Article

Nest box design for a changing climate: The value of improved insulation

Authors:
  • ACT Environment, Planning and Sustainable Development Directorate
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Abstract

Mean air temperatures and the frequency, intensity and duration of extreme weather events such as heatwaves are increasing due to climate change. Nest boxes experience more variable and extreme temperatures than natural cavities, which may reduce survival and reproductive success of the species which utilize them, but little is known about the factors which drive nest box temperature profiles. We quantified the potential for retrofitted insulation on nest boxes to modify internal temperatures and to mimic the thermal characteristics of natural cavities more closely. We tested three types of materials with insulative or reflective properties which were easy to retrofit to nest boxes: 3-cm-thick polystyrene, pleated foil batts and reflective paint. We found that polystyrene and foil batts reduced mean nest box temperatures during the day by 0.31 ± 0.01°C and 0.17 ± 0.01°C, respectively (but up to 5.84°C and 4.02°C). The effects of all insulation types were dependent on the time of day, and only polystyrene had a significant effect at night, with a greater capacity to retain heat (mean 0.21 ± 0.01°C warmer). Contrary to expectations, reflective paint caused a small increase in temperature during the late afternoon. In our study, the temperature modulation provided by insulation was able to match or exceed that due to variation in nest location and surrounding vegetation canopy cover. Our findings show that polystyrene and foil batts may offer effective and tractable means to mitigate the effects of extreme temperatures in nest boxes and thereby help achieve temperature profiles more similar to natural cavities.

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... The internal temperatures of nestboxes documented in some recent Australian studies have been measured in conjunction with temperatures inside neighbouring natural or created hollows (Isaac et al. 2008;Goldingay 2015;Larson et al. 2015;Ellis 2016;Griffiths et al. 2017Griffiths et al. , 2018Rowland et al. 2017;Larson et al. 2018;Stojanovic et al. 2019; see also Goldingay 2020; Goldingay and Thomas 2021). Despite variable methodologies and analyses, some generalisations can be made from these studies. ...
... Nestboxes used for conservation and management are rarely painted white and are often stained in natural wood colours (as were our unpainted boxes) or painted in greens and browns to blend in with the environment and reduce visibility (Goldingay 2015). Two recent studies have examined the thermal effects of painting nestboxes such colours (Goldingay 2015;Griffiths et al. 2017; see also Larson et al. 2018). Griffiths et al. (2017) demon strated that white painted boxes do not get as hot at maximum daytime temperature as dark painted boxes. ...
... These include contributing little weight to the nestbox other than the second wall (compare using thicker or denser wood/ materials), avoiding environmental/biodegradability issues associated with insulators such as polystyrene or foil batts (e.g. Larson et al. 2018), keeping costs down, the ability to easily retrofit existing boxes that are overheating and the bonus that the additional layer will also help protect boxes (Table 2) for Trails III-V. Equations for unpainted nestboxes vs ambient were derived from the larger combined data sets of Trials I, II and V and for painted nestboxes vs ambient from Trials II-IV. ...
... With 2019 being the second warmest year on record (mean global temperature anomaly of +0.95 C above average; NOAA, 2020), temperatures expected to increase 0.4-2.6 C by mid-century (IPCC, 2014), and heat waves expected to increase in frequency, intensity, and duration (Meehl & Tebaldi, 2004), overheating events in bat boxes may become more common (Bideguren et al., 2018;Larson, Eastwood, Buchanan, Bennett, & Berg, 2018). Currently, we lack empirical research on the impacts of climate change on bat box designs and deployment strategies (but see Bideguren et al., 2018;Larson et al., 2018). ...
... C by mid-century (IPCC, 2014), and heat waves expected to increase in frequency, intensity, and duration (Meehl & Tebaldi, 2004), overheating events in bat boxes may become more common (Bideguren et al., 2018;Larson, Eastwood, Buchanan, Bennett, & Berg, 2018). Currently, we lack empirical research on the impacts of climate change on bat box designs and deployment strategies (but see Bideguren et al., 2018;Larson et al., 2018). Addressing this uncertainty is critical for the success of bat boxes as a conservation tool. ...
... For example, Doty, Stawski, Currie, and Geiser (2016) found maximum temperatures in white, single-chamber bat boxes were 7.5 C cooler than in black bat boxes; notably, however, bats preferentially selected black bat boxes in their wintertime study, likely due to the thermal benefits of a warmer microclimate (Wilcox & Willis, 2016). Using dense construction materials with low thermal conductance could also reduce overheating risk (Bideguren et al., 2018) and lead to more stable microclimates (Larson et al., 2018). For example, black, fourchambered bat boxes made of wood-cement (a molded mixture of wood shavings and cement) buffered high temperatures better than an identical design made out of plywood; the wood-cement design was up to 3.2 C cooler during the summer (Rueegger, 2019). ...
Article
Full-text available
Bat boxes are commonly deployed to mitigate the loss of bat roosting habitat. Due to a dearth of microclimate research, numerous untested commercially available bat boxes, and the uncertain impacts of a rapidly changing climate, the overheating risk presented to bats by bat boxes is largely unquantified. Based on limited research, we know many boxes overheat (i.e., temperatures >40°C). A lack of standardized protocols to evaluate microclimate and misleading information available to the public leads to a murky understanding of risks involved with deploying bat boxes. Herein, we evaluate the thermal tolerance of temperate‐zone bats, delineate areas of concern regarding the risks to temperate‐zone bats when bat boxes are deployed, identify strategies for reducing overheating risk, suggest methods for assessing microclimate, and provide a visual framework to assess overheating risk. Identifying suitable design and placement combinations is crucial to developing region‐specific strategies to mitigate against overheating. We urge consideration of the risks involved with using bat boxes, advocate for rigorous testing before deployment, and suggest using alternatives when possible.
... We expand on prior work by interactively investigating the effects of a box's thermal mass, ventilation, and enhanced surface reflectance on DEE and overheating risk. (Larson et al., 2018). Increasing bat box thermal mass should decrease metabolic costs for normothermic endotherms. ...
... When deploying bat boxes for maternal bat populations, practitioners should consider the use of box designs that increase thermal mass (EJW in this study) to buffer against overheating events while simultaneously decreasing DEE endothermic . We recommend further experiments altering thermal mass, thermal conductance and surface reflectance to improve upon current bat box designs, as these modifications will be critical to buffering the immediate effects of overheating and longterm effects of a warming climate (Larson et al., 2018). ...
Article
Bat box microclimates vary spatially and temporally in temperature suitability. This heterogeneity subjects roosting bats to a variety of thermoregulatory challenges (e.g. heat and cold stress). Understanding how different bat box designs, landscape placements, weather and bat use affect temperature suitability and energy expenditure is critical to promote safe and beneficial artificial roosting habitat for species of conservation concern. From April to September 2019, we systematically deployed 480 temperature dataloggers among 40 rocket box style bat boxes of 5 designs and regularly monitored bat abundance. We used bioenergetic models to assess energy costs for endothermic and heterothermic bats and modelled the overheating risk for each box as a function of design, placement, bat abundance and weather. For endothermic bats, predicted daily energy expenditure was lower for solar-exposed placements, large group sizes and a box design with enhanced thermal mass. For heterothermic bats, shaded landscape placements were the most energetically beneficial and bat box design was not important, because all designs generally offered microclimates suitable for torpor use at some position within the box. Overheating risk was highest for solar-exposed landscape placements and for designs lacking modifications to buffer temperature, and with increasing bat abundance, increasing ambient temperature and slower wind speeds. The external water jacket design, with the greatest thermal mass, concomitantly decreased overheating risk and endothermic energy expenditure. By assessing bat box suitability from two physiological perspectives, we provide a robust method to assess the conservation value of bat box design and placement strategies. We recommend future studies examine how changing thermal mass and conductance can be used to diminish overheating risk while also enhancing the effects of social thermoregulation for bat box users.
... The reasons evening bats roosted in our bird nest boxes are unclear. Bats in Europe and Australia have used nest boxes designed for nesting birds (Rueegger, 2016;Larson et al., 2018), but characteristics of our nest boxes differ from those of European and Australian nest boxes (e.g., pine nest boxes, placed on trees 4-5 m off the ground, with a 7.5 cm hole; Larson et al., 2018). Aspect and height are not strong factors in box use by bats (Goldingay and Stevens, 2009). ...
... The reasons evening bats roosted in our bird nest boxes are unclear. Bats in Europe and Australia have used nest boxes designed for nesting birds (Rueegger, 2016;Larson et al., 2018), but characteristics of our nest boxes differ from those of European and Australian nest boxes (e.g., pine nest boxes, placed on trees 4-5 m off the ground, with a 7.5 cm hole; Larson et al., 2018). Aspect and height are not strong factors in box use by bats (Goldingay and Stevens, 2009). ...
Article
Forest bats, including evening bats (Nycticeius humeralis), sometimes roost in manmade structures, such as barns and bridges, but here we report the first observations of evening bats using bird nest boxes for roosting on multiple occasions between 2012 and 2019, a few kilometers north of Jonesboro, Arkansas. Most encounters were in August, when the nesting season is almost finished. We discuss timing and factors that may explain use of bird nest boxes for roosting by bats.
... In one study, white painted boxes tracked ambient temperatures during summer and were several degrees cooler than green painted boxes (Griffiths et al. 2017). In another study, the addition of polystyrene insulation to the roof and west wall of boxes reduced internal temperatures by 0.9-1.7 C relative to controls (Larson et al. 2018). However, as far as we are aware, no studies have explored whether modifying nest box designs (via addition of insulation, painting, or both) can reduce internal temperatures during summer heatwaves. ...
