Experienced Birds Research Articles

Laying date depends on territorial breeders’ age, climatic conditions and previous breeding success: a long-term study (2004–2021) with Bonelli’s eagle in Spain

Adjustment of reproductive timing within the annual cycle is a crucial issue for both offspring and parents’ survival, and breeding success. Early laying date is closely related to successful breeding outcome and better survival. Obtaining long datasets on threatened long-lived species’ breeding performance can contribute to their conservation. Using field observations and telemetry information, here we analyse how laying date of an endangered long-lived raptor varies with nest characteristics, individual factors and climatic variables during an 18-year (2004–2021) study period in eastern Spain. To this end, we estimated how environmental and individual variables affect laying date. Our results showed that average laying date in our study area took place on February 17th. Laying date showed no trend during the study period. Nests placed in higher elevations showed delayed laying dates. Territories occupied by adults with previous successful experience and high brood size showed earlier laying dates. Current year laying date was highly correlated with previous year laying date. Colder territories delayed laying date and the minimum temperature of the previous December were negatively correlated to previous laying date. Our results highlight the importance of experienced birds able to adjust timing of reproduction to maximise biological fitness. High adult mortality allows sub-adults to settle as breeders and jeopardises species’ persistence. Therefore, the reduction of mortality of territorial birds is of the outmost importance to improve the conservation status of declining long-lived species such as the Bonelli’s eagle (Aquila fasciata).

The effect of the biologically active substance Baikal EM-2 on the intestines of quails

5 groups were formed from quails of the Manchurian breed. The control group - the main diet, and the experimental ones were given 0.25% (1 experimental group (EG)); 0.5% (2EG); 0.75 (3EG) and 1% (4EG) Baikal EM-2 solution at the rate of 3 ml per head. Histological studies were performed at the age of 147 days. Egg production per average laying hen in the experimental groups was on average 11.7% higher compared to the control group, the average live weight of quails in the experimental groups is 1.2% higher. In the duodenum, in all experimental groups, there was a better development of villi by 19.8-58.6% (P≤0.001), and in the skinny, the height of the villi was significantly higher in EG1, EG2, and EG4 by 19%-48%. The crypt layer significantly increased in the duodenum of 4EG by 13.9% (P≤0.05). The muscular elements of the duodenum were better developed in the experimental groups. In the cecum, the size of the layers did not differ. We assume that the experienced bird achieved high zootechnical results due to the better development of the villi of the small intestine.

Bacterial detoxification of plant defence secondary metabolites mediates the interaction between a shrub and frugivorous birds

Many plants produce fleshy fruits, attracting fruit-eating animals that disperse the seeds in their droppings. Such seed dispersal results in a conflict between the plant and the animal, as digestion of seeds can be highly beneficial to the animal but reduces plant fitness. The plant Ochradenus baccatus uses the myrosinase-glucosinolates system to protect its seeds. We show that hydrolysis of the O. baccatus fruit glucosinolates by the myrosinase enzyme inhibited digestive enzymes and hampered digestion in naïve individuals of the bird Pycnonotus xanthopygos. However, digestion in birds regularly feeding on O. baccatus fruits was unaffected. We find that Pantoea bacteria, dominating the gut of these experienced birds as well as the fruits, thrive on glucosinolates hydrolysis products in culture. Augmentation of Pantoea protects both naïve birds and plant seedlings from the effects of glucosinolates hydrolysis products. Our findings demonstrate a tripartite interaction, where the plant-bird mutually beneficial interactions are mediated by a communal bacterial tenant.

