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Marlin Meets Tulip—A Systematic Introduction

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In my years working in the zoological world, I have introduced aggressive animals to one another frequently. We moved animals from one zoo to another for breeding purposes, or to facilitate conservation projects. Some species, such as chimpanzees, tigers, and sea lions, can be quite aggressive when first introduced, and some species instinctively fight to the death. Over time, I developed a protocol for introducing potentially dangerous animals through a fence or barrier, working gradually toward safe, barrier-free interactions. Recently, I used this protocol to introduce two resident dogs to each other here at The Ranch.


I brought Tulip, a Maremma sheepdog that I wrote about in my January Letter, to The Ranch to protect the livestock from predators. Tulip has a history of not getting along with other dogs, and she has attacked and injured her previous partner dogs. Livestock-guarding dogs usually work in pairs, but Tulip needed to find a home where she could work alone. Tulip adapted to life on The Ranch quickly and has done a great job protecting our alpacas, mini-donkeys, and goats.


Earlier this year, I brought Marlin to The Ranch from Chicago. Marlin is a bouncy, energetic, 8-year-old black Labrador retriever mix that I adopted from a Chicago shelter in 2013 to be part of an education program at the Shedd Aquarium. When the program ended in early 2018, I was eager to provide Marlin with a new permanent home. He made himself comfortable here on The Ranch immediately, enjoying the spacious pastures and a new life in the shadow of Mount Rainier.

The initial meeting

Tulip lives in the barn and spends her day with the animals that she protects. Marlin lives in the house. I planned to introduce them once Marlin settled into his new home, a few weeks later, but things didn’t go according to plan! One day Marlin was on the back deck when Tulip saw him for the first time from the pasture. Tulip was a long distance away, but when she saw Marlin she launched into her protective-alert barking. This triggered defensive, reactive barking from Marlin, and the two charged at one another. Although they were separated by several fences and barriers, they ran toward each other and their barking became more aggressive and insistent. It happened quickly and unexpectedly; fortunately, I was able to get Marlin to follow me back into the house (hurray for recall training!). That initial incident lasted no more than 20 or 30 seconds, but it was not what I had hoped the dogs’ first meeting would look like! Both had demonstrated serious aggression, and it did not bode well for future meetings.

Meeting on neutral ground

I made sure the two did not meet or see each other again without a plan in place. I decided to start by testing how they would react if they met on leash, from a distance, in a neutral place, away from The Ranch. Two weeks after the initial incident, my helper and I walked both dogs on leash at a nearby field, starting the session half a mile apart. I walked Marlin, my helper walked Tulip, and we reinforced the dogs with high-value treats. As long as we maintained a good distance, the dogs behaved; they saw each other but remained focused on the people walking them. The dogs’ reactivity threshold was just under 100 yards; when we passed that point, both became agitated and began barking, growling, and pulling on their leashes. When we increased the distance between the dogs and passed the 100-yard mark, both dogs refocused on their respective trainers.

To introduce or not?

Did the two have to get along? Since one lives in the barn and the other in the house, the answer was not really. Given the unpredictable nature of life on The Ranch, however, I did not want to risk them ending up in the same space accidentally, especially considering Tulip’s aggressive history.

I decided to use the introduction protocol I had developed working with exotic animals.
I decided to use the introduction protocol I had developed working with exotic animals. I have used the protocol with dogs on several occasions, most notably on a project in which we taught several seriously aggressive dogs to live together. It seemed an easy protocol to follow given the set-up of the Ranch.

