Sources of variation for nutritional condition indices of the plasma of migratory lesser kestrels in the breeding grounds

Although published information on reference values for biochemical parameters in birds of prey has increased during the last years, little is known on their sources of variation. We used an insectivorous and small migratory raptor species, the lesser kestrel Falco naumanni, as a model. We looked for sources of variation of nutritional biochemical parameters (i.e. triglycerides, cholesterol, uric acid and urea) of both nestlings and adults. Reference values indicated that, as a rule, lesser kestrel showed more elevated triglycerides, urea and uric acid levels than other raptors. All analyzed factors except gender (i.e. year, colony, sampling time, presence/absence of a geolocator, body mass, laying date and capture date) reached significance for at least one biochemical parameter. In the morning, we found an important postprandial increase in the concentration of all biochemical parameters in nestlings, and uric acid and urea levels in adults. A positive relationship was detected between triglycerides and body mass in nestlings and adults. Although we did not find differences between blood biochemical parameters of the oldest and youngest chick of each brood, we found that cholesterol levels were lower in nestlings from larger broods. Coloration of tarsi (measured as brightness) was related to triglycerides and urea levels of nestlings and adults, respectively. The feeding habits of lesser kestrel probably explain the different levels and patterns of variation of metabolites in comparison to more carnivorous raptors eating mammals or birds.     

Effects of T-cell-mediated immune response on avian oxidative stress

We evaluated the oxidative cost paid by birds when coping with an immune challenge. We used the phytohaemagglutinin skin test (PHA) to assess the effects of the T-cell-mediated immune response on the concentration of reactive oxygen metabolites (ROMs), total antioxidant barrier (OXY) and total serum carotenoid concentration in wild nestlings of the Eurasian kestrel (Falco tinnunculus). Immunostimulation caused increased levels of ROMs, decreased OXY and increased circulating levels of carotenoids. These results suggest that an immune challenge can increase avian oxidative stress, and that carotenoids were remobilised from other tissues likely because their circulating levels were not sufficiently high to sustain an effective immune response.     

Isolation and characterization of polymorphic microsatellite markers in lesser kestrel (Falco naumanni) and cross-amplification in common kestrel (Falco tinnunculus)

Lesser kestrel, Falco naumanni, is a colonial and migratory species breeding in part of the Mediterranean Basin and part of central Asia and north-east of China and Mongolia. This species is catalogued in IUCN red list category as vulnerable. Twenty microsatellite loci were selected from libraries enriched in AC or AG tandem repeats and specific PCR were devised from their flanking sequences. Most microsatellites (14) were found polymorphic among 30 individuals of F. naumanni representing 20 reproduction areas of the species in the region of Extremadura, Spain. Polymorphisms were detected by size variation of the amplified loci, which allele number and observed heterozygosity ranged from 3 to 20 and from 0.300 to 0.933, respectively. Cross-species amplification showed that 13 of selected loci were also found polymorphic in common kestrel species (Falco tinnunculus). Novel polymorphic microsatellites will serve to conservation studies in lesser kestrel.     

Did organochlorine pesticide use cause declines in Mauritian forest birds?

We examine the hypothesis that organochlorine pesticide use in the 1950s and 1960s caused population declines and local extinctions in two endemic Mauritian birds, the Mauritius kestrel, Falco punctatus, and Mauritius cuckoo-shrike, Coracina typica. This hypothesis was suggested in the 1980s but is dismissed by authorities in Mauritius. The declines and subsequent increases in the populations and range areas of both species, the timing and location of the use of organochlorines for malaria control and in food crop production, the diets of the species, and the known mechanisms for transfer of organochlorine residues into organisms are all consistent with the hypothesis. No alternative explanation can at present account for these population changes. Organochlorine pesticide use cannot therefore be rejected as a reason for the declines and local extinctions of the kestrel and cuckoo-shrike.     