Продуктивное влияние новых сортов сурепицы при выращивании цыплят-бройлеров

Studies have been carried out to determine the effect of seeds of varieties of coleseed (Brassica rapa L.) on the productivity of broiler chickens of the "Cobb 500" cross. According to the scheme of the experi-ment, the control compound feed did not contain coleseed seeds, 7.5% (by weight) were taken into the compound feed of the first experimental group seeds of winter coleseed of the Zarya variety, and in the compound feed of the second experimental group — 7.5% seeds of spring coleseed of the Nadezhda va-riety. The introduction of coleseed seeds into the starting and finishing compound feeds for broiler chick-ens reduced the use of soybean meal and sunflower oil by 3.7 and 4.0% (rel.). The data of physiological experience showed that the digestibility of the nutrients of the compound feed of all groups was at a high level. The digestibility of crude protein was at the control level. Lower digestibility of raw fiber by chick-ens of the first experimental group (less by 3.06%) is associated with a higher content of lignin in the seed shell of the Zarya variety. By the end of the experiment, the live weight of broiler chickens increased 66.8 times, 66.4 times and 66.9 times, respectively, according to the control of the first and second experimen-tal groups. Inclusion of coleseed seeds (7.5% by weight) slightly reduced the consumption of compound feeds by chickens of the experimental groups — by 1.43 and 1.13%, compared with the control. This was facilitated by the higher energy saturation of experimental compound feeds with coleseed seeds, contain-ing a high level of crude fat. The reduction in the use of compound feed and its lower cost affected the efficiency of growing an experienced bird. The efficiency index of poultry meat production by groups in the control was 97.62% and 113.41, 114.54% in the 1st and 2nd experimental groups, respectively.

Naïve individuals promote collective exploration in homing pigeons.

Group-living animals that rely on stable foraging or migratory routes can develop behavioural traditions to pass route information down to inexperienced individuals. Striking a balance between exploitation of social information and exploration for better alternatives is essential to prevent the spread of maladaptive traditions. We investigated this balance during cumulative route development in the homing pigeon Columba livia. We quantified information transfer within pairs of birds in a transmission-chain experiment and determined how birds with different levels of experience contributed to the exploration-exploitation trade-off. Newly introduced naïve individuals were initially more likely to initiate exploration than experienced birds, but the pair soon settled into a pattern of alternating leadership with both birds contributing equally. Experimental pairs showed an oscillating pattern of exploration over generations that might facilitate the discovery of more efficient routes. Our results introduce a new perspective on the roles of leadership and information pooling in the context of collective learning.

Repeated training of homing pigeons reveals age-dependent idiosyncrasy and visual landmark use

Recent research into the navigational strategies of homing pigeons, Columba livia , in the familiar area has highlighted the phenomenon of route fidelity: birds forming idiosyncratic flight paths to which they are loyal over multiple releases from the same site, and even returning to this path when released from a nearby unfamiliar location. Such results highlight the potential importance of visual landmark cues in the homing process. However, not all birds have been found to produce idiosyncratic routes or show this route-joining behaviour. Here we used birds with and without flight experience to study the formation of idiosyncratic routes when released repeatedly from a single location, followed by two off-route releases with differing topography to see how flight experience and local landmark features can influence navigational strategy in the familiar area. We found that, over the course of 20 sequential releases, birds with greater flight experience tended to form idiosyncratic routes whereas less experienced birds did not show this tendency. When released from nearby sites (from which the birds had not previously been released), a range of navigational strategies were seen, including flying parallel to the learned route (suggestive of a learned compass direction), a direct flight path towards home (again indicative of compass use), rejoining the learned route and following the coastline. These latter strategies are suggestive of landmark usage. Analysis using time lag embedding was also used to assess the off-route releases, and the short-term correlation dimension values produced were also indicative of strategies using one or two factors (landmarks, compass or a combination of these two). Individual birds often showed different strategies at different sites, suggesting that the use of different navigational cues is highly flexible and situationally dependent. • Birds with greater flight experience form idiosyncratic routes more readily. • Multiple homing strategies occur when released close to a familiar site. • Age and site-specific biases occurred in which strategies were used. • Flexibility within individuals was seen in terms of strategy choice and cue use.

