcation with conspecifics, as reported by Sloane (1991) for Loggerhead shrikes 4. Discussion and Antczak et al. (2005) for Great Grey Shrikes. Impaling behavior changed with the onset of the breeding sea- Shrikes in our study did not leave uneaten prey in conspicuous son when females joined male territories. Males used the mouse for larders and did not possess any preferred cache sites. It appears that courtship feeding (Lack, 1940) and used the impaling of the mouse Shrikes in the Arava cannot afford leaving a prey as advertisement as a ritual for pair bonding. Male Shrikes offer gifts to females as for male quality as described for conspecifics in Sede Boker (Yosef part of courtship or precopulatory display (Lefrank and Worfolk, and Pinshow, 1989). This is probably due to the scarcity of prey 1997; Yosef, 2008); the size of the gift is considered a signal of male in the hyper-arid environment of the Arava valley. The amount of quality (Tryjanowski and Hromada, 2005). Females gain direct fit- rainfall has a direct effect on food availability and on the breed- ness benefits during this courtship feeding since they learn of the ing success of birds (Lack, 1948; Rodriguez and Bustamante, 2003; males’ hunting capabilities, and the feeding of high quality food can Morrison and Bolger, 2002) and is also true for shrikes at our study increase reproductive success (Yosef and Pinshow, 1989). site (Keynan and Yosef, 2010). It seems that the fact that no impaled During incubation, when females were dependent on their prey was left uneaten is due to the same reasons. Valera et al. (2001) males for food, only males cached and fed their mates after they ate found that the Lesser Grey Shrike (L. minor) hoards only when their the mouse head. However, when there were nestlings, both sexes immediate food needs are satisfied. Impaled food is also a subject to impaled mice and fed them at the nest. During the entire breed- kleptoparasitism; on two occasions we observed Arabian Babblers ing season, impaling served only for dismemberment of large prey, (Turdoides squamiceps) feed on impaled prey. and we found no evidence for the use of this behavior for any addi- Although it appears that caches do not serve as signals for male tional purpose. These findings are consistent with Antczak et al. quality in our population, our findings confirm the prediction that (2005) for the spatio-temporal changes in impaling by Great Grey the impaling pattern would change temporally between the sexes, Shrike in Poland. and will serve for communications during the non-breeding and The correlation between the number of worms given to the courtship periods. shrike, and the chance a meal worm would be impaled, showed The impaling behavior of female shrikes during the non- that shrikes cached food only after they were satiated. This also breeding season has not been reported to date. Southern Grey suggests that in the hyper-arid environment, abundance of food Shrikes are monomorphic (Infante and Peris, 2004) and we found no is the main factor that limits caching of food. It seems that food differences in impaling behavior between male and female shrikes scarcity in our region is not conducive to caching because shrikes during the non-breeding season. Females defended their territories rarely catch large prey items, or many small ones in large num- and impaled mice on the borders of the territories, similar to the bers, and are unable to cross the “impaling threshold” (Valera et al., behavior of males. 2001) in the extreme desert conditions of our study area. Author's personal copy O. Keynan, R. Yosef / Behavioural Processes 85 (2010) 47–51 51 The correlation between the amount of food and hoarding ended female mate choice. Proceedings of the Forty-fifth Annual Meeting of the Zoo- earlier for males than females during the breeding season, since logical Society of Israel. Isr. J. Ecol. Evol. Keynan, O., Yosef, R., 2010. Annual precipitation affects reproduction of the Southern males fed the females during this period. A similar pattern was Grey Shrike (Lanius meridionalis). Wilson J. Ornithol. 122, 334–339. also observed for Bull Headed Shrikes (L. bucephalus; Yamagishi Lack, D., 1940. Courtship feeding in birds. Auk 57, 169–178. and Saito, 1985). Lack, D., 1948. The significance of clutch size. Part 3. Some interspecific comparisons. Ibis 90, 25–45. In conclusion, although food scarcity in our hyper-arid study site Lefrank, N., Worfolk, T., 1997. Guide to the Shrikes of the World. Yale University did not allow shrikes to create conspicuous caches of uneaten food, Press, p. 192. impaling did serve for communication and territorial demarcation Morrison, S.A., Bolger, D.T., 2002. Variation in Sparrow’s reproductive success with during different parts of the annual cycle. Our findings support our rainfall: food and predator-mediated processes. Oecologia 133, 315–324. Nikolov, B.P., Kodzhabashev, N.D., Popov, V.V., 2002. Diet composition and spatial hypothesis that the behavioral patterns of impaling changes tem- patterns of food caching in wintering Great Grey Shrike (Lanius excubitor)in porally and is sex-dependent, and that caching is correlated to the Bulgaria. Biol. Lett. 41 (2), 119–133. amount of available food. Probst, R., Wegleitner, S., Schmid, R., 2003. Relationship of vertebrate prey size to transport mode and distance in the Northern Shrike. Wilson Bull. 115 (2), 201–204. Acknowledgements Rodriguez, C., Bustamante, J., 2003. The effect of weather on Lesser Kestrel breeding success: can climate change explain historical population declines? J.Anim. Ecol. 72, 793–810. We acknowledge the help of Amotz Zahavi from the Faculty Sangster, G., Knox, A.G., Helbig, A.J., Parkin, D.T., 2002. Taxonomic recommendations of Life Sciences, Tel Aviv University, Israel; Ido Izhaki and Moshe for European birds. Ibis 144, 153–159. 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