Aggressive behaviour affects selection on morphology by influencing settlement patterns in a passerine bird.
(57/549)
The importance of behaviours as instigators or inhibitors of evolutionary change remains largely unresolved and this is in part because there are very few empirical examples of how behaviours affect evolutionary processes. By determining the environment of breeding, aggressive interactions over territories have the potential to strongly impact selection pressures experienced by individuals. Western bluebirds (Sialia mexicana) provide a unique opportunity to investigate the evolutionary importance of aggression, since their highly variable breeding habitat favours distinct foraging techniques and they also compete aggressively for nest boxes, a resource that is easy to manipulate. Here, I show experimentally that more aggressive males compete more effectively for territories with a high density of nest boxes and, as a consequence, aggressive and non-aggressive males are sorted into distinct breeding habitats that differ in the strength of selection on morphological traits. Specifically, males with longer tails and tarsi were favoured in open habitats where high agility is required to forage efficiently, whereas in forested habitats, where agility is less important, selection was weak. These results show that aggression can affect selection on a local scale by determining individual settlement patterns. More generally, because territorial interactions are important across a wide variety of taxa, these results suggest that aggressive behaviour has the potential to impact the evolutionary trajectory of many animal populations. (+info)
Reduced mortality selects for family cohesion in a social species.
(58/549)
Delayed dispersal is the key to family formation in most kin-societies. Previous explanations for the evolution of families have focused on dispersal constraints. Recently, an alternative explanation was proposed, emphasizing the benefits gained through philopatry. Empirical data have confirmed that parents provide their philopatric offspring with preferential treatment through enhanced access to food and predator protection. Yet it remains unclear to what extent such benefits translate into fitness benefits such as reduced mortality, which ultimately can select for the evolution of families. Here, we demonstrate that philopatric Siberian jay (Perisoreus infaustus) offspring have an odds ratio of being killed by predators 62% lower than offspring that dispersed promptly after independence to join groups of unrelated individuals (20.6% versus 33.3% winter mortality). Predation was the sole cause of mortality, killing 20 out of 73 juveniles fitted with radio tags. The higher survival rate among philopatric offspring was associated with parents providing nepotistic predator protection that was withheld from unrelated group members. Natal philopatry usually involves the suppression of personal reproduction. However, a lower mortality of philopatric offspring can overcome this cost and may thus select for the formation of families and set the scene for cooperative kin-societies. (+info)
Migratory passerine birds as reservoirs of Lyme borreliosis in Europe.
(59/549)
To define the role of birds as reservoirs and disseminators of Borrelia spirochetes, we characterized tick infestation and reservoir competence of migratory passerine birds in Sweden. A total of 1,120 immature Ixodes ricinus ticks were removed from 13,260 birds and assayed by quantitative polymerase chain reaction (PCR) for Borrelia, followed by DNA sequencing for species and genotype identification. Distributions of ticks on birds were aggregated, presumably because of varying encounters with ticks along migratory routes. Lyme borreliosis spirochetes were detected in 160 (1.4%) ticks. Borrelia garinii was the most common species in PCR-positive samples and included genotypes associated with human infections. Infestation prevalence with infected ticks was 5 times greater among ground-foraging birds than other bird species, but the 2 groups were equally competent in transmitting Borrelia. Migratory passerine birds host epidemiologically important vector ticks and Borrelia species and vary in effectiveness as reservoirs on the basis of their feeding behavior. (+info)
Different post-Pleistocene histories of Eurasian parids.
(60/549)
Previous phylogeographic studies of the great tit (Parus major) and the willow tit (Parus montanus) found a general absence of phylogeographic structure for both species and suggested that each species underwent range contraction during the last Ice Age and survived in relatively low numbers, P. major in southern Europe and P. montanus in southeastern Asia. However, prior studies did not sample the entire range of either species. We analyzed sequence data for the complete mitochondrial ND2 gene from 87 P. major and 139 P. montanus from 15 new Eurasian localities, both to test prior conclusions and to provide better coverage of each species' range. Our analyses confirmed the absence of phylogeographic structure in P. major and P. montanus and supported the prior refuge hypothesis for P. major. For P. montanus, we concluded that besides surviving the Ice Age in southeastern Asia, as previously hypothesized, it apparently sustained a relatively large population in northern Eurasian riverine thickets and then expanded eastward. Genetic diversity was low in P. major (pi = 0.0012, h = 0.64) and moderate in P. montanus (pi = 0.0021, h = 0.88), suggesting higher long-term effective population sizes and the older ages of populations in P. montanus. If molecular substitution rates are similar, P. montanus colonized its current Eurasian range earlier than P. major. Differences between prior studies and ours likely result from sampling gaps in earlier studies. (+info)
A UV signal of offspring condition mediates context-dependent parental favouritism.
