Behind the Scenes: Flying Birds
Fetch your bird watching binoculars and keep your eyes peeled as we uncover the development process for Planet Zoo 2's avians!
Hayo Zookeepers!
This time in our behind the scenes series, we're reaching for the skies with a breakdown of how we've created the new flying species for Planet Zoo 2.
Fetch your bird watching binoculars and keep your eyes peeled as we uncover the development process for Planet Zoo 2's avians!
Looking to the skies
Flying birds were a core part of our vision for Planet Zoo 2 from the earliest days of our planning, but they presented an iceberg's worth of hidden considerations we needed to work our way through.
As with all our animals in Planet Zoo 2, we need to balance game-ready models with anatomical accuracy, trying to be as true to each species as we possibly can. For flying birds, this means considering the number of flight feathers, individual feather silhouettes, how wings work closed and open, colouration and patterns, and sexual dimorphism to name but a few.
We also found there were limited references to look to in the games industry for good examples of how to make game-ready birds at the kind of high visual fidelity we needed for Planet Zoo 2. Birds are often background assets in games and are usually kept fairly simple for performance and budget reasons, but in Planet Zoo 2 our birds are some of the stars of the show!
In order to deliver our new flying avian species, the team here at Frontier developed a bespoke, highly technical pipeline unique to these animals, built around open and closed wing meshes that our animators can swap between freely as the birds move and fly.
Creating these assets required careful planning with our Character Art, Rigging and Animation teams with lots of close collaboration to overcome the various challenges flying birds present.
The first technical challenge is building separate open and closed wings that align seamlessly with both the body and each other, much like interlocking puzzle pieces. This allows us to switch between the meshes being used by the bird model depending on if the wing is to be open or closed, while keeping the swap as natural (and hidden to the player) as possible.
To do this we create a sculpt of the bird with one open and one closed wing, keeping the body itself completely symmetrical. Once this model has been optimised for use in game, we then split the wings off from the body before mirroring them to create a right and left version of each. This process results in a game-ready model with matching open and closed wings that can be seamlessly swapped.
The feathers themselves were another major undertaking for the team to tackle.
Each bird in Planet Zoo 2 combines a mix of bespoke feather cards, hand-painted textures and our custom fur shader. Our talented character artists spend a significant amount of time creating and placing these cards by hand, carefully layering them to create accurate wings, tails and crests for our birds, sometimes with hundreds of feather cards on one bird!
This is key to creating the various layers that make up a bird's wing in Planet Zoo 2:
- The mesh - the bulk of the wing, depicting the skeletal and muscle structure.
- The flight feathers - feather cards slotted into the mesh one by one, stacked closely with each other and provided with individual movement through animation.
- The tertiary feathers - layered above and sometimes below the flight feathers, these feather cards create the transition between the previous layers.
Depending on the requirements of the specific species of bird, an additional two layers can also be added here:
- Capelets - structures overlapping the upper body and wing to represent back feathers. Typically with an open and closed version to go along with our wing swaps.
- Pockets - usually overlapping the chest and lower part of the wing meshes, these allow the closed wing to slot into a pocket of feathers replicating the real behaviour of birds.
Texturing for our birds was also particularly demanding, requiring lots of handcrafted detail to capture the variety of feathers and patterns seen across our birds.
Because each bird calls for such a specific approach, the Character Art team built a huge library of feather brushes and resources to use for this. While texturing our birds, we also had to pay particular attention to the continuity between the wing swap textures and transitions to the body, so the wing swap system can seamlessly change between open and closed wings.
All in all, it took a lot of iteration, collaboration, and R&D to figure out a pipeline for creating flying birds that worked for our Character Art, Animation and Rigging teams. The end result, while some of our most complex assets to produce, are the stunning birds you see in Planet Zoo 2!
Earning our training wings
A key part of our new flying birds for Planet Zoo 2 is their ability to, well, fly!
Flight is a particularly complex form of navigation, so the team spent a lot of time and effort making flight appear authentic with smooth flight paths and animations that match real world behaviour. For example, depending on the phase of flight, animals will have to exert different levels of power to generate enough lift or ascend. To support this we developed dynamic systems that change the intensity of wing-flapping when a bird is ascending sharply, softly, or maintaining their height. We also added a "noise" system to simulate the effect the air has on the birds movement and feathers as it flies.
Similarly to our aquatic animals preference for particular positions in the water column, we have various parameters and preferences that we can tweak for our birds. Species can have a desired altitude at which they would like to fly if possible, as well as how they behave at this altitude. For example, we can choose whether birds prefer to follow true altitude (altitude above sea level) or absolute altitude (altitude above terrain), shaping how they react to the ground they are flying over, such as flying down through a valley or soaring over it.
These parameters enable the team to represent different flight patterns for larger and smaller birds or those who are more maneuverable and those who are perhaps a smidge less graceful. This means that an eagle soaring over a canyon will express different flying behaviour to a great hornbill flying beneath the rainforest canopy.
