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Behavioural Processes 85 (2010) 47–51

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Behavioural Processes

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Temporal changes and sexual differences of impaling behavior in Southern Grey Shrike (Lanius meridionalis)

Oded Keynan a, Reuven Yosef b,∗ a Department of Zoology, George S. Wise Faculty of Life Sciences, Tel Aviv University, ,Israel b International Birding and Research Center in Eilat, P.O. Box 774, Eilat 88000, Israel article info abstract

Article history: The Southern Grey Shrike (Lanius meridionalis) is a common resident along the rift valley. During Received 14 February 2010 2007–2008 we studied the impaling behavior of Southern Grey Shrikes at the Shezaf nature reserve Received in revised form 21 May 2010 by food supplementation. Our findings indicate seasonal shifts in impaling behavior. During the winter, Accepted 3 June 2010 there was no difference between the sexes and shrikes impaled house mice (Mus musculus) close to their territorial boundaries with neighboring conspecifics. All impaled mice disappeared from the tree within a Keywords: few hours of impalement. During the mating season, males impaled the whole prey and let females eat it, Behavior and prey was impaled by both sexes only in order to dismember and feed the nestlings. Shrikes impaled Desert Impaling and cached meal worms only after they were satiated. The number of meal worms taken to be hoarded Southern Grey Shrike increased during the non-breeding season, but during the breeding season male shrikes preferred to feed the females. During the entire research period we did not find any specific cache sites or trees and no prey remained impaled for extended periods of time. In conclusion, impaling prey changed temporally and between sexes: from being a signal for conspecifics to pair bonding. © 2010 Elsevier B.V. All rights reserved.

1. Introduction the ability to impale prey is innate and develops in the early ages of a shrike’s life (Smith, 1973). Shrikes (family: Laniidae) are relatively small passerines which The ability to impale and cache prey provides shrikes with are widespread in Africa, Asia, Europe and North America (between other beneﬁts, like storing more food when it is abundant, dur- the Arctic Circle and 35◦S in Southern Africa). Although they can be ing inclement weather, or during the breeding season when food is found in a large variety of habitats, all shrike species need trees or needed for the rearing of young (Lefrank and Worfolk, 1997; Valera bushes as shelter, nesting sites, and larders. They also need look- et al., 2001; Tryjanwski et al., 2003). Furthermore, it may also serve out posts to use in foraging, and open hunting grounds where prey as a division of labor between the pair during the breeding season can be detected (Yosef, 1993, 2008; Lefrank and Worfolk, 1997). (Applegate, 1977), and for manipulating of nest material during A prominent morphological characteristic of the Laniidae is the nest building (Burton, 1999). Some studies even show that shrike tomial “tooth” on the upper mandible, similar to that of the Fal- impale toxic prey and consume it after the toxin degrades (Yosef cons (Falconidae). Shrikes resemble raptors in other morphological and Whitman, 1992; Fuisz and Yosef, 2001). and behavioral aspects, e.g. the protruding position of the eyes, Although prey caches may serve for all the above reasons, their the large distal digital pads on the toes, and their hunting tech- conspicuousness and their spatial pattern around the territory may niques (Yosef, 2008). However, unlike raptors, although shrikes indicate that this behavior has evolved over time to also serve sev- have relatively strong feet they lack strong talons, so prey is cap- eral purposes including an exaptation for communication. Yosef tured and killed with the beak. Shrikes also differ from raptors in the and Pinshow (1988a,b, 1989) found that cache size served as an absence of a crop, and cannot ingest large prey in one meal (Lefrank honest signal for male Southern Grey Shrikes’ (Lanius meridion- and Worfolk, 1997). Shrikes have overcome these differences by alis) quality; males that had larger caches mated earlier, ﬂedged developing impaling behavior that enables them to dismember and more nestlings and were polygynous. Hromada et al. (2008) found cache large prey items (Yosef and Pinshow, 1989, 2005). Impaling that Red Backed Shrike (L. collurio) use conspicuous caches of Great is considered an evolutionary feeding adaptation (Cade, 1995) and Grey Shrike (L. excubitor) as a cue for territory quality. Antczak et al. (2005) found that Great Grey Shrikes impaled prey in conspicuous locations of their territory. The same pattern was also shown for Loggerhead shrikes (L. ludovicianus; Sloane, 1991). ∗ Corresponding author. Tel.: +972 50 7671290; fax: +972 86376922. Weather and habitat conditions are known to affect the impaling E-mail address: [email protected] (R. Yosef). behavior of shrikes (Valera et al., 2001; Tryjanwski et al., 2003;

