Structural Rearrangements of Pigeon Cryptochrome 4 Undergoing a Complete Redox Cycle.

Cryptochrome is currently the major contender of a protein to underpin magnetoreception, the ability to sense the Earth's magnetic field. Among various types of cryptochromes, cryptochrome 4 has been identified as the likely magnetoreceptor in migratory birds. All-atom molecular dynamics (MD) studies have offered first insights into the structural dynamics of cryptochrome but are limited to a short time scale due to large computational demands. Here, we employ coarse-grained MD simulations to investigate the emergence of long-lived states and conformational changes in pigeon cryptochrome 4. Our coarse-grained simulations complete the picture by permitting observation on a significantly longer time scale. We observe conformational transitions in the phosphate-binding loop of pigeon cryptochrome 4 upon activation and identify prominent motions in residues 440-460, suggesting a possible role as a signaling state of the protein or as a gated interaction site for forming protein complexes that might facilitate downstream processes. The findings highlight the importance of considering longer time scales in studying cryptochrome dynamics and magnetoreception. Coarse-grained MD simulations offer a valuable tool to unravel the complex behavior of cryptochrome proteins and shed new light on the mechanisms underlying their role in magnetoreception. Further exploration of these conformational changes and their functional implications may contribute to a deeper understanding of the molecular mechanisms of magnetoreception in birds.

Parallel executive pallio-motor loops in the pigeon brain.

A core component of the avian pallial cognitive network is the multimodal nidopallium caudolaterale (NCL) that is considered to be analogous to the mammalian prefrontal cortex (PFC). The NCL plays a key role in a multitude of executive tasks such as working memory, decision-making during navigation, and extinction learning in complex learning environments. Like the PFC, the NCL is positioned at the transition from ascending sensory to descending motor systems. For the latter, it sends descending premotor projections to the intermediate arcopallium (AI) and the medial striatum (MSt). To gain detailed insight into the organization of these projections, we conducted several retrograde and anterograde tracing experiments. First, we tested whether NCL neurons projecting to AI (NCLarco neurons) and MSt (NCLMSt neurons) are constituted by a single neuronal population with bifurcating neurons, or whether they form two distinct populations. Here, we found two distinct projection patterns to both target areas that were associated with different morphologies. Second, we revealed a weak topographic projection toward the medial and lateral striatum and a strong topographic projection toward AI with clearly distinguishable sensory termination fields. Third, we investigated the relationship between the descending NCL pathways to the arcopallium with those from the hyperpallium apicale, which harbors a second major descending pathway of the avian pallium. We embed our findings within a system of parallel pallio-motor loops that carry information from separate sensory modalities to different subpallial systems. Our results also provide insights into the evolution of the avian motor system from which, possibly, the song system has emerged.

Investigating pigeon circovirus infection in a pigeon farm: molecular detection, phylogenetic analysis and complete genome analysis.

BACKGROUND: Pigeon circovirus infections in pigeons (Columba livia domestica) have been reported worldwide. Pigeons should be PiCV-free when utilized as qualified experimental animals. However, pigeons can be freely purchased as experimental animals without any clear guidelines to follow. Herein, we investigated the status quo of PiCV infections on a pigeon farm in Beijing, China, which provides pigeons for experimental use. RESULTS: PiCV infection was verified in at least three types of tissues in all forty pigeons tested. A total of 29 full-length genomes were obtained and deposited in GenBank. The whole genome sequence comparison among the 29 identified PiCV strains revealed nucleotide homologies of 85.8-100%, and these sequences exhibited nucleotide homologies of 82.7-98.9% as compared with those of the reference sequences. The cap gene displayed genetic diversity, with a wide range of amino acid homologies ranging from 64.5% to 100%. Phylogenetic analysis of the 29 full-genome sequences revealed that the PiCV strains in this study could be further divided into four clades: A (17.2%), B (10.4%), C (37.9%) and D (34.5%). Thirteen recombination events were also detected in 18 out of the 29 PiCV genomes obtained in this study. Phylogenetic research using the rep and cap genes verified the recombination events, which occurred between clades A/F, A/B, C/D, and B/D among the 18 PiCV strains studied. CONCLUSIONS: In conclusion, PiCV infection, which is highly genetically varied, is extremely widespread on pigeon farms in Beijing. These findings indicate that if pigeons are to be used as experimental animals, it is necessary to evaluate the impact of PiCV infection on the results.

