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Wells CP, Lyon BE, Thow CM, Stair T, Jones M, Hinton M, Eadie JM. Limited evidence of biased offspring sex allocation in a cavity-nesting conspecific brood parasite. Behav Ecol 2024; 35:arae024. [PMID: 39372888 PMCID: PMC11453106 DOI: 10.1093/beheco/arae024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2023] [Revised: 03/08/2024] [Accepted: 03/27/2024] [Indexed: 10/08/2024] Open
Abstract
Sex allocation theory predicts that mothers should bias investment in offspring toward the sex that yields higher fitness returns; one such bias may be a skewed offspring sex ratio. Sex allocation is well-studied in birds with cooperative breeding systems, with theory on local resource enhancement and production of helpers at the nest, but little theoretical or empirical work has focused on birds with brood parasitic breeding systems. Wood ducks (Aix sponsa) are a conspecific brood parasite, and rates of parasitism appear to increase with density. Because female wood ducks show high natal philopatry and nest sites are often limiting, local resource competition (LRC) theory predicts that females should overproduce male offspring-the dispersing sex-when competition (density) is high. However, the unique features of conspecific brood parasitism generate alternative predictions from other sex allocation theory, which we develop and test here. We experimentally manipulated nesting density of female wood ducks in 4 populations from 2013 to 2016, and analyzed the resulting sex allocation of >2000 ducklings. In contrast to predictions we did not find overproduction of male offspring by females in high-density populations, females in better condition, or parasitic females; modest support for LRC was found in overproduction of only female parasitic offspring with higher nest box availability. The lack of evidence for sex ratio biases, as expected for LRC and some aspects of brood parasitism, could reflect conflicting selection pressures from nest competition and brood parasitism, or that mechanisms of adaptive sex ratio bias are not possible.
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Affiliation(s)
- Caitlin P Wells
- Department of Fish, Wildlife, and Conservation Biology; Colorado State University, 901 Amy Van Dyken Way, Fort Collins, CO 80523, USA
- Department of Wildlife, Fish, and Conservation Biology; University of California, 1088 Academic Surge, Davis, CA 95616, USA
| | - Bruce E Lyon
- Department of Ecology and Evolution; University of California, UCSC/Coastal Biology Building 130 McAllister Way, Santa Cruz, CA 95060, USA
| | - Caroline M Thow
- Department of Ecology and Evolution; University of California, UCSC/Coastal Biology Building 130 McAllister Way, Santa Cruz, CA 95060, USA
| | - Tez Stair
- Department of Wildlife, Fish, and Conservation Biology; University of California, 1088 Academic Surge, Davis, CA 95616, USA
| | - Melissa Jones
- Department of Wildlife, Fish, and Conservation Biology; University of California, 1088 Academic Surge, Davis, CA 95616, USA
| | - Mitch Hinton
- Department of Wildlife, Fish, and Conservation Biology; University of California, 1088 Academic Surge, Davis, CA 95616, USA
| | - John M Eadie
- Department of Wildlife, Fish, and Conservation Biology; University of California, 1088 Academic Surge, Davis, CA 95616, USA
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Perrig M, Oppel S, Tschumi M, Keil H, Naef‐Daenzer B, Grüebler MU. Juvenile survival of little owls decreases with snow cover. Ecol Evol 2024; 14:e11379. [PMID: 38770120 PMCID: PMC11103642 DOI: 10.1002/ece3.11379] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2024] [Revised: 04/11/2024] [Accepted: 04/22/2024] [Indexed: 05/22/2024] Open
Abstract
Global environmental changes are associated with warmer average temperatures and more extreme weather events, potentially affecting wildlife population dynamics by altering demographic processes. Extreme weather events can reduce food resources and survival in all seasons of the year. Estimates of season-specific survival probabilities are therefore crucial to understand the moderating effect of extreme events on annual mortality. Here, we analysed survival probabilities of 307 radio-tracked juvenile little owls (Athene noctua) over two-week periods from fledging to their first breeding attempt in the following spring to assess the contribution of extreme weather events. Survival probabilities were typically lowest during the first weeks after fledging in summer but were moderated by seasonal extremes in winter. The duration of snow cover in winter had a strong negative effect on survival probability, while being food supplemented during the nestling stage increased survival during the first weeks after fledging in summer and ultimately led to a larger proportion of birds surviving the first year. Overall annual survival probability over the first year varied by 34.3% between 0.117 (95% credible interval 0.052-0.223) and 0.178 (0.097-0.293) depending on the severity of the winter, and was as high as 0.233 (0.127-0.373) for food-supplemented fledglings. In years with mild winters, the season with the lowest survival was the summer post-fledging period (0.508; 0.428-0.594), but in years with extensive snow cover the winter was the season with the lowest survival (0.481; 0.337-0.626). We therefore show that extreme weather events occurring in a particular season reduced the proportion of first-year survivors. Increasing extreme weather events can moderate seasonal survival probability through altering food supply of juvenile little owls either during the nestling period or in winter, with similarly large effects on annual survival and the viability of populations.