... In one study, researchers compared temperatures of nest boxes that were unpainted, painted white, or were insulated with aluminium foil batts or 3-cm-thick white polystyrene. In that study, temperatures inside polystyrene insulated boxes were 0.9-1.7 C lower than those of uninsulated boxes (Larson et al. 2018). By contrast, the roofing insulation that we used in our study reduced maximum temperatures by 3.1 C, much lower than was achieved with polystyrene. ...
Article
Full-text available
In urban bushland, the installation of nest boxes is widely used to compensate for the loss of natural tree hollows. However, current nest box designs may not provide thermal refuges for wildlife during summer heatwaves, particularly if internal temperatures exceed the upper critical temperatures of wildlife. We investigated whether the addition of roofing insulation to nest boxes deployed for sugar gliders (Petaurus breviceps) and squirrel gliders (Petaurus norfolcensis) in urban bushland would reduce internal nest box temperatures during summer heatwaves. We measured temperatures of 44 insulated and 47 uninsulated nest boxes during one of the hottest summers on record (2018–2019) in the Lake Macquarie region of NSW, Australia, a period during which several prolonged heatwaves occurred. Over the 90-day study, maximum temperatures were, on average, 3.1°C lower in insulated boxes than in uninsulated boxes. The addition of insulation significantly lowered nest box temperatures regardless of aspect (north or south facing) or day of measurement. Temperatures exceeded the upper critical temperature (35.1°C) of gliders more frequently in uninsulated nest boxes (28% of days) than in insulated nest boxes (8% days). Although the addition of insulation to nest boxes lowered their internal temperatures, during heatwaves spanning 23 days, nest box temperatures exceeded the upper critical temperatures of gliders on 58% and 23% of days in uninsulated and insulated nest boxes respectively. These findings underscore the importance of retaining natural hollows in urban bushland to provide thermally suitable refuges for wildlife during extreme heat events.
... Cliff swallows (Petrochelidon 6 pyrrhonota (Vieillot, 1817)) are declining in northeastern North America (annual rate of decline in New Brunswick, Canada: -5.31 [CI: -6.74, -3.77], Sauer et al. 2017), so determining if there is an ecological trap affecting cliff swallow reproductive success is imperative for conservation. If eaves are indeed ecological traps, then it may be possible to mitigate these effects with insulating materials (Maziarz et al. 2017;Larson et al. 2018a). ...
... While some work has begun to consider and investigate possible ways to mitigate the effects of warming temperatures on breeding success for cavity nesters that use nest boxes, including insulation and reflective paint (Maziarz et al. 2017;Larson et al. 2018a), less thought has been given to other species that use human infrastructure for nesting, such as cliff swallows. ...
Article
When an environmental cue that previously signaled a suitable habitat leads an animal to use an unsuitable site, individual fitness can decrease, ultimately leading to population declines. Such “ecological traps” may be particularly likely for birds that use human infrastructure for nesting. Here we tested whether high nest temperatures and the physical properties of barns are associated with lower breeding success for a declining population of Cliff Swallows (Petrochelidon pyrrhonota (Vieillot, 1817)). We monitored nests under barn eaves below wood and metal roofs to determine nestling survival and mass, and recorded temperature under barn eaves, to relate ambient temperature to eave temperature. We found that eave temperature increased with ambient temperatures and was higher at high temperatures and lower at cool temperatures under metal roofs than wood roofs. Nestling survival was lower during periods with higher ambient temperatures, and both survival and mass were lower under metal roofs. Our findings suggest that barn eaves, especially those with metal roofs, may be an ecological trap for Cliff Swallows, where a seemingly suitable nesting site early in the breeding season results in low breeding success. Furthermore, warming temperatures may lead to ecological traps for other bird species, particularly those nesting in man-made structures.
... Moreover, the amount of heat generated by endothermic animals and retained inside cavities might differ between sites, with presumably greater amount of heat retained in those that insulate more efficiently, i.e. more effectively reduce heat loss from inside (Kearney et al. 2011;Larson et al. 2018). Thus, the microclimate of occupied cavities might depend on a combination of ambient temperature, cavity insulation and the heating activity of endothermic occupants. ...
... These findings were in stark contrast to the expectations of greater heat retention in tree cavities that insulate most efficiently. Such expectations were based on observations from nest boxes, where those with improved insulation resulted in a greater internal temperature increase in response to an artificial heat source within, compared to those nest boxes without additional insulation (Kearney et al. 2011;Larson et al. 2018). Following installation of heat pads, Grüebler et al. (2014) recorded only a slightly greater temperature increase in empty tree cavities compared to nest boxes, which insulated less effectively. ...
Article
Full-text available
The microclimate of cavities used by endothermic animals may depend on dynamic relationships between a cavity’s physical properties and the heating activity of cavity users, but the rudiments of these relationships are unclear. I compared the temperature and relative humidity of active tree cavities that were occupied by nesting marsh tits Poecile palustris with the conditions in vacant tree cavities previously used for breeding by this species. I tested how presence of active nests modified initial cavity microclimate, and if this modification changed with nest progression or cavity insulation. In 2013–2014, mean daily internal ambient temperature differences averaged 1.5–4.1 °C higher and relative humidity 8–10% lower, in active cavities relative to vacant sites, with greatest differences in the late nestling period. Compared to vacant cavities and relative to respective ambient values, the greatest daily minimum temperature increase was in active cavities located in the thinnest trees, which insulated least efficiently. As daily minimum temperatures were elevated to a similar level relative to outside within all active cavities, birds appeared to compensate for heat loss from cavities by warming the air within in a homeostatic manner. Similar to vacant cavities, the differences between daily maximum internal and ambient temperatures decreased with tree girth in active cavities, indicating that daily temperature maxima were systematically moderated in the thickest trees. The study demonstrates the modifying effect of birds’ breeding activity on tree-cavity microclimate and highlights the role of a cavity’s thermal properties in reducing the energy expenditure and risk of overheating for cavity users.
... Recently, there has been growing interest in developing better-insulated nest boxes (Larson et al. 2018;Martin Bideguren et al. 2018;Ellis and Rhind 2021;Honey et al. 2021). Alternative habitat-creation methods, such as mechanically carving cavities directly into trees with chainsaws (chainsaw hollows, CHs), or re-attaching hollowed-out logs in trees (log hollows, LHs), also offer potential to provide well insulated shelters. ...
Article
Context. Supplementary shelters for hollow-dependent fauna, such as timber or plywood nest boxes, have much drier and less thermally insulated cavity microclimates than do natural tree hollows. Hollow-dependent endotherms can experience hyperthermia and dehydration when occupying poorly insulated nest boxes during extreme heat. Aims. We investigated the effectiveness of three different types of artificial hollows in buffering hollow-dependent birds and mammals against hyperthermia and dehydration during extremely hot summer weather (ambient air temperatures >40°C). Methods. We recorded microclimate (temperature and relative humidity) data inside (1) chainsaw hollows carved into live trees, (2) log hollows, and (3) plywood nest boxes, during extremely hot weather events in Australia in December 2019–January 2020 (austral summer). We quantified temporal variation in microclimates inside the different supplementary shelters relative to ambient conditions and used statistical models to evaluate the effects of different factors (wall thickness and solar exposure) on internal microclimates. Key results. Microclimates inside chainsaw hollows were significantly different from those in log hollows and nest boxes, remaining >16°C cooler and 50 percentage points more humid than ambient conditions when daytime air temperatures reached 45°C. In comparison, nest boxes closely tracked ambient conditions throughout the day. Log hollows had an intermediate microclimate profile, getting warmer and drier than chainsaw hollows during the day, but remaining cooler and more humid than nest boxes. Conclusions. Our results showed that artificial hollows more effectively mimic the stable microclimates inside naturally occurring hollows if placed inside the tree (e.g. carved into the tree trunk of live trees), rather than attached to the outside. Implications. The chainsaw hollow design we tested could provide microclimate refugia that reduce the risks of hollow-dependent wildlife experiencing either hyperthermia in regions with hot summer climates, or hypothermia in areas with cold winters. We encourage managers to consider incorporating chainsaw hollows into existing nest box programs to provide fauna with well insulated microclimate refugia.
... This study indicated that: white boxes, box materials that buffer warm ambient temperature (e.g., wood-cement over plywood) and box designs that comprise a temperature gradient within the box (e.g., multiple chambers with vents) can negate hot ambient temperature to some extent. Consideration of these box design elements and identifying other design elements to further improve the buffering capacity from extreme heat [56,67] may be particularly important given the predicted climate warming and increased periods of extreme heat [68]. ...
Article
Full-text available
Bat boxes are commonly used as a conservation tool. Detailed knowledge on the influence of box elements on microclimate is lacking, despite eco-physiological implications for bats. Summer and winter box temperature and relative humidity patterns were studied in narrow multi-chambered plywood and wood-cement boxes in eastern Australia. Box exteriors were black or white and plywood boxes comprised vents. Relative humidity was higher in white boxes than black boxes and box colour, construction material, chamber sequence and vents influenced temperatures. Maximum box temperature differences between designs varied by up to 9.0 °C in summer and 8.5 °C in winter. The black plywood box consistently recorded the warmest temperatures. This design comprised a temperature gradient between chambers and within the front chamber (influenced by vent). During the 32-day summer sampling period, the front chamber rarely recorded temperatures over 40.0 °C (postulated upper thermal tolerance limit of bats), while the third and fourth chamber never reached this threshold. At the study site, the tested black boxes are considered most thermally suitable for bats during average summer conditions. However, during temperature extremes black boxes likely become too hot. Wood-cement, a durable material not previously tested in Australia should be considered as an alternative construction material.
