View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Springer - Publisher Connector J Ethol (2013) 31:1–7 DOI 10.1007/s10164-012-0340-2 ARTICLE Comparison of nest defence behaviour between two associate passerines Marcin Polak Received: 20 February 2012 / Accepted: 20 July 2012 / Published online: 23 August 2012 Ó The Author(s) 2012. This article is published with open access at Springerlink.com Abstract Nest predation is one of the most important Introduction factors limiting reproductive success, and antipredator behaviour can significantly reduce the loss of avian broods. Recent empirical studies have suggested that positive I carried out field experiments on two sympatric passerines: interactions may be common, predictable and pervasive the barred warbler and the red-backed shrike. Many authors important forces in different ecosystems (Blanco and Tella have described the protective nature of nesting association 1997; Martin and Martin 2001; Quinn et al. 2003; Sergio between these species. However, we have little knowledge et al. 2004; van Kleef et al. 2007; Nocera et al. 2009). about the true nature of the relationships between associ- Protection of broods from predators using aggressive ates. I examined (1) whether barred warblers and red- behaviour of other species is one of the most unusual backed shrikes respond differently to an avian predator, strategies used by birds to evade predation (Clark and and (2) whether males and females differ in the intensity of Robertson 1979; Norrdahl et al. 1995). One such strategy is nest defence. Decoys of a known nest predator and a non- the creation of protective nesting associations in which one predatory control species were used to examine the types or more species relate and directly benefit from nesting and relative intensity of parental response. I measured within the protective umbrella created by other species behavioural responsiveness by recording aggressive (Blomqvist and Elander 1988; Halme et al. 2004). In the behaviour toward each model during the nestling period. majority of cases, the protective nesting association occurs Barred warblers and red-backed shrikes showed consider- between a less aggressive species and a more aggressive able variation in their response. Warblers more vigorously species (often a raptor; Post and Seals 1993; Blanco and defended their own territories than shrikes. No differences Tella 1997; but see Sergio et al. 2004). Moreover, in birds between the sexes in antipredator behaviour in red-backed reproductive success may increase with the number of shrike were found. By contrast, in barred warbler, male was close, aggressive neighbours, including heterospecifics and more involved in nest defence. The experimental tests conspecifics, because recent studies suggest a direct rela- provide evidence that these two species are able to differ- tionship between group size and mobbing intensity (Pavel entiate between a predator and non-predator species. and Buresˇ 2001; Grim 2008; Krama et al. 2012). Profit for individuals nesting in close proximity to an aggressive Keywords Positive interactions Á Protective nesting neighbour is mainly better protection against predators association Á Nest defence Á Antipredatory response resulting in increased breeding success (Richardson and Bolen 1999). Animals may also refer other additional benefits such as more effective escape from an approaching predator through an early warning system, lower parasit- ism, the dilution effect against nest predation provided by M. Polak (&) other nests in the surroundings, higher mating success and Department of Nature Conservation, Institute of Biology therefore better breeding success (Clark and Robertson and Biochemistry, Maria Curie-Skłodowska University, Akademicka 19, 20-033 Lublin, Poland 1979; Bogliani et al. 1999; Quinn and Ueta 2008). More- e-mail: [email protected] over, recent studies have indeed revealed that conspecifics 123 2 J Ethol (2013) 31:1–7 and heterospecifics are used as a source of information umbrella around its own nest. Barred warbler as the biggest concerning habitat quality, predation risk and food location sylviid warbler in central Europe is not afraid to nest in the (Forsman et al. 2008). There are costs associated with neighbourhood of red-backed shrike. In addition, both mobbing predators, including direct mortality or injury species share the same predators (Neuschulz 1988; caused by a predator (Montgomerie and Weatherhead Goławski 2007). In this study, I compare barred warbler 1988), and reduction in the time and energy available for and red-backed shrike nest defence behaviour towards a other essential activities. Protected associates sometimes stuffed model of the hooded crow Corvus cornix and as a also