Mérő, Thomas Oliver

Žuljević, Antun

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363ACTA ZOOLOGICA BULGARICAActa zool. bulg., 68 (3), 2016: 363-366Terrestrial Ecology and BehaviourResearch Article*Corresponding author: thomas.oliver.mero@gmail.comIntroductionThe nest defence behaviour of the great reed war-bler, Acrocephalus arundinaceus (L.), has been ex-tensively studied in terms of various nest predators and predation mechanisms (Kleindorfer et al. 2005, TrnKa, Grim 2014a), cuckoo, Cucuclus canorus (L.), parasitism (Honza, mosKáT 2008, mosKáT et al. 2008, 2009, TrnKa, Grim 2014b), social mating system (TrnKa, ProKoP 2010), nest position and reed density (Mérő, Žuljević 2015). Whereas various tactics are used against predators (e.g. silent wait-ing or distraction, Mérő, Žuljević 2015), great reed warblers behave highly aggressively against cuckoos (Honza et al. 2010), even killing the parasite bird (TrnKa, Grim 2013a, Mérő, Žuljević 2014). As re-gards the social mating system of the great reed war-bler, the nest defence behaviour differs considerably between monogamous and polygynous pairs, and fe-males have generally been found to be more aggres-sive than males (TrnKa, ProKoP 2010). However, the nest defence of males has been reported to be more aggressive than that of females when the in-truder was a parasitising cuckoo (PoŽgayová et al. 2009). Furthermore, TrnKa et al. (2013b) observed that great reed warbler females demonstrated high repeatability in nest defence behaviour across nest-ing seasons in contrast with males.It is known that birds such as starlings, Sturnus vulgaris L., may roost in large flocks in reed beds (Mérő, Žuljević “2013/14) where, as a result of their weight and droppings, they can cause considerable damage to the reed beds (Meanley 1965), even flat-tening the reed stems (Haslam 2004). Mérő, Žuljević (2015) found that the nest defence behaviour of great reed warbler was more intensive in dense than in sparse reeds. The flattening of the stems may result in sparser reed, less concealed nests and a lower in-tensity of nest defence behaviour, which may lead in turn to lower nesting success because of the in-Effects of Roosting Starlings, Sturnus vulgaris L., on the Nest Defence Behaviour of the Great Reed Warbler, Acrocephalus arundinaceus (L.) (Passeriformes)Thomas Oliver Mérő1,2*, Antun Žuljević11 Nature Protection and Study Society – NATURA, Milana Rakića 20, SRB-25000 Sombor, Serbia2 Department of Tisza Research, Danube Research Institute, Centre for Ecological Research, Hungarian Academy of Sciences; HU-4026 Debrecen, Bem tér 18/c, Hungary”Abstract:  We studied the effects of roosting starlings, Sturnus vulgaris, on the nest defence behaviour of great reed warbler, Acrocephalus arundinaceus, monogamous parents from 54 nests. A generalised linear mixed mod-el was constructed to investigate the effects where the nest defence behaviour was the dependent variable and the independent variables were year (2011, 2014 and 2015), patch (roosting vs. non-roosting reed patches), sex and nest ID (as random effect). We found that the nest defence behaviour of great reed war-blers was more intensive in years when starlings roosted. The significant interaction between year and patch indicated that the nest defence behaviour was more intensive in roosting reed patches. Similarly to previous studies, the females defended the nest more aggressively than the males. In conclusion, we suggest that nest defence behaviour of the great reed warbler in roosting areas might be influenced by various factors, e.g. the excessive noise of roosting starlings or the motion and density of birds in the vicinity of the nests. Key words: roosting, Sturnus vulgaris, nest defence behaviour, Acrocephalus arundinaceus, reed density364Mérő T. O., A. Žuljevićcreased risk of predation (TrnKa et al. 2009). To ex-plore this issue, we studied the effects of roosting starlings on the nest defence behaviour of the great reed warbler.The presence of roosting starlings was regu-larly recorded during the nesting seasons in May and June 2014 and 2015 at the Bager Pond (study area). We recorded the nest defence behaviour of the great reed warblers during regular nest checks involving a human intruder/nest predator (e.g. Hollander et al. 2008, TrnKa, ProKoP 2010). Previous findings led us to predict that the intensity of the nest defence behaviour of the great reed warbler parents would be lower in years when starlings roost and lower in the case of nests located in roosting reed patches.Material and MethodsThe study was conducted at the Bager Pond (N 45.788˚, E 19.098˚) in the region of Sombor (Serbia). For a detailed description of the study area, see Mérő et al. (2014, 2015). The present study com-pared the nesting seasons in 2014 and 2015, when the roosting of starlings was recorded, with the sea-son 2011 as a control, when roosting was absent. During these three nesting seasons, the mean wa-ter depths and the amounts of precipitation varied similarly (Republic Hydro-meteorological Service of Serbia, Table 