Nonparental infanticide in a dense population of

Authors: Sangim Lee Kyungseon Seo Wonyoung Lee Woohjung Kim Jae Chun Choe Piotr Jabłoński

Publish Date: 2011/06/21

Volume: 29, Issue: 3, Pages: 401-407

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Abstract

We report the first case of nonparental infanticide in the Blackbilled Magpie Pica pica Using a video camera installed in the victims’ nest we recorded repeated visits over 4 days of an adult each time one bird who attacked six nestlings at each visit until they died or were evicted The nest was one of 58 nests filmed over four breeding seasons Collected evidence suggests that the perpetrators might have been the female breeder of the neighbouring nest possibly also her male partner The parental female aggressively attacked the perpetrator Postinfanticide expansion of breeding territory by the suspected perpetrator is the hypothetical ultimate explanation of the observed infanticide Movie clips from inside the nest are shown at http//wwwmomopcom/showdetailephpmovieid=momo110422pp01a http//wwwmomopcom/showdetailephpmovieid=momo110422bm01a http//wwwmomopcom/showdetailephpmovieid=momo110422pp02a and http//wwwmomopcom/showdetailephpmovieid=momo110422pp03aIn comparison to avian parental infanticide nonparental infanticide in birds—which refers to the cases where the perpetrator is not a biological parent of the victim—is much rarer and less well understood Hausfater and Hrdy 1984 Three adaptive hypothetical functions have been suggested for nonparental infanticide in animals Hrdy 1979 1 direct exploitation of the nestlings as a resource for nutrients ie cannibalism 2 increasing access to the resource including nest site and food availability “resource competition” hypothesis and 3 increasing mating opportunities for the perpetrator “sexual selection” hypothesis by killing the offspring of other individuals Although several decades of research have brought theoretical advances in understanding the evolution of infanticidal behaviour Hrdy 1979 Mock 1995 Veiga 2000 empirical evidence for evaluating these hypotheses especially in avian females is still relatively scarceSo far infanticidal events have been largely reported in polygamous colonial breeding or groupcooperatively breeding avian species where they can lead to increased access to nesting sites and an increased probability that the affected parents redirect parental care to the perpetrators’ offspring or they may benefit the perpetrator by making the parent of the killed offspring available for mating Emlen et al 1989 Fujioka 1986 Hansson et al 1997 Inoue et al 2010 Kaplan 2004 Kermott et al 1991 Mumme et al 1983 Parsons 1971 Trail et al 1981 Veiga 1990 2000 2003 2004Most evidence in birds concerns infanticide by males Veiga 2000 but the number of species where avian females commit infanticide is increasing However statistically solid evidence of infanticide by females in a traditional mating system is based on indirect Hansson et al 1997 Møller 2004 Veiga 2004 rather than on direct detailed observations of the perpetrators killing the nestlings This is because infanticide in general is rare and difficult to observe as indicated by the fact that only 17 direct observations of infanticide have been reported in 25 years of studies of 98 broods on average of barn swallows per year Møller 2004 or that only three direct observations have been noted in 10 years of studies on 60–80 broods of the house sparrow per year Veiga 2004 Therefore it is important to publish direct observations of infanticide especially in species from which it has not yet been reported examples of papers describing single infanticide events by females Prokop et al 2009 Shimada et al 2002 Despite the scarcity of direct observations some evidence suggests that the likelihood of infanticide in birds increases in highdensity situations eg Møller 2004 Here we present direct videotaped evidence of an aggressive infanticidal event in the dense population of the Blackbilled Magpie Pica pica sericea a socially monogamous and solitarily breeding species where postinfanticide expansion of breeding territory by the suspected female perpetrator is the most likely explanationOur study population on the campus of Seoul National University Seoul Korea has been the subject of a longterm ecological monitoring program since 1998 Lee et al 2010a Its habitat is a mixture of buildings and small patches of grasslands/forests More than 50 pairs of magpies attempt to breed annually average density over 13 years 49 ± 9 pairs/km2 Lee et al 2010a Similar to European subspecies magpies in Korea defend their territories year round but the size of their territories is much smaller 11 ha unpublished data than they are in Europe 5 ha Birkhead 1991 Jerzak 2001Since 2007 we have studied nestling begging behaviour and parental feeding behaviour by installing video cameras in the nests A total of 59 nests 8 in 2007 16 in 2008 19 in 2009 and 16 in 2010 have been recorded so far After the nestlings had been individually marked with small dots of colour nail polish on the forehead and on the tip of the beak we placed a bulletshaped camera Weatherproof Bullet Cam XB421W36 Vision Hitech Company with a pintype microphone CMicrophone Vision Hitech Company in the nest wall opposite to the nest entrance In 2010 begging and feeding were recorded digitally using a DVR located on the ground between 0700 h and 1100 h dailyWe also regularly twice a week in a breeding season twice a month in the following fall and winter visited each territory to watch magpie behaviour outside the nest These visits gave us information on the interactions of the parents from the victims’ and the suspected perpetrator’s nests with other neighbouring magpies

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