Patterns of serum carotenoid accumulation and skin colour variation in kestrel nestlings in relation to breeding conditions and different terms of carotenoid supplementation

Carotenoids are pigments synthesised by autotrophic organisms. For nestlings of raptorial species, which obtain carotenoids from the consumption of other heterotrophic species, the access to these pigments can be crucial. Carotenoids, indeed, have fundamental health maintenance functions, especially important in developing individuals as nestling kestrels. The aim of this study was to investigate how body carotenoid levels and skin pigmentation vary in kestrel nestlings (Falco tinnunculus) in relation to nesting parameters. Furthermore, we experimentally altered carotenoid availability (short- medium- and long-term) for nestlings and investigated skin and serum variance. The skin colour variance of 151 nestlings was explained by nest of origin, age and by the body condition (body mass corrected by age), older nestlings with higher body condition being redder. No difference in skin colour was detected between sexes. Differences in hue (skin “redness”) between treatments did not emerge during the first week, but did occur 15 days after administration between long-term supplemented and control chicks. In contrast, the serum carotenoid concentration showed a treatment-dependent increase after 5 days from the first carotenoid administration and at least after two supplemented feedings. In general, hue but not serum carotenoids, was correlated with the body condition of nestlings. Based on the increased skin pigmentation of nestling kestrels in the long-term experimental group, we suggest carotenoid availability to be limited for colour expression. The small increase of serum carotenoids due to supplementation is consistent with the hypothesis that there is a physiological constraint on these pigments, as well as an environmental limitation. The presented results are useful for the understanding of carotenoid uptake and accumulation by a wild raptorial species, located at the top of the food web, highlighting that carotenoids are a limited resource for kestrel nestlings.     

Retracted: MHC diversity and differential exposure to pathogens in kestrels (Aves: Falconidae)

Pathogen diversity is thought to drive major histocompatibility complex (MHC) polymorphism given that host’s immune repertories are dependent on antigen recognition capabilities. Here, we surveyed an extensive community of pathogens (n = 35 taxa) and MHC diversity in mainland versus island subspecies of the Eurasian kestrel Falco tinnunculus and in a sympatric mainland population of the phylogenetically related lesser kestrel Falco naumanni. Insular subspecies are commonly exposed to impoverished pathogen communities whilst different species’ ecologies and contrasting life‐history traits may lead to different levels of pathogen exposure. Although specific host traits may explain differential particular infections, overall pathogen diversity, richness and prevalence were higher in the truly cosmopolitan, euriphagous and long‐distance disperser Eurasian kestrel than in the estenophagous, steppe‐specialist, philopatric but long‐distance migratory lesser kestrel. Accordingly, the continental population of Eurasian kestrels displayed a higher number (64 vs. 49) as well as more divergent alleles at both MHC class I and class II loci. Detailed analyses of amino acid diversity revealed that significant differences between both species were exclusive to those functionally important codons comprising the antigen binding sites. The lowest pathogen burdens and the smallest but still quite divergent set of MHC alleles (n = 16) were found in island Eurasian kestrels, where the rates of allele fixation at MHC loci seem to have occurred faster than at neutral markers. The results presented in this study would therefore support the role of pathogen diversity and abundance in shaping patterns of genetic variation at evolutionary relevant MHC genes.     

Correlates of oxidative stress in wild kestrel nestlings (Falco tinnunculus)

The fitness of an organism can be affected by conditions experienced during early development. In light of the impact that oxidative stress can have on the health and ageing of a bird species, this study evaluated factors accounting for the variation in oxidative stress levels in nestlings of the Eurasian kestrel (Falco tinnunculus) by measuring the serum concentration of reactive oxygen metabolites and the serum antioxidant barrier against hypochlorite-induced oxidation. The ratio between these two variables was considered as an index of oxidative stress, with higher values meaning higher oxidative damage. Six-chick broods showed the highest level of oxidative stress, while no effect of sex was found. Age showed an inverse relationship with the oxidants and the levels of oxidative stress, with younger birds having higher levels. Hatching date, body condition, body mass and carotenoid concentration did not show any relationship with oxidants, antioxidants or degree of oxidative stress. These findings suggest that intrabrood sibling competition could play a role in determining oxidative stress, and that in carnivorous birds other antioxidant molecules could be more important than carotenoids to reduce oxidative stress.     