1). These conditions are important because the nesting density and breeding success of the great reed warbler have been shown to depend on these factors (Mérő et al. 2014). The main char-acteristics of the roosting of starlings are given in Table 1.The fieldwork was conducted from May to July in 2011, 2014 and 2015, when the entire area of the pond was completely surveyed for nests. We iden-tified altogether 54 monogamous great reed war-bler nests (19 in 2011, 14 in 2014 and 21 in 2015), which were checked regularly at five-day intervals. We recorded the numbers of eggs and nestlings, the nest-losses due to the abandonment of nests, or egg or nestling predation, the nest defence behaviour of the great reed warbler parents and the numbers of roosting Starlings. In the present study we included nests of monogamous pairs, both with successfully raised broods and those which failed, while nests of polygynous males were excluded because monoga-mous males defend their nests more vigorously than polygynous males (TrnKa, ProKoP 2010). The pres-ence of a cuckoo nestling was regarded as an average great reed warbler young, because the nest defence behaviour of the great reed warbler parents did not differ in the cases of cuckoo or great reed warbler nestlings (Honza et al. 2010). All nests were found in the egg-laying or incubation stage. To categorise the behaviour of the parents, we used scores rang-ing from 0 to 4 (Table 2) following Mérő, Žuljević (2015). Both sexes were marked using coloured rings. The birds were ringed at the beginning of the nesting season at the end of April and during May. Great reed warblers were attracted with male songs played from mobile devices, and captured with mist nets. During the regular nest checks, birds were identified via the codes on the colour rings with a camera. The boundaries between the roosting and the non-roosting areas were delineated with a hand-held GPS receiver.We constructed a generalised linear mixed model (GLMM), where the nest defence behaviour was the dependent variable (modelled as ordinal), and the year (2011, 2014 and 2015), patch (roosting vs. non-roosting patches), sex and nest ID were the independent variables. The nest ID was taken as a random effect in the GLMM in order to avoid pseu-doreplication. Further, in the GLMM we tested the effects of interactions of the independent variables (e.g. year * patch) on the nest defence behaviour of the great reed warbler. Multi-collinearity was not observed among the independent variables; the vari-ance inflation factors ranged from 1.01 to 1.39. The significance of the effects of the sexes in the nest defence behaviour was tested with t-test. Statistical analyses were implemented in SPSS 17.0 statistical software (SPSS Inc., Chicago, USA).ResultsIn contrast with our predictions, we found that nest defence behaviour of the great reed warbler was in-fluenced significantly by year and sex, and the inter-action between year and patch (Table 3). Significant coefficient estimates showed that nest defence be-haviour of the parents was more vigorous in years when starlings were roosting, and that the defence behaviour of the females was more aggressive than that of the males (t-test, t125 = 3.65, p < 0.0001). The interaction between year and patch indicated that the nest defence behaviour was more aggressive in years when Starlings were roosting in the roosting reed patches. However, other interactions did not influ-ence nest defence behaviour (Table 3).DiscussionOur results revealed that the nest defence behaviour of the great reed warbler was more intensive in the years when starlings were roosting than in the year Effects of Roosting Starlings, Sturnus vulgaris L., on the Nest Defence Behaviour of the Great Reed Warbler...365when starling roosting was absent. The interaction between year and patch indicated that the great reed warblers defended their nests more strongly in the roosting patches. In previous studies, nest conceal-ment and reed density proved to be positively related to nest defence behaviour, indicating that nests in dense reed were better protected than those in sparse reed (Mérő, Žuljević 2015). As a result of the flat-tening of the reed stems in the patches where star-lings were roosting, the reed density became sparser and the nests of the great reed warbler in the roosting patches became more visible (authors’ unpublished observation). In contrast with the results of Mérő, Žuljević (2015), in the present study the great reed warblers defended their nests more aggressively in the starling-caused sparse reed than in the intact denser reed. We therefore assume that the enhanced nest defence behaviour in roosting years and patches might be influenced, for example, by the excessive noise of roosting birds or the motion and density of birds in the vicinity of the great reed warbler nests. However, for proper conclusions in this respect, fur-ther specific studies are needed.Similarly to TrnKa, ProKoP (2010), TrnKa, Grim (2013b) and Mérő, Žuljević (2015), we found that females defended the nests