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Human‐provided nesting shelters such as nest‐boxes mitigate the shortage of natural breeding sites. Since artificial nests are not where animals evolved and optimised their reproductive performance, it remains inconclusive if these are adequate substitutes, ensuring equivalent fitness returns while breeding. In particular, most knowledge on the ecology of cavity‐nesting birds comes from nest‐box populations, but no study has directly compared fitness consequences of breeding inside nest‐boxes in relation to natural cavities in cities. We directly compare the reproductive performance, life‐history trait variation and fitness consequences for two small passerines, blue and great tits, breeding in nest‐boxes as opposed to natural cavities in an urban deciduous forest. We use a quasi‐experimental setting to comprehend the conservation potential of these artificial cavities and to support/question generalisations stemming from nest‐box studies. We show that the effects of cavity type vary between species: in blue tits, fitness proxies were negatively affected by nest‐boxes (lower fledging success and fledgling numbers, longer time spent in the nest and later fledging date relative to natural cavities), while in great tits, the fitness proxies were unaffected by cavity type. Importantly, we detected accelerated incubation in both species breeding in nest‐boxes. No differences in pre‐hatching traits (lay date, clutch size, hatching rates) between cavity types suggest that the fitness deterioration occurred because of post‐hatching effects. We highlight the ecological importance of old‐growth tree stands, providing natural cavities for city‐breeding animals and the need for quantifying alterations of reproductive ecology in other taxa using human‐provided nests. Owing to the detected cavity type‐dependent variation in reproductive performance, we support the criticism regarding the unconditional extrapolation of evolutionary and ecological interpretations of nest‐box studies to general populations.

Anthropomorphic activities have a large impact on ecosystems in many ways, one of which is how animals behave. Non‐motorised nature recreation is a popular human activity of which the impacts on nature are largely unknown. These activities, which include hiking, biking, pet walking and horseback riding, tend to increase during the commencement of the breeding activity for most passerine forest birds in temperate zones. We here investigated whether variation in recreational activity associates with patterns of nest box occupation and reproductive success in a long‐term study of personality‐typed great tits Parus major. We measured human disturbance in the area by recording the frequency of non‐motorised recreational activities by observations. We were particularly interested in the relationship between disturbance levels and nest box occupancy as well as the relationship between disturbance levels of occupied nest boxes and exploratory scores of the great tits that occupied them. We also investigated whether reproductive characteristics such as fledging success, clutch size, chick weight and tarsus length varied with disturbance levels at occupied nest boxes. We did not find a direct association between nest box occupation and disturbance. Habitat quality rather than disturbance explained the nest occupation. Furthermore, more exploratory individuals occupied boxes in less disturbed areas, independent of habitat quality. Fitness decreased with increasing disturbance independent of habitat quality. Chicks were heavier and had longer tarsi, and clutch sizes were bigger in less disturbed areas. In conclusion, we found breeding site choice of great tits to be independent of human activity, although there are clear fitness effects of human disturbance.

1. Suppression of pest species via a native predator is a regulating ecosystem service that has the potential to limit crop damage and produce economic benefits. American kestrels Falco sparverius are widespread, highly mobile, generalist predators that hunt in human-dominated habitats and have the potential to provide previously undocumented ecosystem services in agricultural landscapes. 2. We hypothesized that kestrel activity associated with nest boxes and artificial perches acts to increase perceived predation risk that, in combination with direct predation, can reduce fruit-eating bird abundances in orchards. We used counts and observations of fruit-eating birds from fixed-width transect surveys to investigate variation in bird abundances and to estimate sweet cherry loss in cherry orchards with and without active kestrel boxes. We also conducted a benefit-cost analysis of nest box installation and used regional economic modelling to estimate macroeconomic impacts of increased sweet cherry production in Michigan, an important US fruit production region. 3. Fruit-eating bird counts were significantly lower at orchards with active kestrel boxes. Although kestrels used the perches in young orchard blocks and may benefit from them, the presence of perches did not have a significant effect on bird counts. 4. Benefit-cost ratios for kestrel nest boxes indicated that for every dollar spent on nest boxes, $84 to $357 of sweet cherries would be saved from fruit-eating birds. Regional economic modelling predicted that increased sweet cherry production from reduced bird damage would result in 46-50 jobs created and $2.2 million to $2.4 million in increased income for the state of Michigan over a 5-year period. 5. Synthesis and applications. Kestrel nest boxes in sweet cherry orchards provide a highly cost-effective ecosystem service with potential reverberating benefits for a regional economy. Box occupancy rates will undoubtedly vary across landscapes and regions. However, costs to install and maintain boxes are small and, even if box occupancy rates are low, boxes can direct kestrel activity to particular places in agricultural landscapes where they can deter pest birds. Thus, the potential benefits for fruit crops greatly outweigh the costs of this pest management strategy.

