Experimental evaluation of sex differences in territory acquisition in a cooperatively breeding bird

In many species, territory ownership is a prerequisite for reproduction;consequently, factors that affect success in territory acquisitioncan have a large impact on fitness. When competing for territories,some individuals may have an advantage if, for example, theyare phenotypically superior or more familiar with the site thanothers. The relative importance of the many factors involvedin territory acquisition is, at present, unclear. We studiedpatterns of natural territory acquisition in a closed and saturatedpopulation of Seychelles warblers. Furthermore, by removingbreeders, we experimentally investigated the relative importance,to territory acquisition, of a range of factors and assessedwhether this differed between the sexes. In both sexes, themain route to natural territory acquisition was to dispersefrom the natal territory to immediately claim a vacant dominantposition. Males were older than females when acquiring a territoryfor the first time. In the removal experiment, for both sexes,the proximity of an individual's natal territory to a vacantdominant position was positively related to the individual'schance of claiming the vacancy. Older males were more likelyto gain an experimental vacant dominant position than were youngmales, whereas age did not affect territory acquisition in females.In the Seychelles warbler, the degree of intrasexual competitionfor territory ownership may be stronger for males than for femalesbecause territory ownership is a prerequisite for male reproduction,whereas females can reproduce on their natal territory. In suchcompetition, young males subsequently lose out to older ones.     

Individual and sex‐related patterns of prolonged flights during both day and night by great reed warblers crossing the Mediterranean Sea and Sahara Desert

A wide variety of the barrier crossing strategies exist among migrating songbirds, ranging from strict nocturnal flights to non‐stop flights over a few days. We evaluate barrier crossing strategies in a nocturnally migrating songbird crossing the Mediterranean Sea and the Sahara Desert, the great reed warbler, exploring variation between the sexes and within individuals. We used data from 31 year‐round light‐level geolocators tracks from 26 individuals (13 males and 13 females), with four individuals tracked for 2–3.5 consecutive years. Almost all individuals (25 of 26) prolonged their flights into the day at least on one occasion. The mean duration of these prolonged flights was 19.9 h and did not differ between sexes or seasons. Fifteen birds performed non‐stop flights during more than one full day and night (≥ 24 h; mean = 31.9 h; max = 55 h) in autumn and/or spring, but these flights were generally too short to cross an entire barrier (such as the Sahara Desert) in one non‐stop flight. Patterns of prolonged flights showed considerable within‐individual variation in females between seasons (autumn versus spring) and in both males and females between years, suggesting high individual flexibility in migration strategy. Significantly more males than females performed prolonged flights during autumn migration, but not spring, possibly reflecting sex‐specific carry‐over effects. We conclude that great reed warblers have the ability to conduct prolonged continuous flights for up to several nights and days, which potentially would allow them to cross the Sahara Desert in one non‐stop flight. However, they typically use a mixed strategy of several nocturnal flights with intermittent stopovers in combination with 1–3 prolonged flights. Prolonged flights covered less than half (44%) of the total flight time across the barriers, and the diurnal parts of the flights covered only 18% of this time.     

Survival of Reed Warbler Acrocephalus scirpaceus clutches in relation to nest position

Nest survival was studied in relation to nest position of 164 nests of the Reed Warbler Acrocephalus scirpaceus in the Southeastern part of the Czech Republic in 1993. Breeding was successful in 91 (55.5%) cases, whereas 40 (24.4%) were predated, 19 (11.6%) were parasitized by the Cuckoo Cuculus canorus and 14 (8.5%) were destroyed by other causes. Of the predated nests, small mammals accounted for 26 (65.0%) and unknown predators for 14 (35.0%) nests. Rates of predation and parasitism varied in relation to a series of habitat factors and Reed Warblers avoided nest sites most vulnerable to predation or parasitism. Concealed places in the vegetation far away from trees were the safest nest sites.     

Blood parasites shape extreme major histocompatibility complex diversity in a migratory passerine

Pathogens are one of the main forces driving the evolution and maintenance of the highly polymorphic genes of the vertebrate major histocompatibility complex (MHC). Although MHC proteins are crucial in pathogen recognition, it is still poorly understood how pathogen‐mediated selection promotes and maintains MHC diversity, and especially so in host species with highly duplicated MHC genes. Sedge warblers (Acrocephalus schoenobaenus) have highly duplicated MHC genes, and using data from high‐throughput MHC genotyping, we were able to investigate to what extent avian malaria parasites explain temporal MHC class I supertype fluctuations in a long‐term study population. We investigated infection status and infection intensities of two different strains of Haemoproteus, that is avian malaria parasites that are known to have significant fitness consequences in sedge warblers. We found that prevalence of avian malaria in carriers of specific MHC class I supertypes was a significant predictor of their frequency changes between years. This finding suggests that avian malaria infections partly drive the temporal fluctuations of the MHC class I supertypes. Furthermore, we found that individuals with a large number of different supertypes had higher resistance to avian malaria, but there was no evidence for an optimal MHC class I diversity. Thus, the two studied malaria parasite strains appear to select for a high MHC class I supertype diversity. Such selection may explain the maintenance of the extremely high number of MHC class I gene copies in sedge warblers and possibly also in other passerines where avian malaria is a common disease.     

Temporal patterns of occurrence and transmission of the blood parasite Haemoproteus payevskyi in the great reed warbler Acrocephalus arundinaceus

We studied the prevalence and intensity of the haemosporidian blood parasite Haemoproteus payevskyi in great reed warblers at Lake Kvismaren (6 years) and Lake Segersj? (3 years) in Sweden. Based on microscopic inspection of slides from 282 adult birds, 20.6% showed infection of H. payevskyi in circulating red blood cells in at least 1 year. For parasite prevalence, there was no difference between years, sex, and age classes. However, parasite intensity was higher in females than in males, and this was most pronounced in 1-year-old birds. Individuals scored to carry parasites in year _n were more likely to show parasite infection year _n + 1 than birds scored to be parasite-free in year _n . None of 99 juvenile birds examined at the breeding site in late summer, 4–9 weeks after hatching, showed infection of H. payevskyi. Parasite intensity in infected adult birds decreased in the course of the breeding season and no new or relapse infections were observed during this period. Thus, our data imply that in the great reed warbler, a long-distance migrant to tropical Africa, transmission of H. payevskyi occurs on wintering sites or at stopover sites during migration.     

Bird mitochondrial gene order: insight from 3 warbler mitochondrial genomes

Two main gene orders exist in birds: the ancestral gene order and the remnant control region (CR) 2 gene order. These gene orders differ by the presence of 1 or 2 copies of the CR, respectively. Among songbirds, Oscines were thought to follow the ancestral gene order, with the exception of the lyrebird and Phylloscopus warblers. Here, we determined the complete mitochondrial genome sequence of 3 non-Phylloscopus warblers species and found that the blackcap (Sylvia atricapilla) and the reed warbler (Acrocephalus scirpaceus) have 2 almost identical copies of the CR, whereas the eastern orphean warbler (Sylvia crassirostris) follows the remnant CR 2 gene order. Our results contradict previous studies suggesting that Acrocephalus and most sylvioid warblers exhibit the ancestral gene order. We were able to trace this contradiction to a misidentification of gene order from polymerase chain reaction length determination. We thus suggest that passerine gene order evolution needs to be revised.