Song parameters, repertoire size and song sharing within and across age classes in the saffron finch

Birds sing mostly to attract partners or to defend territories or resources. In relation to the first function, song can vary with age if older experienced males signal their quality through their vocal output. Regarding the second function, song can also vary with age if singing behavior helps mediate social interactions through repertoire sharing with neighbors. Here, we investigate whether song parameters change with age, and in which direction, in saffron finches Sicalis flaveola pelzelni, obligate secondary cavity nesters which produce elaborate melodious songs and show delayed plumage maturation. Cross‐sectional comparisons revealed that second year (SY) males sing shorter syllables, and shorter and less versatile songs than older after second year males (ASY), as expected if the latter are more experienced singers. Longitudinal comparisons, which better depict age‐related changes, showed that as birds age one year, song length and repertoire size do not change significantly, syllable duration shortens and, as expected for experienced singers, song versatility increases. Correlations between repertoire distance and nesting distance suggest that both SY and ASY males might be adjusting their repertoires to those of ASY neighbors; the former pattern conforms to the expectations if young birds try to emulate the songs of more experienced birds, while the latter is expected if song sharing helps de‐escalating antagonistic social interactions amongst males. This research, which provides the first description of song parameters in young second year saffron finches, expands our knowledge of song variation across age classes in songbirds.

Low Breeding-Site Fidelity Suggests Dispersal of Cerulean Warblers

Site fidelity can have significant impacts on population dynamics and may be influenced by both demographic and environmental characteristics, including age, sex, and habitat quality. We examined breeding-site fidelity of Setophaga cerulea (Cerulean Warbler), a small Nearctic–Neotropical migrant that is listed as endangered in Indiana and in decline throughout its range. Our research was part of a long-term demographic study in the research units of the Hardwood Ecosystem Experiment, southern Indiana. From 2013 to 2018, we banded 128 Cerulean Warblers, 10.2% of which returned the year following initial capture and banding. We did not find significant differences in return rates between adult males (n = 92) and adult females (n = 19; P = 0.69), novice (second-year, n = 20) and experienced (after-second-year, n = 91; P = 1) birds, or successful (n = 40) and unsuccessful breeders (n = 26; P = 0.39). We have yet to detect a bird banded as a hatch-year subsequently return the following season as a second-year (n = 0/17). Our return rates are likely affected by a combination of mortality between breeding seasons, our ability to detect returning birds, and dispersal between breeding seasons. We encourage other researchers to publish rates of Cerulean Warbler site fidelity across its range for comparison of populations and habitats to determine source/sink dynamics.

Preference for supernormal stimuli tends to override initially learned associations for conspicuous prey traits: implications from a laboratory study

How predators select on conspicuous prey traits is not well understood. We used a laboratory setup to investigate the role of learning in predator choice of conspicuous visual traits. We used a generalist predator, the great tit, and coloured wings of males of two species of damselflies as prey. Wing pigmentation differs between the species in colour (green vs. blue) and size (large vs. small). Wing pigmentation is a sexually selected trait that experiences negative selection by avian predators. Inexperienced great tits showed no preference for the colour or the size of wing pigmentation. Great tits were then repeatedly exposed to rewarded wings with either large or small wing patch size. When these experienced birds were exposed to both wing patch sizes for the first time, they tended to prefer the wings with the large patch, irrespective of their previous experience. Our results suggest that the choice of the predator was based on an initial association of the trait to a reward followed by a preference for a supernormal stimulus, probably due to a larger sensory stimulation. We discuss the implications of our laboratory results in the light of previous estimates of damselfly predation risk under field conditions.

Flying on their own wings: young and adult cuckoos respond similarly to long-distance displacement during migration

Common cuckoos Cuculus canorus are obligate nest parasites yet young birds reach their distant, species-specific wintering grounds without being able to rely on guidance from experienced conspecifics – in fact they never meet their parents. Naïve marine animals use an inherited navigational map during migration but in inexperienced terrestrial animal migrants unequivocal evidence of navigation is lacking. We present satellite tracking data on common cuckoos experimentally displaced 1,800 km eastward from Rybachy to Kazan. After displacement, both young and adult travelled similarly towards the route of non-displaced control birds. The tracking data demonstrate the potential for young common cuckoos to return to the species-specific migration route after displacement, a response so far reported exclusively in experienced birds. Our results indicate that an inherited map allows first-time migrating cuckoos to locate suitable wintering grounds. This is in contrast to previous studies of solitary terrestrial bird migrants but similar to that reported from the marine environment.

