Pathway In Birds Research Articles

A histological and diceCT-derived 3D reconstruction of the avian visual thalamofugal pathway

Amniotes feature two principal visual processing systems: the tectofugal and thalamofugal pathways. In most mammals, the thalamofugal pathway predominates, routing retinal afferents through the dorsolateral geniculate complex to the visual cortex. In most birds, the thalamofugal pathway often plays the lesser role with retinal afferents projecting to the principal optic thalami, a complex of several nuclei that resides in the dorsal thalamus. This thalamic complex sends projections to a forebrain structure called the Wulst, the terminus of the thalamofugal visual system. The thalamofugal pathway in birds serves many functions such as pattern discrimination, spatial memory, and navigation/migration. A comprehensive analysis of avian species has unveiled diverse subdivisions within the thalamic and forebrain structures, contingent on species, age, and techniques utilized. In this study, we documented the thalamofugal system in three dimensions by integrating histological and contrast-enhanced computed tomography imaging of the avian brain. Sections of two-week-old chick brains were cut in either coronal, sagittal, or horizontal planes and stained with Nissl and either Gallyas silver or Luxol Fast Blue. The thalamic principal optic complex and pallial Wulst were subdivided on the basis of cell and fiber density. Additionally, we utilized the technique of diffusible iodine-based contrast-enhanced computed tomography (diceCT) on a 5-week-old chick brain, and right eyeball. By merging diceCT data, stained histological sections, and information from the existing literature, a comprehensive three-dimensional model of the avian thalamofugal pathway was constructed. The use of a 3D model provides a clearer understanding of the structural and spatial organization of the thalamofugal system. The ability to integrate histochemical sections with diceCT 3D modeling is critical to better understanding the anatomical and physiologic organization of complex pathways such as the thalamofugal visual system.

Short-term mercury exposure disrupts muscular and hepatic lipid metabolism in a migrant songbird

Methylmercury (MeHg) is a global pollutant that can cause metabolic disruptions in animals and thereby potentially compromise the energetic capacity of birds for long-distance migration, but its effects on avian lipid metabolism pathways that support endurance flight and stopover refueling have never been studied. We tested the effects of short-term (14-d), environmentally relevant (0.5 ppm) dietary MeHg exposure on lipid metabolism markers in the pectoralis and livers of yellow-rumped warblers (Setophaga coronata) that were found in a previous study to have poorer flight endurance in a wind tunnel than untreated conspecifics. Compared to controls, MeHg-exposed birds displayed lower muscle aerobic and fatty acid oxidation capacity, but similar muscle glycolytic capacity, fatty acid transporter expression, and PPAR expression. Livers of exposed birds indicated elevated energy costs, lower fatty acid uptake capacity, and lower PPAR-γ expression. The lower muscle oxidative enzyme capacity of exposed birds likely contributed to their weaker endurance in the prior study, while the metabolic changes observed in the liver have potential to inhibit lipogenesis and stopover refueling. Our findings provide concerning evidence that fatty acid catabolism, synthesis, and storage pathways in birds can be dysregulated by only brief exposure to MeHg, with potentially significant consequences for migratory performance.

A functional polymorphism of inhibin alpha subunit at miR-181b-1-3p-binding site regulates proliferation and apoptosis of chicken ovarian granular cells.

INHA, the gene encoding the inhibin alpha subunit, was involved in folliculogenesis in mammals, but no study was reported for its working pathway in birds. Here we hypothesize that gene polymorphism in INHA 3'UTR might influence miRNAs binding efficiency and further affect the function of this gene. Thus, we investigated the association between the 3'UTR single-nucleotide polymorphisms (SNPs) in INHA and the laying performance in chickens and further explore their possible molecular cascades in granulosa cells (GC). Five SNPs were detected in Tianfu green-shell layers and g. 22,178,975 G > A was significantly associated with total egg numbers at the age of 300days (EN, n = 286). Birds carrying the AA genotype laid more EN than those with GG (P < 0.05). The allele transition from G to A in the 3'UTR of INHA gene destroyed a binding site which was targeted by miR-181b-1-3p. The expression abundances of INHA mRNA increased firstly and then decreased with follicle growing, and reached the top in the sixth largest pre-ovulation follicle, whereas miR-181b-1-3p levels in chicken pre-hierarchical follicles had the contrary tendency. Further studies indicated that high levels of miR-181b-1-3p increased apoptosis and reduced GC proliferation while miR-181b-1-3p inhibitors decreased apoptosis and promoted GC proliferation. Additionally, depression of INHA increased apoptosis and reduced GC proliferation via a caspase-3-dependent mitochondrial pathway. Generally, the mutation in INHA 3'UTR was tightly correlated with egg production in chickens, and blocked a binding site of miR-181b-1-3p. miR-181b-1-3p inhibited GC proliferation and promoted apoptosis by targeting INHA.