... As a result, rectilinear nest boxes can entrap their inhabitants [6]. Their geometry and materials overheat [7]. Nest boxes can be hard to install, and their lifespan is short. ...
Chapter
Full-text available
Anthropogenic degradation of the environment is pervasive and expanding. Human construction activities destroy or damage habitats of nonhuman lifeforms. In many cases, artificial replacement habitats become necessary. However, designing for the needs and preferences of nonhuman lifeforms is challenging. Established workflows for this type of designing do not exist. This paper hypothesises that a multi-scale modelling approach can support inclusive, more-than-human design. The case-study project tests this approach by applying computational modelling to the design of prosthetic habitats for the powerful owl (Ninox strenua). The proposed approach simulates owls’ perception of the city based on scientific evidence. The tools include algorithmic mapping, 3D-scanning, generative modelling, digital fabrication and augmented-reality assembly. Outcomes establish techniques for urban-scale planning, site selection, tree-scale fitting, and nest-scale form-making. The findings demonstrate that computational modelling can (1) inform more-than-human design and (2) guide scientific data collection for more inclusive ecosystem management.
... Over eight breeding seasons, we trapped breeding P. elegans in nest boxes (Berg and Ribot 2008;Larson et al. 2015Larson et al. , 2018, and fitted them with an ABBBS leg band, collected approximately 80 µl of blood from the brachial vein of both nestlings and their putative parents, stored this in ethanol and noted egg hatching rates. Birds were sampled at 14 sites in south-eastern Australia, from two subspecies and the WS hybrid. ...
Article
Full-text available
Genetic analyses have revolutionised our understanding of avian mating systems. However, the majority of such studies to date have focused on passerine species. Despite this taxonomic bias, extra-pair paternity (EPP) and conspecific brood parasitism (CBP) are usually concluded to be less common in taxa with pronounced longevity, socially monogamous mating systems, and bi-parental care. The order Psittaciformes, with around 350 species worldwide, has long-lived species that are relatively under-studied with respect to parentage and pair fidelity. Although studies have revealed a variety of mating systems in Psittaciformes, there is little work testing whether EPP or CBP occur in Psittaciformes. To test for genetic and social pair fidelity we studied an Australian parrot, the Crimson Rosella (Platycercus elegans), over 8 years at three sites in south-eastern Australia. Using nine microsatellite markers in 42 pairs and their offspring, we found no cases of EPP. However, we found one case of CBP, suggesting that P. elegans females do adopt alternative breeding strategies, albeit at low levels. We also show that over the 8 years of study 32% of recaptured individuals paired with more than one partner in different years. Our results are consistent with assumption of low EPP in parrots, but challenge the notion that this is associated with long-term pair bonds.
... Nest boxes are often used as additional refuges in disturbed landscapes (Dashper and Myers 2003;Myers 1997). The use of nest boxes may be inappropriate for future conservation programs as they are unlikely to offer an optimal thermal protection during extreme weather events (Goldingay 2015;Griffiths et al. 2018;Griffiths et al. 2017;Larson et al. 2018;Rueegger 2017). Retention of existing old growth trees that already possess large thermal protective hollows will be essential for long-term conservation of phascogales as these provide a greater level of protection from external climatic temperatures . ...
Article
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Climate change has the potential to have a major impact on flora and fauna across Australia. There is a need to investigate the potential impact of climate change at a subspecies level to inform effective conservation management. To date, there have been no studies that have considered the effects of climate change on the distribution and habitat of the Brush-tailed Phascogale Phascogale tapoatafa tapoatafa. In this research, the potential changes to the phascogale climatic envelope were modelled to simulate low emissions (RCP2.6) and high emissions (RCP8.5) scenarios for 2075. Six bioclimatic parameters were selected, based on their likelihood of influencing phascogale occupancy. Modelling was conducted separately on two groupings of phascogale that occur in central Victoria and from northern New South Wales to southern Queensland. Of the selected parameters, the maximum temperature of the hottest month was found to have the greatest influence over phascogale distribution. The high emission scenario for 2075 suggests that climatically suitable phascogale habitat would contract by 79% in Queensland, 67% in Victoria and 17% in New South Wales. Suitable habitat would also increase in some areas with large expansions in New South Wales. Habitat connectivity will be essential for allowing phascogales to move through the landscape to reach areas where climate may be most suitable under warming. These projections do not take into account the increase in bushfires and other natural disasters that could exacerbate the effects of climate change. (The Victorian Naturalist 137(5), 2020, 128–139)
... Practitioners thinking of adopting our spout box design should therefore consider using thicker timber (>25 mm) for box construction, which will increase their capacity to buffer occupants from external ambient conditions during extremely hot and cold weather events. Further modifications, such as the addition of insulation or the use of reflective surfaces to buffer nest boxes from weather extremes may also warrant consideration (Griffiths et al., 2017;Larson, Eastwood, Buchanan, Bennett, & Berg, 2018). Potential modifications, do however, require careful assessment. ...
Article
Full-text available
Artificial tree hollows (e.g., nest‐boxes) are commonly deployed to mitigate the loss of mature trees within human‐disturbed landscapes. Their effectiveness as a habitat resource, and thus conservation management tool, is strongly influenced by the suitability of internal microclimate conditions. In south‐eastern Australia, spout hollows are a nesting resource used by a diverse community of vertebrate species. We tested the suitability of a novel nest box design (spout boxes) that mimicked the physical characteristics of spout hollows. We monitored the occupancy (n = 193) and internal microclimate (n = 131) of natural hollows and spout boxes within a woodland where natural tree hollows were once abundant. Both natural hollows and spout boxes were occupied and used for breeding by birds and mammals. Natural hollows had consistently higher humidity, and thermal maxima and minima were buffered, when compared with spout boxes. These differences were largely explained by wall thickness. Spout boxes displayed even more extreme temperature variation and lower humidity when not shaded. While more extreme microclimate conditions did not prevent usage, tolerable thresholds for hollow‐dependent species may soon be exceeded under current climate change projections. Managers need to carefully consider nest box design and positioning to ensure the suitability of these supplementary resources for conservation purposes.
... It is clear that climate change and accompanying temperature increases could alter breeding success and the phenotypic development of nestlings. Even though cavity nests are by nature buffered against weather variation, their microclimate is strongly associated with ambient temperatures and they are thus not immune from the effects of climate change (Larson et al., 2018;Maziarz et al., 2017). These climate-driven changes in body size could have further population-level consequences later in the season because adult body size is an important predictor of adult survival, especially over winter (Rodríguez et al., 2016;Tinbergen & Boerlijst, 1990). ...
Article
Full-text available
1. For birds, maintaining an optimal nest temperature is critical for early-life growth and development. Temperatures deviating from this optimum can affect nestling growth and fledging success with potential consequences on survival and lifetime reproductive success. It is therefore particularly important to understand these effects in relation to projected temperature changes associated with climate change. 2. Targets set by the 2015 Paris Agreement aim to limit temperature increases to 2°C, and, with this in mind, we carried out an experiment in 2017 and 2018 where we applied a treatment that increased Great Tit Parus major nest temperature by approximately this magnitude (achieving an increase of 1.6°C, relative to the control) during the period from hatching to fledging to estimate how small temperature differences might affect nestling body size and weight at fledging and fledging success. 3. We recorded hatching and fledging success and measured skeletal size (tarsus length) and body mass at days 5, 7, 10, and 15 posthatch in nestlings from two groups of nest boxes: control and heated (+1.6°C). 4. Our results show that nestlings in heated nest boxes were 1.6% smaller in skeletal size at fledging than those in the cooler control nests, indicating lower growth rates in heated boxes, and that their weight was, in addition, 3.3% lower. 5. These results suggest that even fairly small changes in temperature can influence phenotype and postfledging survival in cavity-nesting birds. This has the potential to affect the population dynamics of these birds in the face of ongoing climatic change, as individuals of reduced size in colder winters may suffer from decreased fitness.