First report of the morphological and molecular characterization of Pseudolynchia canariensis (Diptera: Hippoboscidae) from Al-Baha region, Saudi Arabia.

This study aims to study the morphological and molecular characterization of (Pseudolynchia canariensis; Macquart, 1839)in the Al-Baha region of Saudi Arabia. Ninety-four pigeons were obtained from traditional pigeon breeding farms of the Al-Baha region, and fly samples were collected. Taxonomic keys were used to define the morphology of flies, whereas molecular characteristics were identified based on cytochrome c oxidase subunit 1. The rate of Pseudolynchia canariensis infestation in the examined pigeons was 44.5%. The genetic sequences of the fly samples were deposited in GenBank (accession number OQ073507). The match rate between the fly samples from the present study and those previously recorded in GenBank (accession numbers: EF531220, OM073981, and MW853922) displayed 99.66%. This study demonstrates that Pseudolynchia canariensis is common in the Al-Baha region; thus, further studies are required to detect other species from the same genus and their geographical distribution.

On the value of advanced information about delayed rewards.

In a variety of laboratory preparations, several animal species prefer signaled over unsignaled outcomes. Here we examine whether pigeons prefer options that signal the delay to reward over options that do not and how this preference changes with the ratio of the delays. We offered pigeons repeated choices between two alternatives leading to a short or a long delay to reward. For one alternative (informative), the short and long delays were reliably signaled by different stimuli (e.g., SS for short delays, SL for long delays). For the other (non-informative), the delays were not reliably signaled by the stimuli presented (S1 and S2). Across conditions, we varied the durations of the short and long delays, hence their ratio, while keeping the average delay to reward constant. Pigeons preferred the informative over the non-informative option and this preference became stronger as the ratio of the long to the short delay increased. A modified version of the Δ-Σ hypothesis (González et al., J Exp Anal Behav 113(3):591-608. https://doi.org/10.1002/jeab.595 , 2020a) incorporating a contrast-like process between the immediacies to reward signaled by each stimulus accounted well for our findings. Functionally, we argue that a preference for signaled delays hinges on the potential instrumental advantage typically conveyed by information.

Age-related reductions in whole brain mass and telencephalon volume in very old white Carneau pigeons (Columba livia).

While studies have identified age-related cognitive impairment in pigeons (Columba livia), no study has detected the brain atrophy which typically accompanies cognitive impairment in older mammals. Instead, Coppola and Bingman (Aging is associated with larger brain mass and volume in homing pigeons (Columba livia), Neurosci. Letters 698 (2019) 39-43) reported increased whole brain mass and telencephalon volume in older, compared to younger, homing pigeons. One reason for this unexpected finding might be that the older pigeons studied were not old enough to display age-related brain atrophy. Therefore, the current study repeated Coppola and Bingman, but with a sample of older white Carneau pigeons that were on average 5.34 years older. Brains from young and old homing pigeons were weighed and orthogonal measurements of the telencephalon, cerebellum, and optic tectum were obtained. Despite having a heavier body mass than younger pigeons, older pigeons had a significant reduction in whole brain mass and telencephalon volume, but not cerebellum or optic tectum volume. This study is therefore the first to find that pigeons experience age-related brain atrophy.

The role of lateral hypothalamic nucleus in mediating locomotive behaviors in pigeons (Columba livia).

The lateral hypothalamic nucleus (LHy) is located in the dorsolateral hypothalamus of birds, and it is essential to many life processes. However, limited information is available about the role of LHy in mediating locomotive behaviors. In this work, we investigated the structure and function of LHy in pigeons (Columba livia) by Nissl staining, immunohistochemical (IHC) staining, insituhybridization (ISH) staining and constant current stimulation methods. The results showed that LHy appears crescent in shape, and three-dimensional coordinate value range of LHy is: A: 5.0-8.0 mm, L: 0.7-1.2 mm, D: 9.5-10.3 mm. The dopaminergic neurons in LHy were distributed in small amount and concentrated manner, while the glutamatergic neurons were distributed in a large number and uniform manner. The distribution of the above two neurons at each coronal level showed a significant positive correlation (R2 = 0.7516, P < 0.001). Our work demonstrated that LHy mainly mediates forward movement (P < 0.01) and ipsilateral lateral movement (P < 0.001), and these movements were significantly effected by electrical stimulation intensity. Our results showed that LHy can mediate the generation of directional behavior and this will provide technical support for the study of locomotor behavior regulation in birds.

