These so-called flooded forests, or\u00a0v\u00e1rzeas, are renowned for being highly productive ecosystems<\/a>, and that probably explains why South America\u2019s largest felid appears to be doing well.<\/p>\n \u201cThe peak density we found was 15 individuals per 100km2,\u201d says researcher Ra\u00edssa Sepulvida from the Federal University of Mato Grosso do Sul. \u201cIn comparison, in the Pantanal<\/a> which is considered a hotspot for the species, the mean is about six per 100km2.\u201d<\/p>\n But in this reserve that spans more than 11,000km2\u00a0\u2013 more than half the size of Wales \u2013 statistics can be deceptive.\u00a0<\/p>\n Sepulvida and her colleagues dug into 17 years of camera-trap data and discovered a dark secret hiding within the dataset. While the population has remained stable during this time, numbers of males have increased while females decreased by 77 per cent between 2005 and 2022, they report in a study published in the\u00a0Journal of Applied Ecology<\/a>.\u00a0<\/p>\n \u201cThe increase in male numbers is probably due to them coming in from other areas,\u201d Sepulvida says. \u201cAnd what we see for other big cats is that when you have external males entering a population, it causes higher rates of infanticide.\u201d<\/p>\n New males will kill young cubs so they can mate with females and ensure their offspring \u2013 and their genes \u2013\u00a0form the next generation. But they don\u2019t know if this happening or not. \u201cWe don\u2019t have much information about cub survival,\u201d Sepulvida says. \u201cWe haven\u2019t recorded many cubs on the cameras.\u201d<\/p>\n And there is the concern that if female numbers are dropping, that will also reduce how many cubs are being born. While the population is healthy now, this could change if there is insufficient recruitment.\u00a0<\/p>\n Sepulvida says they don\u2019t know why this is happening. She and her colleagues have theorised that hunting of male jaguars by local people \u2013\u00a0possibly as a result of conflict or it could simply be opportunistic \u2013\u00a0is creating a vacuum into which outside males are drawn.<\/p>\n Killing of jaguars is not permitted, but hunting of other animals for food is, so is this reducing prey density and impacting the jaguars? Environmental changes connected to climate change could be another factor they need to consider, but Sepulvida says they need an even longer-term dataset for this to become clear.<\/p>\n![\"An](\"https:\/\/www.newsbeep.com\/il\/wp-content\/uploads\/2026\/07\/Jaguar-1.jpeg\")
Mamirau\u00e1 Reserve’s jaguars, such as this adult female, have adapted to living and hunting in trees. Cred Bruno Kelly\/Instituto Mamiraua<\/p>\n![\"A](\"https:\/\/www.newsbeep.com\/il\/wp-content\/uploads\/2026\/07\/Jaguar-cub.jpeg\")
A jaguar cub seen among a tangle of shrubs during the high-water season in the floodplain area of \u200b\u200bthe Mamirau\u00e1 Reserve, Brazil. Credit: Bruno Kelly\/Instituto Mamiraua<\/p>\n
![\"A](\"https:\/\/www.newsbeep.com\/il\/wp-content\/uploads\/2026\/07\/Jaguar-scaled.jpeg\")
A melanistic jaguar in the Amazon floodplains. Credit: Miguel Monteiro\/Instituto Mamiraua<\/p>\n