Effects of dietary corticosterone on the central adenosine monophosphate-activated protein kinase (AMPK) signaling pathway in broiler chickens.

Glucocorticoids (GCs) induce the activation of the central adenosine 5'-monophosphate-activated protein kinase (AMPK) signaling pathway in birds. In this study, we aimed to investigate the effects of corticosterone (CORT) supplemented in diet on the central AMPK signaling pathway in broilers. The average daily gain was reduced by CORT treatment, and the average daily feed intake remained unchanged. Plasma glucose, triglyceride, total cholesterol, and CORT contents were increased by CORT administration. In addition, CORT treatment decreased the relative weights of heart, spleen, and bursa and increased the relative weights of liver and abdominal fat. The glycogen contents in the liver and breast muscle were higher in the chicks treated with CORT. CORT treatment upregulated the gene expression of mammalian target of rapamycin, glucocorticoid receptor, AMPKα2, neuropeptide Y(NPY), liver kinase B1 (LKB1), AMPKα1, and fatty acid synthase in the hypothalamus. Moreover, CORT treatment increased the protein levels of acetyl-coenzyme A carboxylase (ACC) phosphorylation and total AMPK and phosphorylated AMPK in the hypothalamus. Hence, CORT administration in the diet activated the LKB1-AMPK-NPY/ACC signaling pathway in the hypothalamus of broiler.

Adaptation of the master antioxidant response connects metabolism, lifespan and feather development pathways in birds

Birds (Aves) display high metabolic rates and oxygen consumption relative to mammals, increasing reactive oxygen species (ROS) formation. Although excess ROS reduces lifespan by causing extensive cellular dysfunction and damage, birds are remarkably long-lived. We address this paradox by identifying the constitutive activation of the NRF2 master antioxidant response in Neoaves (~95% of bird species), providing an adaptive mechanism capable of counterbalancing high ROS levels. We demonstrate that a KEAP1 mutation in the Neoavian ancestor disrupted the repression of NRF2 by KEAP1, leading to constitutive NRF2 activity and decreased oxidative stress in wild Neoaves tissues and cells. Our evidence suggests this ancient mutation induced a compensatory program in NRF2-target genes with functions beyond redox regulation—including feather development—while enabling significant metabolic rate increases that avoid trade-offs with lifespan. The strategy of NRF2 activation sought by intense clinical investigation therefore appears to have also unlocked a massively successful evolutionary trajectory.

Delay activity in the Wulst of pigeons (Columba livia) represents correlates of both sample and reward information.

The avian Wulst is the pallial (analogous to mammalian cortex) termination point of the thalamofugal pathway, one of two main visual pathways in birds, and is considered to be equivalent to primate striate cortex. We recorded neuronal activity from the Wulst in pigeons during two versions of a delayed matching-to-sample procedure. Two birds were trained on a common outcomes (CO) procedure, in which correct responses following both the skateboarder and the flower stimuli were associated with reward. Two other birds were trained on a differential outcomes (DO) procedure in which correct responses following only the skateboarder stimulus were associated with reward, while correct responses following the flower stimulus were not rewarded. In line with previous studies, under CO conditions, and for both excitatory and inhibitory neurons, delay activity in the Wulst was significantly different from baseline activity following both sample stimuli, which may indicate that Wulst delay activity is a neural correlate of working memory for the sample stimulus. On the other hand, under DO conditions, Wulst delay activity appeared to be a neural correlate of the upcoming reward. We argue that Wulst neurons display flexibility in their encoding in that they can encode both sample and reward information, but may default to one type of coding over the other based on the demands of the task. The current study provides the first evidence that delay activity in the Wulst represents both a neural correlate for sample information as well as reward information.

Simulation of the song motor pathway in birds: A single neuron initiates a chain of events that produces birdsong with realistic spectra properties.