When it came to our birds landing, we needed to make sure our flying species could hit their targets smoothly from any approach onto any surface, while also keeping in mind that many birds will land differently, with some preferring a long glide and others short and fast. To allow the Animation team the freedom to reflect this, we dedicated planning time to handle the distance and speed of each landing animation for each of our birds, resulting in seamless landing behaviour which is bespoke and authentic to each species.
Seeing the first flight of our white-tailed sea eagle in game was a spectacular moment for the team. While it couldn't land properly yet, and would frequently fly into the ground (and stay there), it was the inspiring push we needed early in development to continue to improve and refine our birds.
Bird brained
Building systems for our birds to fly was all well and good, but we also had to consider how they land, perch on objects, interact with the environment and utilise our new animal brain framework.
Our flying animals use the same brain and decision making process as other animals in Planet Zoo 2, but their pool of behaviours and situations can differ somewhat to terrestrial animals.
For example, birds that are primarily arboreal (live in trees) will prefer to perch, which is a new type of behaviour that enables animals to perch on trees and certain habitat objects. Depending on their preferences, birds will also exhibit specific behaviours like stretching and sunbathing on these perch points. Other birds which have a more terrestrial preference may prefer to either walk around on the ground or in shallow water.
Depending on their species, birds will also evaluate the cost of flying differently and weigh this into how they behave. A wading bird and arboreal bird that want to get to a feeding station on the other side of a habitat will go about it in different ways. The arboreal bird will consider a flying path to that feeding bowl more efficient than walking there, while the wader will prefer walking there on land or in the water if possible.
Implementing perching behaviour was a fairly complicated problem for us to tackle - just because an animal could perch on something doesn't mean it has a clear, unobstructed path to get there. We also have some physics-enabled perches that add another layer of complexity when animals are perching on them, as they need to react to how the perch is moving and move with it.
We had a lot of fun mishaps along the way while implementing these systems, but they all contributed to more varied and authentic behaviour for our birds!
Feathering your nest
In the original Planet Zoo, we simplified birth for our oviparous animals by omitting nests entirely and using the same live birth system for all our animals.
For Planet Zoo 2, with our roster of new flying birds, returning flightless birds and reptilian egg-layers, we had the perfect excuse to tackle nesting behaviours.
You will now need to provide these animals with appropriate nesting sites per breeding pair within a habitat so they can reproduce. Animals with a nesting requirement will not be able to conceive until a nest is present in their habitat and they have claimed it. After mating, the female will then lay eggs within the nesting site, which will be incubated by either male of female (sometimes both!) depending on the species. This will work slightly differently for reptiles, who will leave their eggs to incubate on their own (although some mothers may guard their nests).
Once the eggs have incubated, it's time to welcome some new faces!
For reptiles or flightless birds, this will be in a recognisable form from the original Planet Zoo, with juveniles free to explore the world around them. Flying birds will instead be nestbound upon hatching and remain in their nest under the care of their parents. At fledging age, they grow up and trade their shaggy look for adult plumage, but are still considered juvenile and don't count against adult population limits until they become sexually mature.
Nesting is a core characteristic of avian animals and will be critical for our zookeepers to help these new flying species flourish.
A place to stretch your wings
Our new flying animals also mean a completely new way for zookeepers to build habitats: aviaries!
Habitats can now be enclosed with roofs that are attached to barrier posts and, optionally, roof pillars to create quick and custom escape-proof air space for your birds, keeping both guests and the animals safe.
While we call these habitats aviaries, these roofs can actually be used in other habitats and are a perfect tool for more diverse builds for climbing animals or those with a bit more pep in their step.
All flying animals in Planet Zoo 2 have a flyable areas space requirement, which you'll need to keep in mind when creating your aviaries. Much like our aquatic animals have a preferred water depth, birds will need enough space to really stretch their wings.
Along with building an appropriately sized aviary, you'll also need to give your birds ample things to perch on, enrichment toys, feeders and nests for reproduction.
Birds' flight and the preference of many species to perch in trees mean that guests will often have to look up to see the animals they came to visit. To provide your guests with appropriate views, elevated walkways (both in and outside) aviary habitats will be a common sight in Planet Zoo 2's zoos!
Onwards and upwards
Along with our aquatic species, flying birds were a huge leap forward for Planet Zoo 2, requiring new processes, new technologies and plenty of brainstorms to reach the authentic depictions we strive for.
It's been a pleasure for the team to see all this hard work pay off and it will be an even bigger pleasure when we see you start to introduce these new flying animals to your zoos and Wildlife Reserves in October!
Planet Zoo 2 is available to pre-order now on PC, PS5 and Xbox Series X|S. Join the conversation and keep in touch by following our social channels, subscribing to our mailing list (for an exclusive in-game reward) and watching closely for updates on the website.
