Double-brooding and annual breeding success of great tits in urban and forest habitats

Urban areas differ from natural habitats in several environmental features that influence the characteristics of animals living there. For example, birds often start breeding seasonally earlier and fledge fewer offspring per brood in cities than in natural habitats. However, longer breeding seasons in cities may increase the frequency of double-brooding in urban compared with nonurban populations, thus potentially increasing urban birds’ annual reproductive output and resulting in lower habitat difference in reproductive success than estimated by studies focusing on first clutches only. In this study, we investigated 2 urban and 2 forests great tit Parus major populations from 2013 to 2019. We compared the probability of double-brooding and the total number of annually fledged chicks per female between urban and forest habitats, while controlling for the effects of potentially confounding variables. There was a trend for a higher probability of double-brooding in urban (44% of females) than in forest populations (36%), although this was not consistent between the 2 urban sites. Females produced significantly fewer fledglings annually in the cities than in the forest sites, and this difference was present both within single- and double-brooded females. Furthermore, double-brooded urban females produced a similar number of fledglings per season as single-brooded forest females. These results indicate that double-brooding increases the reproductive success of female great tits in both habitats, but urban females cannot effectively compensate in this way for their lower reproductive output per brood. However, other mechanisms like increased post-fledging survival can mitigate habitat differences in reproductive success.     

Nest desertion by Grey Fantails during nest building in response to perceived predation risk

ABSTRACT Grey Fantails (Rhipidura albiscapa), a common Australian flycatcher, commonly desert their nests before egg‐laying. We tested the hypothesis that Grey Fantails desert incomplete nests in response to the attention of predators by placing a mounted Pied Currawong (Strepera graculina), a common nest predator, near fantail nests that were under construction. As a control, we placed a mounted King Parrot (Alisteris scapularis), a nonpredatory bird similar in size to Pied Currawongs, near other fantail nests. Four of six female fantails (67%) deserted incomplete nests in response to the presentation of the Pied Currawong. In contrast, none of the seven females presented with a mounted King Parrot deserted. Female Grey Fantails may use the attention of a predator at the nest during the building stage as a cue to desert. Such desertion may be adaptive for Grey Fantails because currawongs are large predators, making successful nest defense unlikely, and they also present considerable risk to adults. In addition, fantails may raise multiple broods during a breeding season and, therefore, have a high renesting potential.     

Canopy height and seed yield in winter linseed (Linum usitatissimum) can be influenced by proximity to pink canes

Changes to growth and development in a winter linseed crop were observed adjacent to pink canes used as markers in 1997. Notably, canopy height was increased in plants positioned up to 40 cm from the pink canes. In 1998 these effects were confirmed and further characterised in a replicated experiment: extension growth occurred approximately one week earlier and canopy height was increased by 14.5 cm in plants adjacent to pink canes. The number of seed capsules was 953 m^?2 in control plots and 2567 m^?2 in plots with pink canes. Seed yield, calculated from a 0.25 m² quadrat, was 12.4 g m² in control plots and 56.1 g m^?2 in plots with pink canes. The R:FR (red:far red) ratio of light reflected from canes was approximately 1.7 compared with approximate R:FR ratios of 1.4 in incident daylight and 0.2 in light reflected from a linseed canopy (assessed using a spectral analysis system). Possible mechanisms to explain the changes in crop performance are discussed.     

City limits: Heat tolerance is influenced by body size and hydration state in an urban ant community

Cities are rapidly expanding, and global warming is intensified in urban environments due to the urban heat island effect. Therefore, urban animals may be particularly susceptible to warming associated with ongoing climate change. We used a comparative and manipulative approach to test three related hypotheses about the determinants of heat tolerance or critical thermal maximum (CT_max) in urban ants—specifically, that (a) body size, (b) hydration status, and (c) chosen microenvironments influence CT_max. We further tested a fourth hypothesis that native species are particularly physiologically vulnerable in urban environments. We manipulated water access and determined CT_max for 11 species common to cities in California's Central Valley that exhibit nearly 300‐fold variation in body size. There was a moderate phylogenetic signal influencing CT_max, and inter (but not intra) specific variation in body size influenced CT_max where larger species had higher CT_max. The sensitivity of ants’ CT_max to water availability exhibited species‐specific thresholds where short‐term water limitation (8 hr) reduced CT_max and body water content in some species while longer‐term water limitation (32 hr) was required to reduce these traits in other species. However, CT_max was not related to the temperatures chosen by ants during activity. Further, we found support for our fourth hypothesis because CT_max and estimates of thermal safety margin in native species were more sensitive to water availability relative to non‐native species. In sum, we provide evidence of links between heat tolerance and water availability, which will become critically important in an increasingly warm, dry, and urbanized world that others have shown may be selecting for smaller (not larger) body size.     

Cysteine, γ-glutamyl-cysteine and glutathione contents of spinach leaves as affected by darkness and application of excess sulfur. II. Glutathione accumulation in detached leaves exposed to H2S in the absence of light is stimulated by the supply of glycine to the petiole

When illuminated leaf discs and detached leaves of spinach ( Spinacia oleracea L. cv. Estivato) were exposed to 0.4 and 0.25 μl 1^-1 H₂S, respectively, pool sizes of cysteine and glutathione increased. In the dark, apart from these compounds, the level of γ-glutamyl-cysteine also increased. Incubation of leaf discs with 1.0 m M buthionine sulfoximine (BSO) resulted in the accumulation of cysteine only, both in the light and in darkness. When glycine was supplied to the petioles of detached leaves exposed to H₂S in the dark, the accumulation of glutathione was stimulated, while γ-glutamyl-cysteine accumulation was prevented completely. Glycolate and glyoxylate, precursors of glycine in the glycolate pathway, had nearly the same effect as glycine. Although other amino acids were apparently taken up equally well as glycine when supplied to the petiole, they were much less effective, or not effective at all, in restoring glutathione synthesis in the dark. These results provide evidence, that H₂S-induced glutathione accumulation in spinach leaves in the dark is limited by the availability of glycine, giving rise to the accumulation of the metabolic precursor γ-glutamyl-cysteine.