pay costs when their aggressive associate kills them or control—a stuffed model of the green woodpecker Picus their young, or when they are forced to abandon their viridis. Red-backed shrikes are heavier than barred war- territory (Ebbinge and Spaans 2002). Although descriptive blers (25–36.5 versus 21.5–32.0 g, respectively; Cramp studies on protective nesting associations are fairly exten- 1992; Kuz´niak and Tryjanowski 2003; Tøttrup et al. 2011) sive (Blomqvist and Elander 1988; Post and Seals 1993; and dominate in aggressive interactions between the two van Kleef et al. 2007), experimental tests are urgently species (Polak M., unpublished data). Moreover, shrikes needed to determine the fitness costs and benefits to species are raptorial passerines and have a thick, hooked beak and involved in positive behavioural interactions (Haemig strong legs (Cramp 1992). In this context red-backed shrike 2001; Quinn and Ueta 2008). should be the protective associate, and barred warbler as a Risk of predation has played a central role in the evolution protected associate would show less aggressive response of avian life strategies (Conway and Martin 2000). Animals, toward a predator and would ‘‘parasitize’’ for the shrike’s trying to minimise the risk of predation, use a variety of mobbing reaction. In contrary to this, recent study indi- behavioural adaptations (Regelmann and Curio 1983; Quinn cated that red-backed shrike had higher breeding success and Ueta 2008). Nest predation is one of the most important while breeding close to barred warbler territories (Goław- factors limiting reproductive success, and antipredator ski 2007). It was supposed that close nesting of these two behaviour can significantly reduce the loss of avian broods species reduces the risk of predation due to barred warblers (Grim 2008). The main factors affecting the nest defence that actively attack predators (Cramp 1992). Moreover, intensity are: sex of parents (Pozˇgayova´ et al. 2009), according to recent research (Stenhouse et al. 2005; Grim potential for renesting (Hogstad 2005), value of nestlings 2008; Welbergen and Davies 2011), I also expected that (Pavel and Buresˇ 2001), age and parental experience shrikes and warblers would be able to discriminate between (Stenhouse et al. 2005), the group effect in mobbing (Pavel predators and harmless animals and that nest defence and Buresˇ 2001; Grim 2008), predator distance and type intensity should be higher in males than females (Pavel and (Klvanˇova´ et al. 2011) and nest construction and conceal- Buresˇ 2001; Klvanˇova´ et al. 2011; Krysˇtofkova´ et al. ment (Krysˇtofkova´ et al. 2011). However, the ways in which 2011). This research focusses on the following detailed birds assess the risk of nest predation in unclear, and we have questions: (1) Which of these two species exhibits more poor knowledge regarding how nest defence interacts with intense antipredator behaviour? (2) Whether the distance other aspects of decision-making by parents (Lima 2009), between the focal nest and associate (both conspecific and especially in the context of the creation of protective nesting heterospecific) could affect the decision of the birds to join associations. According to predictions of the dynamic risk mobbing of a predator at a neighbouring nest. (3) Whether assessment hypothesis (Kleindorfer et al. 2005), for mob- they are able to distinguish between predators and a non- bing birds, it is essential to assess the imminent risk and predatory species. (4) Are there differences between sexes adjust their investment in antipredator behaviour. in their defensive effort? (5) Whether some features of Investigations of parental investment strategies are offspring (brood size, brood age and laying date) may typically conducted on a single species, whereas compar- affect the intensity of nest defence behaviour. isons between species are rare (Ghalambor and Martin 2000). Here I experimentally test for differences in anti- predator behaviour between two sympatric passerines: the Materials and methods barred warbler Sylvia nisoria and the red-backed shrike Lanius collurio. Many researchers have described the The field experiment examined whether the type of decoy association between these two avian species (Nankinov and affected the behavioural response of warblers and shrikes, Darakchiev 1979; Neuschulz 1981, 1988), but some by comparing their reaction to a known predator and a non- authors suggest that this is an apparent relationship predatory species. The study was carried out in a research resulting from similar habitat preference (Gotzman 1965; area located in Lublin Region near Ste˛zyca_ at middle Kuz´niak et al. 2001). It is possible that one or two associate Vistula River valley (central