Success In Tree Swallows Research Articles

The influence of conspecific and heterospecific neighbours on avian reproductive success

Abstract We investigated the influence of conspecific and heterospecific neighbours on the reproductive success of mountain bluebirds (Sialia currucoides) and tree swallows (Tachycineta bicolor) over eight breeding seasons. The abundance of heterospecific neighbours was negatively associated with reproductive success in mountain bluebirds but positively associated with reproductive success in tree swallows during the early nesting period (i.e., hatching rate). For bluebirds, conspecific and heterospecific neighbour abundance was associated with higher reproductive success (i.e., fledging rate) during the later stages of the nesting period; the same was true for conspecific abundance for tree swallows. These findings could be explained by either positive behavioural interactions (e.g., shared defence) or by habitat quality. We found contrasting effects of nearest neighbour distance. For both mountain bluebirds and tree swallows, having a tree swallow neighbour in close proximity was positively associated with reproductive success during the early nesting period, while having a mountain bluebird neighbour in close proximity was negatively associated with reproductive success during the late nesting period for mountain bluebirds. Together, these results indicate that the effects of conspecific and heterospecific neighbours on reproductive success are species-specific and vary depending on the phase of reproduction.

Experimental anthropogenic noise impacts avian parental behaviour, nestling growth and nestling oxidative stress

Human-produced noise, from transport, urbanization and industry, is widespread. Studies of noise pollution show a wide range of effects on birds, such as alterations in communication, parental behaviour, physiology and reproductive success. These human-induced changes are likely to have long-term impacts, such as altered nestling physiology and survival, as well as reduced local population size. Further experimental field studies that simultaneously investigate the effects of noise exposure on avian behaviour, physiology and reproductive success are needed. Here, we used an experimental field study to investigate impacts of short-term traffic noise exposure on parental behaviour (i.e. vigilance and feeding rate), nestling body size and oxidative stress (as measured by oxidative status) and nestling fledging success in tree swallows, Tachycineta bicolor. Our results show negative consequences of traffic noise exposure, despite a relatively modest playback regime (6 h, every other day). Adults in noise-exposed territories were less vigilant earlier in the nestling period and fed at a higher rate later in the nestling period, compared to controls. However, increased feeding rate in noise-exposed nests did not compensate for noise impacts on nestlings: noise-exposed nestlings were smaller and had higher oxidative status, compared to control nestlings. Noise-exposed nestlings took longer to fledge, but we found no effect of noise on fledging success. These results highlight the potential long-term consequences of short-term noise exposure (decreased nestling size and increased oxidative status) and add to a growing body of literature, showing that noise pollution can negatively impact birds through both direct and indirect pathways.

Experimental evidence that brighter males sire more extra-pair young in tree swallows.

Across taxa, extra-pair mating is widespread among socially monogamous species, but few studies have identified male ornamental traits associated with extra-pair mating success, and even fewer studies have experimentally manipulated male traits to determine whether they are related directly to paternity. As a consequence, there is little experimental evidence to support the widespread hypothesis that females choose more ornamented males as extra-pair mates. Here, we conducted an experimental study of the relationship between male plumage colour and fertilization success in tree swallows (Tachycineta bicolor), which have one of the highest levels of extra-pair mating in birds. In this study, we experimentally dulled the bright blue plumage on the back of males (with nontoxic ink markers) early in the breeding season prior to most mating. Compared with control males, dulled males sired fewer extra-pair young, and, as a result, fewer young overall. Among untreated males, brighter blue males also sired more extra-pair young, and in paired comparisons, extra-pair sires had brighter blue plumage than the within-pair male they cuckolded. These results, together with previous work on tree swallows, suggest that extra-pair mating behaviour is driven by benefits to both males and females.

