Infanticide is defined as the killing of young offspring that are dependent on maternal care and can be driven by a variety of reasons (Li, 2022). It may be unintentional, occurring as a by-product of behavior not directly aimed at killing conspecifics or intentional, when the individual gains a certain benefit from the act (Hausfater Ryazanov, 2021). In biological and ecological contexts, male-motivated infanticide may serve various adaptive functions. According to the predation hypothesis, males may kill infants to gain nutritional benefits or as a by-product of aggression toward other males or females (Doidge et al. , 1984; Ebensperger, 1998; Hrdy, 1979). In some cases, males also consume the cubs they kill (Hausfater Palombit, 2012). The sexual selection hypothesis proposes that males commit infanticide to eliminate the offspring of other males and increase their chances of mating. When a female is caring for her young, she typically remains in anestrus for an extended period. However, if her brood is lost, she often returns to reproductive receptivity within days or weeks, depending on the species' life history. Following such a loss, the male responsible for the act frequently stays near the female, who subsequently mates with him (Pusey Pusey Ruth et al. , 2011), leopards (Panthera pardus; Balme Steyaert et al. , 2014). Until now, infanticide had not been confirmed in the northern raccoon (Procyon lotor), a native North American carnivore that has become an invasive species in Eurasia over the past century. European raccoon populations are genetically less diverse than native ones, mainly due to founder effects, although some variation has been maintained through multiple introductions and mixing of individuals (Biedrzycka et al. , 2014). As an opportunistic species, the raccoon adapts to new environments and occupies comparable habitats in Europe as in its original North American range, including forests, mixed agricultural landscapes, and urban areas (Cunze et al. , 2023). Despite its widespread distribution, relatively little is known about its ecology and behavior. Yet, due to its predominant nocturnal habits, studying the raccoon through direct observation is challenging. Although infanticide had not been confirmed before (Gehrt Hauver et al. , 2010), certain behaviors of females that may function to protect their cubs suggest that the threat of infanticide does exist in this species. For instance, after giving birth, females typically minimize the size of their home range and spend less time foraging at night (Schneider, 1968). Females also become more aggressive toward conspecific visitors (Bissonnette Hauver et al. , 2010). In some instances, females may also relocate their cubs from the original den site (Hauver et al. , 2010; Wilson & Nielsen, 2007). Since spring 2024, raccoons have been monitored via GPS telemetry in the Karlovy Vary region, Czech Republic, to better understand their spatial ecology. The population of this non-native species has been known from this area for approximately 20 years (Matějů et al. , 2012). A modified version of the FELIS transmitter (Ecotone, Telemetry Company, Poland) was used for data collection, and individuals were also ear-tagged for visual identification in the field. Based on GPS data, resting sites were systematically investigated. An adult raccoon female (Hermína, 5. 1 kg) was captured on 1 March and monitored until 31 May 2025. During this period, she used at least three distinct resting sites within a 14. 5-ha forest patch near the Nová Kyselka village (50°15′ N 12°59′ E). The resting places were found in a hollow in an old linden tree (Tilia cordata) and in broken willow (Salix alba) and alder (Alnus glutinosa) trees, all at heights between 10 and 15 m above the ground. Later, Hermína started favoring the hollow in the linden tree, which suggested that she might have given birth there. From 21 April, the tree was monitored using a photo trap. A careful personal inspection of the hollow on 8 May 2025 revealed three cubs. On the same day, a Reolink camera was installed two meters from the hollow to allow continuous monitoring without disturbing the female or her cubs. The camera recorded continuously for eight consecutive days. From the footage, we extracted all instances of Hermína entering and exiting the maternal den, including any notable events occurring in or around the tree hollow. These observations were then used to assess maternal behavior and activity patterns during the early postnatal period. From 8 May 2025, Hermína stayed in the tree hollow with her cubs during the day, regularly leaving at night (between 21: 00 and 23: 00) and returning in the early morning (between 03: 00 and 04: 00 h). On 10 May, another adult-sized raccoon entered the hollow for the first time (01: 38) and killed one of the cubs. Based on the external genitalia, the intruder was identified as a male. When Hermína returned to the hollow during his presence, a fight broke out as she attempted to defend her cubs and successfully drove the male away. A similar incident occurred on 13 May when