(61/549)
As fitness returns during a breeding attempt are context-dependent, parents are predicted to bias their food allocation within a brood from poor towards good condition nestlings when environmental conditions deteriorate. We tested this prediction in the Alpine swift and the European starling, two migratory bird species, by modifying an ultraviolet (UV) visual signal of condition in nestlings and exploring how parents allocate food to their young as the season progresses. We show in both species that: (i) UV light reflected by the body skin of offspring positively correlates with their stature (i.e. body mass and skeletal size) and (ii) parental favouritism towards young with more UV reflective skin gradually increases as the season progresses. Early-breeding parents supplied food preferentially to UV pale (i.e. small stature) nestlings, whereas late-breeding parents favoured UV bright offspring (i.e. large stature). These results emphasize that parents use UV signals of offspring condition to adjust their feeding strategies depending on the ecological context. (+info)
Short-term energy regulation of whitebellied sunbirds (Nectarinia talatala): effects of food concentration on feeding frequency and duration.
(62/549)
Avian nectarivores show compensatory feeding by adjusting their volumetric intake in response to variation in nectar concentration. This study used an infrared photo-detection system to investigate the short-term feeding patterns of whitebellied sunbirds (Nectarinia talatala) consuming three different sucrose concentrations (10, 20 and 30% w/w). Sunbirds increased their feeding frequency on the most dilute diet, but there was no change in feeding duration. Thus, the increase in total time spent feeding on the dilute diet was due to the increased feeding frequency. No difference in short-term feeding patterns was found between the 20% and 30% diets. Total time spent feeding was extremely short on all diets (96-144 s in every hour). Birds maintained the same steady increase in body mass over the course of the day on all three diets. Daily rhythms in feeding patterns were evident, with longer feeding duration and lower feeding frequency in the early morning and evening than during the rest of the day. Because ingestion rates on a particular diet may vary through the day, caution must be exercised in using feeding duration as a surrogate for meal size. Individual birds varied greatly in their feeding patterns irrespective of diet concentration. (+info)
Terrestrial passerines in an Atlantic forest remnant of Southern Brazil.
(63/549)
Microhabitats of four terrestrial passerines were studied in an Atlantic forest remnant of southern Brazil, in two areas (northern and southern) of the Mata dos Godoy State Park (PG). Grallaria varia and Hylopezus nattereri showed low abundance and occurred in only one PG area, while Chamaeza campanisona and Corythopis delalandi were recorded in two. The microhabitats of C. campanisona, G. varia, and H. nattereri had many large trees and a dense understory. Corythopis delalandi was in areas having few large trees. (+info)
Does the roosting behavior of birds affect transmission dynamics of West Nile virus?
(64/549)
The potential role of many urban passerine birds in the transmission of West Nile virus (WNV) is well-documented by studies on host competency, seroprevalence in wild birds, and identification of vector blood meal source. In contrast, the impact of bird behavior on transmission dynamics is largely unexplored. Bird roosting (perching) behavior may be a critical component regulating WNV transmission because of the crepuscular/nocturnal feeding behavior of Culex mosquitoes, the primary vectors of WNV. We used radio telemetry to determine the roosting behavior of American crows (Corvus brachyrhynchos) and northern cardinals (Cardinalus cardinalus). On average, healthy crows moved slightly shorter distances between roosts than viremic crows, 1,038.3 meters versus 1,255.5 meters, while cardinals only moved 54.7 meters. Given the average movements of crows and cardinals between roosts, crows, which are viremic for five days, could spread the virus throughout a mean +/- SE area of 20.84 +/- 0.79 km(2), while viremic cardinals would, on average, only spread the virus over a mean +/- SE area of 0.03 +/- 0.01 km(2). Because the crow population in Illinois is decreasing at a rate of 11.5% per year and up to 35.6% per year in certain locations, crows are becoming scarce in some areas, thus reducing their role as wild bird sentinels. We suggest that if crows are important in dispersing WNV, large decreases in their abundance will shift transmission cycles to a more focal nature because of the differences in roosting behavior of crows compared with other urban birds, such as cardinals. (+info)