Technical Report
The report describes the results of a study on the effects of climate change on lichens and selected groups of plants and animals in 2019. These studies are repeated annually in the area of the state capital of Düsseldorf (Germany). Summary of the chapter "Lichens" (Author: NJ Stapper): In late autumn 2019, epiphytic lichens were again recorded at four measuring stations distributed over the Düsseldorf urban area according to a standardised procedure, which was developed in close cooperation with the working group "Effect assessment on lower plants" of the Commission on Air Pollution Control (KRdL) in the VDI and DIN and published in 2017 as VDI Guideline 3957 Part 20. The measured value is the VDI Climate Change Indicator Index (KWI), defined as the average number of climate change indicators per standard tree in a study area. These climate change indicators are epiphytic lichen species with temperate Mediterranean and sub-Mediterranean-Subatlantic temperate distribution ("southern species"), which in the past were either considerably rarer or not yet present in western Germany. The paired comparison of the data from 13 surveys including older findings shows a statistically highly significant increase in the KWI between 2003 and 2017, averaged over all stations. Since then, the values of the individual stations have remained at about the same high level, or have declined again at the 'Hafen' station. There, the diversity of all lichen species on the trees has decreased by almost one third since 2017, possibly due to high immissions and/or strong urban overheating of the carrier tree sites. The most probable causes for the shift in the species spectrum towards more climate change indicators are, in addition to the further decrease in immissions since 2000, increasingly considered to be the observable effects of climate change, namely the steadily rising average temperature, especially the rising winter temperature, and other associated climate changes. Conversely, it can also be said that the above-mentioned bioclimatic and climatic zones have now extended into the study area, because lichen species that were more typical of southwestern France some 60 years ago are now found in the Düsseldorf area. Zusammenfassung des Kapitels "Flechten" (Autor: NJ Stapper): Im Spätherbst 2019 wurden erneut epiphytische Flechten an vier über das Düsseldorfer Stadtgebiet verteilten Messstationen nach einem standardisierten Verfahren aufgenommen, das in enger Zusammenar-beit mit der Arbeitsgruppe „Wirkungsfeststellung an Niederen Pflanzen“ der Kommission Reinhaltung der Luft (KRdL) im VDI und DIN entwickelt und 2017 als VDI-Richtlinie 3957 Blatt 20 veröffentlicht worden ist. Messwert ist der VDI-Klimawandelzeiger-Index (KWI), definiert als die mittlere Anzahl von Klimawandelindikatoren pro Baum in einem Untersuchungsgebiet. Diese Klimawandelindikatoren sind epiphytisch vor-kommende Flechtenarten mit gemäßigt-mediterranem und submediterran-subatlantisch-gemäßigtem Ver-breitungsschwerpunkt ("südliche Arten"), die früher auch im Westen von Deutschland entweder erheblich seltener oder noch gar nicht vorkamen. Der gepaarte Vergleich der Daten von inzwischen 13 Erhebungen einschließlich älterer Befunde zeigt über alle Stationen gemittelt einen statistisch hochsignifikanten An-stieg des KWI zwischen 2003 und 2017. Seither verharren die Werte der einzelnen Stationen auf etwa gleichbleibend hohem Niveau, bzw. gehen an der Station Hafen wieder zurück. Dort ist die Diversität aller Flechtenarten an den Bäumen seit 2017 um fast ein Drittel eingebrochen, möglicherweise aufgrund hoher Immissionen und/oder starker urbaner Überwärmung der Trägerbaumstandorte. Als wahrscheinlichste Ursachen für die Verschiebung des Artenspektrums hin zu mehr Klimawandelzeigern werden neben den seit 2000 weiter gesunkenen Immissionen zunehmend die beobachtbaren Wirkungen des Klimawandels betrachtet, namentlich die stetig ansteigende Durchschnittstemperatur, insbesondere die steigende Win-tertemperatur, sowie weitere damit einhergehende Klimaveränderungen. Im Umkehrschluss kann man auch sagen, dass sich die oben genannten Biom- bzw. Klimazonen inzwischen ins Untersuchungsgebiet hinein ausgedehnt haben, weil im Raum Düsseldorf heute Flechtenarten vorkommen, die vor rund 60 Jahren eher für Südwestfrankreich typisch waren.
Article
Nest boxes are used to manage populations of tree-cavity dependent birds and mammals. Concerns have been raised that due to their poor insulative properties nest boxes may cause heat stress and occasionally death during summers of extreme maximum temperatures. Our study investigated whether this nest box heat stress hypothesis applies to two small cavity-dependent mammals (brush-tailed phascogales and sugar gliders). Focusing on days when ambient temperature reached ≥40 °C, we recorded: i) temperatures within occupied nest boxes, ii) temperatures within nearby unoccupied tree cavities, iii) the duration of temperatures of ≥40 °C within nest boxes, iv) whether direct mortality was observed, and v) the relative abundance of these species in nest boxes before and after a very hot summer. When ambient temperature reached ≥40 °C, nest boxes were equivalent to ambient or 1–2 °C cooler, whereas tree cavities were 3–7 °C cooler than ambient. Exposure in nest boxes to temperatures of ≥40 °C lasted an average of 2–8 h. We observed no mortality over 65 records of phascogales and 31 records of gliders in nest boxes on days when ambient reached ≥40 °C. No decline in abundance was recorded after a summer with 11 days of temperatures ≥40 °C, with each species subsequently occupying >40 nest boxes. Our observations suggest these species are tolerant of the high temperatures that occurred. Nonetheless, provision of nest boxes designed to minimise summer heating is recommended.
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Cavity-using birds and mammals reliant on nest boxes may be negatively affected by the poor thermal buffering of nest boxes. I investigated whether nest box use by the eastern pygmy-possum (Cercartetus nanus) over a 4-year period was influenced by maximum ambient temperature, which ranged from 15.6 to 34.9°C during survey occasions. Occupancy modelling of 144 site detections over 30 survey occasions suggested that a model that included maximum temperature had little support whereas a model involving time-varying detection (i.e. detection differed across sample occasions) was the most plausible. I also investigated how temperatures in nest boxes and tree hollows varied over the four hottest days of summer, including one day when the temperature reached 40.6°C. Maximum temperatures were 3–4°C cooler in plywood nest boxes and 5–8°C cooler in tree hollows compared with ambient temperatures. Together, these results suggest that eastern pygmy-possums using nest boxes in coastal areas are unlikely to experience heat stress. Cavity-using species are a heterogeneous group such that empirical studies are required to identify those that may be vulnerable to heat stress if nest boxes are used to provide population support.
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Animals that breed in cavities formed through decay or mechanical damage often face limitations to reproduction due to a shortage of nest sites. Artificial nests are commonly deployed to increase the short‐term availability of breeding sites for these species. Often this is an effective approach; however artificial nests are costly and may be ignored by the target species or inadvertently benefit non‐target species. Here we consider the use of modified natural hollows and artificial nest sites to support endangered Norfolk Island green parrots Cyanoramphus cookii. We recorded the characteristics of all modified and artificial nests in the Norfolk Island National Park and used eight years of nesting data to study nest selection by green parrots and introduced crimson rosellas Platycercus elegans. Artificial nests (those lacking a natural base) were never used by green parrots. Nests with thicker walls were more likely to be used by green parrots, but there was no nest site characteristic that predicted frequency of use. Crimson rosella nest use was not predicted by any of the nest characteristics measured. A better understanding of the reasons behind green parrots’ avoidance of artificial nests and preference for thicker nest walls is required to inform the future design and management of nest sites. Our study shows that evaluation of how artificial sites are used by the target species is important to maximize the efficacy of conservation efforts. This article is protected by copyright. All rights reserved.
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Bat boxes have become the most popular compensation and mitigation measure in the last few decades and large numbers are being sold by specialized companies. Although bats seem to prefer warm bat boxes, in particular maternity colonies, overheating in southern countries is becoming a problem under the influence of climate change. Literature with regards to this subject in the Netherlands is scarce but there are indications that overheating of bat boxes might also occur in this country. Therefore this study aimed to get more insight into the microclimate of single-chambered, flat bat boxes that can serve as summer or mating roosts. At two locations near Borculo and Neede, the Netherlands, black and wood-coloured woodcrete, Douglas wood and plywood bat boxes were placed on poles. With the help of data loggers, temperature and relative humidity were measured in these unoccupied bat boxes for 90 days during the summer of 2019. Bat box colour significantly influenced daily temperature response variables and also daily minimum bat box relative humidity. Also daily fluctuation of temperature and relative humidity within a bat box were influenced significantly by bat box colour. Bat box material only significantly influenced relative humidity response variables. Wood-coloured bat boxes reacted more slowly to changes in ambient microclimate than black bat boxes. In particular woodcrete bat boxes had a higher buffer capacity of ambient circumstances than bat boxes from Douglas wood and plywood. Although all models experienced overheating (bat box temperature >= 40 ⁰C), wood-coloured bat boxes were found to encounter significantly less (70,6%) overheating events than black bat boxes. Material did not have a significant effect on the number of overheating events. Nonetheless, the black Douglas wood and black plywood bat box had a lower ambient-temperature-threshold for causing overheating (20,5 ⁰C) than the black woodcrete bat box (27 ⁰C). The lower this threshold, the sooner a bat box experienced overheating. This threshold was highest for all wood-coloured bat boxes (32,5-33,5 ⁰C). Dark-coloured, single-chambered bat boxes can rapidly experience overheating when exposed to direct sunlight; at such locations light-coloured bat boxes are recommended. The risk of fatal overheating events occurring in the Netherlands will likely increase due to climate change and should not be underestimated, therefore overheating should be included as a subject in new guidelines for choosing and placing bat boxes. When selecting and placing bat boxes, a situation-dependent approach is recommended, taking local microclimate and environment into account.
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Thermal properties of tree hollows play a major role in survival and reproduction of hollow- dependent fauna. Artificial hollows (nest boxes) are increasingly being used to supplement the loss of natural hollows; however, the factors that drive nest box thermal profiles have received surprisingly little attention. We investigated how differences in surface reflectance influenced temperature profiles of nest boxes painted three different colors (dark-green, light-green, and white: total solar reflectance 5.9%, 64.4%, and 90.3% respectively) using boxes designed for three groups of mammals: insectivorous bats, marsupial gliders and brushtail possums. Across the three different box designs, dark-green (low reflectance) boxes experienced the highest average and maximum daytime temperatures, had the greatest magnitude of variation in daytime temperatures within the box, and were consis- tently substantially warmer than light-green boxes (medium reflectance), white boxes (high reflectance), and ambient air temperatures. Results from biophysical model simulations demonstrated that variation in diurnal temperature profiles generated by painting boxes either high or low reflectance colors could have significant ecophysiological consequences for animals occupying boxes, with animals in dark-green boxes at high risk of acute heat- stress and dehydration during extreme heat events. Conversely in cold weather, our model- ling indicated that there are higher cumulative energy costs for mammals, particularly smaller animals, occupying light-green boxes. Given their widespread use as a conservation tool, we suggest that before boxes are installed, consideration should be given to the effect of color on nest box temperature profiles, and the resultant thermal suitability of boxes for wildlife, particularly during extremes in weather. Managers of nest box programs should consider using several different colors and installing boxes across a range of both orienta- tions and shade profiles (i.e., levels of canopy cover), to ensure target animals have access to artificial hollows with a broad range of thermal profiles, and can therefore choose boxes with optimal thermal conditions across different seasons.