Birdsong is a complex learned behavior regulated by Neuromuscular coordination of different muscle sets necessary for producing relevant sounds. We developed a heterogeneous and stochastically connected neural network representing the pathway from the high vocal center (HVC) to the robust nucleus of the arcopallium (RA) neurons that drive the muscles to generate sounds. We show that a single active neuron is sufficient to initiate a chain of spiking events that results to excite the entire network system. The network could synthesize realistic bird sounds spectra, with spontaneous generation of intermittent sound bursts typical of birdsong (song syllables). This study confirms experiments on animals and on humans, where results have shown that single neurons are responsible for the activation of complex behavior or are associated with high-level perception events.

Parrots have evolved a primate-like telencephalic-midbrain-cerebellar circuit

It is widely accepted that parrots show remarkable cognitive abilities. In mammals, the evolution of complex cognitive abilities is associated with increases in the size of the telencephalon and cerebellum as well as the pontine nuclei, which connect these two regions. Parrots have relatively large telencephalons that rival those of primates, but whether there are also evolutionary changes in their telencephalon-cerebellar relay nuclei is unknown. Like mammals, birds have two brainstem pontine nuclei that project to the cerebellum and receive projections from the telencephalon. Unlike mammals, birds also have a pretectal nucleus that connects the telencephalon with the cerebellum: the medial spiriform nucleus (SpM). We found that SpM, but not the pontine nuclei, is greatly enlarged in parrots and its relative size significantly correlated with the relative size of the telencephalon across all birds. This suggests that the telencephalon-SpM-cerebellar pathway of birds may play an analogous role to cortico-ponto-cerebellar pathways of mammals in controlling fine motor skills and complex cognitive processes. We conclude that SpM is key to understanding the role of telencephalon-cerebellar pathways in the evolution of complex cognitive abilities in birds.

Avian influenza.

Previous introductions of highly pathogenic avian influenza virus (HPAIV) to the EU were most likely via migratory wild birds. A mathematical model has been developed which indicated that virus amplification and spread may take place when wild bird populations of sufficient size within EU become infected. Low pathogenic avian influenza virus (LPAIV) may reach similar maximum prevalence levels in wild bird populations to HPAIV but the risk of LPAIV infection of a poultry holding was estimated to be lower than that of HPAIV. Only few non‐wild bird pathways were identified having a non‐negligible risk of AI introduction. The transmission rate between animals within a flock is assessed to be higher for HPAIV than LPAIV. In very few cases, it could be proven that HPAI outbreaks were caused by intrinsic mutation of LPAIV to HPAIV but current knowledge does not allow a prediction as to if, and when this could occur. In gallinaceous poultry, passive surveillance through notification of suspicious clinical signs/mortality was identified as the most effective method for early detection of HPAI outbreaks. For effective surveillance in anseriform poultry, passive surveillance through notification of suspicious clinical signs/mortality needs to be accompanied by serological surveillance and/or a virological surveillance programme of birds found dead (bucket sampling). Serosurveillance is unfit for early warning of LPAI outbreaks at the individual holding level but could be effective in tracing clusters of LPAIV‐infected holdings. In wild birds, passive surveillance is an appropriate method for HPAIV surveillance if the HPAIV infections are associated with mortality whereas active wild bird surveillance has a very low efficiency for detecting HPAIV. Experts estimated and emphasised the effect of implementing specific biosecurity measures on reducing the probability of AIV entering into a poultry holding. Human diligence is pivotal to select, implement and maintain specific, effective biosecurity measures.

The ascending projections of the nuclei of the descending trigeminal tract (nTTD) in the zebra finch (Taeniopygia guttata).

In our traditional view of the avian somatosensory system, input from the beak and head reaches the telencephalon via a disynaptic pathway, involving projections from the principal sensory nucleus (PrV) directly to nucleus basorostralis (previously called nucleus basalis), whereas input from the rest of the body follows a trisynatic pathway similar to that in mammals, involving projections from the dorsal column nuclei to the thalamus, and thence to somatosensory wulst. However, the role of the nuclei of the descending trigeminal tract (nTTD) in this scenario is unclear, partly because their ascending projections have been examined in only one species, the mallard duck. Here we examine the ascending projections of the nTTD in the zebra finch, using in vivo injections of biotinylated dextran amine and verification of projections by means of retrograde transport of the beta subunit of cholera toxin. The results show a high degree of interconnectivity within the nTTD, and that these nuclei project to PrV. We also find a projection from nTTD to the contralateral thalamic nucleus uvaeformis, a multi-sensory nucleus connected to the song system. Furthermore, our finding of a projection from nTTD to the contralateral somatosensory thalamic nucleus dorsalis intermedius ventralis anterior (DIVA) is consistent with the well-known projection in mammals from nTTD to the ventrobasal thalamus, suggesting that the ascending trigeminal pathways in birds and mammals are more similar than previously thought.