Do nonapeptides regulate parental care depending on experience in zebra finches?

Recent research suggests that the nonapeptide neurohormones regulate parental behaviors in a diverse array of vertebrates. However, it remains unclear how these neurohormones regulate parental care among birds, especially those which exhibit biparental care, or whether hormonal effects are contingent on a bird's previous experience as a parent. We measured the effects of nonapeptides on parental behaviors by peripherally injecting, over three treatment days, a short-acting nonapeptide receptor antagonist (OTA) or a saline control into breeding pairs of zebra finches (Taeniopygia guttata) that either did or did not have previous parental experience. We then compared how the duration of parental behaviors changed over the five days of observation (including one day before and two days after injections were administered). To compare treatment effects on parental outcomes, we also measured chick growth and mortality rates for each pair. There was a nearly significant interaction between treatment and experience for the amount of time birds spent in the nest, with time in the nest declining across the experiment inexperienced and experienced OTA birds. There was also a significant treatment by trial day interaction for nest guarding and a treatment by experience by trial day interaction for nest maintenance. Chicks reared by parents that received the OTA had significantly lower growth rates than chicks reared by control parents and, among experienced birds, higher mortality relative to control birds. Together, these results provide some support for the hypothesis that nonapeptides play a role in regulating parental outcomes and some parental behaviors in both experienced and inexperienced zebra finches.

Selection on multiple sexual signals in two Central and Eastern European populations of the barn swallow.

Variation in intensity and targets of sexual selection on multiple traits has been suggested to play a major role in promoting phenotypic differentiation between populations, although the divergence in selection may depend on year, local conditions or age. In this study, we quantified sexual selection for two putative sexual signals across two Central and East European barn swallow (Hirundo rustica rustica) populations from Czech Republic and Romania over multiple years. We then related these differences in selection to variation in sexual characters among barn swallow populations. Our results show that tail length and ventral coloration vary between populations, sexes, and age classes (first‐time breeders vs. experienced birds). We found that selection on tail length was stronger in first‐time breeders than in experienced birds and in males than in females in the Romanian population, while these differences between age groups and sexes were weak in Czech birds. We suggest that the populational difference in selection on tail length might be related to the differences in breeding conditions. Our results show that ventral coloration is darker (i.e., has lower brightness) in the Romanian than in the Czech population, and in experienced birds and males compared with first‐time breeders and females, respectively. The sexual difference in ventral coloration may suggest sexual selection on this trait, which is supported by the significant directional selection of ventral coloration in first‐time breeding males on laying date. However, after controlling for the confounding effect of wing length and tarsus length, the partial directional selection gradient on this trait turned nonsignificant, suggesting that the advantage of dark ventral coloration in early breeding birds is determined by the correlated traits of body size. These findings show that ventral coloration may be advantageous over the breeding season, but the underlying mechanism of this relationship is not clarified.

Rainfall at African wintering grounds predicts age‐specific probability of haemosporidian infection in a migratory passerine bird

In migratory species breeding in temperate zones and wintering in tropical areas, the prevalence of blood parasites may be affected by migratory strategies and winter habitat choice. We explored whether African winter habitat was linked to the probability of haemosporidian infection in the House Martin Delichon urbicum breeding in Spain, and tested for potential differences between age‐classes. As a proxy for winter habitat features, we analysed stable isotope (δ2H, δ13C and δ15N) values of winter‐grown feathers moulted in tropical Africa. Rainfall at the African winter grounds was related to the probability of being infected with haemosporidians and this effect differed among age‐classes. We found that haemosporidian prevalence was similar for young and experienced birds wintering in habitats of higher rainfall (2H‐depleted), whereas there were great differences in winter habitats of lower rainfall (2H‐enriched), with young having a much higher prevalence compared with experienced birds. Likewise, experienced birds wintering in habitats of higher rainfall had a higher probability of haemosporidian infection compared with experienced birds wintering in habitats of lower rainfall. By contrast, young birds wintering in habitats of lower rainfall had a higher probability of haemosporidian infection compared with young birds wintering in habitats of higher rainfall. These outcomes highlight the interaction of age with haemosporidian infection in the migratory ecology of the House Martin, which may drive carry‐over effects in this long‐distance aerial insectivore.