48 O. Keynan, R. Yosef / Behavioural Processes 85 (2010) 47–51

Nikolov et al., 2004), and aridity affects the life history and breeding Table 1 success of Southern Grey Shrikes (Keynan and Yosef, 2010). We Total number of mice given to southern grey shrikes in each period. hypothesized that this could also influence their impaling behavior. Period Number of tested shrikes Number of The main objective of our study was to examine how hyper-arid mice given conditions affect impaling by Southern Grey Shrike, a species only Non-breeding 12 (9 males, 3 females) 18 recently separated from the northern Great Grey Shrike (Sangster Courtship 12 pairs 12 et al., 2002), for which comparatively few studies have been done. Incubation 6 pairs 9 Rearing of nestlings 7 pairs 7 We hypothesized that (1) Shrikes would impale less since food and fledglings is scarce in an hyper-arid environment; (2) but because of the open habitat and the ease of visual communications, they would use conspicuous caches as a display of male quality and for territorial 2.3. Impaling of house mice demarcation; and (3) temporal changes and requirements would affect the intensity and duration of impaled prey. Mice were given to the shrikes during the research period and Since some of the females remained at the study site and were released at random locations in the territories. In each of the maintained territories between breeding seasons (Keynan et al., trials, during the non-breeding period, we gave one mouse to each in press), we studied differences between the sexes throughout a territorial Shrike, and during the breeding period one mouse to each year of their life-cycles. couple. We divided the breeding season into periods of courtship, Although there are many studies of impaling by shrikes, few incubation, and rearing of nestlings and fledglings. A total of 46 have undertaken experimental manipulations (e.g. Carlson, 1983; mice were given throughout the entire study (Table 1) but in eight Yosef and Pinshow, 1989; Probst et al., 2003; Hromada et al., 2008). cases were unable to discern the location of the impaled mouse or In our study we examined the impaling behavior of Southern Gray to follow the subsequent behavior of the shrikes. The parameters Shrike by providing house mice (Mus muscullus) and meal worms evaluated at each trial were: (Zophobas morio). • identity and sex of the shrike that took and impaled the mouse; • 2. Materials and methods species and phonological state (dry, green) of the plant on which the mouse was impaled; • 2.1. Study area coordinates of the plant on which the mouse was impaled were taken with a GPS device; • The study was conducted at the Shezaf Nature Reserve dur- time that the mouse was not consumed. We watched the ing April 2006 to July 2009 in southern Israel, ∼30 km south of impaling site with a spotting scope during the first hour the Dead Sea in the Arava Rift Valley between the settlements after impaling, and then visited the location after 3, 12 and of Hazeva (30◦46N, 35◦16E) and Ein Yahav (30◦45N, 35◦15E). 24 h. The Arava Valley is an extremely arid zone (UNESCO, 1977) with a mean annual winter rainfall of 35 mm that occurs in a range of We measured the distance of the impaling site from the cen- 6–9 days with large annual variations in total rainfall and temporal ter of the shrike’s territory and the borders, and compared it to and spatial distribution (Anava et al., 2000). The mean tempera- the average distance of 30 random dots in the territory, in order ture during summer is 38 ◦C with daily temperatures that can rise to determine if the choice of the impaling site was deliberate or to 49 ◦C(Goldreich and Karni, 2001). The flora of the Shezaf Nature random. Reserve is dominated by Acacia trees (Acacia tortilis and A. raddiana) and scattered shrubs (Zilla spinosa, Lycium shawii, and Haloxylon 2.4. Impaling of meal worms persicum) that occur only in the dry riverbeds (wadis). Shrikes were fed 5–10 meal worms in every trial during the study. Worms were thrown from a distance of 3–10 m to a perched 2.2. Field methods shrike. During the non-breeding period we repeated the sessions for every territorial shrike in the study area. During the breeding During the study, we color banded 122 shrikes for individual season we gave meal worms to each of the two shrikes of each recognition (Keynan and Yosef, 2010). Of these, 49 (40.2%) adults couple separately. were caught in a treadle trap (Yosef and Lohrer, 1992) and 73 A total of 1500 meal worms were given to the shrikes during the (59.8%) nestlings banded at the nest 10–11 days post-hatching. We entire study period (Table 2). assumed, and were proved correct, that in the open, hyper-arid All basic statistics were performed using SPSS software. If vari- environment, the pairs would not be able to transfer their nestlings ables met requirements of normality, then parametric tests (paired (cf. Yosef and Pinshow, 1988a,b). t-test, linear regression) were used. If not, non-parametric meth- All shrikes were accustomed to the presence of human observers. Territories were mapped by watching the shrikes’ move- ments in their home ranges and by watching aggressive behavior Table 2 towards conspecifics; territory size was calculated as the minimum Number of individual/pairs tested in every period, number of sessions, and the polygon bounded by defended points of the habitat (cf. Yosef and number of meal worms given to southern grey shrikes in each period. Grubb, 1992). Period Number of tested Number of Total of meal Shrikes were followed in order to study their impaling behavior, individuals/pairs sessions worms given the plant species, its location in the territory, and the amount of Non- 13 (9 males, 4 females) 53 385 time that the impaled prey remained uneaten. breeding We conducted two separate food manipulation experiments Courtship 17 pairs 46 315 Incubation 13 pairs 26 185 during the study wherein we fed the shrikes with house mice (Mus Rearing of 18 pairs 47 330 muscullus) or meal worms (Zophobas Morio). nestlings Our experiments were supervised by, and meet the require- Rearing of 15 pairs 47 285 ments of, the Tel Aviv University animal welfare concerns authority. fledglings Author's personal copy

O. Keynan, R. Yosef / Behavioural Processes 85 (2010) 47–51 49 ods (2 with Yates correction, Freedman ANOVA, Kruskal–Wallis ANOVA) were performed.