Despite concerns about invasive Common Mynas (Acridotheres tristis), few studies have experimentally demonstrated their impact on native birds. Using a Before-After-Control-Impact (BACI) design with 142 nest boxes, we assessed how Myna presence affected House Sparrows (Passer domesticus) and Great Tits (Parus major) before (2009–2010) and after (2020–2021) their arrival in 2015. Half the boxes had large entrances accessible to all three species; half had small entrances accessible only to Great Tits. In a 2022 field experiment, we manipulated nest box entrances and used cameras to study Myna predation and nest usurpation. Following the establishment of Myna, House Sparrow breeding declined by 68.1%. Great Tits increased use of small entrance boxes by 59.9% and decreased use of large entrance boxes by 45.4%. Although overall Great Tit breeding increased, fledging success declined in large entrance boxes, but not small entrance ones. In the 2022 experiment, 46% (n = 26) of Great Tit nests were predated; Common Mynas were responsible for 50% of these cases and subsequently bred in the usurped nests. This study experimentally demonstrates that House Sparrow breeding numbers decrease and that Great Tits change their nesting behavior after the appearance of the Common Myna. Additionally, this research found that Common Mynas impact native species by predating and usurping nests. Installing small-entrance boxes can help manage Great Tit populations. Further research should explore nest box designs for House Sparrows and their impacts on other cavity-nesting and non-cavity-nesting bird species.

Nest boxes have been used for many decades as tools for conservation and to study avian population dynamics. Plastic is increasingly used as a material for nest boxes, but no studies have investigated effects of this different material. Two consecutive studies were conducted to investigate effects of nest-box environment on nidicolous parasites, bacteria and fungi, as well as nest success, in blue tits Cyanistes caeruleus and great tits Parus major. The first compared microclimate and parasite and pathogen load in plastic and wooden nest boxes. The second tested the nest protection hypothesis – that birds naturally incorporate aromatic herbs into nests to decrease nest parasites and pathogens – by comparing parasite and pathogen load in plastic nest boxes to which aromatic or non-aromatic plant material was added. No significant difference in nest-box temperature or relative humidity was found between plastic and wooden boxes. Wooden boxes, however, contained 30-fold higher numbers of fleas and a higher total bacterial load on chicks. Fledging success for blue tit broods was significantly higher in wooden boxes. Parasites and bacteria did not decrease by the inclusion of aromatic herbs. The results increase the evidence base for nest-box design in support of plastic, which can provide an appropriate alternative nest-box material to wood, with apparently no difference in microclimate and no increase in the load of measured parasites and pathogens.

Some secondary cavity-nesting birds use nest material to cover their eggs when they are out foraging during the egg-laying stage. Egg covering presumably helps regulate nest temperature and/or prevents predation or parasitism. A recent study suggested that egg covering might prevent nest usurpation and therefore, we set up nest boxes with three different treatments to test this hypothesis: bottom of the nest box covered with moss containing two eggs covered with moss (type A); floor of the nest box covered with moss and two eggs exposed on top of the moss (Type B); and bare floor of the nest box, with two eggs added (Type C). The results showed the lowest egg predation rates in Type A nest boxes, which was significantly lower than those in type C boxes; the proportion of maritime striped squirrels (Tamiops maritimus), first appearing in the three types of nest box was not significantly different; however, the rate of first entry into Type A was significantly lower than that into Type C boxes. The rate of first entry and the time the squirrels spent in Type A boxes were significantly lower and shorter than those in Type C boxes. Our results suggest that the egg-covering behavior of secondary cavity-nesting birds delayed the entry of nest competitors and accelerated the departure of nest encroachers from the nest, thus provided experimental evidence for the usurpation hypothesis.Significance statementSeveral non-mutually exclusive hypotheses have been proposed to explain the function of egg covering by bird species. The present study showed that egg covering by secondary cavity-nesting birds delayed the entry of maritime striped squirrels and accelerated the departure of nest encroachers from the nest, suggesting that egg covering might reduce the cost of nest defense for birds and thus prevent nest encroachment by other species. We provided experimental evidence for the new hypothesis proposed by Slagsvold and Wiebe (2021a) that egg-covering behavior of birds deters nest encroachers from easily entering unfamiliar, poorly lit cavities due to fear, thereby effectively preventing nest usurpation by squirrels.