Turbulence causes kinematic and behavioural adjustments in a flapping flier.

Turbulence is a widespread phenomenon in the natural world, but its influence on flapping fliers remains little studied. We assessed how freestream turbulence affected the kinematics, flight effort and track properties of homing pigeons (Columba livia), using the fine-scale variations in flight height as a proxy for turbulence levels. Birds showed a small increase in their wingbeat amplitude with increasing turbulence (similar to laboratory studies), but this was accompanied by a reduction in mean wingbeat frequency, such that their flapping wing speed remained the same. Mean kinematic responses to turbulence may therefore enable birds to increase their stability without a reduction in propulsive efficiency. Nonetheless, the most marked response to turbulence was an increase in the variability of wingbeat frequency and amplitude. These stroke-to-stroke changes in kinematics provide instantaneous compensation for turbulence. They will also increase flight costs. Yet pigeons only made small adjustments to their flight altitude, likely resulting in little change in exposure to strong convective turbulence. Responses to turbulence were therefore distinct from responses to wind, with the costs of high turbulence being levied through an increase in the variability of their kinematics and airspeed. This highlights the value of investigating the variability in flight parameters in free-living animals.

Flying fast improves aerodynamic economy of heavier birds.

A paradox of avian long-distance migrations is that birds must greatly increase their body mass prior to departure, yet this is presumed to substantially increase their energy cost of flight. However, here we show that when homing pigeons flying in a flock are loaded with ventrally located weight, both their heart rate and estimated energy expenditure rise by a remarkably small amount. The net effect is that costs per unit time increase only slightly and per unit mass they decrease. We suggest that this is because these homing flights are relatively fast, and consequently flight costs associated with increases in body parasite drag dominate over those of weight support, leading to an improvement in mass-specific flight economy. We propose that the relatively small absolute aerodynamic penalty for carrying enlarged fuel stores and flight muscles during fast flight has helped to select for the evolution of long-distance migration.

Genetic diversity of Cryptosporidium spp., Encephalitozoon spp. and Enterocytozoon bieneusi in feral and captive pigeons in Central Europe.

Cryptosporidium spp., Enterocytozoon bieneusi and Encephalitozoon spp. are the most common protistan parasites of vertebrates. The results show that pigeon populations in Central Europe are parasitised by different species of Cryptosporidium and genotypes of microsporidia of the genera Enterocytozoon and Encephalitozoon. A total of 634 and 306 faecal samples of captive and feral pigeons (Columba livia f. domestica) from 44 locations in the Czech Republic, Slovakia and Poland were analysed for the presence of parasites by microscopy and PCR/sequence analysis of small subunit ribosomal RNA (18S rDNA), 60 kDa glycoprotein (gp60) and internal transcribed spacer (ITS) of SSU rDNA. Phylogenetic analyses revealed the presence of C. meleagridis, C. baileyi, C. parvum, C. andersoni, C. muris, C. galli and C. ornithophilus, E. hellem genotype 1A and 2B, E. cuniculi genotype I and II and E. bieneusi genotype Peru 6, CHN-F1, D, Peru 8, Type IV, ZY37, E, CHN4, SCF2 and WR4. Captive pigeons were significantly more frequently parasitised with screened parasite than feral pigeons. Cryptosporidium meleagridis IIIa and a new subtype IIIl have been described, the oocysts of which are not infectious to immunodeficient mice, whereas chickens are susceptible. This investigation demonstrates that pigeons can be hosts to numerous species, genotypes and subtypes of the studied parasites. Consequently, they represent a potential source of infection for both livestock and humans.

GPS tracking technology and re-visiting the relationship between the avian visual Wulst and homing pigeon navigation.

Within their familiar areas homing pigeons rely on familiar visual landscape features and landmarks for homing. However, the neural basis of visual landmark-based navigation has been so far investigated mainly in relation to the role of the hippocampal formation. The avian visual Wulst is the telencephalic projection field of the thalamofugal pathway that has been suggested to be involved in processing lateral visual inputs that originate from the far visual field. The Wulst is therefore a good candidate for a neural structure participating in the visual control of familiar visual landmark-based navigation. We repeatedly released and tracked Wulst-lesioned and control homing pigeons from three sites about 10-15 km from the loft. Wulst lesions did not impair the ability of the pigeons to orient homeward during the first release from each of the three sites nor to localise the loft within the home area. In addition, Wulst-lesioned pigeons displayed unimpaired route fidelity acquisition to a repeated homing path compared to the intact birds. However, compared to control birds, Wulst-lesioned pigeons displayed persistent oscillatory flight patterns across releases, diminished attention to linear (leading lines) landscape features, such as roads and wood edges, and less direct flight paths within the home area. Differences and similarities between the effects of Wulst and hippocampal lesions suggest that although the visual Wulst does not seem to play a direct role in the memory representation of a landscape-landmark map, it does seem to participate in influencing the perceptual construction of such a map.