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Avian adjustments to desert environments are characterized by an integration of behavior and physiology. These responses serve to maintain homeostasis and conserve vital resources such as water. The small size of birds confers a close coupling to the thermal environment and demands rapid adjustments to environmental challenges. Physiological responses to heat stress include hyperthermia, and increased evaporative cooling as environmental temperatures approach body temperature. Behaviorally, desert birds respond to heat stress by drastically reducing activity during the hottest parts of the day and selecting cool shaded microsites. This characteristic behavioral response presents a potential problem in the face of global warming. If birds totally forgo foraging during extremely hot periods, increased evaporative water loss rates due to higher environmental temperatures could lead to significant episodes of direct mortality for birds in these regions. A simple model is presented which integrates behavior and physiology to predict survival times based on dehydration tolerance, microsite selection and environmental temperature.
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Twelve species of vertebrates occupied nest boxes located in foothill forest trees in Gippsland, Vic., between 1977 and 1980. Boxes varied in entrance diameter, height above ground, and orientation. Over the study period 38% of boxes were found occupied and another 40% showed signs of having been visited. Occupancies were higher at the site with fewer natural hollows. Seasonal use of boxes varied between mammals and birds and between species. Boxes with small entrances were preferred, and low boxes were avoided by all species except the brown antechinus. Preference for the highest boxes was significant at one site only. Preference for diameter of entrance hole was significant for brown antechinus, sugar glider and crimson rosella; height was significant for sugar glider and brown antechinus; orientation was not significant for any species.
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Tree swallow (Tachycineta bicolor) breeding success in Ithaca, NY, USA, over the past quarter century has shown generally healthy fledgling production punctuated by years of high nestling mortality. This study tested the potential effects that temperature may have on the food supply and breeding success of swallows. Data from 17 years of daily insect samples were used to relate flying insect abundances to daily maximum temperatures and to define “cold snaps” as strings of consecutive days when the maximum temperatures did not exceed critical temperatures. The distributions of cold snaps and chick mortality events were investigated both through detailed reconstructions of the fates and fate dates of individual chicks, focused on the three breeding seasons of lowest fledging success, and with less detailed brood-level analyses of a larger 11-year dataset including years of more moderate mortality. Mark–recapture analyses of daily brood survival rate (DSR) reveal very strong support for the effects of cold temperatures on brood survival rates, and all the top models agree on a critical temperature of 18.5 °C for insect flight activity in Ithaca. The individual-level analyses, focused on years of higher mortality, favored a 3-day cold snap definition as the most predictive of DSR effects, whereas the larger-scale brood-level analyses revealed 1- and 2-day cold snaps as having the most significant effects on DSR. Regardless, all analyses reveal that, in an age of generally warmer climates, the largest effect of weather on swallow fledgling production is from cold temperatures. Electronic supplementary material The online version of this article (doi:10.1007/s00442-013-2605-z) contains supplementary material, which is available to authorized users.
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Barrow's Goldeneye (Bucephala islandica) and Bufflehead (B. albeola) are cavity-nesting waterfowl that have received considerable attention in studies using nest boxes, but little is known about their nesting ecology in natural cavities. We found larger clutch size, lower nesting success, and different major predators for Barrow's Goldeneyes nesting in boxes versus those nesting in natural cavities, but few differences for Bufflehead. These differences are attributed to the location and physical differences between Barrow's Goldeneye nest boxes and natural cavities that affect their conspicuousness to predators and conspecific nest-parasitizing females. Goldeneye boxes were concentrated in highly visible locations such as trees at water or forest edge. Natural cavity nests, on the other hand, were often abandoned Pileated Woodpecker (Dryocopus pileatus) cavities, which were more dispersed throughout the forest interior and concealed under dense canopy cover. Bufflehead natural cavity nests were typically closer to edges, which may account for their similarity with boxes. We conclude that in some respects, studies of Barrow's Goldeneye that use nest boxes may not be representative of birds nesting in natural cavities, whereas those of Bufflehead are more likely to be so.
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ABSTRACT Tree cavities likely vary in their thermal quality for cavity-nesting animals, which could be especially important during winter. We conducted a winter field experiment to test whether cavities vary either in their buffering capacity or in their mean temperature according to predictable characteristics. We found that cavities buffered temperature and that there was a lag effect in temperature that appeared to be related to heating and cooling. Diameter at breast height was the most important variable influencing cavity temperature during the day, with smaller trees warming up more. During the night, diameter at breast height and tree decay class were important, such that larger, live trees cooled down less. Maintaining live trees with cavities in managed forests should be considered in addition to snag retention, because live trees appear to provide warmer structures during winter.
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Nest boxes are frequently used in conservation programs for tree-cavity dependent wildlife. There is growing concern that the poor insulation properties of nest boxes may produce an ecological trap, because species may require microclimates less extreme or less variable than those experienced inside nest boxes. I investigated the fitness consequences of nest box use in a non-flying mammal. Fifty-two of 104 squirrel gliders (Petaurus norfolcensis) trapped over a 3-year period used nest boxes. Population modelling of the capture data revealed that the probability of apparent survival increased with increasing nest box use. There was no difference in breeding frequency between females that used or did not use nest boxes. There was no evidence that offspring development was hindered within nest boxes. These findings may arise because: (1) gliders could access tree hollows during extreme temperatures, (2) ambient temperatures were mild during the study, (3) gliders construct leaf nests which insulate against low temperatures in winter, and (4) gliders breed between autumn and spring when temperatures are relatively benign. The estimate of annual survival of animals using nest boxes (0.60), was equivalent to estimates at locations where squirrel gliders were either reliant on nest boxes (0.54) or on tree cavities (0.55) for shelter. Studies such as this need to be conducted on a range of species across a range of locations to better understand the influence of nest box use on non-flying mammals.
Article
The provision of nest-boxes is widely used as a conservation intervention to increase the availability of cavities for hole-nesting birds, particularly in managed forests, but it is uncertain whether nest-boxes are an appropriate substitute for tree cavities. Tree cavities and nest-boxes may differ in many aspects, including microclimate, but there are few data with which to examine this. We measured the air temperature and relative humidity in vacant tree cavities previously used by breeding marsh tits Poecile palustris (a non-excavating forest passerine) and in nest-boxes provided for this species that had similar dimensions to natural nest sites, and we compared values from both with ambient conditions. We examined how tree cavity characteristics influenced microclimate and if similar conditions were replicated in nest-boxes. Tree cavities, particularly those in thicker parts of trees, were more efficient thermal insulators, with temperature extremes dampened to a greater extent relative to ambient values. In contrast, the nest-boxes provided poor insulation with negligible buffering against ambient temperatures. Mean daily relative humidity was high (on average c. 90%) in tree cavities, which all had walls of living wood, and this averaged 24% higher than in nest-boxes at comparable ambient conditions (mean humidity 76–78%). These results support previous studies that incorporated various types of tree cavities and nest-boxes, indicating that the environment within nest-boxes differs significantly from that of tree cavities. We conclude that providing nest-boxes may affect microclimatic conditions available for cavity-users, which may have ecological implications for nesting birds.
Article
Nest boxes have been widely used across the world to provide shelter for animal species, often to restore areas following the loss of natural tree hollows. While the microclimates of installed nest boxes have been studied, limited attention has been paid to whether microclimate is influenced by nest box size, shape and entrance dimensions. In this study the temperature and humidity patterns were recorded within six nest box designs that were exposed to direct sunshine. All were constructed of 19 mm plywood but varied in length by a factor of 2X, in volume by 3.5X and in entrance areas by 5X. All next boxes behaved the same thermally, closely following ambient during the night, but during the day they heated to 5 ºC warmer than ambient by mid-afternoon. Fluctuations in humidity varied, with small nest boxes with large entrances being closer to ambient humidity than those with small entrances or large volumes. Overall, nest box size and shape had no detectable influence on the internal temperature fluctuations, but did to a slight extent on humidity patterns. Construction material and nest box placement are the likely drivers of the temperature and humidity patterns within nest boxes, and need to be the focus of efforts to keep nest boxes habitable when deployed, and designs should be selected on the basis of the target animal's preferences for size and shape.
Article
Nest boxes are frequently installed in Australia to provide shelter sites for arboreal mammals. Little is known about the temperatures that may be experienced inside nest boxes or the factors that may influence those temperatures. I established paired nest boxes on the south-east and north-west sides of trees at two locations in south-east Queensland to investigate the influence of nest box aspect on nest box temperature. Squirrel gliders (Petaurus norfolcensis) occupied boxes at both locations. I recorded temperatures over a 1-month period in two summers. Temperature varied by up to 20°C within a 24-h period and some nest boxes experienced temperatures above 40°C. There was no significant difference in maximum temperature with nest box aspect but south-east boxes could be 1°C cooler during hot weather. Nest box construction material, colour (brown or green) and volume (0.008m3 or 0.025m3) had variable influences on temperature. Nest box installations for non-flying mammals should place nest boxes to minimise extreme temperatures. Further studies are required to determine whether temperature limits the effectiveness of nest boxes at some locations.