Size-biased allocation of prey from male to offspring via female: family conflicts, prey selection, and evolution of sexual size dimorphism in raptors

In birds with bi-parental care, the provisioning link between prey capture and delivery to dependent offspring is regarded as often symmetric between the mates. However, in raptors, the larger female usually broods and feeds the nestlings, while the smaller male provides food for the family, assisted by the female in the latter part of the nestling period, if at all. Prey items are relatively large and often impossible for nestlings to handle without extended maternal assistance. We video-recorded prey delivery and handling in nests of a raptor with a wide diet, the Eurasian kestrel Falco tinnunculus, and simultaneously observed prey transfer from male to female outside the nest. The male selectively allocated larger items, in particular birds and larger mammals, to the female for further processing and feeding of nestlings, and smaller items, in particular lizards and smaller mammals, directly to the nestlings for unassisted feeding. Hence, from the video, the female appeared to have captured larger prey than the male, while in reality no difference existed. The female’s size-biased interception of the male’s prey provisioning line would maximize the male’s foraging time, and maximize the female’s control of the allocation of food between her own need and that of the offspring. The male would maximize his control of food allocation by capturing smaller prey. This conflict would select for larger dominant females and smaller energy-efficient males, and induce stronger selection the longer the female depends on the male for self-feeding, as a proportion of the offspring dependence period.     

Interaction between components of the type III secretion system of Chlamydiaceae

Members of the family Chlamydiaceae possess at least 13 genes, distributed throughout the chromosome, that are homologous with genes of known type III secretion systems (TTS). The aim of this study was to use putative TTS proteins of Chlamydophila pneumoniae, whose equivalents in other bacterial TTS function as chaperones, to identify interactions between chlamydial proteins. Using the BacterioMatch Two-Hybrid Vector system (Stratagene, La Jolla, Calif.), lcrH-2 and sycE, positions 1021 and 0325, respectively, from C. pneumoniae CM-1 were used as "bait" to identify target genes (positions 0324, 0705, 0708, 0808 to 0810, 1016 to 1020, and 1022) in close proximity on the chromosome. Interaction between the products of the lcrH-2 (1021) and lcrE (copN) (0324) genes was detected and confirmed by pull-down experiments and enzyme immunoassays using recombinant LcrH-2 and LcrE. As further confirmation of this interaction, the homologous genes from Chlamydia trachomatis, serovar E, and Chlamydophila psittaci, Texas turkey, were also cloned in the two-hybrid system to determine if LcrH-2 and LcrE would interact with their orthologs in other species. Consistent with their genetic relatedness, LcrH-2 from C. pneumoniae interacted with LcrE produced from the three species of Chlamydiaceae; LcrH-2 from C. psittaci reacted with LcrE from C. pneumoniae but not from C. trachomatis; and C. trachomatis LcrH-2 did not react with LcrE from the other two species. Deletions from the N and C termini of LcrE from C. pneumoniae identified the 50 C-terminal amino acids as essential for the interaction with LcrH-2. Thus, it appears that in the Chlamydiaceae TTS, LcrH-2 interacts with LcrE, and therefore it may serve as a chaperone for this protein.     

Are predatory birds effective secondary seed dispersers?

We have studied the unusual phenomenon of secondary seed dispersal of Lycium intricatum seeds on a small oceanic Atlantic island (Alegranza, Canarian Archipelago) in which a small frugivorous lizard ( Gallotia atlantica ) and two different predatory birds participate, a shrike ( Lanius excubitor ) and a kestrel ( Falco tinnunculus ). Endemic lizards that are common prey of both bird species consume Lycium fruits. Lizard remains were significantly matched with the presence of Lycium fruits in the regurgitation pellets of the two predatory birds. Seeds were found in 7.3% of the lizard droppings, 31.0% of kestrel pellets and 55.7% of shrike regurgitations. The mean number of seeds per dropping or pellet was 4.8 ±4 in lizard, 20.2 ±34.5 in shrike and 6.7 ±8.1 in kestrel. The percentage of viable seeds showed significant differences among all four treatments, decreasing in the following direction: seeds collected directly from plants (98.0%), shrikes (88.0%), lizards (72.3%), and kestrels (31.7%). Seeds from Lycium fresh fruits and shrike pellets showed significantly higher germination rates than those from lizard droppings and kestrel pellets. While lizards and shrikes are effective seed dispersers, kestrel gut treatment decreases seed viability. Seed viability is always higher than seed germination in each of the four treatments. In this island environment, Lycium seeds are under an important random influence during the seed dispersal process. Secondary seed dispersal seems to acquire a relevant dimension in small and remote insular environments or isolated continental systems where interactions among the different elements involved are intense, all of them are abundant native residents, and they have been coexisting for a long time. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 345–352.     