Avian brood parasites depend upon locating host nests to lay their eggs. However, how brood parasites locate host nests and select the nests for parasitism remains poorly studied. Here, we examined how a non-evicting brood parasite, the Asian koel (Eudynamys scolopaceus) were able to locate host nests in locally novel nest sites. We provided a set of novel nest sites (i.e., nestboxes, n = 100) to the common myna (Acridotheres tristis), a regular host of the Asian koel, at a field site in Central Bangladesh. We found that common myna quickly utilized the novel breeding sites (n = 99 nests across 59 boxes) and similarly, 21.2% of these nests were parasitized by the Asian koel. Unsurprisingly, none of the inactive nest boxes were parasitized, neither were empty nests of common myna (i.e., either predated or fledged clutches, thus lack of parental activity, n = 83). Our results provide an experimental demonstration of the Asian koel ability to rapidly locate nests in locally novel nest sites, potentially facilitated by close monitoring of host activity and behavior around the nest site. However, the underlying mechanisms for this rapid adjustment to novel nest sites remain unresolved.

Human interaction with nature often exhibits negative aspects, such as vandalism, which involves the destruction of or damage to property. Unfortunately, very little is known about the extent, causes, and frequency of this phenomenon. Therefore, in this paper, we investigate a scale of vandalism in studies using nest-boxes in Poland. Data from published papers ( n  = 256) indicated that researchers are aware of the devastation and destruction of nest-boxes, but often lacking detailed reports. We further validated this data through emails or phone calls to the authors. Surprisingly, only 14 (5.5%) papers mentioned vandalism, and during interviews, we found that vandalism occurred in 51.7% of studies. In response to vandalism, researchers have taken measures to reduce the scale of damages, such as hanging boxes far from paths and roads, placing them above 3 m from the ground, or, more recently, using security cameras. Although vandalism was quite common, its scale was rather marginal, with some local exceptions. For a better understanding of this phenomenon, we suggest including more detailed information on vandalism in future papers, which could aid in the interpretation of scientific data, as well as in nature conservation.

According to the alternative prey hypothesis (APH), the temporal synchrony in population fluctuations of microtine rodents and other small herbivores in boreal areas is caused by generalist predators with numerical and functional response to microtines, leading to an increased predation of prey alternative to microtines in the low phase of the microtine population fluctuations. The tree‐climbing pine marten ( Martes martes ) is a food generalist that includes bird eggs among its alternative prey, also eggs of the cavity‐nesting common goldeneye ( Bucephala clangula ). We used long‐term data to test whether pine marten predation of goldeneye eggs in nest boxes varied as predicted by the APH. As a measure of microtine abundance at the time of nesting, we applied two measures. First, for goldeneye nests located <40 km from our microtine trapping site, we applied the trapping index of microtine rodents. Second, to also use data from nests located >40 km from our microtine trapping site, and from nests in years when trapping was not conducted, we used two proxies for the microtine abundance: whether boreal owls ( Aegolius funereus ) nested in any of our boxes <40 km from each goldeneye nest and the average clutch size of these boreal owls. The probability of predation of a goldeneye nest was independent of the microtine trapping index and independent of the proxies for microtine abundance. However, it increased with cavity age, taken as the number of nesting seasons elapsed since the actual nest box was installed, and declined with distance from habitat with forest canopy. The effect of cavity age confirms that the long‐term spatial memory of pine marten is an important factor in the pattern of its predation on nests in tree cavities.

Nestboxes are commonly used to increase the number and quality of nest sites available to birds that usually use tree cavities and are considered an important conservation intervention. Although usually safer than natural cavities, birds nesting in simple, unmodified wooden nestboxes remain at risk of depredation. Accordingly, numerous design and placement modifications have been developed to ‘predator-proof’ nestboxes. These include: (1) adding metal plates around entrance holes to prevent enlargement; (2) affixing wire mesh to side panels; (3) deepening boxes to increase distance to nest cup; (4) creating external entrance ‘tunnels’ or internal wooden ledges; (5) using more robust construction materials; (6) developing photosensitive shutters to exclude nocturnal predators; (7) using baffles to block climbing mammals; and (8) regular replacement and relocation. However, the benefits and costs of these modifications are not always well understood. In this global review, we collate information on predator-proofing avian nestboxes designed for tree cavity-nesting birds to assess the efficacy of techniques for different predators (mammalian, avian, and reptilian) in different contexts. We critique the potential for modifications to have unintended consequences—including increasing nest building effort, altering microclimate, reducing provisioning rate, and elevating ectoparasite and microbial loads—to identify hidden costs. We conclude by highlighting remaining gaps in knowledge and providing guidance on optimal modifications in different contexts.