Resonances and Spectral Characteristics of a Neural Network for the Song Motor Pathway in Birds

Birdsong is a complex learned behavior regulated in an intricate way. Neuromuscular coordination of different muscular sets is necessary for producing high quality and consistent songs. We developed a realistic neural network that emulates neurons from the High Vocal centre (HVc) and the robust nucleus of the archistriatum (RA) neurons that drive the muscles to generate birdsong sounds. We used modern computational tools and neural architecture to simulate the entire motor pathway up to the physical oscillator muscle system and its spectral characteristics. Several network parameter dependences were analysed and elucidated. An optimal network size within 10 to 25 neurons within which minimal and smooth frequency variations occur, was found. Beyond that range we observe, instead, strong frequency dependence. Moreover, response frequency is influenced by the pathway input current; also in this case frequency response keeps smooth within a certain range of current, but shows interesting resonant values where negative peaks are observed. Resonant values are found in respect to the non-linear dissipation constant of the equation of motion for the bird's labial oscillation and also in respect of the network background noise level (stochastic resonance). This work demonstrate that is possible to achieve a realistic computational model for the motor pathway leading to generation of sounds in birds, which contributes to the understanding of its spectral and dynamical fundamental properties and characteristics.

Functional organization of telencephalic visual association fields in pigeons

Birds show remarkable visual abilities that surpass most of our visual psychophysiological abilities. In this study, we investigated visual associative areas of the tectofugal visual system in pigeons. Similar to the condition in mammals, ascending visual pathways in birds are subdivided into parallel form/color vs. motion streams at the thalamic and primary telencephalic level. However, we know practically nothing about the functional organization of those telencephalic areas that receive input from the primary visual telencephalic fields. The current study therefore had two objectives: first, to reveal whether these visual associative areas of the tectofugal system are activated during visual discrimination tasks; second, to test whether separated form/color vs. motion pathways can be discerned among these association fields. To this end, we trained pigeons to discriminate either form/color or motion stimuli and used the immediate early gene protein ZENK to capture the activity of the visual associative areas during the task. We could indeed identify several visual associative telencephalic structures by activity pattern changes during discriminations. However, none of these areas displayed a difference between form/color vs. motion sessions. The presence of such a distinction in thalamo-telencephalic, but not in further downstream visual association areas opens the possibility that these separate streams converge very early in birds, which possibly minimizes long-range connections due to the evolutionary pressure toward miniaturized brains.

Gene expression of ionotropic glutamate receptor subunits in the tectofugal pathway of the pigeon

The tectofugal pathway in birds consists of four stations, the retina, optic tectum, rotundal nucleus, and entopallium, and it conveys visual information via three ascending pathways. These pathways consist of retino-tectal, tecto-rotundal and rotundo-entopallial cells, all of which are glutamatergic. The present study examined the localization of ionotropic glutamate receptors (iGluRs) to identify the target areas of glutamatergic projections in the tectofugal pathway in pigeons. Nine subunits of iGluRs were analyzed using in situ hybridization as follows: AMPA receptors (GluA1, GluA2, GluA3, and GluA4), kainate receptors (GluK1, GluK2, and GluK4), and NMDA receptors (GluN1 and GluN2A). Hybridization signals of subunits showed various intensities in different cells. In the optic tectum, a strong to moderate expression was observed in layer 10 (GluA2, GluA3, GluK4, and GluN1) and layer 13 (GluA2, GluK4, GluN1, and GluN2A). The rotundal nucleus intensely expressed GluA3, GluA4, GluK1, and GluK4. In the entopallium, an intense to moderate expression of GluK1 and GluK4, and a moderate to weak expression of AMPA and NMDA receptors were observed. Furthermore, the parvocellular and magnocellular parts of the isthmic nuclei showed a strong expression of GluA2, GluA3, GluK4, and GluN1. The present findings demonstrate the expression of iGluRs in glutamatergic projection targets of the tectofugal pathway in birds and suggest a diversity of iGluRs in the transmission of visual information.