Shorter migration distances associated with higher winter temperatures suggest a mechanism for advancing nesting phenology of American kestrels Falco sparverius

Global climate change has affected avian migration patterns and nesting phenology. Changes in one phase of a bird's cycle will most likely affect other stages, but few studies focus simultaneously on multiple life‐history events. We used western North American ringing records and Christmas Bird Counts to examine whether changes in migration patterns were concordant with advancing American kestrel Falco sparverius nesting phenology. Consistent with previous findings, male kestrels migrated shorter distances than female kestrels, and kestrels nesting in southern latitudes migrated shorter distances than kestrels nesting in more northern areas. In addition, kestrel migration distance decreased significantly from 1960 to 2009 and was negatively associated with winter minimum temperatures. Christmas Birds Counts from the same time period showed increasing indices of overwintering kestrel abundance in northern states (Washington, Idaho, and Utah), where winter minimum temperatures have increased significantly, and concomitant decreases in southern states (California and Arizona). Finally, changes in nesting phenology of kestrels in southwestern Idaho were best explained by warmer winters, not springs. Warmer winters may decrease energetic demands on migrants by allowing for shorter migration distances, decreasing thermoregulatory costs, or both. Decreased energy demands during winter may allow birds to gain resources necessary for reproduction earlier in the nesting season. Higher winter temperatures that decrease (former) constraints on early nesting may be a particularly important mechanism leading to advancing nesting phenology for species with strong seasonal declines in fecundity or intense early season competition for high‐quality nesting areas.     

Detection of sequence variation in PCR-amplified fragments of omp2 gene from three species of the family Chlamydiaceae using agarose gel electrophoresis containing bisbenzimide-PEG

A simple technique providing a means for rapid genetic differentiation of chlamydial strains is described. The technique is based on a single-step sequence-specific separation of PCR-amplified DNA fragments by electrophoresis in an agarose gel containing a DNA ligand - bisbenzimide-PEG. A hypervariable region at the 5' end of the omp2 gene of Chlamydiaceae species encoding the 60-kDa cysteine-rich outer membrane protein was selected as a target for PCR. The appropriate fragments were amplified from strains of Chlamydia trachomatis, Chlamydophila pneumoniae, and Chlamydophila psittaci, and the PCR products originating from different species were electrophoretically separated in the presence of the DNA ligand. We therefore demonstrated that PCR with a single pair of primers followed by simple agarose gel electrophoresis with bisbenzimide-PEG can be applied to the differentiation of three members of the family Chlamydiaceae which are commonly recognized as human pathogens.     

Body condition variation in kestrel (<Emphasis Type="Italic">Falco tinnunculus</Emphasis>) nestlings in relation to breeding conditions

The body condition index (i.e., body mass corrected for age or size differences) is commonly used to investigate offspring condition in nestling birds. The body condition index reflects different parameters related to the general nutritional state of nestlings and may predict survival prospects. Since conditions experienced during the growth period can affect the fitness of nestlings in adulthood, we investigated proximate and ultimate factors underlying body condition index variation in kestrel (Falco tinnunculus) nestlings in a 9-year field study and we carried out two cross-fostering experiments to disentangle the origin (genetics plus maternal effects) and rearing (environment effect) components of body condition index variation. In total, we sampled 2,065 nestlings from 464 broods and used 121 nestlings from 24 broods in the cross-fostering experiments. We found that nestlings from larger broods had higher body condition index than nestlings from smaller ones, but this pattern did not emerge in two of the 9 years of study; nestlings born later in the breeding season had lower body condition index in some years but not in others; the decrease of body condition index over the breeding season emerged in all but three-chick broods; males and females did not differ neither in body condition index nor in the covariation between body mass and wing length, while this result was limited to one of the nine field study years; the annual mean value of body condition index did not covary with the total rainfall; both the origin and rearing components explained body condition index variation, but their relative contributions varied from a year to another. Overall, these results suggest that the brood size is not a good predictor of body condition index; the rule “nesting early in the season is better” is less general than previously thought; the body condition index may contain origin variance, whose expression may be modulated by environmental conditions.     

Inclusion body disease of falcons (Herpesvirus infection) in an American kestrel.