Distribution and breeding ecology of the Ferruginous Duck Aythya nyroca in Algeria

We conducted a survey of the distribution of Ferruginous Duck Aythya nyroca across Algeria and analysed the influence of nest-site characteristics on nesting success at a Ramsar site, Lake Tonga. The species was found to occupy different wetlands (freshwater lakes, brackish marshes and salt lakes) across three major climatic belts (subhumid coastal strip, semi-arid Hauts Plateaux and arid Sahara). Mean clutch size of successful nests was 13.3 ± 6.0 eggs (N = 26) with a hatching rate of 74% for successful clutches. Nesting success was recorded for 44% of nests with clutch desertion (72.7%) accounting for the majority of failed clutches. Egg size of the study population, which breeds at the southern limit of the species’ range, was significantly smaller than that of its northerly counterparts. Clutch size was negatively related to egg size and positively associated with depth of water below the nest, suggesting that older, more experienced or high-quality birds monopolised the safest sites. Successful clutches were significantly associated with tall vegetation, suggesting that when nesting is carried out mainly on offshore floating islets, protection against aerial predators and heat stress determine nesting outcome. Conspecific brood parasitism was significantly and positively associated with deferred egg-laying and smaller egg size, suggesting an age-dependent mechanism.

Wintering areas predict age‐related breeding phenology in a migratory passerine bird

Understanding connections between breeding, stopover and wintering grounds for long‐distance migratory birds can provide important insight into factors influencing demography and the strength of carry‐over effects among various periods of the annual cycle. Using previously described, multi‐isotope (δ13C, δ15N, δ2H) feather isoscapes for Africa, we identified the most probable wintering areas for house martins Delichon urbica breeding at Badajoz in southwestern Spain. We identified two most‐probable wintering areas differing in isotopic signature in west Africa. We found that the probability to winter in the isotopic cluster two was related to age and sex of individuals. Specifically, experienced males (i.e. two years or older) winter in the isotopic cluster two with a greater probability than experienced females, whereas first‐year females winter in the isotopic cluster two with a greater probability than first‐year males. In addition, wintering area was correlated with breeding phenology, with individuals wintering in the isotopic cluster two initiating their clutches earlier than those wintering in the isotopic cluster one. For birds wintering in the isotopic cluster two, there was no relationship between age and clutch initiation date. In contrast, young birds wintering in the isotopic cluster one initiated their clutches earlier than experienced birds wintering in this area. There was no significant correlation between wintering area and clutch size or the number of fledglings produced. We hypothesize that the relationship among social status, population density and winter habitat quality should be the most important driver of the carry‐over effect we found for this population.

Homing pigeons as a model for avian navigation?

The findings on the navigational mechanisms of homing pigeons and the available data on those of wild birds, in particular migrants, are compared. There are important parallels in the use of the magnetic field and the sun for directional orientation. Also the findings on the navigational ‘map’, its preferred use by experienced birds and the strategy of using route information to acquire the necessary knowledge to establish the ‘map’, obtained in pigeons studies, can probably be generalized to wild birds and migrants in their home region. It seems that birds share a common navigational system. Special development of migratory birds, however, is the innate migration program that enables young first‐time migrants to reach their still unknown wintering area.

Can experience reduce collisions between birds and vehicles?

AbstractBird collisions with vehicles cause serious safety, financial and conservation concerns worldwide, but the causes of such collisions are poorly described. We investigated how experience with vehicles influenced avian avoidance responses. We trained three groups of vehicle‐naïve rock pigeons Columba livia with 32 near‐miss vehicle approaches over 4 weeks at 60 and 120 km h−1, and also included individuals that heard but did not see the approaches (control group). We subsequently measured flight initiation distance (FID) and whether individuals ‘collided’ with a virtual vehicle directly approaching at 120 or 240 km h−1 using video playback. We found that inexperienced individuals (i.e. the control group) had longer FIDs than experienced birds, although only one of 90 individuals across groups successfully avoided virtual collision. Vehicle approach speed during video playback and the interaction of approach speed and training group did not influence FID. Our results suggest that a habituation‐like effect based on repeated observations of passing vehicles could contribute to ineffective vehicle avoidance responses by birds when collisions are imminent. Novel strategies should be developed to enhance avoidance responses to high‐speed vehicles to minimize bird mortality.

