Modern Weights and Measurements of Jaguars

[Balam]

@peter thanks for the remarks on the captive jaguars, this is going to be a very long post based on all the points you brought forward and I think that this conversation can help us get a better idea of the relationship between size and environment not just in jaguars but also big cats for those interested in that topic. 

I've heard from other people that historically jaguars have been avoided in circuses precisely because they are much harder to "tame" and follow orders than the other big cats, that's why we see so few of them in circus acts.
Interestingly, jaguars can be rather calm and gentle in captivity with people that they trust. They are almost goofy-looking and my theory is that while they cannot be told what to do, they will allow those whom they have developed a bond with to be by their side.

The captive male from Florida I mentioned Ravager a few replies back seemed really comfortable with human contact. He is also the one non-obese captive specimen that I have the correspondence of at 158 kg. I made this comparison of said jaguar next to Joker to see how well they compared in dimensions, the photo was provided by my friend and fellow jaguar enthusiast Litchsoldat on Jaguarland as he knew the lady in the picture who was the one who provided the photo, and information to him. Needless to say, I'm convinced Joker is in his weight class:

*This image is copyright of its original author

I will try to look for the tables you mentioned on the EOE thread when I have the time. For now, I think the data from Cooch Behar posted by Guate sufficed to do some really good analyses on the body proportions of a record-sized jaguar and how well he fared next record-size tigresses and modest-sized male tigers. And Joker is undoubtedly in that size class while Shaka is closer to the size class of an average tigress in weight and body proportions.


Going back to captive specimens, recently I came across this huge melanistic pair from what looks like a roadside zoo, likely in the US. They are overweight in a similar manner to what we see in other captive cats that lack proper exercise but their skeletal frame (shoulder height and length) are what caught my attention. They look huge next to the keeper:

*This image is copyright of its original author

*This image is copyright of its original author

*This image is copyright of its original author

*This image is copyright of its original author

Another, somewhat obese, but very famous jaguar with tens of millions of views is "Tank" from the SingleVision holding facility, also in Florida. This jaguar is held with his partner Binta the lioness who is the same age. She is obviously taller than him at the shoulder but he seems to match her rather well in body length and skull size. They are both 3-year-old subadults:

He is often seen interacting with care with Binta and their keeper, suggesting a very deep bond between them.

Your points about jaguars from the Guyanas are interesting, and I think the reason why your conclusions based on their sizes have validity is due to the location. A lot of people think of Amazonian jaguars as a monolith when this could not be further from the case. The Amazon basin is a gigantic area that encompasses many eco-regions, and biomes and that nowadays has different degrees of degradation.

Based on the data we have collected from Hoogesteijn and Mondolfi, the heaviest jaguars they were able to study from the Amazon basin came from areas in the peripheries of the rainforest in Venezuela, Bolivia, and Brazil, which border wetland areas. In wetlands, you tend to find much higher concentrations of prey in the form of caimans, capybaras, deer, and peccaries. In the deep rainforest, the numbers of these animals, with the exception of peccaries, is greatly reduced so the diets of jaguars there tend to be more varied and consist of smaller vertebrates like birds and armadillos. As a result, they have to dwarf in size to survive with lesser resources.

The case of Mamirauá in Brazil is particularly fascinating to me as I have been doing a lot of research with some colleagues in that area and with the help of biologists in the field we've been able to gather all the scientific weight data for that population in the Amazon tab of our data set, here's what we have so far:

*This image is copyright of its original author

This population is fascinating because during the monsoon season, the forest ground becomes completely flooded and the jaguars have adapted to this change by moving exclusively to the canopy. Jaguars spend months on end living on the trees, mating, giving birth, and hunting. Their main prey in this area are howler monkeys during the wet season, and caimans supplement their diets in dryer months.
One of the field biologists we spoke with stated that the physical state of some of the jaguars he captured was not optimal. They were almost frail because they did not have much food to eat (I would assume relying on monkeys and birds for long periods of time is not ideal for a big cat), so naturally, the cats are forced to dwarf in size to sustain themselves with fewer resources but also to have an appropriate size to live in the forest canopy.

In Guyana and Suriname, there are quite a few wetland areas that can foster larger jaguars, but it's not the only area of the Amazon like this. While Brazil has done some amazing work capturing and studying jaguars from the Pantanal, I would like to see more work being done for jaguars in the country's portion of the Amazon as beside Mamirauá and the island of Amapá (which also harbors a dwarfed small population), there is partially no tracking of jaguars. There are areas like Sinop and Xingu that have some seriously big specimens roaming, and this is all thanks to the better-preserved rainforest with high prey densities (mainly large herds of while-lipped peccary).

Here are some specimens from said areas:

The last melanistic male comes from Xingu, this is the same area where two huge and robust females were sourced for rewilding project in Iberá:

The juvenile female offspring of Juruna can be seen here at less than a year old at the time free in Iberá. Absolutely dense and robust female cubs, the result of good genes and ample prey base (Iberá has a higher percentage of capybara and feral hogs per km2 than then Pantanal), it will be fascinating to see how this population develops as it grows but that's another topic:

*This image is copyright of its original author

Lastly, in regard to the skull. I think I disagree with you on the conclusion of the affinity between jaguars and lions as opposed to tigers. I obviously don't have nearly as much hands-on experience dealing with and measuring big cat skulls so my opinions are based mostly on pictures and measurements, but it seems to me that jaguars differ quite broadly from lions and are closer to tigers in their rather stout but wide skulls, as opposed to the more oval-shaped skulls seen in lions and leopards. This doesn't mean that tiger and jaguar skulls are identical. From what I've seen, tigers tend to have a more concave skull at the top whereas jaguars have a more convex skull with a particularly protruded forehead. My belief is that the kinship in morphology between jaguars and tigers in the result of parallel evolution where both species have fulfilled practically identical niches and living conditions in most forested and wetland habitats, despite the phylogeny of the jaguar being closer to that of lions and leopards.

In terms of size, I would like to see more recent data from jaguar skulls. We have tons of weight data but none published on the former. For example, the skull of the record jaguar female Troncha (110 kg) is currently being held by Onçafari, or the skull of the 130 kg male jaguar Sandro is currently being held by Reprocon.

The data from Hoogesteijn and Mondolfi for the Pantanal also combined a few specimens from the Chaco where they are slightly smaller (although historically likely matched the size of those in the Pantanal), so that likely reduced the overall average. I think without the Chaco specimens the GSL for the population would've been closer to 300 mm and 200 mm for the ZGW. The data from Almeida also shows that his jaguars with the biggest skulls reached the lower end in size of the lion skulls recorded by Smuts from what I can recall. This is despite the fact that his jaguars were much lighter in weight. A good friend and mentor of mine who works at a very important museum shared with me a photo of the frontal part of a broken Pantanal jaguar skull next to a male African lion and the jaguar almost perfectly matched it in the rostrum. Sadly I don't have permission to share this picture.

Nowadays I expect a mature male Pantanal jaguar (110+ kg) to have a skull well within the 300+ mm threshold more often than not in GSL, but obviously I can't confirm this until we get enough statistically sufficient data to back up my hypothesis. Reply