Postmortem examination of a captive-bred American kestrel (Falco sparverius) showed numerous white necrotic foci 1-2 mm in diameter throughout the liver and spleen. The results of light and spleen. The results of light and electron microscopic studies and experimental transmission to a captive American kestrel and a barred owl (Strix varia) suggests a herpesvirus similar to those dsecribed for owls and other falcons in the U.S. This is the first report of a naturally occurring case of inclusion body disease of falcons in the American kestrel.     

Acute oral toxicity of sodium cyanide in birds

Sensitivities of six avian species, black vulture (Coragyps atratus), American kestrel (Falco sparverius), Japanese quail (Coturnix japonica), domestic chicken (Gallus domesticus), eastern screech-owl (Otus asio), and European starling (Sturnus vulgaris), to acute poisoning by sodium cyanide (NaCN) were compared by single dose LD50's. Three species, domestic chickens, black vultures, and turkey vultures (Cathartes aura), were dosed with NaCN to determine cyanide residues in those that died and also in survivors, in addition to postmortem fate. Three flesh-eating species (black vulture, American kestrel, and eastern screech-owl; LD50's 4.0-8.6 mg/kg) were more sensitive to NaCN than three species (Japanese quail, domestic chicken, and European starling; LD50's 9.4-21 mg/kg) that fed predominantly on plant material. Elevated concentrations of cyanide were found in the blood of birds that died of cyanide poisoning; however, concentrations in birds that died overlapped those in survivors. Blood was superior to liver as the tissue of choice for detecting cyanide exposure. No gross pathological changes related to dosing were observed at necropsy.     

The Eye in the Sky: Combined Use of Unmanned Aerial Systems and GPS Data Loggers for Ecological Research and Conservation of Small Birds

Technological advances for wildlife monitoring have expanded our ability to study behavior and space use of many species. But biotelemetry is limited by size, weight, data memory and battery power of the attached devices, especially in animals with light body masses, such as the majority of bird species. In this study, we describe the combined use of GPS data logger information obtained from free-ranging birds, and environmental information recorded by unmanned aerial systems (UASs). As a case study, we studied habitat selection of a small raptorial bird, the lesser kestrel Falco naumanni, foraging in a highly dynamic landscape. After downloading spatio-temporal information from data loggers attached to the birds, we programmed the UASs to fly and take imagery by means of an onboard digital camera documenting the flight paths of those same birds shortly after their recorded flights. This methodology permitted us to extract environmental information at quasi-real time. We demonstrate that UASs are a useful tool for a wide variety of wildlife studies.     

Seropositivity and risk factors associated with Toxoplasma gondii infection in wild birds from Spain

Toxoplasma gondii is a zoonotic intracellular protozoan parasite of worldwide distribution that infects many species of warm-blooded animals, including birds. To date, there is scant information about the seropositivity of T. gondii and the risk factors associated with T. gondii infection in wild bird populations. In the present study, T. gondii infection was evaluated on sera obtained from 1079 wild birds belonging to 56 species (including Falconiformes (n=610), Strigiformes (n=260), Ciconiiformes (n=156), Gruiformes (n=21), and other orders (n=32), from different areas of Spain. Antibodies to T. gondii (modified agglutination test, MAT titer ≥1:25) were found in 282 (26.1%, IC(95%:)23.5-28.7) of the 1079 birds. This study constitute the first extensive survey in wild birds species in Spain and reports for the first time T. gondii antibodies in the griffon vulture (Gyps fulvus), short-toed snake-eagle (Circaetus gallicus), Bonelli's eagle (Aquila fasciata), golden eagle (Aquila chrysaetos), bearded vulture (Gypaetus barbatus), osprey (Pandion haliaetus), Montagu's harrier (Circus pygargus), Western marsh-harrier (Circus aeruginosus), peregrine falcon (Falco peregrinus), long-eared owl (Asio otus), common scops owl (Otus scops), Eurasian spoonbill (Platalea leucorodia), white stork (Ciconia ciconia), grey heron (Ardea cinerea), common moorhen (Gallinula chloropus); in the International Union for Conservation of Nature (IUCN) "vulnerable" Spanish imperial eagle (Aquila adalberti), lesser kestrel (Falco naumanni) and great bustard (Otis tarda); and in the IUCN "near threatened" red kite (Milvus milvus). The highest seropositivity by species was observed in the Eurasian eagle owl (Bubo bubo) (68.1%, 98 of 144). The main risk factors associated with T. gondii seropositivity in wild birds were age and diet, with the highest exposure in older animals and in carnivorous wild birds. The results showed that T. gondii infection is widespread and can be at a high level in many wild birds in Spain, most likely related to their feeding behaviour.     

