A Better Bait Station

Target Species Commonalities 

Both types of rats are also known to exhibit hoarding behavior when an excess of food (or bait) is presented to them. The rats will take bait out of stations and store it for later, potentially back to nests that multiple rats inhabit, poisoning more than one.

(Morris et al.1) This makes the use of pellet style bait advantageous as the rats are able to quickly and easily remove a piece of bait compared to block or liquid styles of bait. 

There is also a strong precedent for both species of rats willing to climb to reach bait stations. Studies conducted in California, Galapagos islands, and the Channel islands national park investigated whether raising bait stations off the ground could help to exclude certain native species of rats. In the case of these tests the traps were elevated using a pipe wide enough for ship and Norway rats to climb up but too wide for the native rat species to climb up. This means that mounting traps in raised positions could be a viable way to keep non-target species like dogs or children away from bait stations while minimising the compromise to rat accessibility. (Erickson et al.) (Phillips et al.) (Burke et al.)

Traps, bait stations, and tunnels may have to be left out for around 3 weeks before rats will begin to interact with them before their natural neophobia is passed. This is a phase where non-poisoned bait can be used in order to teach the rats that there is food in the bait stations. Rats can also pass on the knowledge of food locations to each other during this time. (Practical Guide to Trapping) 

Non-Target Species Commonalities

The main way to prevent access for non-target species is to ensure that a station is securely mounted. If the station in question has a layout that fully excludes non-targets using a method like positioning the bait behind a zig-zag or at an angle to the entryway, then the only reasonable way for bait to be accessed would be flipping the station. If a station is flipped, using block bait that is slid onto a rod rather than loose pellet bait would help to prevent bait from falling out.

Closing stations with a clasp that requires a specialized key to open can also be a good way to stop a station from being opened.

Interview with John Hambridge - Former Project Director of Predator Free Wellington

The cleaning of tunnels is a major aspect of their function. Each time a station is serviced they remove any debris that may have found its way into the tunnel, often with a small plastic scraper that can be hard to get into the small corners of the stations. Snails are often found in stations that they must remove. They suggested having an easy way to clear a tunnel of debris like the internal walls being attached to the top of the station, potentially a slide away floor.

Run through tunnels are preferred, designs where the rat can see all the way through the tunnel unobstructed so that they can see an exit and know they aren’t entering a fully enclosed space.

Stations are sometimes required to be placed in fully concreted areas like parking lots. In the past stations have been glued to heavy pavers to keep them in place. This is something to be especially considered moving into the CBD.

PFW rarely put more than 100 grams of bait in a station at a time confirming my earlier suspicions. When looking for full eradication John referred to presenting the bait as a “premium”. This means that the bait should be as attractive as possible to rats. Bait degrades fairly quickly out in the field and absorbs water making rats ignore it. This is part of the reason they replace bait so regularly. 

When they refill stations they measure the amount of bait remaining in the station and measure out 100 grams of fresh bait. On a hopper design it could be possible to make that hopper removable and keep most of the unused bait inside. This would make the bait removal process much smoother. Putting the new bait in the hopper could also act as a scoop to measure out the right amount of bait and then directly clip back onto the station.

Often extra lures are placed inside the station like peanut butter to increase the smell of the station and to attract rats. Currently this is just smeared inside the station and can become another thing to clean out. Having a defined spot for this could be good.

Pre-Baiting as a technique is rarely used. It is only really applied in areas where there is a significant risk of a dog getting in and they want to check if a dog could actually break in first.

A modular clip design for the mounting points could be a good option. Think of a stake that could be pushed into the ground and then the station can clip on top. This could be swapped out for a unit that can be nailed to a post or tree or something to attach to concrete surfaces.

Station Deployment Process

I went out with Jed, a field operator at Predator Free Wellington to observe station placement operations and identify pain points and issues with existing stations. The stations used were Zip Lola's that had been modified by the people at PFW.

Deployment Process Takeaways

The amount of different terrain is high:

During my time following Jed, six ZIP Lola stations were placed and each one was in slightly different positions. Notably one was slid deep underneath a tree trunk covered by dense vines.

This highlights the need for flexible mounting options if station placement is going to be fast and easy. The use of a screw on mounting system is a good option but only works when a vertical surface is available, which can be rare in the bush.

The GoldenRod and bungee cord system is obviously effective and something similar to that could be adapted into a design alongside a stake. Stakes can also find issues however and can be insufficient to hold a station secure in very soft ground or may not be able to enter very hard ground.

Entryways have to be flush with the ground:

One of the main considerations when placing a station was making sure that both ends of the tunnel were directly against the ground. This helps to remove barriers to entry for a rat and applies to most other station types as well.

Dirt and leaf litter is applied to the floor:

With each station placement a small amount of dirt and leaves were put into each tunnel to make it a more natural

feeling for rats. This is also done to any other stations that the rat would enter. The GoldenRod system could be improved: Jed mentioned that he had cut his fingers many times on the sharp edges of the rebar rods when trying to pull the bungee cords over the tunnel. It also sometimes took a few tries to find a bungee loop of the right length for the rod spacing.

Water damage is a major issue with existing designs:

Every one of the Lola stations had a strip of duct tape over the top and bottom to cover up the holes that can be used to screw the tunnel to an object.

PFW (and other operations) will often modify stations:

The Zip Lola tunnels that were used had modified bait mounting using a set of 4 screws punched through the bottom of the station. The bait blocks fitted over these screws were held secure by a small rubber cap. The standard method is a small tray. PFW also ignores 4 out of the 6 screws used to close the tunnel, seeing them

as a waste of time.

Servicing Process Takeaways

Cleaning out the stations is particularly fiddly:

Both the Pelgar and the protecta have a number of raised edges and compartments that make scraping

debris out the station difficult. A flat, smooth base can help with this.

Block bait is always used in public areas:

In stations placed in direct view of a road, path or in a backyard block bait is always used. This is because it can be fixed directly to a solid metal rod and is more secure inside the trap. A station has to be able to take both block and pellet bait easily.

Clearing out droppings is important:

Checking for droppings inside a station is an easy way to identify if rats have visited. Each service the droppings are removed so that any new droppings can beidentified to tell if rats have visited again.

There is a trade off to be had with bait blocks:

One advantage of the blocks of bait is that rat bite marks can be identified on the blocks that remain in the station. This can’t be done as easily with pellet bait. Some stations are mounted directly to solid objects: All of the Protecta stations were screwed directly to the side of a Wooden DOC trap. While this isn’t a placement strategy that is used often anymore it shows that mounting directly to a solid object works well.

A design where rats can easily enter and leave has a trade off:

If a station doesn’t require rats to fully enter they become unlikely to leave identifiable droppings. This makes it slightly harder to identify what is taking the bait and chew cards would be relied upon more. The trade off may be worth it though if a rat is more willing to enter a more open station.

Unattached stations can be knocked around easily:

The stations are made of light and thin plastic and if they aren’t strapped to the ground they can be knocked and

blown around.

Stations can require a considerable turn from the rats:

Both the Protecta and PelGar stations need the rat to enter a set of rooms separate to the main. A rat would have to turn roughly 90 degrees and move its shoulders and front legs into the compartment to access the bait. This is a point of interaction that could be smoothed out to remove barriers to entry.