The great escape: Houdini skills of horses laid bare in fresh research

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Door and gate mechanism types opened by horses.
The arrows indicate the direction of the animals’ head movements. Image: Krueger et al. https://doi.org/10.1371/journal.pone.0218954

Horses can rightly lay claim to being the Houdinis of the animal world, with researchers acknowledging they could not identify a conventional door or gate latch beyond their ability to open.

Horses even managed to open two locks with keys.

Researchers have delved into the ability of horses to open fastened doors and gates, warning that pretty much any mechanism commonly employed is potentially vulnerable to being opened, even carabiners and electric fence handles.

Konstanze Krueger and her colleagues, writing in the open-access journal PLOS ONE, described anecdotal reports of horses opening fastened doors and gates as an intriguing way of exploring the possible scope of horses’ problem-solving abilities.

The horses’ natural environment has no comparable mechanisms, they noted, meaning that any success in dealing with such human-made devices must be based on general learning capacities.

“Scientific studies on the topic are missing, because the rate of occurrence is too low for exploration under controlled conditions.”

Indeed, until now, the opening of fastening mechanisms had been investigated only in animals with claws and paws.

For their study, Krueger, Laureen Esch and Richard Byrne set up a website and invited owners and caretakers of horses, donkeys, and mules to report on door and gate-opening incidents. The study was promoted widely through several channels.

They also collected videos from YouTube, taking care to select raw data footage of unedited, clearly described and clearly visible cases of animals with no distinct signs of training or reduced welfare.

Their final database comprised 513 case reports of doors or gates on hinges being opened. There were an additional 49 sliding doors opened, and 33 barred doors or gateways.

The closing mechanisms cracked by horses included 260 cases of horizontal bars and 155 cases in which vertical bars were employed. There were 43 cases of twist locks being beaten, 42 door handles, 34 electric fence handles, 40 carabiners, and even two locks with keys.

Door and gate types opened by horses. The arrows indicate door and gate opening directions. Doors and gates on hinges were opened in the same or opposite direction to the animals’ movement direction. The doors and gates c1)–c3) are subcategories of the category c) barred door or gateways. At b), horses had to grasp and pull down a pipe with their mouth at the dotted arrow and then move the door into the direction of the continuous arrow. Image: Krueger et al. https://doi.org/10.1371/journal.pone.0218954

Opening, they said, was usually for escape, but also for access to food or stablemates, or out of curiosity or playfulness.

While 56 percent of the horses in their case reports opened a single mechanism at one location, 44 percent showed an ability to open several types of mechanisms, with a median of two and a remarkable maximum of five. These multi-latch Houdinis showed an ability to escape from different places, with a median of two locations and a maximum of four.

The more complex the mechanism, the more movements were applied, varying from around two for door handles to 10 for carabiners.

Mechanisms requiring head or lip-twisting needed more movements, with significant variation between individuals.

Seventy horses had the option of observing unlatching behavior by stablemates before making their own escape. However, 183 did not, which indicates they learned to open doors and gates either individually or from observing humans.

Experience favored opening efficiency, the researchers found. “Subjects which opened several door types applied fewer movements per lock than horses which opened only one door type,” they reported.

“We failed to identify a level of complexity of door-fastening mechanism that was beyond the learning capacity of the horse to open.

“Thus, all devices in frequent use, even carabiners and electric fence handles, are potentially vulnerable to opening by horses, something which needs to be considered in relation to keeping horses safely.”

After opening the doors and gates of a box, enclosure or pasture, 87% of the animals walked out, 62% ran around in the area surrounding their stable, 22% went into other horse boxes or stables, 15% freed other horses, and 22% broke into other places such as feed storage rooms or human houses.

Discussing their findings, Krueger and her colleagues said that crowd-sourcing resulted in a large number of case reports being received.

“Most of the horses opened only one door, gate or mechanism type at a single location.

“However, some individuals opened the same type of door or gate mechanism at several locations, some operated several types of mechanisms, and some were even able to open doors and gates secured with several mechanism types at different positions. These horses seemed to have understood and generalized the concept of ‘locked doors’.”

While some of the horses had the option of observing other horses opening latches, most didn’t.

“In general, we cannot exclude individual trial and error learning as the main mechanism for learning how to open locked doors and gates.

“Also, horses may have learned to handle the locking devices through observing humans doing so. If so, the subjects were innovative in acquiring door opening techniques from observing humans, as they would have to use different body parts and to approach the locking mechanisms from different angles than the observed persons.

“Interestingly, animals which had prior opportunity to observe the door-opening procedure in stablemates were over-represented among horses which remained in a stable even after opening its locked door.”

They continued: “In our survey, most horses were reported to open doors and gates on hinges, with bars or handles which could be opened on one plane with only a few head movements.

“However, an impressive number of horses handled more complicated mechanisms, which required movements in more than one plane and specific sequences of actions to be applied.

“In the main, horses applied similar numbers of movements to those needed by humans to open doors and gates, but twice as many when opening locks.

“The range of fastening devices that horses have learnt to open apparently spans the gamut of devices in frequent use in the nations participating in the study: thus, we found no obvious limit to the complexity which horses can learn to master,” the trio reported.

Horses, they concluded, open a far wider range of human-made mechanical devices on doors and gates than previously reported, generally handling the mechanisms with their mouths.

“Although most horses are confined by simple bolts or handles, and most reports were of opening such devices, a surprising range of fastenings, including carabiners and electric fence handles, proved vulnerable to opening by horses confined by them.

“Indeed, within the range of locking devices in frequent use for restraining horses, we found no clear cognitive limit to horses’ ability to open them and some evidence for experience improving the horses’ skills.

“The ability of horses and other ungulates to open human-made fastenings therefore needs to be reconsidered to minimise damage caused by escapes.”

Krueger is with the University of Regensburg in Germany; Esch is with Nürtingen-Geislingen University in Germany; and Byrne is with the University of St Andrews in Scotland.

Krueger K, Esch L, Byrne R (2019) Animal behaviour in a human world: A crowdsourcing study on horses that open door and gate mechanisms. PLoS ONE 14(6): e0218954. https://doi.org/10.1371/journal.pone.0218954

The study, published under a Creative Commons License, can be read here

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