more aggressively than males. A number of factors can influence the nest defence behaviour of the sexes of this species, resulting in differences in aggressiveness of males and females (e.g. PoŽgayová et al. 2009). For exam-ple, polygynous males which simultaneously have two or more active nests defend their nests less vig-orously than monogamous males. The nest defence behaviour of females in both mating statuses is simi-lar, indicating a greater difference in aggressiveness between a polygynous male and its females than within a monogamous pair (TrnKa, ProKoP 2010). Furthermore, the female nest defence behaviour is found to be independent of the presence or absence of the male partner, while monogamous males do not compensate for when the females are absent (TrnKa, Grim 2013). These previous findings suggest that several factors can influence the nest defence behav-iour of the great reed warbler, and therefore result in significant differences between the sexes in nesting seasons when the roosting of starlings was present. Table 1. Water depth at nest sites, precipitation amount during nesting season and main characteristics of the roosting patches of starlingsYear Mean water depth (±SE)Precipitation amount (mm)Size of roosting area (ha)Mean number (±SE) of roosting starlingsEstimated number  of roosting starlings per hectare2011 77 ± 26.9 146.4 - - -2014 72 ± 6.7 212.2 0.15 197 ± 35.2 1 3132015 80 ± 5.2 160.5 0.35 223 ± 53.7  637Table 2. Nest defence behaviour scores and their description taken from Mérő, Žuljević (2015)Score Description of nest defence behaviour of great reed warblers0 neither of parents was present1 one or both of the parents were present, but silent at a distance of more than 3 m from the nest2 parents gave alarm calls at a distance of more than 3 m from the nest3 parents gave a loud alarm at a distance of between 1 and 3 m from the nest4 parents gave a loud alarm at a distance of less than 1 m from the nest, or participated in a direct physical attackTable 3. Results of generalised linear mixed-model (GLMM) testing main effects and interactions of the predictor variables on the nest defence behaviour of the great reed warblers. Predictor variables Coefficient ± SE F value df P valueMain effects Year -0.29 ± 0.235 4.963 2 0.008Patch -0.13 ± 0.213 0.200 1 0.655Sex 0.51 ± 0.262 19.157 1 < 0.0001Interactions Year * Patch 0.64 ± 0.340 4.161 1 0.042Year * Sex 0.07 ± 0.364 0.314 2 0.731Patch * Sex -0.14 ± 0.347 0.998 1 0.319Year * Patch * Sex -0.22 ± 0.514 0.187 1 0.665366Mérő T. O., A. ŽuljevićThis issue must be properly clarified in future stud-ies. For example, starling dummies might be placed in or above great reed warbler nests in both roost-ing and non-roosting patches. If various numbers of dummies are placed per nest, the effects of the den-sity of roosting birds on the nest defence behaviour could be studied.In conclusion, the nest defence behaviour of the great reed warbler was found to be more intensive in years when starlings roosted and highest in the case of nests located in roosting patches. We assume that various factors may play a role in the nest defence behaviour of great reed warblers in roosting patch-es, e.g. the excessive noise of roosting starlings or their motion and density in the vicinity of the nests. As reported in previous studies females exhibit sig-nificantly more aggressive nest defence behaviour, but we suggest that this is not a constant pattern: the study by PoŽgayová et al. (2009) revealed that males displayed more intensive nest defence behav-iour than females against the parasitising cuckoo.Acknowledgements: This study was supported by the Nature Protection and Study Society – NATURA from Sombor (Serbia). T.O.M. was funded by a grant from the National Scientific Re-search Base Programs of Hungary (OTKA K106133).ReferencesHaslam, s. m. 2004. Understanding Wetlands: Fen, bog and marsh. Taylor & Francis, London and New York. Hollander, F. a., T. van overveld, i. Tokka, e. MaTTHysen 2008. 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To compensate or not to compensate: testing the negotiation model in context of nest defense. – Behavioral Ecology, 24 (1): 223-228.Trnka, a., M. PoŽgayová, P. saMaŠ, M. Honza 2013. Repeat-ability of host female and male aggression towards brood parasite. – Ethology, 119 (10): 907-917.TrnKa, a., T. Grim 2014a. Dynamic risk assessment: does a nearby breeding nest predator affect nest defence of its potential victim? – Journal of Ethology, 32 (2): 103-110.TrnKa, a., T. Grim 2014b. Testing for correlations between behaviours in a cuckoo host: why do host defences not covary? – Animal Behaviour, 92 (1): 185-193.Received: 24.09.2015 Accepted: 16.12.2015

Effects of Roosting Starlings, Sturnus vulgaris L., on the Nest Defence Behaviour of the Great Reed Warbler, Acrocephalus arundinaceus (L.) (Passeriformes)

Effects of Roosting Starlings, Sturnus vulgaris L., on the Nest Defence Behaviour of the Great Reed Warbler, Acrocephalus arundinaceus (L.) (Passeriformes)

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