Causes and Consequences of Intraspecific Variation in Nesting Behaviors: Insights from Blue Tits and Great Tits

Abstract

Nest building is an important and yet under-studied stage of the reproductive cycle in many taxa, including birds, and whilst we have a decent understanding of interspecific variation in avian nesting behaviors, our understanding of intraspecific variation in nesting behaviors is much less developed. This is largely because an insufficient number of studies have been performed on any one species to draw robust conclusions. Fortunately, though, the amount of research on the nesting behaviors of nestbox-breeding blue tits (Cyanistes caeruleus) and great tits (Parus major) has increased dramatically in recent years and their nesting behaviors are now sufficiently well-studied to offer useful insights into intraspecific variation in avian nesting behaviors. Studies show that individuals of both species select nest sites based on the presence and/or absence of conspecifics and heterospecifics and whilst neighbors were assumed to adversely affect focal individuals by competing for resources, they are now considered beneficial as they provide information about habitat quality and contribute to anti-predator defenses. Nest-building females accurately gauge local weather conditions and respond to predictable variation in environmental conditions by building nests with variable amounts of cup lining material to create suitable nest microclimates for nestlings. Meanwhile, both species vary the amount of aromatic plant materials in their nests in relation to the abundance of nest-dwelling parasites and pathogens and as aromatic plant materials also play a role in sexual selection then nest materials can have multiple functions. The height of nests is negatively correlated with the local risk of predation but whilst predator avoidance favors lower nests, sexual selection favors taller nests. In fact, higher quality females build taller nests that contain more green plant material which in turn influences the amount of care provided by males. This suggests there is considerable intraspecific variation in nesting behaviors in blue and great tits, and in birds generally, and highlights that birds are adept at adaptively varying their nesting behaviors in response to multiple factors. There is, however, a paucity of evidence directly linking such variation in nest building behaviors to reproductive success or fitness more broadly and so further studies could usefully examine such links because trade-offs between competing selection pressures may constrain adaptive nesting behaviors.

Nest height is affected by lamppost lighting proximity in addition to nestbox size in urban great tits

“…To conclude, against the common view that artificial light at night disturbs organism physiology, behaviour and reproduction, our study highlights its novel and unexpected, potential benefits for urban cavity-nesting species: shallower nests further from nest entrance in response to the presence of artificial light at night may both involve less effort to build and procure a better protection against predation (Mainwaring 2017), which may, at least partly, explain the equal reproductive success between urban and rural great tits . Of course, the interpretation of our correlative results requires some cautiousness as lamppost light-bulb specification may affect the area effectively exposed to light at night and, as a consequence, the light intensity at the nest.…”

“…behaviour. A minimal threshold of nest comfort might have been reached in the small wood-concrete and medium wood nestboxes (in which nests were already shallower) in response to selective pressures unrelated to light availability at the nest, but associated to other abiotic factors, such as protection against heavy rain or thermoregulation benefits that higher nests may confer , Mainwaring 2017). An alternative, and perhaps more likely explanation, is that the presence of lampposts in the bird territory may increase the (perceived) risks of predation and disturbance preventing the birds to search for enough nesting material to fill the largest nestboxes.…”

“…Here we provide the first field report that urban artificial light at night may cause intraspecific variation in nestbuilding behaviours, an important and yet under-studied stage of the reproductive cycle in many taxa (Mainwaring 2017). Optimal nest design protecting breeders and offspring results from evolutionary trade-offs between competing selection pressures associated with abiotic factors (e.g.…”

“…climate, illumination), conspecifics and hetero-specific organisms (e.g. predators, parasites) (Mainwaring 2017). In this context, species nesting in dark conditions (e.g.…”

“…Indeed, most nest functions in cavity-nesting birds, including maintenance of proper light, humidity, thermal and sanitary conditions for eggs and nestlings, seem to globally improve with nest sizes (reviewed in Table 1). In contrast, the risk of nest predation, which increases with nest sizes (height within the nestbox; Table 1), is likely avoided by building nests further away from the cavity entrance, rendering them either unreachable for large predators, which are unable to enter the cavity or pull out the contents, or undetectable for small predators able to enter the cavity (Mainwaring 2017). Artificial light at night could also lead cavity-nesting birds to build thinner nests because such nocturnal light may increase nest detection and the visibility of nest content at times of the day where it is undetectable (Holveck et al 2010, Gomez et al 2014) (potentially to the benefits of the parents at dusk and dawn) as well as disturb the birds sleeping in the cavity (reference herein).…”