Broadband 75–85 MHz radiofrequency fields disrupt magnetic compass orientation in night-migratory songbirds consistent with a flavin-based radical pair magnetoreceptor

The light-dependent magnetic compass sense of night-migratory songbirds can be disrupted by weak radiofrequency fields. This finding supports a quantum mechanical, radical-pair-based mechanism of magnetoreception as observed for isolated cryptochrome 4, a protein found in birds’ retinas. The exact identity of the magnetically sensitive radicals in cryptochrome is uncertain in vivo, but their formation seems to require a bound flavin adenine dinucleotide chromophore and a chain of four tryptophan residues within the protein. Resulting from the hyperfine interactions of nuclear spins with the unpaired electrons, the sensitivity of the radicals to radiofrequency magnetic fields depends strongly on the number of magnetic nuclei (hydrogen and nitrogen atoms) they contain. Quantum-chemical calculations suggested that electromagnetic noise in the frequency range 75–85 MHz could give information about the identity of the radicals involved. Here, we show that broadband 75–85 MHz radiofrequency fields prevent a night-migratory songbird from using its magnetic compass in behavioural experiments. These results indicate that at least one of the components of the radical pair involved in the sensory process of avian magnetoreception must contain a substantial number of strong hyperfine interactions as would be the case if a flavin–tryptophan radical pair were the magnetic sensor.

Assessment of Morphometric Indices Related to Vernal Flight in Migratory Buntings

Migratory songbirds fly over long distances to avoid adverse conditions at their breeding and wintering grounds, and this phenomenon is known as ‘migration’. This migratory phenomenon is highly energy demanding. The present study was aimed to analyze the morphometric analysis of body mass, beak, wings, tail, and tarsus length of two migratory finches i.e., red-headed (RHB) and black-headed buntings (BHB) to investigate whether they showed differences in their morphological attributes. This observational study shows an understanding of the characterization of wing patterns and differences in the length of tarsus, tail, beak, and wings of both species. The size of the beak, tail, and wings of BHB is significantly different when compared to RHB. In addition, body mass was significantly high in BHB than that of RHB during their spring migration (preparatory phase). T

Navigation of migratory songbirds: a quantum magnetic compass sensor

The remarkable ability of migratory birds to navigate accurately using the geomagnetic field for journeys of thousands of kilometres is currently thought to arise from radical pair reactions inside a protein called cryptochrome. In this article, we explain the quantum mechanical basis of the radical pair mechanism and why it is currently the dominant theory of compass magnetoreception. We also provide a brief account of two important computational simulation techniques that are used to study the mechanism in cryptochrome: spin dynamics and molecular dynamics. At the end, we provide an overview of current research on quantum mechanical processes in avian cryptochromes and the computational models for describing them.

The secrets of cryptochromes: photoreceptors, clock proteins, and magnetic sensors

A class of light-activated proteins in the eyes of birds, called cryptochromes, are thought to act as the primary magnetic sensors allowing night-migratory songbirds to navigate over thousands of kilometers using the earth’s magnetic field. Having evolved from DNA-repairing photolyases, cryptochromes have redirected the energy from light to fuel a variety of other functions: as photoreceptors, as regulators of the circadian clock – and, in some species, most likely as sensors of the magnetic field. While the quantum effects of magnetic fields on cryptochromes are already being studied in detail, almost nothing is known about the signaling cascade involving cryptochrome as the primary receptor protein. Two different screening methods have identified potential interaction partners that suggest an involvement of the visual phototransduction pathway, the visual cycle, potassium channels or glutamate receptors, but more pioneering research is needed to unravel the signaling cascade responsible for transducing the magnetic signal.

Photoperiodically driven transcriptome-wide changes in the hypothalamus reveal transcriptional differences between physiologically contrasting seasonal life-history states in migratory songbirds

