Background complexity can mitigate poor camouflage

Avoiding detection through camouflage is often key to survival. However, an animal's appearance is not the only factor affecting conspicuousness: background complexity also alters detectability. This has been experimentally demonstrated for both artificially patterned backgrounds in the laboratory and natural backgrounds in the wild, but only for targets that already match the background well. Do habitats of high visual complexity provide concealment to even relatively poorly camouflaged animals? Using artificial prey which differed in their degrees of background matching to tree bark, we were able to determine their survival, under bird predation, with respect to the natural complexity of the background. The latter was quantified using low-level vision metrics of feature congestion (or ‘visual clutter’) adapted for bird vision. Higher background orientation clutter (edges with varying orientation) reduced the detectability of all but the poorest background-matching camouflaged treatments; higher background luminance clutter (varying achromatic lightness) reduced average mortality for all treatments. Our results suggest that poorer camouflage can be mitigated by more complex backgrounds, with implications for both camouflage evolution and habitat preferences.

Double-countershading as a means of camouflage in larvae of Orange-tip Anthocharis cardamines (Linnaeus, 1758) (Lepidoptera: Pieridae)

In Shaw & Otto (2020), Shaw described larvae of the butterfly, Orange-tip Anthocharis cardamines (Linnaeus, 1758), that were visually obvious yet apparently immune to bird predation. He speculated that mustard oils in the foodplants may render them distasteful to birds so that being conspicuous is of little consequence, allowing them to bask in sunshine possibly to aid digestion. In contrast, I argue that in certain lighting conditions larger larvae of Orange-tip can be very well camouflaged. These two different defence mechanisms are not mutually exclusive and each may come into play under different conditions of lighting, larval age and/or food-plant availability. For disguise the larvae make use of double-countershading in what Süffert (1932) called the 'two-surface effect'. Here I briefly describe its mechanism along with that of the better-known ordinary (single) countershading. Photographs are shown of both.

Maternal care and secretive behaviour of neonates in the highly social lizard Liolaemus leopardinus (Squamata: Liolaemidae) from the central Chilean Andes may relate to size-specific bird predation

Predation prompts the evolution of antipredator traits, molds behaviour, and can lead to the evolution of parental care. We investigated parental care and predator-avoidance behaviour of neonates in the social lizard Liolaemus leopardinus. We used clay models to quantify bird predation pressure on L. leopardinus. Predation was significantly greater on small models and models in open habitat. Late-term pregnant females left their social groups on rock outcrops and gave birth in solitary underneath flat rocks in vegetated microhabitat. Mothers stayed with their litters inside natal chambers for at least 24 h and when they left, sealed the neonates inside. Mothers remained close to their natal chamber and neonates when neonates emerged. Neonates and young yearlings moved significantly less and occupied vegetated microhabitat significantly more than older age classes. We suggest that the maternal behaviour and secretive behaviour of neonates may be related to the heavy avian predation on neonates.