Spatial and Temporal Patterns In Population Trends and Burrow Usage of Burrowing Owls In North America

2021

Ecology

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Variation in life‐history strategies is central to our understanding of population dynamics and how organisms adapt to their environments. Yet we lack consensus regarding the ecological processes that drive variation in traits related to reproduction and survival. For example, we still do not understand the cause of two widespread inter‐ and intraspecific patterns: (1) the ubiquitous positive association between avian clutch size and latitude; and (2) variation in the extent of asynchronous hatching of eggs within a single clutch. Well‐known hypotheses to explain each pattern have largely focused on biotic processes related to food availability and predation risk. However, local adaptation to maintain egg viability could explain both patterns with a single abiotic mechanism. The egg viability hypothesis was initially proposed to explain the cause of asynchronous hatching and suggests that asynchronous hatching results from early incubation onset in response to unfavorable nest microclimatic conditions, which otherwise reduce egg viability. However, allocation of resources to early incubation, prior to clutch completion, may energetically constrain clutch size and help explain the positive association between clutch size and latitude. We measured intraspecific variation in five functionally linked life‐history traits of burrowing owls at five study sites spanning a 1,400‐km latitudinal transect in western North America: clutch size, the timing of incubation onset, the degree of hatching asynchrony, the probability of hatching failure, and nestling survival. We found that most traits varied clinally with latitude, but all the traits were more strongly associated with individual nest microclimates than with latitude, and all varied with nest microclimate in the directions predicted by the egg viability hypothesis. Furthermore, incubation began earlier, hatching asynchrony increased, and clutch size declined across the breeding season. These results suggest that nest microclimate drives an important life‐history trade‐off and that thermal gradients are often sufficient to account for observed biogeographic and seasonal patterns in life‐history strategies. Furthermore, our results reveal a potentially important indirect mechanism by which reproductive success and recruitment could be affected by climate change.

Section: Methodsmentioning

confidence: 99%

Nest microclimate and limits to egg viability explain avian life‐history variation across latitudinal gradients

Lundblad

2021

Ecology

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“…Burrowing owls inhabit the western hemisphere from southern Argentina to southern Canada and lay their eggs underground in burrows, typically those constructed by other burrowing animals (Conway, 2018). Clutch size varies from 3 to 14 eggs and is positively correlated with latitude.…”

Section: Methodsmentioning

confidence: 99%

Intraspecific variation in incubation behaviours along a latitudinal gradient is driven by nest microclimate and selection on neonate quality

Lundblad

2021

Functional Ecology

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The strategies by which animals allocate reproductive effort across their lifetimes vary, and the causes of variation in those strategies are actively debated. In birds, most research has focused heavily on variation in clutch size and fecundity, but incubation behaviour and other functionally related traits have received less attention. Variation in incubation period duration is notable because time‐dependent sources of clutch mortality should impose strong directional selection to minimize the incubation period. However, life‐history theory predicts multiple mechanisms by which inter‐ and intraspecific variation in incubation behaviours may be adaptive. We conducted one of the first studies of intraspecific latitudinal variation in avian incubation behaviours across a large portion of a single species’ range. We placed motion‐activated nest cameras inside burrowing owl nests at five study sites to quantify variation in daily nest attentiveness, cumulative nest attendance and incubation period duration. We tested predictions of two alterative hypotheses that have been proposed to explain variation in incubation periods: the parental risk tolerance hypothesis and the neonate quality hypothesis. Daily nest attentiveness, cumulative nest attendance and incubation period duration in burrowing owls were all positively correlated with latitude. Burrowing owls reduced their daily nest attentiveness at low latitudes and on days when the average nest temperature was within the range that is optimal for embryo development. Further, longer incubation periods were most strongly associated with greater cumulative nest attendance instead of reduced daily nest attentiveness. These results support predictions of the neonate quality hypothesis: longer incubation periods result from stronger selection on neonate quality rather than selection to reduce reproductive effort in response to low extrinsic mortality risk. However, some owls facultatively reduced their daily nest attentiveness, and this result supports the general hypothesis that incubation decisions reflect a trade‐off between reproduction and self‐maintenance, and that the optimal solution to that trade‐off varies systematically in response to latitudinal gradients in adult mortality. A free Plain Language Summary can be found within the Supporting Information of this article.

“…This information would help determine the species' meta-population dynamics (colonization and extinction of local populations) in central Mexico and help to assess owl population viability in Texcoco. Moreover, detailed demographic studies are needed in both locations to determine the threats that these unique populations face, the burrowing animals that they rely on (Conway 2018), and whether they are self-sustaining.…”

Section: Discussionmentioning

confidence: 99%

Genetic Variation among Island and Continental Populations of Burrowing Owl (Athene cunicularia) Subspecies in North America

Macías‐Duarte¹,

Journal of Raptor Research

Holroyd³

et al. 2019

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Burrowing Owls (Athene cunicularia) have a large geographic range spanning both North and South America and resident populations occur on many islands in the eastern Pacific Ocean and the Caribbean Sea. Many owl populations are isolated and disjunct from other populations, but studies on genetic variation within and among populations are limited. We characterized DNA microsatellite variation in populations varying in size and geographic isolation in the Florida (A. c. floridana), the Western (A. c. hypugaea), and the Clarion (A. c. rostrata) subspecies of the Burrowing Owl. We also characterized genetic variation in a geographically isolated population of the western subspecies in central Mexico (near Texcoco Lake). Clarion Burrowing Owls had no intrapopulation variation (i.e., fixation) at 5 out of 11 microsatellite loci, a likely outcome of genetic drift in an isolated and small population. The Florida subspecies had only polymorphic loci but had reduced levels of genetic variation compared with the more-widespread western subspecies that occurs throughout western North America. Despite the extensive geographic distribution of the Western Burrowing Owl, we found genetic differentiation between the panmictic population north of the Trans-Mexican Volcanic Belt and the resident Texcoco Lake population in central Mexico.