In vitro anti-Trichomonas gallinae effects of Ziziphus vulgaris L. and Camellia sinensis (L.) Kuntze extracts.

BACKGROUND: Trichomonas gallinae is a parasite that causes canker and severe loss and death, especially in young pigeons. Metronidazole (MTZ) is the recommended drug for treating avian trichomoniasis. Due to drug resistance, non-chemical alternatives, such as medicinal plant extracts, are also considered possible therapies for this disease. OBJECTIVES: This study compares the antitrichomonal effects of MTZ with extracts of Camellia sinensis and Ziziphus vulgaris on T. gallinae in vitro. METHODS: Samples of T. gallinae were taken from infected pigeons. Multi-well plates with different concentrations (5, 10, 25, 50 and 100 µg/mL) of plant extracts were used for the in vitro study. RESULTS: The minimum inhibitory concentration (MIC) of C. sinensis extract was 25 µg/mL over 24 h, compared to 50 µg/mL for MTZ. The MIC value of the Z. vulgaris extracts was 50 µg/mL. CONCLUSIONS: The results suggest that the extracts of Z. vulgaris and C. sinensis, as potential natural agents, could have anti-avian trichomoniasis properties. This study also shows that MTZ, C. sinensis and Z. vulgaris are equally effective in preventing the growth of T. gallinae trophozoites in the culture.

Prevalence and molecular characterization of Trichomonas gallinae from pigeons in Anhui, China.

Trichomonas gallinae, a protozoan parasite causing avian trichomonosis, exhibits a widespread global prevalence. It primarily affects the upper digestive tract of birds and has resulted in significant ecological problems worldwide. This study aimed to investigate the prevalence and genotypes of T. gallinae in Anhui Province, China. A total of 1612 oropharyngeal swab samples were collected from pigeon farms in Anhui Province to determine the prevalence of T. gallinae infection. The results revealed 565 (35.1%) positive samples of T. gallinae. Significant differences in infection rates were observed among different regions and age groups. Furthermore, the ITS1/5.8 S/ITS2 region was amplified, sequenced, and subjected to phylogenetic analysis. Genotypes A and B of T. gallinae were identified, and genotype B was the dominant genotype in Anhui Province. This is the first report on the prevalence and molecular characterization of T. gallinae in Anhui Province, China. Additionally, we integrated reports on the prevalence and genotype of T. gallinae in relevant provinces in China.

A GPS assisted translocation experiment to study the homing behavior of red deer.

Many animals return to their home areas (i.e., 'homing') after translocation to sites further away. Such translocations have traditionally been used in behavioral ecology to understand the orientation and migration behavior of animals. The movement itself can then be followed by marking and recapturing animals or by tracking, for example, using GPS systems. Most detailed studies investigating this behavior have been conducted in smaller vertebrates (e.g., birds, amphibians, and mice), whereas information on larger mammals, such as red deer, is sparse. We conducted GPS-assisted translocation experiments with red deer at two sites in the Czech Republic. Individuals were translocated over a distance of approximately 11 km and their home journey was tracked. Circular statistics were used to test for significant homeward orientation at distances of 100, 500, 1000, and 5000 m from the release site. In addition, we applied Lavielle trajectory segmentation to identify the different phases of homing behavior. Thirty-one out of 35 translocations resulted in successful homing, with a median time of 4.75 days (range 1.23-100 days). Animals were significantly oriented towards home immediately after release and again when they came closer to home; however, they did not show a significant orientation at the distances in between. We were able to identify three homing phases, an initial 'exploratory phase', followed by a 'homing phase' which sometimes was again followed by an 'arrival phase'. The 'homing phase' was characterized by the straightest paths and fastest movements. However, the variation between translocation events was considerable. We showed good homing abilities of red deer after translocation. Our results demonstrate the feasibility of conducting experiments with environmental manipulations (e.g., to impede the use of sensory cues) close to the release site. The homing behavior of red deer is comparable to that of other species, and might represent general homing behavior patterns in animals. Follow-up studies should further dissect and investigate the drivers of the individual variations observed and try to identify the sensory cues used during homing.