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The use of nest boxes by Vaux's Swifts (Chaetura vauxi) was investigated because of the loss of large-diameter hollow trees used for nesting in northwestern North America. Nest attempts and nest success were compared in nest boxes among three habitat types in northeastern Oregon. Air temperatures in the boxes were monitored to determine if boxes overheated and resulted in nestling mortality. Thirty of 103 nest boxes were used by nesting Vaux's Swifts for at least one year during 1999–2002. Of 51 nest attempts, 53% successfully fledged 1–6 young (x̄ = 3.5 nestlings). Over this 4-yr period, 47% of the nests were in late-seral stage grand fir (Abies grandis) stands, 31% were in harvested stands of grand fir, and 22% were in ponderosa pine (Pinus ponderosa) stands. It appeared that temperature did not affect nest success in boxes because there were no significant differences in maximum and minimum temperatures between successful and unsuccessful nest attempts. Nest boxes provided alternative nest sites for Vaux's Swifts in habitats traditionally used by this species as well as in habitats that currently lack natural nest sites.
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1. Introduction 2. Estimation 3. Hypothesis testing 4. Graphical exploration of data 5. Correlation and regression 6. Multiple regression and correlation 7. Design and power analysis 8. Comparing groups or treatments - analysis of variance 9. Multifactor analysis of variance 10. Randomized blocks and simple repeated measures: unreplicated two-factor designs 11. Split plot and repeated measures designs: partly nested anovas 12. Analysis of covariance 13. Generalized linear models and logistic regression 14. Analyzing frequencies 15. Introduction to multivariate analyses 16. Multivariate analysis of variance and discriminant analysis 17. Principal components and correspondence analysis 18. Multidimensional scaling and cluster analysis 19. Presentation of results.
Article
Climate change is predicted to affect many species by reducing range, habitat suitability and breeding success. Cavity-nesting species, already threatened by deforestation and declining natural hollows, may be particularly at risk because they are limited in nest-site location, and climatic alterations may further reduce usability of natural cavities. It is therefore essential to determine how cavity-users may be affected. We recorded internal nest box temperatures and modelled the relationships of four temperature parameters (relating to mean temperature, variability in temperature, low temperature extremes and high temperature extremes) with breeding success and nestling growth in an Australian cavity-nesting parrot, the Crimson Rosella (Platycercus elegans). We found that less extreme low temperatures resulted in heavier nestlings; however, higher mean temperatures tended to result in lighter nestlings. Greater temperature variability tended to reduce fledging success; however, no temperature variables had a clear effect on clutch size or hatching success. Our findings indicate that there may be a complex relationship between nestling growth and temperature, and although less extreme cold temperatures may benefit nestlings, continued increases in mean temperature and variability may have negative consequences.
Article
The use ducks made of artificial nest sites, of various designs and materials, in Victoria (1,230 examined in 1975-76) and Western Australia (2,440, 1969-74) was determined. Usage was minimal in Western Australia (1.0% of 1,999 boxes in 1974) but was higher in Victoria (36%) where 83 percent of records were of chestnut teal (Anas castanea), an uncommon nesting species in Western Australian study areas. Victorian data suggested that chestnut teal selected boxes in increased cover, those more than 1 m above ground or water, located in permanent wetlands. Low usage of boxes (mainly plastic drums) in Western Australia was probably attributable to their location in unsuitable wetlands.
Article
Exclusion is the recommended method for removing roosting bats from buildings, but is often difficult to accomplish. A simpler way to limit bat-human conflicts may be to modify new and existing buildings to discourage colonies from initially taking up residence. An understanding of the physical and microclimatic characteristics of maternity roosts is a prerequisite when modifying buildings to discourage colonies. We investigated factors influencing maternity roost selection in big brown bats (Eptesicus fuscus) by comparing characteristics of bat-occupied buildings with bat-unoccupied buildings at 10 sites. Bat-occupied buildings were significantly older, more likely to have galvanized steel (tin) roofs, more accessible to bats, and taller than randomly selected unoccupied buildings. In paired surveys, occupied attics were significantly more accessible to bats than physically similar unoccupied attics and exhibited significantly higher temperatures and wider temperature gradients. Disturbance levels, light levels, and humidity did not differ between occupied and paired unoccupied attics. To discourage bats from initially establishing a maternity roost within a building, limit all access points. In buildings where this is difficult, attics can be made less suitable as roost sites by reducing attic temperatures during the summer months. Bat boxes intended to house displaced maternity colonies should be designed to provide high daily temperatures and wide temperature gradients.
Article
Olfaction is an ancient sensory capability, and yet while it is now widely recognized that birds have olfactory mechanisms, use of the sense within a social context has been largely overlooked. In our study, we aimed to determine, for the first time, whether plumage odour may contribute to avian subspecies discrimination. We used a species complex, the crimson rosella, Platycercus elegans, which exhibits large geographical and phenotypic differences. Across 2 years in a wild population of P. elegans elegans we tested whether females at the nest could: (1) discriminate odours of conspecifics; (2) discriminate odours of subspecies; (3) discriminate odours of sexes of conspecifics; and (4) habituate at different rates to odour treatments. We found that female response differed between odours of feathers of consubspecifics, heterosubspecifics, heterospecific controls and sham controls and between odours of sexes of conspecifics. Across all odour treatments, we found habituation to the odour and the rate of habituation differed between odour treatments. Our results indicate that P. e. elegans females are able to discriminate conspecifics, consubspecifics and sexes based on plumage odour. To our knowledge, this is the first work to show that birds of a certain subspecies can discriminate the odour of its own subspecies from that of other subspecies. Our findings suggest that olfaction in birds may play a larger role than hitherto considered, and may even act as a signal to maintain or promote population divergence.
Article
The golden-cheeked warbler (Setophaga chrysoparia), listed by the U.S. Fish and Wildlife Service as endangered in 1990 due primarily to habitat loss and fragmentation, is a Neotropical migrant songbird that breeds exclusively in mature juniper–oak (Juniperus–Quercus) woodlands in central Texas, USA. Previous studies suggested suitable breeding habitat consists of >35% canopy closure (with 50–70% cover optimal), and ≥10% oak composition. However, little is known about this species' habitat relationships at the southwestern edge of its breeding range. Therefore, within this portion of the species' breeding range, we investigated influences of canopy closure and tree species composition on pairing and reproductive success of golden-cheeked warblers during 2009 and 2010. We used remote sensing and ground sampling to acquire variables to describe habitat characteristics, and we estimated pairing for breeding and reproductive success by golden-cheeked warblers. We found successfully breeding pairs in areas with >20% canopy cover, 35% juniper composition, and only 3% oak composition. A logistic model for pairing success retained juniper, oak, and the interaction between these 2 variables, and the model for reproductive success retained juniper, canopy closure, study area, and the interaction between canopy closure and study area. Our results expand our knowledge of habitat conditions that warblers use for breeding, thus expanding the range of habitat management options available for this species during breeding season. © 2012 The Wildlife Society.
Article
Maternity colonies of big brown (Eptesicus fuscus) and little brown (Myotis lucifugus) bats are vulnerable to exclusion from buildings. We monitored the use of bat boxes as alternative roosts for displaced colonies at 15 sites in Pennsylvania. When successfully excluded, colonies moved to bat boxes that received ≥7 hours of direct sunlight and were attached to the building that formerly housed the colony. Preferred bat boxes offered high temperatures (8-10°C>ambient), an internal temperature gradient, and were wide enough (76 cm) to enable many bats to roost side by side. Our results suggest that bat boxes of the proper design and placement can serve as important tools in managing nuisance or displaced bat maternity colonies.
Article
Variable environments impose constraints on adaptation by modifying selection gradients unpredictably. Optimal bird development requires an adequate thermal range, outside which temperatures can alter nestling physiology, condition and survival. We studied the effect of temperature and nest heat exposure on the reproductive success of a population of double-brooded Spotless Starlings Sturnus unicolor breeding in a nestbox colony in central Spain with a marked intra-seasonal variation in temperature. We assessed whether the effect of temperature differed between first and second broods, thus constraining optimal nest-site choice. Ambient temperature changed greatly during the chick-rearing period and had a strong influence on nestling mass and all body size measures we recorded, although patterns of clutch size or nestling mortality were not influenced. This effect differed between first and second broods: nestlings were found to have longer wings and bills with increasing temperature in first broods, whereas the effect was the opposite in second broods. Ambient temperature was not related to nestling body mass or tarsus-length in first broods, but in second broods, nestlings were lighter and had smaller tarsi with higher ambient temperatures. The exposure of nestboxes to heat influenced nestling morphology: heat exposure index was negatively related to nestling body mass and wing-length in second broods, but not in first broods. Furthermore, there was a positive relationship between nest heat exposure and nestling dehydration. Our results suggest that optimal nest choice is constrained by varying environmental conditions in birds breeding over prolonged periods, and that there should be selection for parents to switch from sun-exposed to sun-protected nest-sites as the season progresses. However, nest-site availability and competition for sites are likely to impose constraints on this choice.
Article
1. The optimality model of thermoregulation predicts that as the cost of thermoregulation increases, thermoregulation effort will decrease. 2. We designed a manipulative experiment to quantify the energetic cost of thermoregulation on growth rates in eastern collared lizards (Crotaphytus collaris) by comparing growth of hatchling lizards from high- and low energetic cost of thermoregulation treatments. 3. We designed treatments to mimic restricted thermal microenvironments (which require lizards to devote more time and energy to maintain preferred body temperatures) and unrestricted thermal micro-environments (which minimize time and energy needed to maintain body temperature). 4. Lizards maintained similar body temperature between treatments — contradicting predictions of the optimality model of thermoregulation — but grew more slowly in the high-cost thermoregulation treatment than in the low-cost thermoregulation treatment. 5. The reduction in growth rates in the high energetic cost thermoregulation treatment was most consistent with animals diverting energy from growth to locomotion for thermoregulation.