Individual and environmental determinants of reproductive success in male tree swallow (Tachycineta bicolor)

Evaluating the contribution of individual and environmental determinants of reproductive success is essential to improve our understanding of sexual selection. In socially monogamous bird species with high rates of extrapair paternity, traits or environmental contexts affecting the number of within-pair young (WPY) produced by males can differ from those affecting the number of extrapair young fathered (EPY). Here, we use a 4-year dataset collected in contrasted environments to assess the factors affecting male reproductive success in tree swallows (Tachycineta bicolor), a species showing high levels of extrapair paternity. Our analyses revealed that the number of WPY was higher under better environmental conditions, while the number of EPY was mainly related to male characteristics. Males nesting in more intensive agricultural areas had fewer WPY produced and a lower reproductive success. Also, males breeding earlier in the season had more WPY. The presence of parasites reduced males’ reproductive success, mainly by reducing the number of EPY. The influence of male phenotype varied according to population density: Tarsus length variation had a greater effect on reproductive success at low population density than at high density, while wing length was also positively related to the number of EPY, more so at high than at low density. Altogether, our results suggest a complex interplay between individual and environmental determinants of reproductive success and imply that sexual selection dynamics varies depending on environmental contexts.

The role of weather in mediating the effect of mercury exposure on reproductive success in tree swallows

Mercury is a heavy metal that has contaminated countless ecosystems throughout the world. A large body of literature has documented reproductive, physiological, and behavioral impairments associated with mercury exposure in laboratory settings, but whether and how such effects are manifest in free-living populations remains poorly understood. The purpose of this study was to evaluate whether tree swallow (Tachycineta bicolor) breeding success at a site with high mercury exposure varied with ambient temperature or precipitation at various points in the breeding cycle. Tree swallows nesting along the South River had significantly elevated blood total mercury (mean ± SE: 3.03 ± 0.15 μg/g) compared to swallows breeding on reference sites (mean ± SE: 0.16 ± 0.005 μg/g). These high levels of mercury were associated with reduced hatching and fledging success, and contaminated birds produced approximately one less fledgling per nest than their reference counterparts. The magnitude of this difference was weather-dependent: unusually high ambient temperatures encountered early in the nestling period were associated with reduced reproductive output in contaminated, but not in reference, birds. In contrast, little effect of mercury on success of nestlings was observed when temperatures were cooler, and precipitation also had no detectable interaction with mercury. These results provide insight into mechanisms underlying reproductive effects of mercury. In addition, these findings underscore the importance of considering variable environmental conditions when assessing effects of contaminants on free-living wildlife. In particular, projections about the effects of global climate change on ecotoxicological impacts must take into account the kinds of weather-mediated effect demonstrated here.

Sperm quantity and quality effects on fertilization success in a highly promiscuous passerine, the tree swallow Tachycineta bicolor

Sperm competition is widespread among animal taxa and considered a major force in sperm evolution. Recent comparative studies have indicated that sperm competition selects for high sperm production capacity and long and fast-swimming spermatozoa across species. Here, we examine the role of sperm quantity and quality for fertilization success of individual males in a Canadian population of tree swallows Tachycineta bicolor, a socially monogamous, but highly promiscuous passerine. Male fertilization success (the sum of withinpair and extrapair young) was significantly associated with the size of the cloacal protuberance (a proxy for sperm quantity), but not with sperm size or in vitro sperm swimming speed. In a multivariate analysis, both cloacal protuberance volume and relative sperm midpiece size (i.e. high mitochondrial loading) had significant effects on male fertilization success. However, relative sperm midpiece size was not associated with fertilization success in a simple regression. Further, both cloacal protuberance volume and relative midpiece size had significant effects on sperm velocity, both in simple regressions and in a multivariate analysis. The finding that males with large relative midpiece size had both higher fertilization success and faster swimming sperm, suggests an indirect link between sperm morphology and male fertility mediated through sperm velocity. In conclusion, both quantitative and qualitative sperm traits seem to affect male fertilization success in tree swallows.