We investigated time course of photoperiodically driven transcriptional responses in physiologically contrasting seasonal life-history states in migratory blackheaded buntings. Birds exhibiting unstimulated winter phenotype (photosensitive state; responsive to photostimulation) under 6-h short days, and regressed summer phenotype (photorefractory state; unresponsiveness to photostimulation) under 16-h long days, were released into an extended light period up to 22 h of the day. Increased tshβ and dio2, and decreased dio3 mRNA levels in hypothalamus, and low prdx4 and high il1β mRNA levels in blood confirmed photoperiodic induction by hour 18 in photosensitive birds. Further, at hours 10, 14, 18 and 22 of light exposure, the comparison of hypothalamus RNA-Seq results revealed transcriptional differences within and between states. Particularly, we found reduced expression at hour 14 of transthyretin and proopiomelanocortin receptor, and increased expression at hour 18 of apolipoprotein A1 and carbon metabolism related genes in the photosensitive state. Similarly, valine, leucine and isoleucine degradation pathway genes and superoxide dismutase 1 were upregulated, and cocaine- and amphetamine-regulated transcript and gastrin-releasing peptide were downregulated in the photosensitive state. These results show life-history-dependent activation of hypothalamic molecular pathways involved in initiation and maintenance of key biological processes as early as on the first long day.

Habitat loss on the breeding grounds is a major contributor to population declines in a long-distance migratory songbird

Many migratory species are declining and for most, the proximate causes of their declines remain unknown. For many long-distance Neotropical migratory songbirds, it is assumed that habitat loss on breeding or non-breeding grounds is a primary driver of population declines. We integrated data collected from tracking technology, community science and remote sensing data to quantify migratory connectivity (MC), population trends and habitat loss. We quantified the correlation between forest change throughout the annual cycle and population declines of a long-distance migratory songbird, the Connecticut warbler ( Oporornis agilis , observed decline: −8.99% yr −1 ). MC, the geographic link between populations during two or more phases of the annual cycle, was stronger between breeding and autumn migration routes (MC = 0.24 ± 0.23) than between breeding and non-breeding locations (MC = −0.2 ± 0.14). Different Connecticut warbler populations tended to have population-specific fall migration routes but overlapped almost completely within the northern Gran Chaco ecoregion in South America. Cumulative forest loss within 50 km of breeding locations and the resulting decline in the largest forested patch index was correlated more strongly with population declines than forest loss on migratory stopover regions or on wintering locations in South America, suggesting that habitat loss during the breeding season is a driver of observed population declines for the Connecticut warbler. Land-use practices that retain large, forested patches within landscapes will likely benefit breeding populations of this declining songbird, but further research is needed to help inform land-use practices across the full annual cycle to minimize the impacts to migratory songbirds and abate ongoing population declines.

Wetter climates select for higher immune gene diversity in resident, but not migratory, songbirds

Pathogen communities can vary substantially between geographical regions due to different environmental conditions. However, little is known about how host immune systems respond to environmental variation across macro-ecological and evolutionary scales. Here, we select 37 species of songbird that inhabit diverse environments, including African and Palaearctic residents and Afro-Palaearctic migrants, to address how climate and habitat have influenced the evolution of key immune genes, the major histocompatibility complex class I (MHC-I). Resident species living in wetter regions, especially in Africa, had higher MHC-I diversity than species living in drier regions, irrespective of the habitats they occupy. By contrast, no relationship was found between MHC-I diversity and precipitation in migrants. Our results suggest that the immune system of birds has evolved greater pathogen recognition in wetter tropical regions. Furthermore, evolving transcontinental migration appears to have enabled species to escape wet, pathogen-rich areas at key periods of the year, relaxing selection for diversity in immune genes and potentially reducing immune system costs.

A newly identified trigeminal brain pathway in a night-migratory bird could be dedicated to transmitting magnetic map information

Night-migratory songbirds can use geomagnetic information to navigate over thousands of kilometres with great precision. A crucial part of the magnetic ‘map’ information used by night-migratory songbirds is conveyed via the ophthalmic branches of the trigeminal nerves to the trigeminal brainstem complex, where magnetic-driven neuronal activation has been observed. However, it is not known how this information reaches the forebrain for further processing. Here, we show that the magnetically activated region in the trigeminal brainstem of migratory Eurasian blackcaps ( Sylvia atricapilla ) represents a morphologically distinctive neuronal population with an exclusive and previously undescribed projection to the telencephalic frontal nidopallium. This projection is clearly different from the known trigeminal somatosensory pathway that we also confirmed both by neuronal tracing and by a thorough morphometric analysis of projecting neurons. The new pathway we identified here represents part of a brain circuit that—based on the known nidopallial connectivities in birds—could potentially transmit magnetic ‘map’ information to key multisensory integration centres in the brain known to be critically involved in spatial memory formation, cognition and/or controlling executive behaviour, such as navigation, in birds.