Attack behaviour in naïve Gyrfalcons is modelled by the same guidance law as in Peregrines, but at a lower guidance gain

The aerial hunting behaviours of birds are strongly influenced by flight morphology and ecology, but little is known of how this relates to the behavioural algorithms guiding flight. Here we use GPS loggers to record the attack trajectories of captive-bred Gyrfalcons (Falco rusticolus) during their maiden flights against robotic aerial targets, which we compare to existing flight data from Peregrines (Falco peregrinus). The attack trajectories of both species are well modelled by a proportional navigation (PN) guidance law, which commands turning in proportion to the angular rate of the line-of-sight to target, at a guidance gain. However, naïve Gyrfalcons operate at significantly lower values of N than Peregrines, producing slower turning and a longer path to intercept. Gyrfalcons are less manoeuvrable than Peregrines, but physical constraint is insufficient to explain the lower values of N we found, which may reflect either the inexperience of the individual birds or ecological adaptation at the species level. For example, low values of N promote the tail-chasing behaviour that is typical of wild Gyrfalcons and which apparently serves to tire their prey in a prolonged high-speed pursuit. Likewise, during close pursuit of typical fast evasive prey, PN will be less prone to being thrown off by erratic target manoeuvres at low guidance gain. The fact that low-gain PN successfully models the maiden attack flights of Gyrfalcons suggests that this behavioural algorithm is embedded in a guidance pathway ancestral to the clade containing Gyrfalcons and Peregrines, though perhaps with much deeper evolutionary origins.

Forest stratification shapes allometry and flight morphology of tropical butterflies

Studies of altitudinal and latitudinal gradients have identified links between the evolution of insect flight morphology, landscape structure and microclimate. Although lowland tropical rainforests offer steeper shifts in conditions between the canopy and the understorey, this vertical gradient has received far less attention. Butterflies, because of their great phenotypic plasticity, are excellent models to study selection pressures that mould flight morphology. We examined data collected over 5 years on 64 Nymphalidae butterflies in the Ecuadorian Chocó rainforest. We used phylogenetic methods to control for similarity resulting from common ancestry, and explore the relationships between species stratification and flight morphology. We hypothesized that species should show morphological adaptations related to differing micro-environments, associated with canopy and understorey. We found that butterfly species living in each stratum presented significantly different allometric slopes. Furthermore, a preference for the canopy was significantly associated with low wing area to thoracic volume ratios and high wing aspect ratios, but not with the relative distance to the wing centroid, consistent with extended use of fast flapping flight for canopy butterflies and slow gliding for the understorey. Our results suggest that microclimate differences in vertical gradients are a key factor in generating morphological diversity in flying insects.

Attack behaviour in naïve Gyrfalcons is modelled by the same guidance law as in Peregrines, but at a lower guidance gain

ABSTRACTThe aerial hunting behaviours of birds are strongly influenced by their flight morphology and ecology, but little is known of how this variation relates to the behavioural algorithms guiding flight. Here we use onboard GPS loggers to record the attack trajectories of captive-bred Gyrfalcons (Falco rusticolus) during their maiden flights against robotic aerial targets, which we compare to existing flight data from Peregrines (Falco peregrinus) The attack trajectories of both species are modelled most economically by a proportional navigation guidance law, which commands turning in proportion to the angular rate of the line-of-sight to target, at a guidance gain N. However, Gyrfalcons operate at significantly lower values of N than Peregrines, producing slower turning and a longer path to intercept. Gyrfalcons are less agile and less manoeuvrable than Peregrines, but this physical constraint is insufficient to explain their lower guidance gain. On the other hand, lower values of N promote the tail-chasing behaviour that is typical of wild Gyrfalcons, and which apparently serves to tire their prey in a prolonged high-speed pursuit. Moreover, during close pursuit of fast evasive prey such as Ptarmigan (Lagopus spp.), proportional navigation will be less prone to being thrown off by erratic target manoeuvres if N is low. The fact that low-gain proportional navigation successfully models the maiden attack flights of Gyrfalcons suggests that this behavioural algorithm is embedded in a hardwired guidance loop, which we hypothesise is ancestral to the clade containing Gyrfalcons and Peregrines.SUMMARY STATEMENTNaïve Gyrfalcons attacking aerial targets are modelled by the same proportional navigation guidance law as Peregrines, but with a lower navigation constant that promotes tail-chasing rather than efficient interception.

Dispersal and migration have contrasting effects on butterfly flight morphology and reproduction

Movement may fundamentally alter morphology and reproductive states in insects. In long-distance migrants, reproductive diapause is associated with trade-offs between diverse life-history traits such as flight morphology and lifespan. However, many non-diapausing insects engage in shorter resource-driven dispersals. How diapause and other reproductive states alter flight morphology in migrating versus dispersing insects is poorly understood. To find out, we compared flight morphology in different reproductive states of multiple butterfly species. We found that dispersers consisted of ovulating females with higher egg loads compared with non-dispersing females. This trend was in stark contrast with that of migrating female butterflies in reproductive diapause, which made substantially higher investment in flight tissue compared with reproductively active, non-migrating females. Thus, long-distance migration and shorter resource-driven dispersals had contrasting effects on flight morphology and egg loads. By contrast, male flight morphology was not affected by dispersal, migration or associated reproductive states. Thus, dispersal and migration affected resource allocation in flight and reproductive tissue in a sex-specific manner across relatively mobile versus non-dispersing individuals of different species. These findings suggest that dispersals between fragmented habitats may put extra stress on egg-carrying females by increasing their flight burdens.

Flight morphology and visual obstruction predict collision risk in birds

ABSTRACTCollisions with buildings are a major source of mortality for wild birds, but these instantaneous events are difficult to observe. As a result, the mechanistic causes of collision mortality are poorly understood. Here, we evaluate whether sensory and biomechanical traits can explain why some species are more collision-prone than others. We first examined concordance of species vulnerability estimates across previous North American studies to determine whether these estimates are repeatable, and whether vulnerability is more similar among closely-related species. We found moderate concordance and phylogenetic signal, indicating that some bird species are consistently more collision-prone than others. We next tested whether morphological traits related to flight performance and sensory guidance explain these differences among species. Our comparative analysis shows that two traits primarily predict collision vulnerability within passerines: relative beak length and relative wing length. Small passerine species with relatively short wings and those with relatively long beaks are more collision-prone, suggesting that greater maneuverability and obstructed vision contribute to risk. Together, these findings can help inform mitigation strategies and predict which species will be most at risk in other regions.