Environmental conditions, age, and senescence differentially influence survival and reproduction in the Storm Petrel

Demographic parameters in wild populations are expected to be shaped by individual covariates and environmental variability. Thus, the understanding of the effects of age and/or environmental conditions on variability in vital rates is of special importance in ecological and evolutionary studies. Early age-related improvements in survival and reproduction and later declines due to senescence are expected, above all in long-lived species. Survival in these species is predicted to be a more conservative parameter than reproduction, thereby giving rise to less temporal variability. We studied age-dependent patterns of survival and breeding success in a long-lived seabird, the Mediterranean Storm Petrel Hydrobates pelagicus melitensis, and the additive influence of individual heterogeneity and environmental climatic variables using 22 years of individual-based data (1993–2014). The North Atlantic Oscillation index (NAO) and sea surface temperature (SST) were selected as proxies of environmental conditions in both breeding and wintering areas. Our results show that vital rates improved with age for both survival and breeding success. A slow effect of senescence at older ages was detected for breeding success, whereas models did not disentangle the occurrence or the absence of actuarial senescence. Reproduction was also influenced by the age of first observed reproduction: at the same age, more experienced birds that recruited earlier had a higher breeding success than less experienced ones. Breeding success (but not survival) also showed great temporal variability in accordance with theoretical predictions. Neither the NAO nor the SST explained this variability, probably because petrels feed on lower trophic levels than most pelagic seabirds and other physical features such as river runoffs and winds may be involved, as well as other environmental stressors such as predation by sympatric gulls.

Age and sex determination of Mallards Anas platyrhynchos in autumn

Male and female mallards Anas platyrhynchos are easily told apart, whereas ageing is problematic, due to individual timing of moult and lack of easily defined age criteria. From examination and photographic documentation of mallards caught at Ottenby Bird Observatory (56°12′N, 16°24′E), we describe nine characters of plumage and bare parts to be used for ageing in autumn. The reliability of these characters was tested by letting experienced bird ringers determine putative age of birds from photos. Age determination from any single character proved to be uncertain, as correctly assigned mallard photos of each character was in the range of 51–85% for males and 48–89% for females. For both sexes, the lowest figure represented post-humerals and the highest represented tertials. Rectrices, tertial coverts, and greater coverts had high scores (71–85%). Using all characters, 91% of the males and 95% of the females were correctly aged. As young mallards, with the progress of pre-breeding moult (completed from October onwards), acquire tail and tertials identical to adults, untypical individuals are better not assigned to an age category.

Lack of experience-based stratification in homing pigeon leadership hierarchies.

In societies that make collective decisions through leadership, a fundamental question concerns the individual attributes that allow certain group members to assume leadership roles over others. Homing pigeons form transitive leadership hierarchies during flock flights, where flock members are ranked according to the average time differences with which they lead or follow others' movement. Here, we test systematically whether leadership ranks in navigational hierarchies are correlated with prior experience of a homing task. We constructed experimental flocks of pigeons with mixed navigational experience: half of the birds within each flock had been familiarized with a specific release site through multiple previous releases, while the other half had never been released from the same site. We measured the birds' hierarchical leadership ranks, then switched the same birds' roles at a second site to test whether the relative hierarchical positions of the birds in the two subsets would reverse in response to the reversal in levels of experience. We found that while across all releases the top hierarchical positions were occupied by experienced birds significantly more often than by inexperienced ones, the remaining experienced birds were not consistently clustered in the top half—in other words, the network did not become stratified. We discuss our results in light of the adaptive value of structuring leadership hierarchies according to ‘merit’ (here, navigational experience).