Conspicuous female plumage is common among open cup-nesting passerine birds

Alfred Russel Wallace hypothesized that the use of cavity or dome nests releases incubating birds from predation risk, and that this allows the evolution of conspicuous coloration in females. By this hypothesis, females that use open nests are subject to strong selection for crypsis. Here, we test the validity of Wallace’s proposed evolutionary correlation between nest type and conspicuous coloration in females across the largest avian radiation, the Passeriformes, using phylogenetic comparative methods. We also test an alternate hypothesis that cavity-nesting results in greater conspicuousness because competition for cavities is stronger than for other nest sites, and such competition can drive social selection on female plumage. By this hypothesis, dome-nesting females should generally be less conspicuous than cavity-nesting species. We found no support for Wallace’s hypothesis that concealed nests yield conspicuous plumage while open nests yield dull plumage, and some support for the social selection hypothesis in smaller-bodied, gregarious species. While our analyses do not support the core part of Wallace’s hypothesis, they corroborate his contention that evolutionary transitions in nest type are rare, indicating that nest types may influence macroevolutionary selective regimes for other traits.

Low incubation temperature retards the development of cold tolerance in a precocial bird

Incubating birds trade off self-maintenance for keeping eggs warm. This causes lower incubation temperature in more challenging conditions, with consequences for a range of offspring traits. It is not yet clear how low developmental temperature affects cold tolerance early in life. This is ecologically important because before full thermoregulatory capacity is attained, precocial chicks must switch between foraging and being brooded when their body temperature declines. Hence, we studied how cold tolerance during conditions similar to a feeding bout in the wild was affected by incubation temperature in Japanese quail (Coturnix japonica). Cold-incubated (35.5°C) chicks took the longest to develop, hatched smaller, and remained smaller during their first week of life compared to chicks incubated at higher temperatures (37.0°C, 38.5°C). This was reflected in increased cooling rate and reduced homeothermy, probably on account of reductions in both heat-producing capacity and insulation. Lower cold tolerance could exacerbate other temperature-linked phenotypic effects and, hence, also the trade-off between future and current reproduction from the perspective of the incubating parent.

Short-term behavioural impact contrasts with long-term fitness consequences of biologging in a long-lived seabird

Biologging has emerged as one of the most powerful and widely used technologies in ethology and ecology, providing unprecedented insight into animal behaviour. However, attaching loggers to animals may alter their behaviour, leading to the collection of data that fails to represent natural activity accurately. This is of particular concern in free-ranging animals, where tagged individuals can rarely be monitored directly. One of the most commonly reported measures of impact is breeding success, but this ignores potential short-term alterations to individual behaviour. When collecting ecological or behavioural data, such changes can have important consequences for the inference of results. Here, we take a multifaceted approach to investigate whether tagging leads to short-term behavioural changes, and whether these are later reflected in breeding performance, in a pelagic seabird. We analyse a long-term dataset of tracking data from Manx shearwaters (Puffinus puffinus), comparing the effects of carrying no device, small geolocator (GLS) devices (0.6% body mass), large Global Positioning System (GPS) devices (4.2% body mass) and a combination of the two (4.8% body mass). Despite exhibiting normal breeding success in both the year of tagging and the following year, incubating birds carrying GPS devices altered their foraging behaviour compared to untagged birds. During their foraging trips, GPS-tagged birds doubled their time away from the nest, experienced reduced foraging gains (64% reduction in mass gained per day) and reduced flight time by 14%. These findings demonstrate that the perceived impacts of device deployment depends on the scale over which they are sought: long-term measures, such as breeding success, can obscure finer-scale behavioural change, potentially limiting the validity of using GPS to infer at-sea behaviour when answering behavioural or ecological questions.

Evaluating UAV-based techniques to census an urban-nesting gull population on Canada’s Pacific coast

The use of unmanned aerial vehicles, or drones, in wildlife monitoring has increased in recent years, particularly in hard-to-access habitats. We used fixed-wing and quadcopter drones to census an urban-nesting population of Glaucous-winged Gulls in Victoria, Canada. We conducted our study over 2 years and asked whether (i) drones represent a suitable survey method for rooftop-nesting gulls in our study region; and (ii) Victoria’s urban gull population had increased since the last survey >30 years earlier. Using orthomosaic imagery derived from drone overflights, we estimated at least a threefold increase over the 1986 count reported for the entire city (from 114 to 346 pairs), and an approximate tenfold increase in the number of gulls nesting in the downtown core. Drones proved to be an excellent platform from which to census rooftop-nesting birds: occupied nests were readily discernible in our digital imagery, and incubating birds were undisturbed by drones. This lack of disturbance may be due to Victoria’s location in an aerodrome; gulls experience dozens of floatplane and helicopter flights per day and are likely habituated to air traffic. Glaucous-winged Gulls have declined considerably at their natural island colonies in the region since the 1980s. Our results indicate that although urban roofs provide replacement nesting habitat for this species, local gull populations have not simply relocated en masse from islands to rooftops in the region.

