A novel mode of bathing behavior of hummingbirds recorded in the Brazilian ruby Heliodoxa rubricauda and allies (Aves: Trochilidae)

Abstract

The Brazilian ruby, Heliodoxa rubricauda, is a forest species of hummingbird endemic to the Atlantic Forest. It belongs to an Andean clade of birds with robust and strong legs and adapted to feed on inflorescences of plants from high regions and influenced by strong winds. It occurs from northeastern to southern Brazil on slopes, sierras, and mountains and has the little-known behavior of bathing in waterfalls and forest streams. Based on five field observations made in the state of São Paulo, and records available from online photo platforms, we concluded that H. rubricauda is the only species of hummingbird in Brazil that bathes by settling on rocks of forest waterfalls with medium to strong currents. This behavior is made possible by the robust and strong legs the species inherited from its evolutionary lineage, which, in the Atlantic Forest, are used for feeding, defense, and bathing. We hypothesize that this behavior is more efficient for body hygiene than other existing behaviors because it allows a greater amount of water to pass over the body, thereby eliminating traces of food and parasites, in addition to reducing risks of predation.

First record of crab-eating mongoose (Herpestes urva formosanus) in coastal forest and use of anvils during predation on land hermit crabs in Taiwan

Abstract

Crab-eating mongooses (Herpestes urva) are widely distributed across Southeast Asia. In Taiwan, the mongoose (H. urva formosanus, endemic subspecies) is a protected species under the Wildlife Protection Act. Crab-eating mongooses have been observed near streams, riversides, agricultural lands, and shallow mountain areas. Additionally, as described in this short communication, by using a remote camera, we observed a small population of mongooses in the coastal forest in Kenting National Park in Taiwan. The mongooses in the coastal forest were observed eating land hermit crabs, which is the first-ever recorded observation of this behavior. Mongooses are known to consume crabs (Brachyura), insects, and some small reptiles. However, this article presents the first record case of mongooses using stone anvil to crack open land hermit crabs. From our observations and field records, we determined that mongooses use flat rocks as anvils and their front paws to tap hermit crabs’ shells repeatedly to break the shells and remove the hermit crabs. We also observed that the mongooses only ate the abdomens of large hermit crabs. Additional studies are necessary to determine why the mongooses migrated to the coastal forest and how they learned to open hermit crab shells. This behavior of mongooses might help them move into living in coastal forests.

Impact of environmental complexity and stocking density on affective states of rainbow trout (Oncorhynchus mykiss)

Abstract

Environmental condition, such as environmental complexity or stocking density, can directly or indirectly influence animal emotion and ultimately, affective state. Affective states of animals can be assessed through judgement bias tests, evaluating responses to ambiguous situations. In this study, we aimed to determine whether environmental complexity and stocking density impacted rainbow trout affective state. Rainbow trout (n = 108) were housed in recirculating aquaculture systems under commercial conditions while trained at tank-level to discriminate between a positively reinforced chamber (feed) in one location and a negative chamber (positive punishment; chase by net for 1 s) in the opposing location. Fish from successful tanks (two out of five tanks) were then housed in treatment tanks of either high- or low- environmental complexity at either high (165 fish/m3) or low (69 fish/m3) stocking density. Trained fish were tested for latencies to approach three intermediate, ambiguous chambers. Fish housed in high-density tanks were faster to enter all chambers than those housed in low-density tanks (8.5 s vs. 15.2 s; P = 0.001), with faster entries into the positive (7.4 s vs. 15.2 s; P = 0.02) and near-negative chambers (10.2 s vs. 17.4 s; P = 0.006), suggesting that these fish were more optimistic to receive a feed reward. Tank complexity did not affect test outcomes. No differences between treatments were observed between body weight, length, and plasma cortisol. Overall, rainbow trout are capable of discriminating between cues during a judgement bias test and fish housed in high-density environments respond more optimistically in ambiguous situations compared to fish in low-density environments.