Epigenetics and the evolution of Darwin's Finches.

The prevailing theory for the molecular basis of evolution involves genetic mutations that ultimately generate the heritable phenotypic variation on which natural selection acts. However, epigenetic transgenerational inheritance of phenotypic variation may also play an important role in evolutionary change. A growing number of studies have demonstrated the presence of epigenetic inheritance in a variety of different organisms that can persist for hundreds of generations. The possibility that epigenetic changes can accumulate over longer periods of evolutionary time has seldom been tested empirically. This study was designed to compare epigenetic changes among several closely related species of Darwin’s finches, a well-known example of adaptive radiation. Erythrocyte DNA was obtained from five species of sympatric Darwin’s finches that vary in phylogenetic relatedness. Genome-wide alterations in genetic mutations using copy number variation (CNV) were compared with epigenetic alterations associated with differential DNA methylation regions (epimutations). Epimutations were more common than genetic CNV mutations among the five species; furthermore, the number of epimutations increased monotonically with phylogenetic distance. Interestingly, the number of genetic CNV mutations did not consistently increase with phylogenetic distance. The number, chromosomal locations, regional clustering, and lack of overlap of epimutations and genetic mutations suggest that epigenetic changes are distinct and that they correlate with the evolutionary history of Darwin’s finches. The potential functional significance of the epimutations was explored by comparing their locations on the genome to the location of evolutionarily important genes and cellular pathways in birds. Specific epimutations were associated with genes related to the bone morphogenic protein, toll receptor, and melanogenesis signaling pathways. Species-specific epimutations were significantly overrepresented in these pathways. As environmental factors are known to result in heritable changes in the epigenome, it is possible that epigenetic changes contribute to the molecular basis of the evolution of Darwin’s finches.

Mistletoebirds and xylose: Australian frugivores differ in their handling of dietary sugars.

Carbohydrate-rich mistletoe fruits are consumed by a wide range of avian species. Small birds absorb a large portion of water-soluble nutrients, such as glucose, via the paracellular pathway. d-xylose, a pentose monosaccharide, is abundant in some nectars and mistletoe fruits consumed by birds, and it has been suggested that it is most likely absorbed via the paracellular pathway in birds. We measured apparent assimilation efficiency ([Formula: see text]) and bioavailability (f) for d-xylose and d- and l-glucose in three frugivorous Australian bird species. Mistletoebirds, silvereyes, and singing honeyeaters showed significantly lower [Formula: see text] for d-xylose than for d-glucose. Across two diet sugar concentrations, silvereyes and singing honeyeaters significantly increased f of both l-glucose (a metabolically inert isomer of d-glucose commonly used to quantify paracellular uptake) and d-xylose on the more concentrated diet, probably because of increased gut processing time. By contrast, mistletoebirds (mistletoe fruit specialists) did not vary f of either sugar with diet concentration. Mistletoebirds also showed higher f for d-xylose than l-glucose and eliminated d-xylose more slowly than silvereyes and singing honeyeaters, demonstrating differences in the handling of dietary xylose between these species. Our results suggest that d-xylose may be absorbed by both mediated and nonmediated mechanisms in mistletoebirds.

Chicken IL-6 is a heat-shock gene

The febrile response is elicited by pyrogenic cytokines including IL-6 in response to microorganism infections and diseases in vertebrates. Mammalian HSF1, which senses elevations in temperature, negatively regulates the response by suppressing pyrogenic cytokine expression. We here showed that HSF3, an avian ortholog of mammalian HSF1, directly binds to and activates IL-6 during heat shock in chicken cells. Other components of the febrile response mechanism, such as IL-1β and ATF3, were also differently regulated in mammalian and chicken cells. These results suggest that the febrile response is exacerbated by a feed-forward circuit composed of the HSF3-IL-6 pathway in birds.