Cosmetic colouring by Bearded Vultures Gypaetus barbatus: still no evidence for an antibacterial function

Bearded Vultures regularly visit ferruginous springs for cosmetic purposes to obtain their reddish plumage colouration. Different hypotheses have been proposed to explain this deliberate application of adventitious colouration: (1) to signal individual dominance status; (2) to exploit an anti-bacterial effect of iron oxides or ochre to reduce feather degradation by bacteria and, in parallel (3) to enable incubating birds to transfer this protection to their developing embryos to increase hatching success. Here, we re-evaluate the antibacterial hypothesis using three experimental approaches: (a) by applying feather-degrading bacteria to stained and unstained bearded vulture feathers; (b) by assessing the antibacterial activity of ochre; and (c) by comparing the breeding success of orange individuals with pale ones. Our findings suggest that the in vitro addition of feather degrading Bacillus licheniformis to naturally stained Bearded Vulture feathers did not retard feather degradation compared to controls. Iron particles from red soil (ochre) or iron salts had no antibacterial effect on the growth of three species of bacteria (Escherichia coli, Kocuria rhizophila and Bacillus licheniformis), incubated either in the dark or under visible light. Finally, breeding success did not differ between territories occupied by pale individuals versus orange ones. These results run counter to the hypothesis that iron oxides have an antibacterial role in Bearded Vultures. The use of red soils by Bearded Vultures may function as a territorial status signal, but may also be involved in other processes, such as pair formation and the long-term maintenance of the pair bond, as suggested for the closely related Egyptian vulture Neophron percnopterus.

Incubation temperature influences sex ratio and offspring’s body composition in Zebra Finches (Taeniopygia guttata)

Incubation temperature has the potential to influence offspring sex, phenotype, and survival, particularly in species with temperature-dependent sex determination. However, relatively little is known about how incubation temperature affects sex ratio and offspring condition in other animals. Incubating birds allocate varying time for egg incubation depending on the parents’ condition and ambient temperature, likely altering nest microclimate. To understand how incubation temperature impacts offspring phenotype in birds, we artificially incubated Zebra Finch (Taeniopygia guttata (Vieillot, 1817)) eggs at 36.2, 37.4, or 38.4 °C during the entire incubation period and examined sex ratio and offspring quality. We found that incubation temperature of 36.2 °C resulted in a greater likelihood of a young being male compared with 37.4 °C, indicating that it is more likely for males to survive until the juvenile stage compared with females in the 36.2 °C group. We also found sex-specific effects of incubation temperature on body composition. Although incubation temperature did not affect fat or lean mass of female young, male offspring from the 38.4 °C group had significantly less lean mass throughout their lives compared with males from 37.4 or 36.2 °C. This study shows that there are sex differences in the effects of incubation temperature, and variable incubation temperature has a capacity to influence offspring secondary sex ratio and body condition in songbirds.

Temporary mate removal during incubation leads to variable compensation in a biparental shorebird

ABSTRACTBiparental care for offspring requires cooperation, but it is also a potential source of conflict, since one parent may care less at the expense of the other. How, then, do parents respond to the reduction of their partner’s care? Theoretical models predict that parents that feed offspring should partially compensate for the reduced care of their partner. However, for incubating birds partial compensation is unlikely the optimal strategy, because the entire brood can fail with reduced care. Although biparental incubation dominates in non-passerine birds, short-term manipulations of parental care and evaluations of individual differences in the response, both crucial to our understanding of parental cooperation, are scarce. Here, we describe the response of semipalmated sandpiper (Calidris pusilla) parents to a 24-hour removal of their partner during the incubation period, explore factors that can explain individual variation in the response, and describe how incubation rhythms changed after the removed parent returned. On average, the parents compensated partially for the absence of their partner’s care (59%; 95%CI: 49-70%,N= 25 individuals). The level of compensation did not differ between the sexes. However, individual responses varied from no to full compensation (2-101%). In seven nests where the removed parent never returned, the widowed parent attended the nest for 0-10 days (median: 4 days). In contrast to patterns observed in undisturbed nests or in uniparental species, nest attendance during compensation tended to be higher during the warmer part of the day. Although the level of compensation was not related to the before-experimental share of incubation, more responsive parents (that left the nest earlier upon human approach) compensated more. The quality of incubation in the after-experimental period was lower than usual, but improved quickly over time. Our findings suggest that full compensation might be limited by energetic constraints or by variation in responsiveness to the absence of the partner. Nevertheless, semipalmated sandpiper parents are able to adjust their subsequent incubation behaviour to take full responsibility for the nest when widowed. Because (nearly) full compensation was the most common response, we speculate that all individuals attempt full compensation, but that some fail because their energy stores get depleted, or because they are less responsive to the absence of their partner.

Parental Risk-Taking at Natural Northern Bobwhite Nests

Parental risk-taking at the nest is critical to examining the trade-offs between current and future reproduction. Using Northern Bobwhites ( Colinus virginianus) at camera-monitored nests in the natural environment, we examined how parental and offspring characteristics, predator community, and predator type affected flush distance of incubating birds to approaching predators. During 1999–2006, we monitored 118 predation interactions at nests at two pairs of study sites in southern Georgia and northern Florida, USA where mesomammalian predators were experimentally reduced or not reduced. The results showed that incubating parent birds allowed closer approaches by predators that typically only consumed eggs ( e.g. Nine-banded Armadillos Dasypus novemcinctus, Virginia Opossums Didelphis virginiana, and snakes) than by predators that could harm the adults (including Bobcats Lynx rufus and Raccoons Procyon lotor) prior to flushing from the nest. Our data did not support the hypotheses that parent-offspring characteristics and predator community affect parental risk-taking at the nest. Our findings suggest that parent birds incorporate information about predator identity over parental and offspring characteristics or predator community into anti-predator decisions at the nest in systems with high predation risk.