Old Nest Material in Nestboxes of Tree Swallows: Effects on Reproductive Success

Researchers studying hole-nesting birds breeding in nestboxes typically remove old nests from boxes. In natural cavities, old nest material accumulates with successive use. Here, we report on a two-year experiment concerned with the effects of the accumulation ofused nest material in nestboxes on the reproductive success of Tree Swallows (Tachycineta bicolor). Tree Swallows nested in clean boxes, boxes with old, unmanipulated material, and in boxes with old nests that had been microwaved to kill parasites inside. Bird fleas (Ceratophyllus idius) were more numerous in boxes with old nest material compared to clean boxes in both years. Reproductive output and nestling size were significantly reduced in the second year of the study, possibly because of higher numbers of bird fleas in two box-types that year. However, all instances of entire brood loss that year occurred during two periods of extreme weather, so we cannot distinguish between the possible effects of parasites and climate. In one year, the swallows nested later in boxes with old material. Otherwise, nesting phenology, reproductive output, and nestling size were not different between pairs using boxes with and without old material in either year. In both years, there was a significant, positive correlation between clutch size and cavity size. Contrary to some recent studies, there were no significant associations between the numbers of fowl mites (Ornithonyssus sylviarum), bird fleas, or blowflies (Protocalliphora sialia) per nestling, and any measures of reproductive output or nestling size in either year. We discuss our results in light of a recent critique of studies of birds breeding in nestboxes.

Sexual Dimorphism and Breeding Success in Tree Swallows and Collared Flycatchers

The common pattern of small differences in body size between the sexes of many bird species has been related to a number of ecological factors, including functional differences in niche utilization (Selander 1966, Wallace 1974, Hogstad 1978), sexual differences in nest defense requirements (e.g., Wiklund and Stigh 1983, Safina 1984), and to differential migration strategies (Ketterson and Nolan 1983). While a number of these studies assume that a small degree of sexual dimorphism in body size leads to differential flight performance (see Andersson and Norberg 1981), the possible consequences of such differences have rarely been investigated empirically. Gosler (1987a, 1987b) suggested that sexual differences in the bill length of Great Tits (Parus major) may enhance the ability of pair members to aquire food, through decreased intrapair competition. This same argument has been made for the evolution of reversed sexual size dimorphism in raptors (Newton 1979), typically in reference to differences in wing size/shape and flight performance. This argument rests on the premise that pair members that differ in body size/shape are able to exploit a wider range of prey items. Gosler's (1987a, 1987b) studies of Great Tits provided such evidence and also drew a direct link between the degree of within-pair sexual dimorphism and breeding success. However, more recent work by Matthysen et al. (1991) found no such link among Blue (P. caeruleus) and Great Tits in Belgium. Previous studies have demonstrated significant effects of small differences in wing length and shape on the foraging behavior of several species of birds (e.g., Andersson and Norberg 1981, Lifjeld and Slagsvold 1988). In this paper, we assess the relationship between reproductive success and intra-pair differences in wing length. This study differs from previous efforts by focusing on an aerial insectivore, the Tree Swallow (Tachycineta bicolor), and on a species that feeds by gleaning and flycatching, the Collared Flycatcher (Ficedula albicollis).

Aggression, superterritories, and reproductive success in tree swallows

The relationship between territorial aggression and reproductive success was studied on a well-established, insular population of tree swallows. Four treatments of nest boxes that differed in interbox distances were created. Short interbox distances significantly reduced the occupancy of nest boxes both between and within years. Swallows in short interbox distance treatments defended more than one nest box, which was an additional resource not necessary for their successful reproduction. Excluded potential breeders attempted to colonize vacant boxes within another swallow's territory throughout the nestling period, but were usually prevented by the aggression of the resident pair. Aggressive activity had no direct effect on three measures of a swallow's reproductive output: percent young fledged, nestling growth, and fledgling weights. The concept of intraspecific aggressive neglect is questioned. However, by excluding potential breeders from nesting, for whatever reason, breeding tree swallows increased their relative genetic contribution to future generations.