Biochemical and hematological effects of lead ingestion in nestling American kestrels (Falco sparverius)

One-day old American kestrel (Falco sparverius) nestlings were orally dosed daily with 5 microliters/g of corn oil (controls), 25, 125 or 625 mg/kg of metallic lead in corn oil for 10 days. Forty per cent of the nestlings receiving 625 mg/kg of lead died after 6 days and growth rates were significantly depressed in the two highest lead dosed groups. At 10 days hematocrit values were significantly lower in the two highest lead treated groups, and hemoglobin content and red blood cell delta-aminolevulinic acid dehydratase (ALAD) activity was depressed in all lead treated groups. Plasma creatine phosphokinase decreased in the two highest treatment groups. Brain, liver and kidney ALAD activities, brain RNA to protein ratio and liver protein concentration decreased after lead exposure whereas liver DNA, DNA to RNA ratio and DNA to protein ratio increased. Brain monoamine oxidase and ATPase were not significantly altered. Measurements of the ontogeny of hematological variants and enzymes in normal development, using additional untreated nestlings, revealed decreases in red blood cell ALAD, plasma aspartate amino transferase, lactate dehydrogenase, brain DNA and RNA and liver DNA, whereas hematocrit, hemoglobin, plasma alkaline phosphatase, brain monoamine oxidase, brain ALAD and liver ALAD increased during the first 10 days of posthatching development. Biochemical and hematological alterations were more severe than those reported in adult kestrels or precocial young birds exposed to lead. Alterations may be due in part to delayed development.     

Does avian predation risk depress reproduction of voles?

Reproductive output and the growth of captive voles were quantified under high and low avian predation risk in a semi-natural experiment. Voles were exposed to Eurasian kestrels (Falco tinnunculus), the main avian predator of vole species studied (Clethrionomys glareolus, Microtus agrestis and M. rossiaemeridionalis). Vole pairs were housed in cages settled under nest-boxes occupied by breeding kestrels or in control cages settled under empty nest-boxes for 2 weeks. The experiment was conducted in mid-summer when kestrels had half-grown nestlings, because in that time hunting adults and begging nestlings produce noise and scats which may indicate significant predation threat to voles housed underneath the nest-boxes. The risk of kestrel predation did not have any obvious impact on pregnancy rates, mean litter sizes, or growth rates of kestrel-exposed voles compared with control voles studied. These results indicate that the risk of avian predation does not depress the reproductive investment of voles. Received: 3 November 1997 / Accepted: 16 February 1998     

Genetic favouring of pheomelanin‐based pigmentation limits physiological benefits of coloniality in lesser kestrels Falco naumanni

Pheomelanin contributes to the pigmentation phenotype of animals by producing orange and light brown colours in the integument. However, pheomelanin synthesis in melanocytes requires consumption of glutathione (GSH), the most important intracellular antioxidant. Therefore, a genetic control favouring the production of large amounts of pheomelanin for pigmentation may lead to physiological costs under environmental conditions that promote oxidative stress. We investigated this possibility in the context of breeding coloniality, a reproductive strategy that may affect oxidative stress. We found in lesser kestrel Falco naumanni nestlings that the GSH:GSSG ratio, which decreases with systemic oxidative stress, increased with the size of the colony where they were reared, but the expression in feather melanocytes of five genes involved in pheomelanin synthesis (Slc7a11, Slc45a2, CTNS, MC1R and AGRP) did not vary with colony size. The antioxidant capacity (TEAC) of lesser kestrel nestlings also increased with colony size, but in a manner that depended on Slc7a11 expression and not on the expression of the other genes. Thus, antioxidant capacity increased with colony size only in nestlings least expressing Slc7a11, a gene with a known role in mediating cysteine (a constituent amino acid of GSH) consumption for pheomelanin production. The main predictor of the intensity of pheomelanin‐based feather colour was Slc45a2 expression followed in importance by Slc7a11 expression, hence suggesting that the genetic regulation of the pigmentation phenotype mediated by Slc7a11 and a lack of epigenetic lability in this gene limits birds from benefiting from the physiological benefits of coloniality.