Landmarks, beacons, or panoramic views: What do pigeons attend to for guidance in familiar environments?

Birds and social insects represent excellent systems for understanding visually guided navigation. Both animal groups use surrounding visual cues for homing and foraging. Ants extract sufficient spatial information from panoramic views, which naturally embed all near and far spatial information, for successful homing. Although egocentric panoramic views allow for parsimonious explanations of navigational behaviors, this potential source of spatial information has been mostly neglected during studies of vertebrates. Here we investigate how distinct landmarks, a beacon, and panoramic views influence the reorientation behavior in pigeons (Columba livia). Pigeons were trained to search for a location characterized by a beacon and several distinct landmarks. Transformation tests manipulated aspects of the landmark configuration, allowing for a dissociation among navigational strategies. Quantitative image and path analyses provided support that the panoramic view was used by the pigeons. Although the results from some individuals support the use of beaconing, overall the pigeons relied predominantly on the panoramic view when spatial cues provided conflicting information regarding the goal location. Reorientation based on vector and bearing information derived from distinct landmarks as well as environmental geometry failed to account fully for the results. Thus, the results of our study support that pigeons can use panoramic views for reorientation in familiar environments. Given that the current model for landmark use by pigeons posits the use of different vectors from an object, a global panorama-matching strategy suggests a fundamental change in the theory of how pigeons use surrounding visual cues for localization.

Serological survey reveals enzootic circulation of St. Louis encephalitis and West Nile viruses in semiarid Monte ecosystem of Argentina.

St. Louis encephalitis virus (SLEV) and West Nile virus (WNV) are arboviruses transmitted by Culex mosquitoes and amplified in avian hosts. The present study aimed to investigate the presence and seasonal circulation of SLEV and WNV in La Rioja province, within the semiarid ecoregion of the Monte, Argentina. Over a two-year period, avian sera were collected and tested for neutralizing antibodies against SLEV and WNV. Our results reveal the enzootic activity of both viruses in this challenging environment. SLEV seroprevalence was 4.5% (35/778), with higher activity in spring (2016) and autumn (2017). WNV seroprevalence was 3.5% (27/778), peaking during the summer 2016-2017. Greater seroprevalence for SLEV in 2016 was detected for the Lark-like Brushrunner (Coryphistera alaudina) and the Short-billed Canastero (Asthenes baeri) and in 2017 for the Black-crested Finch (Lophospingus pusillus) and Lark-like Brushrunner, whereas for WNV greater seroprevalence in 2016 was detected for the Picui Ground Dove (Columbina picui) and in 2017 for the Lark-like Brushrunner and Band-tailed Seedeater (Catamenia analis). Additionally, five avian individuals experienced seroconversion during the sampling period, namely the Lark-like Brushrunner and White-fronted Woodpecker (Melanerpes cactorum) for SLEV, and the Lark-like Brushrunner, Greater Wagtail Tyrant (Stigmatura budytoides) and Many-colored Chaco Finch (Saltatricula multicolor) for WNV. The study highlights the persistence and circulation of these viruses in a semiarid ecosystem, raising questions about overwintering mechanisms and transmission dynamics. This research contributes to understanding arbovirus ecology in diverse environments. Further investigations are needed to assess the specific mechanisms facilitating virus persistence in the Monte ecoregion.

Small deviations in kinematics and body form dictate muscle performances in the finely tuned avian downstroke.

Avian takeoff requires peak pectoralis muscle power to generate sufficient aerodynamic force during the downstroke. Subsequently, the much smaller supracoracoideus recovers the wing during the upstroke. How the pectoralis work loop is tuned to power flight is unclear. We integrate wingbeat-resolved muscle, kinematic, and aerodynamic recordings in vivo with a new mathematical model to disentangle how the pectoralis muscle overcomes wing inertia and generates aerodynamic force during takeoff in doves. Doves reduce the angle of attack of their wing mid-downstroke to efficiently generate aerodynamic force, resulting in an aerodynamic power dip, that allows transferring excess pectoralis power into tensioning the supracoracoideus tendon to assist the upstroke-improving the pectoralis work loop efficiency simultaneously. Integrating extant bird data, our model shows how the pectoralis of birds with faster wingtip speed need to generate proportionally more power. Finally, birds with disproportionally larger wing inertia need to activate the pectoralis earlier to tune their downstroke.