Article
Animals living in tropical regions may be at increased risk from climate change because current temperatures at these locations already approach critical physiological thresholds. Relatively small temperature increases could cause animals to exceed these thresholds more often, resulting in substantial fitness costs or even death. Oviparous species could be especially vulnerable because the maximum thermal tolerances of incubating embryos is often lower than adult counterparts, and in many species mothers abandon the eggs after oviposition, rendering them immobile and thus unable to avoid extreme temperatures. As a consequence, the effects of climate change might become evident earlier and be more devastating for hatchling production in the tropics. Loggerhead sea turtles (Caretta caretta) have the widest nesting range of any living reptile, spanning temperate to tropical latitudes in both hemispheres. Currently, loggerhead sea turtle populations in the tropics produce nearly 30% fewer hatchlings per nest than temperate populations. Strong correlations between empirical hatching success and habitat quality allowed global predictions of the spatiotemporal impacts of climate change on this fitness trait. Under climate change, many sea turtle populations nesting in tropical environments are predicted to experience severe reductions in hatchling production, whereas hatching success in many temperate populations could remain unchanged or even increase with rising temperatures. Some populations could show very complex responses to climate change, with higher relative hatchling production as temperatures begin to increase, followed by declines as critical physiological thresholds are exceeded more frequently. Predicting when, where, and how climate change could impact the reproductive output of local populations is crucial for anticipating how a warming world will influence population size, growth, and stability. This article is protected by copyright. All rights reserved.
Article
Spring et al. (D.A. Spring, M. Bevers, J.O.S. Kennedy, and D. Harley. 2001. Can. J. For. Res. 31: 1992–2003) recently published a paper on the economics of a nest-box program for the endangered arboreal marsupial, Leadbeater's possum (Gymnobelideus leadbeateri) in southeastern Australian forests. While their paper is a useful one, there are some important limitations of nest-box programs that need to be highlighted. In the case of Leadbeater's possum, we have undertaken extensive nest-box studies in Victoria mountain ash (Eucalyptus regnans F. Muell.) forests, where the vast majority of populations of the species now occur. Although large numbers of nest boxes have been deployed, very few have actually been occupied, which is a major problem since the effectiveness of any nest-box program will depend on patterns of use by the target species. Given very low levels of nest-box occupancy, harvesting regimes such as those that lead to on-site tree retention are needed to better conserve hollow-dependent species like Leadbeater's possum. Moreover, the need for nest boxes in the first place indicates that logging practices are presently not ecologically sustainable, and modified forestry practices need to be adopted.
Article
As hollow-bearing trees become scarcer due to habitat loss, the use of nest boxes as a management tool for hollow-dependent species is likely to increase. However, nest-box use can be variable among species and habitats, and one possible reason may be that nest boxes offer little protection against extreme temperatures compared with natural hollows; this may be particularly important in the tropics. Here, we measured the microclimate of 16 nest boxes, installed as part of a recovery program for an endangered arboreal marsupial, the mahogany glider, during the summer in tropical north Queensland. We also measured the microclimate of 14 naturally occurring refuges (hollows in standing and fallen trees) at the same study sites. Nest boxes were significantly hotter during the day than were natural refuges (either in fallen or standing live trees) and experienced a greater range of temperatures. The most important factors explaining variation in daytime temperature in boxes was box aspect and the amount of canopy cover directly above the box: boxes that faced north, and those with greater canopy cover, were up to 7°C cooler than those that faced south or had little cover. We discuss our results in relation to the use of nest boxes in management plans for arboreal marsupials in the tropics.
Book
Overview chapter: avian energetics, ecology and evolution. Nutrition. Digestive flexibility in avian energetics and feeding ecology. Metabolism of major nutrients in birds. Energetic features of avian thermoregulatory responses. Energetics of hypothermia. Energetics of starvation. Energetics of flight. Energetics of migratory and winter fattening. Energetics of moult. Energetics of reproduction. Energetics of incubation. Embryonic energetics. Energetics of post-natal growth. Populational energetics.
Article
Orientation of nests can influence nest microclimate, particularly temperature. However, few investigators have examined orientation preference and microclimate simultaneously. We examined the possible correlation between entrance orientation of artificial nest boxes used by Tree Swallows (Tachycineta bicolor) and the internal temperature of boxes. Tree Swallows showed a preference for east- and south-facing boxes, but only during the first half of the breeding season (before I June). During the second half of the breeding season (after 1 June), Swallows selected boxes based on availability. We found that east- and south-facing boxes were warmer than north- and west-facing boxes, but only during the first half of the breeding season when those boxes were preferred. Entrance orientation and box temperature were only correlated during the morning (06:00-12:00); the temperature of all boxes was similar during the afternoon. Our results suggest that Tree Swallows show a preference for nest boxes with a certain entrance orientation only when orientation influences microclimate, suggesting that warmer nest temperatures may provide fitness benefits.
Article
We studied the relationships among weather, reproductive success, and population density over 21 years (1980-2000) in a resident Song Sparrow (Melospiza melodia) population in coastal scrub habitat. Our goals were to test potential relationships between annual variation in weather and reproductive success, to evaluate whether reproductive success is density dependent, and to explore the effects of weather and population density on population dynamics. We analyzed the following components of reproductive success: clutch size, hatching success, fledging success, number of young fledged per successful nest, nestling weight, number of fledglings produced per female, number of broods per female, and probability of nest survival. During the study period, several very wet El Niño-Southern Oscillation (ENSO) events as well as an eight-year period of below-average rainfall occurred. Annual reproductive success and population density showed strong positive relationships to annual rainfall levels. Song Sparrow r
Article
I measured structural characteristics of 160 Northern Flicker (Colaptes auratus) nests at Riske Creek, British Columbia, and placed electronic data-loggers in a subsample of 86 nests to record internal temperatures after the flickers completed nesting. Using multiple regression, I found that the best predictors of a variety of nest-cavity temperature variables were tree health, diameter of the tree at cavity height, and orientation of the cavity. Small and dead trees showed the most extreme (maximum and minimum) temperatures during the day, but, on average, were the coldest nests from the perspective of incubation. South-facing cavities reached the highest temperatures during the day, and the orientation of natural cavities was also biased towards the south. I predicted that cold nests would be energetically expensive for adults and nestlings, and found that clutch size was positively correlated with mean cavity temperature. However, there did not appear to be any relationship among nest temperature and hatching or fledging success.
Article
We studied the breeding habitat of Cerulean Warblers (Dendroica cerulea) in southern Indiana in the Ohio River Valley in 2002–2003 to identify similarities and differences in habitat characteristics compared to breeding habitats reported for this species in other geographical regions. Ten 259-ha study plots were surveyed for Cerulean Warblers and territories were mapped using locations of perched, singing males. We measured slope and vegetation characteristics including canopy height and cover, ground cover, number of shrubs and shrub species, number of trees, DBH, and number of snags at Cerulean Warbler territories and non-use sites. Habitat characteristics associated with Cerulean Warbler territories compared to non-use sites were higher canopy height (28 m) and cover (84%), larger trees (>38 cm DBH), higher slope (11°), fewer number of trees (30), and fewer trees between 3 and 23 cm DBH. Calculated Mayfield estimate of nest productivity (0.165) was lower compared to Mississippi Alluvial Valley sites (0.242).
Article
We examined abiotic and biotic variables potentially associated with Northern Bobwhite (Colinus virginianus) nest-site selection and nest success in southern Texas, USA during 2002–2005. These data were used to characterize bobwhite nest-site selection, and to develop and evaluate models of daily nest survival in Program MARK. Nest sites (n = 123) had greater visual obscurity (3.50 vs. 2.60 dm) and vegetation height (64 vs. 47 cm), and less bare ground (11 vs. 25%) compared to random locations (n = 123). The two best models indicated daily nest survival increased with increasing mean maximum temperature and increasing cumulative precipitation. The model-averaged (± SE) estimate for bobwhite daily nest survival was 0.9593 ± 0.0060. These results suggest that bobwhites selected for a specific range of nest-site microhabitat attributes, but that nest predation was largely random. Bobwhite nest survival and productivity in semiarid, subtropical, southern Texas may be largely dependent on weather factors (e.g., temperature and precipitation).
Article
The endangered Gouldian Finch Erythrura gouldiae is the only Australian finch to nest exclusively in tree hollows or, more rarely, in termite mounds. It is sympatric with the abundant Long-tailed Finch Poephila aculicauda which nests frequently in tree hollows. The aim of this study was to define the characteristics of nest sites and breeding areas of Gouldian and Long-tailed Finches to determine whether nest hollows were in short supply, and where finches fed relative to their nest sites. The Gouldian Finch chose hollows with smaller, more northerly entrances than Long-tailed, or randomly chosen hollows, nested deeper down the hollow and on steeper hill-slopes. Both species preferred single to multi-trunked trees of larger diameter than trees with randomly chosen hollows. Discriminant analysis classified 22–25% of the randomly chosen hollows and 28–38% of Long-tailed nesting hollows as Gouldian hollows. Gouldian Finches were more specific in their choice of nest sites than Long-tailed Finches. The vegetation at the two sites differed floristically, but within each site there was no floristic distinction between feeding or breeding sites or sites chosen at random. Gouldian Finches chose feeding habitat where trees were more spaced, on less rocky, barer ground than around breeding sites. On the basis of the criteria measured, there was no shortage of suitable hollows available to the Gouldian Finch for nesting. The overlap between feeding and breeding sites indicates the importance of managing breeding habitat for conservation.