Capacity for Absorption of Water-Soluble Secondary Metabolites Greater in Birds than in Rodents

Plant secondary metabolites (SMs) are pervasive in animal foods and potentially influence feeding behavior, interspecies interactions, and the distribution and abundance of animals. Some of the major classes of naturally occurring SMs in plants include many water-soluble compounds in the molecular size range that could cross the intestinal epithelium via the paracellular space by diffusion or solvent drag. There are differences among species in paracellular permeability. Using Middle Eastern rodent and avian consumers of fruits containing SMs, we tested the hypothesis that avian species would have significantly higher paracellular permeability than rodent species. Permeability in intact animals was assessed using standard pharmacological methodology to measure absorption of two radiolabeled, inert, neutral water-soluble probes that do not interact with intestinal nutrient transporters, L-arabinose (Mr = 150.1 Da) and lactulose (Mr = 342.3 Da). We also measured absorption of labeled 3-O-methyl-D-glucose (3OMD-glucose; Mr = 194.2 Da), which is a nonmetabolized analogue of D-glucose that is passively absorbed through the paracellular space but also transported across the enterocyte membranes. Most glucose was absorbed by all species, but arabinose fractional absorption (f) was nearly three times higher in birds (1.03±0.17, n = 15 in two species) compared to rodents (0.37±0.06, n = 10 in two species) (P<0.001). Surprisingly, the apparent rates of absorption in birds of arabinose exceeded those of 3OMD-glucose. Our findings are in agreement with previous work showing that the paracellular pathway is more prominent in birds relative to nonflying mammals, and suggests that birds may be challenged by greater absorption of water-soluble, dietary SMs. The increased expression of the paracellular pathway in birds hints at a tradeoff: the free energy birds gain by absorbing water-soluble nutrients passively may be offset by the metabolic demands placed on them to eliminate concomitantly absorbed SMs.

Spiking models for level-invariant encoding

Levels of ecological sounds vary over several orders of magnitude, but the firing rate and membrane potential of a neuron are much more limited in range. In binaural neurons of the barn owl, tuning to interaural delays is independent of level differences. Yet a monaural neuron with a fixed threshold should fire earlier in response to louder sounds, which would disrupt the tuning of these neurons. How could spike timing be independent of input level? Here I derive theoretical conditions for a spiking model to be insensitive to input level. The key property is a dynamic change in spike threshold. I then show how level invariance can be physiologically implemented, with specific ionic channel properties. It appears that these ingredients are indeed present in monaural neurons of the sound localization pathway of birds and mammals.

The spatial tuning of achromatic and chromatic vision in budgerigars

Birds are assumed to use half of their cones (double cones) to detect fine spatial detail while their other half (single cones) is used for color vision. However, the spatial resolution of the color pathway in birds has never been studied. We determined the spatial contrast sensitivity to achromatic and isoluminant red-green and blue-green color gratings in budgerigars (Melopsittacus undulatus). Contrast sensitivity to achromatic gratings has band-pass characteristics while that for red-green and blue-green gratings has low-pass properties. Maximum sensitivity is lower to blue-green than to red-green gratings and the acuity for both color gratings is less than half (ca. 4.5 cycles/degree) of that for achromatic gratings (ca. 10 cycles/degree). This suggests that achromatic vision in birds, as in humans and bees, is tuned for detecting fine detail while chromatic vision is tuned for viewing larger fields. Similar to humans, blue-sensitive cones contribute little to spatial vision. Moreover, budgerigars detected gratings having both achromatic and chromatic contrasts more reliably at high spatial frequencies than gratings with either of these contrasts, suggesting that the single and double cone pathways are incompletely separated. The study demonstrates the importance of the spatial dimension of color vision; fine patterns remain unresolved even if they present large color contrasts.

Magnetoreception in an Avian Brain in Part Mediated by Inner Ear Lagena

Many animals use the Earth's geomagnetic field for orientation and navigation, but the neural mechanisms underlying that ability remain enigmatic. Support for at least two avian magnetoreceptors exists, including magnetically activated photochemicals in the retina and ferrimagnetic particles in the beak. The possibility of a third magnetoreceptor in the inner ear lagena organs has been suggested. The brain must process magnetic receptor information to derive constructs representing directional heading and geosurface location. Here, we used the c-Fos transcription factor, a marker for activated neurons, to discover where in the brain computations related to a specific set of magnetic field stimulations occur. We found that neural activations in discrete brain loci known to be involved in orientation, spatial memory, and navigation may constitute a major magnetoreception pathway in birds. We also found, through ablation studies, that much of the observed pathway appears to receive magnetic information from the pigeon lagena receptor organs.