Acute metformin induces hyperglycemia in healthy adult mourning doves, Zenaida macroura.

Birds have the highest blood glucose among vertebrates. Several mechanisms may explain this including the lack of a functional insulin-responsive glucose transport protein, high glucagon concentrations, and reliance on lipid oxidation resulting in the production of gluconeogenic precursors. The hypothesis was that interruption of gluconeogenesis using the diabetes medication metformin would lower glucose concentrations in wild-caught birds. We captured two cohorts of adult mourning doves, Zenaida macroura, and acclimated them to captivity for two weeks. In this crossover study, cohort 1 was administered a single dose of one of the following oral treatments each week: metformin (150 or 300 mg/kg), glycogenolysis inhibitor (2.5 mg/kg 1,4-dideoxy-1,4-imino-D-arabinitol (DAB)), or water (50 µL). Whole blood glucose was measured using a glucometer at baseline, 30, 60, and 120 min following the oral doses. In contrast to mammals and chickens, 300 mg/kg metformin did not alter blood glucose (p > 0.05) whereas 150 mg/kg metformin increased blood glucose compared to water (p = 0.043). To examine whether 150 mg/kg metformin stimulated glycogenolysis, we co-administered 150 mg/kg metformin and 2.5 mg/kg DAB, which prevented the hyperglycemic response. Cohort 2 was administered the same treatments and the early response was examined (0, 5, 10, 15 min). Low-dose metformin increased blood glucose within 5 min (p = 0.039) whereas the high dose had no effect. DAB did not prevent the early response to metformin nor did it alter blood glucose concentrations when administered alone (p = 0.887). In conclusion, metformin increases endogenous blood glucose via glycogenolysis in healthy adult male mourning doves.

Long-term, high-resolution in vivo calcium imaging in pigeons.

In vivo 2-photon calcium imaging has led to fundamental advances in our understanding of sensory circuits in mammalian species. In contrast, few studies have exploited this methodology in birds, with investigators primarily relying on histological and electrophysiological techniques. Here, we report the development of in vivo 2-photon calcium imaging in awake pigeons. We show that the genetically encoded calcium indicator GCaMP6s, delivered by the adeno-associated virus rAAV2/7, allows high-quality, stable, and long-term imaging of neuronal populations at single-cell and single-dendrite resolution in the pigeon forebrain. We demonstrate the utility of our setup by investigating the processing of colors in the visual Wulst, the avian homolog of the visual cortex. We report that neurons in the Wulst are color selective and display diverse response profiles to light of different wavelengths. This technology provides a powerful tool to decipher the operating principles that underlie sensory encoding in birds.

Effects of different stocking densities on the development of reproductive and immune functions in young breeder pigeons during the rearing period.

1. Stocking density (SD) is closely related to animal performance. This experiment was designed to evaluate the development of reproductive and immune functions of young pigeons under different SDs.2. A total of 288 (half male and half female) 40-day-old pigeons (body weight 400 ± 15 g) were allocated into four groups: High stocking density (HSD; 0.308 m3/bird), standard stocking density (SD; 0.616 m3/bird), and low stocking density (LSD; 1.232 m3/bird) and a caged (control; 0.04125 m3/bird). Every group had six replicates of the same sex.3. The results showed that caged male pigeons had the highest testis index, testosterone content, and gene expression of the androgen receptor gene. LSD treatment induced the highest concentrations of oestradiol, progesterone and mRNA levels of reproductive hormone receptor genes in female pigeons. In male pigeons, the spleen index (organ weight calculated as a percentage of total body weight) showed a peak level (0.09 ± 0.020) in the LSD group, and the thymus index peaked (0.23 ± 0.039) in SD group. However, the index for ovary, spleen, thymus and bursa of Fabricius in female pigeons showed no significant changes among different groups.4. The IL-1ß, IL-8, IFN-γ, TGF-ß and toll-like receptor 2 (TLR-2) mRNA levels reached their maximum values in both male and female pigeon spleens in the LSD group.5. Young male pigeons housed in cages showed increased testicular development while low stocking density increased the development of reproductive function in young female pigeons. A larger activity space could help enhance the immune function of both male and female pigeons.