the male was observed entering the maternal den again (00: 28, Figure 1a, b) and killing the second cub. Another fight ensued, and Hermína once more managed to chase him off. The following day, she attempted to relocate the last cub from the hollow twice, first at 15: 14 in the afternoon and then again at 21: 02 in the evening. However, she was unsuccessful and ultimately remained with the last cub in the hollow throughout the day and night, not leaving until 15 May. On 15 May, the intruding male raccoon returned at (22: 15, Figure 1c) and killed, then consumed the last remaining cub (Figure 1d). Hermína encountered him at the site once again, resulting in another confrontation. The now-empty hollow was last visited by Hermína on 16 May, while the male raccoon was last recorded there on 18 May. Whether the intruding raccoon was the same male remained unclear. However, based on the visual record and the fact that the raccoon was present at regular two-day intervals, we consider it nearly certain. The entire monitoring period of Hermína and her cubs is shown in Figure 2 (see videos in Brynychová et al. , 2025 in the Dryad repository). One possible motivation for the male's infanticidal behavior could be the availability of an easy food source in the form of defenseless cubs. In this case, the cubs were killed and consumed, meaning that the male raccoon committed cannibalism. Nutritional motivation may be supported by the relatively long delays between the killing and consumption of individual cubs. In contrast, if the behavior were driven by competition over mating opportunities, one would expect all of the cubs to have been killed rapidly and in a single event. Another possible motivation for male infanticidal behavior may have been an attempt to increase his mating opportunities during the ongoing reproductive season. This behavior may be particularly advantageous given that raccoon females can enter a second estrus within the same season after the loss of their initial cubs, thereby providing the infanticidal male with an opportunity to sire his own cubs (Gehrt & Fritzell, 1999). However, we are unable to confirm this, as no additional interactions between the individuals were recorded. Beyond the functional motivations of male raccoons, this observation also invites a broader consideration of the evolutionary and ecological role of infanticide, particularly within invasive populations. In this context, a study of the bank vole (Myodes glareolus) is relevant because it involved testing the success of infanticidal vs. non-infanticidal populations in a simulated invasion experiment (Mappes et al. , 2012). Their findings suggested that infanticidal behavior was heritable across sexes and that a rare infanticidal type could invade a non-infanticidal population, particularly when food resources were limited, and that all of this led to the elimination of unrelated offspring of competitors. These findings support the hypothesis that the infanticide tactic may enhance the reproductive success of immigrants in newly colonized areas under certain ecological conditions. Further support for this hypothesis comes from field observations of male-driven infanticide in the American mink (Neovison vison), another invasive carnivore introduced to Europe. García-Díaz and Lizana (2013) proposed both nutritional and reproductive motivations of infanticide in this species. Their findings highlight that male infanticide may be a recurring adaptive strategy in mustelids, particularly where male turnover is high or paternity is uncertain, such as in low-density or newly established populations. Given the mink's ecological impact and invasion success in Europe, the potential role of male infanticide in invasion dynamics deserves closer attention. These examples suggest that infanticide can affect not only individual fitness and social behavior but also the genetic structure of expanding populations. While infanticide may reduce short-term population growth by increasing offspring mortality, it can act as a form of sexual selection that facilitates gene flow and the spread of infanticidal behavioral traits, especially if they are heritable. This first documented case of infanticide in a free-ranging raccoon population highlights the need for long-term monitoring of reproductive behavior to improve our understanding of the causes of infanticide and how frequently it occurs both in native and in newly established invasive populations. Moreover, it provides information about behavioral ecology and if infanticide is a common phenomenon in raccoons, it may play a crucial role in the autoregulation of invasive populations. The research was funded by the Technology Agency of the Czech Republic (project no. SS07020021) and by the Ministry of Agriculture of the Czech Republic, institutional support MZE-RO0123, and by the Czech University of Life Sciences (IGA A₂5₂5). The authors declare no conflicts of interest. Data and video (Brynychová et al. , 2025) are available in Dryad: https: //doi. org/10. 5061/dryad. 2fqz61328.
Brynychová et al. (Sun,) studied this question.