Many types of chemical pollutants biomagnify across the food chain and reach their highest levels in predators such as kestrels. In urban and suburban environments, kestrels are also being exposed to non-chemical pollutants (e.g. electromagnetic fields, light and noise pollution), which are becoming a growing concern. This chapter summarises the ways through which a range of chemical and non-chemical pollutants may influence the behaviour, physiology and reproduction of kestrels, and describes how patterns of population recovery have followed the control and withdrawal of some chemical pollutants.

The size of home ranges of common kestrels can vary dramatically among individuals. Within the home range, each individual kestrel defends from intruders a small area around the nest that is referred to as territory. Home ranges are dynamic because their size varies across the year. Also, kestrels do not use all habitat types within their home range homogeneously, but show preferences for certain habitats. The first GPS-tracking study reported in this chapter supports early findings, but opens new avenues to improve data collection on habitat use and home-range size estimate. Finally, this chapter shows that the urban environment might not be a particularly suitable home range for kestrels, because the available evidence suggests that urban kestrels have a poorer reproductive performance than rural kestrels.

Common kestrels are defined as partial migrants because they have variable migratory strategies over their geographic distribution, from obligate migrants in the north of Europe to more sedentary habits in central and southern regions. Migratory strategies are subject to a multiplicity of external and internal drivers, which are still not well understood. Many individual kestrels also disperse, rather than migrate, from the breeding or birth area. Dispersal distances are longer in females than in males and in yearlings than in older individuals. The dispersal is influenced by a number of factors, such as individual propensity and food availability. The deployment of GPS data-loggers and geolocators on kestrels will greatly improve our understanding of their movement ecology and help to discriminate between migration and dispersal.

This chapter describes the breeding cycle of kestrels from egg laying to the nestling-rearing phase. It illustrates the different reproductive strategies of males and females, the endogenous mechanisms and environmental conditions that affect the laying date and the clutch size, the adaptive meanings of egg volume and of hatching asynchrony, and the factors that affect the probability of nestlings surviving until fledging.

Production of secondary sexual traits is a key component of reproductive investment in many sexually reproducing species. In this chapter, we have illustrated the secondary sexual traits and behaviours that are implicated in mate choice; the potential meaning of colourations of females and of their eggs as postmating sexual traits; and the signalling role of colourations in young kestrels. We have also described the biochemical bases of body colourations and the physiological costs associated with their production.

The family Falconidae constitutes a group of small to medium-sized diurnal raptors whose monophyly is strongly supported. Kestrels are included in the subfamily Falconinae. There are at least 13 species that belong to the kestrel group, but recent genetic studies suggest that the number of kestrel species might be larger, possibly 16. The paleontological and molecular evidence are congruent in suggesting an evolutionary radiation of kestrels from the Late Miocene (5.6–9.8 million years ago) through the Early Pleistocene. However, the geographic area where kestrels have originated and dispersed from is as yet unclear.

The common kestrel is a generalist predator. However, it also shows significant within-species variation in food habits, such as local specialisations on given prey (e.g. voles in northern or lizards in southern Europe) or even individual food preferences. This chapter illustrates the factors that affect the diet composition of kestrels, their foraging strategies and the processes of food competition, including kleptoparasitism. It also explores the last-generation techniques, such as stable isotope analyses and accelerometer-GPS loggers, that would enable the limits of classic methods used to study the feeding ecology of kestrels to be overcome.

The quantification of physiological and immunological functions provides fundamental information on individual state. It fosters our understanding of the costs of and constraints on life-history strategies. Research in this area on kestrels has mainly focused on immunity, energetics, hormones and antioxidants. This chapter discusses the factors that impact the immune function and describes a number of parasites and pathogens that can be detected in kestrels. It shows how the different phases of reproduction face males and females with different energetic and physiological demands. It discusses the costs associated with sibling competition, and how male and female nestlings may differ in how they optimise the trade-off between growth and self-maintenance. Finally, this chapter describes the moult phase, which represents an understudied feature of kestrel biology.

The common kestrel is evaluated as Least Concern at global level. However, at the European level, the species is considered of conservation concern due to a continuous moderate decline since the 1980s due to agriculture intensification, landscape simplification, pesticide use and loss of nesting sites. Moreover, the conservation status of some subspecies of common kestrel appears problematic. This chapter discusses the conservation status of kestrel species and subspecies, and the main top-down and bottom-up factors that affect the viability and stability of their populations. It also points out the strong limitations of our knowledge about the density-dependent and independent processes that regulate the demography and dynamics of kestrel populations. Important conservation-related topics, such as urbanisation, pesticides, or use of artificial nest boxes, have been discussed in detail in prior chapters.

The number of birds breeding in a given area (breeding density) is affected by several abiotic and biotic factors. Availability of suitable nesting sites plays a major role in determining the size of the local breeding population of birds, particularly in those species, like the common kestrel, that do not build their own nests. Kestrels do actually use old nests of corvids or holes in buildings to breed. By provisioning kestrels with artificial nest boxes, it is possible to increase the number of breeding individuals and, possibly, the population size. However, a number of factors need careful consideration to evaluate a priori the characteristics of nest boxes and locations to install them and to assess a posteriori the effects of the nest box provisioning on the reproductive ecology and population dynamics of kestrels.