Article
In order to assess the potential impact that artificial nest boxes may have on the occupa- tion rate or physical condition of adults and chicks of little penguins (Eudyptula minor), we recorded temperature continuously for 37 days simultaneously inside 7 nest boxes and in surrounding bush. Temperature inside the boxes was always higher than that in the bush, the difference being greatest around noon. Solar radiation caused temperature inside the boxes to increase. Temperature differences between box interiors and exteri- ors were smaller on windy and dry days. To prevent hyperthermic conditions, we suggest improvements in the ventilation of nest boxes.
Article
Adaptation to climate change has recently become a crucial element on the climate change policy agenda as it is now recognized that even the most stringent mitigation efforts may not arrest the effects of climate warming. The ecological impacts and costs of predicted weather-related extreme events, such as extreme temperatures, are not fully understood and may present unexpected challenges to conservationists that require solutions. In Portugal, provisioning of artificial nests has been the main driver of the spectacular increase in the endangered lesser kestrel population. Nevertheless, atypically high temperatures recorded during the 2009 breeding season coincided with a mortality of 22% of surveyed chicks in provided nests. Hot days did not affected prey delivery rates to the nestlings, suggesting that the die-off was due to chicks’ acute dehydration. Chick mortality was significantly higher amongst younger individuals. Within survivors, physiological costs of high temperatures significantly affected chick growth and body condition at fledging. Nest-site microclimate was influenced by nest-type and compass orientation: wooden nest-boxes attained the highest temperatures, exceeding 55 °C when facing south, so explaining the recorded higher mortality, lower growth rates and lower fledging body condition among broods in these nests. Simulated scenarios of global warming with increasing occupation rate of artificial nests due to reductions in alternatives predicted a reduction in population growth rate. In the worst scenario, with a 100% occupancy of nest-boxes, the population growth would decline on average 7% per year. The impact of high temperatures on lesser kestrel breeding success highlights a need for actions to modify and research to adapt conservation efforts and future planning to account for climate change.
Article
The recognition of the rapid and ongoing biodiversity loss has been leading to increasing conservation efforts. To maximise conservation success it is important to evaluate when interventions are likely to be effective. In Portugal, previous research identified that lack of suitable nest-sites was limiting the populations of the endangered lesser kestrel (Falco naumanni). Consequently, a massive provisioning of artificial nest-sites and the implementation of a medium term monitoring scheme was established. Our study showed that artificial nest-site provisioning is an effective measure in mitigating the lack of traditional sites. The lesser kestrel population increased from 155–158 pairs in 1996 to 527–552 in 2007, with 52% breeding in artificial nests. We investigate the factors affecting colony growth and found that colony growth was positively affected by the provisioning of artificial nests but negatively affected by predation rate and human disturbance. Between 2003 and 2007, mean colony growth was estimated at 6.46 ± 1.86 pairs for colonies where artificial nests were provided and −0.69 ± 0.5 pairs in colonies without nest-site provisioning. Moreover, predation rate was significantly lower in artificial nests than in natural ones and, although the number of competitor pairs in lesser kestrel colonies increased, the proportion of nests occupied by competitor species decreased. High risk of collapse and restoration of rural abandoned farmhouses may jeopardize the future of the lesser kestrel in Portugal. Nest-site provisioning and the establishment of a protection status for buildings holding colonies are likely the most effective means to guarantee the long-term survival of this species in the area.
Article
Summary • Cavity quality is important for the productivity and survival of many species of tree-dwelling wildlife. Intensive land management practices, such as logging and agriculture, frequently reduce cavity availability and potentially affect the long-term viability of populations. • The New Zealand long-tailed bat Chalinolobus tuberculatus selects roosts in small knot-hole cavities with specific structural properties relative to available cavities. They also change roosts daily among a large pool of different roosts. Such behaviour is likely to make C. tuberculatus vulnerable to human-induced deterioration in roosting habitat. • This study represents a case study of the degree of sophistication sometimes required to assess availability and quality of roost sites, by testing whether roosts selected by C. tuberculatus also have specific microclimates. • Selection for microclimate was demonstrated by comparing temperature and humidity inside unoccupied maternity roosts with available, apparently unused, knot-hole cavities, large trunk-hollows and ambient conditions. • Compared with ambient conditions, roost and available knot-hole cavities had stable microclimates displaying only small ranges in temperature and humidity. Temperature inside cavities was lower than ambient temperature in the day and was warmer (and peaked) at night. Humidity in cavities was constantly high. Mean temperatures within trunk-hollows (not known to be used by C. tuberculatus) were cooler than mean ambient and roost temperatures, and temperature ranges in hollows were large and fluctuated similarly to ambient temperatures. • Compared with available cavities and hollows, roost cavities had higher minimum temperatures, and maximum temperatures occurred significantly later in the day and continued for significantly longer. Humidity ranges were less and high humidity was maintained for longer. • The results suggest that C. tuberculatus selects maternity roost sites with microclimatic conditions that are likely to accrue substantial energetic benefits. Predicted energy savings for adult bats using roost cavities compared with available knot-holes were 1·1–3·3%, and compared with hollows 3·4–7·3%. Greater energy savings would occur at night and benefit non-volant young. • In order to evaluate adequately and mitigate the full impacts of land-use practices, there is a need for wider tests to provide direct evidence of interactions between habitat management, cavity provision and survival of cavity-dependent wildlife.
Article
We analysed clutch size versus nest size in 153 broods of the Northern Flicker Colaptes auratus, a woodpecker using natural cavities in British Columbia, Canada. Larger volume cavities were less susceptible to predation and cavity size was positively associated with the age and body size of males and with the body condition of female parents. Although clutches varied between 4 and 11 eggs, and the floor area of cavities varied about 5-fold, we found no relationship between clutch size and floor area or cavity volume. To see if there were fitness consequences to clutch size relative to nest size, we examined hatching success and nestling mortality in flicker broods. Hatching success was not related to cavity size, but crowding slightly reduced nestling survival even when clutch size was controlled statistically. However, there was no effect of cavity size on the total number of nestlings fledged. Newly excavated flicker cavities were smaller than reused cavities suggesting a cost to excavation. This cost, coupled with the minimal fitness consequences of overcrowding, may explain why flickers do not adjust clutch size to cavity size.
Article
We compared how breeding parameters differ according to prevailing weather conditions between a marginal, subarctic (69°N) and temperate (61°N) population of the pied flycatcher Ficedula hypoleuca, a small migratory insectivorous passerine. We predicted that the effects of weather on breeding performance (clutch size, hatching success, nestling growth, fledging success) would be greater at northern latitudes, where the weather conditions are more extreme and unpredictable. We found that the breeding parameters, except clutch size, were not, however, inferior in the north. Northern birds, unlike the southern ones, responded to colder conditions by laying smaller clutches and maintaining a larger energy reserve (indicated by higher female body mass and higher levels of subcutaneous fat). If a cold spell occurred during the nestling period, southern flycatchers had 5–10% lower fledging success than the northern ones. Our results indicate that in the north, the breeding individuals coped with cold and variable weather better than the individuals in the southern population. This could be adaptive, because at high latitudes there is a higher probability of cold weather at the time of breeding.
Article
Summary • Maternal effects often explain a significant amount of variation in offspring phenotype, and can be important in the evolution of life histories. Incubation of eggs is an important maternal effect, and optimal growth and development of avian embryos takes place within a narrow range of incubation temperatures, but the effect of incubation microclimate on neonate phenotype remains relatively unexplored in birds. • In this study of Wood Ducks (Aix sponsa Linnaeus) we examined effects of incubation temperature on the length of incubation period and neonate quality. We monitored nest temperatures and incubation periods of naturally incubated Wood Duck nests and found a strong inverse relationship between incubation period and average nest temperature. • Next, we collected three unincubated eggs from each of 48 nests, and randomly assigned eggs from each nest to one of three incubation temperatures (34·6, 36·0 and 37·4 °C). Experimental incubation temperatures overlapped average nest temperatures of naturally incubated Wood Duck nests. • Hatching success varied with incubation temperature and was lowest for eggs incubated at the lowest temperature. Incubation period of experimental eggs decreased with increasing temperature but was not affected by fresh egg mass. • Wood Duck embryos catabolized an estimated 34–38% of egg lipids and 25–33% of egg protein during incubation. Percentage change of lipids increased with decreasing incubation temperature, but not significantly. Embryos incubated at lower temperatures used a greater percentage of protein than embryos incubated at higher temperatures. • In analyses using fresh egg mass as the covariate, we found that wet and dry mass of ducklings increased with increasing incubation temperature. Decreases in lipid content of Wood Duck neonates with decreasing incubation temperature were not significant, but eggs incubated at low temperatures produced ducklings that had reduced protein mass and that were structurally larger than ducklings from eggs incubated at high temperatures. • Our study illustrates the importance of incubation temperature on the development of Wood Duck embryos. Decisions made by incubating parents that influence egg temperature can modify incubation period and offspring phenotype. Investigations of incubation as a reproductive cost should consider how parental decisions influence both parents and offspring. Functional Ecology (2006) 20, 307–314 doi: 10.1111/j.1365-2435.2006.01108.x