3. Results

During the entire study, we did not ﬁnd any speciﬁc cache trees, and no prey was left uneaten. Large prey was scarce and rarely impaled, and the shrikes fed mostly on small inver- tebrates, consuming them immediately. Impaling of large prey was observed mostly during the breeding season, and the prey were consumed or fed to nestlings immediately after impaling. Observed impaled prey was large insects, reptiles and birds (Table 3).

3.1. Impaling of house mice Fig. 2. Annual variation in the percentage of impaled meal worms (average ± SD, % impaled out of 10 given). Both males (N = 9) and females (N = 4) defended a territory during the non-breeding season. We found no differences between the sexes in any of the parameters (impaling plant species and pheno- diately after impaling, males consumed the head and fed the body logical condition, location in territory, and behaviour of shrike after to the female. impaling). All shrikes impaled mice significantly nearer to their ter- Both males and females (N = 7 pairs) caught mice during the ritorial borders with conspecifics than to the center of their territory rearing of young and there was no difference between the sexes 2 (paired t-test: N = 11, df = 10, t = 9.32, p < 0.001 Fig. 1). The distance in their impaling behavior ( = 1.29, df = 1, p = 0.26). All adults ate of observed impaling locations from the border of the territory was the head immediately after impaling and fed the rest to the young. also significantly smaller than the average distance of the random dots (N = 11, df = 10, t = 4.56, p < 0.001, Fig. 1). 3.2. Impaling of meal worms The average distance of the impaling location from territorial borders was also significantly smaller in the non-breeding sea- We found no evidence for the use of impaled meal worms for son in comparison to the breeding season (Friedman ANOVA: N =4, communication purposes. All meal worms were impaled randomly 2 = 8.83, df = 3, p = 0.032) this comparison was made only for four on nearby bush or trees. We did find annual variation in the per- males that defended a year-round territory. centage of impaled meal worms (median 2 test: 2 = 36.02, df = 4, None of the mice were consumed during the first hour after p < 0.001, Fig. 2). impaling, but no mouse was found after 24 h (Table 4). We found no difference between the sexes in the impaling of Impaling behaviour changed differentally during the breed- meal worms during the non-breeding season (males N = 9, females ing season between the sexes. During the courtship period, mice N = 4). Both males and females impaled greater numbers when were caught almost exclusively by the males (binomial probabil- we supplied an increasing number of worms. None of the males, ity, N = 12 pairs, p = 0.02) who impaled it and allowed the females and almost none of the females, impaled and cached the first to eat it. meal worm, while the chance that the tenth meal worm would be During the incubation period, only males caught the mice and impaled was 57.15% for females (R2 = 0.69 df = 9, f = 18.2, p = 0.003, impaled it while the female incubated the eggs (N = 6 pairs). Imme- Fig. 3A) and 76.47% for males (R2 = 0.83, df = 9, f = 40.58, p < 0.001). During courtship, the correlation between the amount of meal worms given and the chances of the meal worm to Table 3 Observed prey items impaled by southern grey shrikes during the study period. be impaled remained significant for both sexes (N = 17 pairs, df = 9; males—R2 = 0.58, f = 93.34, p < 0.001; females—R2 = 0.9, df = 9, Insects Reptiles Birds f = 11.11, p = 0.01, Fig. 3B) although males impaled less since they Adesmia abbreviata Ptyodactylus guttatus Oenanthe oenanthe fed the females with some of their meal worms. Xylocopa pubescens Stenodactylus sthenodactylus Sylvia curruca During incubation, the numbers impaled by both sexes (N =13 Stenodactylus doriae Luscinia luscinia pairs, Fig. 2) was lower and the correlation between the number Urmastyx aegyptius of meal worms given and the chances of the meal worm to be impaled remained significant for females (R2 = 0.8, N = 13, df = 9, f = 33.3, p < 0.001, Fig. 3C) but not for males (R2 = 0.31, N = 13, df = 9, f = 3.58, p = 0.09); males fed females with most of their meal worms. During the nestling period, there was another decrease in the amount of meal worms impaled by both sexes (N = 18 pairs, Fig. 2), and there was no correlation between the amount of meal worms given and the chances of the meal worm to be impaled since both

Table 4 Time (h) between impaling of a mouse until it was consumed by Southern Grey Shrikes.

Hours from impaling Number of mice found % of all mice

1 11 100 3 8 72.7 12 2 18.2 Fig. 1. Shrikes impaled house mice signiﬁcantly closer to territory’s border than to 24 0 0 the center. Author's personal copy

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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

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