Implementing the training plan

I was able to teach Tulip and Marlin to get along and share the same space after about six weeks of focused training. Here are the steps I followed:


  1. Each trainer works a dog in separate pastures at the same time, with visual access to each other and starting just beyond their reactivity threshold. I started this step with each dog as far away from the separation fence as possible, approximately 75 yards apart. Marlin was on the house lawn and Tulip in an adjoining pasture. They seemed unconcerned about each other and more interested in working with their trainers.
  2. Relaxed interaction through the fence.
    Approximate them closer together until they can work on opposite sides of the fence without aggression or any signs of agitation
    . This step took less time than anticipated. We moved 10 to 15 yards closer at each session and conducted three sessions each week. The dogs were able to work side by side on opposite sides of the fence by the end of two weeks.  
  3. Let them see each other regularly outside of sessions, but at a greater distance. We continued training sessions across a shared fence line twice a week. When we were not in sessions, we gave them daily visual access to each other, always with more than one fence or barrier between them. Marlin was in the lawn area while Tulip was two or more pastures away, at a distance of at least 30 yards, with clear visual access.
  4. Allow them free time with a shared fence line outside of a training session. We continued twice weekly training sessions opposite each other with the fence between them, and began allowing them supervised free access through the fence between sessions. At first, they ignored each other, but after eight days they became more curious, sniffing each other through the fence and chasing each other playfully along the fence line. 
  5. Try brief off-leash introduction in a neutral space. After a week of calm interactions through the fence during free time, I decided to allow them to interact without a fence in a neutral space, an enclosed lawn that neither dog sees or uses regularly and, presumably, nor would be likely to want to resource-guard. That went well (a more detailed description is provided below). Note that we had been training with a shared fence line twice each week for a full month by this time.
  6. Move from neutral space into one of the pastures for short periods of time, 20-30 minutes. After the initial introduction in the neutral space went well for 5 minutes, I moved the dogs into one of the pastures to play.  
  7. Gradually increase supervised pasture time. These sessions went well (a more detailed description is provided below), and we continue them once or twice every week. So far, the interactions are peaceful and playful.

I tend to progress slowly when I deal with aggression and reactivity. I am conservative, because moving too quickly can trigger a reaction that can be dangerous and set back the training. After four weeks of training, however, I noticed that Tulip and Marlin were relaxed and showed no obvious signs of discomfort around each other when they had a fence between them. I moved cautiously, but ended up progressing quickly because their behavior seemed to indicate that it was safe to do so. I always supervised and observed the dogs closely in case of trouble.

Tulip’s and Marlin’s social interactions 

Marlin meets Tulip

Tulip’s and Marlin’s reactions have become almost ritualized. They repeat the same sequence of behaviors each time they meet, just as they did the first time they were allowed off-leash together (step 5 above). As soon as they are brought into the same pasture, they run toward each other, sniff each other for at least 30 seconds, and then they bounce around playfully for another 30 seconds. After this greeting sequence, one of them takes off running with the other in quick pursuit. They run around for several minutes at top speed until one of the dogs disengages, and then they each proceed to sniff the ground and do their own thing for a short time. Tulip and Marling seem to ignore each other and move to separate areas in the pasture for three to five minutes, and then one of them will approach the other and repeat the greeting ritual, followed again by the chasing game. On the occasions when I allow them to spend more than 20 minutes together, Tulip will reach a point where she goes into guardian-dog mode; she moves to the highest point in the pasture to lie down and survey the landscape. Marlin seems to take that as a cue to leave her alone and to sniff the pasture and explore on his own. I usually separate them shortly after that. This interaction is good enough for my needs here at The Ranch.

Trained introductions, a useful tool

I have used this protocol successfully with hundreds of animals and have found that it reduces aggressive responses and increases compatibility. I often use the protocol even when I am introducing animals that have shown no aggressive tendencies, because I believe it creates a more comfortable introduction and reduces the likelihood of unexpected problems coming up later. Although I did not originally design it as an aggression-treatment protocol, when used properly it reduces the likelihood of aggressive behavior.

Why does the protocol work?

The dogs were counter-conditioned to each other’s presence while being reinforced for calm cooperative behavior. I used multiple reinforcers during their training sessions: high-value treats, social interactions with favorite people, play, and mental stimulation; the dogs were desensitized to one another through very gradual exposure.


I present this protocol hoping that others may find it useful in their training.
Aggression-related training is never complete; social interactions are always changing and aggressive behavior, once learned, is not forgotten. I present this protocol hoping that others may find it useful in their training. Proceed with caution, as it may not be the right approach for every new animal introduction. With luck, it will be a valuable addition to your behavioral toolbox.

Happy Training,


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