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Affiliation(s)
- Marco Perrig
- Swiss Ornithological InstituteSempachSwitzerland
- Institute of Evolutionary Biology and Environmental StudiesUniversity of ZurichZurichSwitzerland
| | | | | | - Herbert Keil
- Forschungsgemeinschaft zur Erhaltung einheimischer Eulen (FOGE)OberriexingenGermany
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Brood sex ratio variation in a colonial raptor, the Eleonora's falcon, Falco eleonorae. Anim Behav 2022. [DOI: 10.1016/j.anbehav.2022.11.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
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BARTLOW ANDREWW, JANKOWSKI MARKD, HATHCOCK CHARLESD, RYTI RANDALLT, RENEAU STEVENL, FAIR JEANNEM. Sex ratio of Western Bluebirds Sialia mexicana is mediated by phenology and clutch size. THE IBIS 2021; 163:977-989. [PMID: 35801167 PMCID: PMC9257600 DOI: 10.1111/ibi.12935] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2020] [Accepted: 01/25/2021] [Indexed: 06/15/2023]
Abstract
Mothers may produce more of one sex to maximize their fitness if there are differences in the cost of producing each sex or there are differences in their relative reproductive value. Breeding date and clutch size are known to influence offspring sex ratios in birds through sex differences in dispersal, social behaviours, differential mortality, and available food resources. We tested if breeding date, clutch size and drought conditions influenced offspring sex ratios in a sexually size-monomorphic species, the Western Bluebird, by interrogating a 21-year dataset. After controlling for differential mortality, we found that hatch dates late in the breeding season were associated with the production of more females, suggesting that the value of producing males declines as the breeding season progresses. When clutch size was taken into account, small clutches yielded significantly more females late in the breeding season compared to the early and middle parts of the breeding season that produced significantly more males. Large clutches early in the season tended to produce more females, although this was not significant. Drought severity was not correlated with sex ratio adjustment. We propose and discuss several explanations for these patterns, including male offspring, but not female offspring, acting as helpers, increased female nestling provisioning late in the breeding season, differences in food abundance, and egg-laying order. Future work will help to uncover the mechanisms leading to these patterns. Identifying patterns and mechanisms of sex ratio skew from long-term datasets is important for informing predictions regarding life-history trade-offs in wildlife populations.
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Affiliation(s)
- ANDREW W. BARTLOW
- Los Alamos National Laboratory, Biosecurity and Public Health, Mailstop M888, Los Alamos, NM 87545, USA
| | - MARK D. JANKOWSKI
- Laboratory Services and Applied Science Division, U.S. Environmental Protection Agency, 1200 6 Avenue, Suite 900, Seattle, WA 98101, USA
| | - CHARLES D. HATHCOCK
- Los Alamos National Laboratory, Environmental Stewardship, Los Alamos, NM 87545, USA
| | - RANDALL T. RYTI
- Neptune and Company, Inc., 1505 15th St #B, Los Alamos, NM 87544, USA
| | - STEVEN L. RENEAU
- Los Alamos National Laboratory, PO Box 1663, Los Alamos, NM 87545
| | - JEANNE M. FAIR
- Los Alamos National Laboratory, Biosecurity and Public Health, Mailstop M888, Los Alamos, NM 87545, USA
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Fattebert J, Perrig M, Naef-Daenzer B, Grüebler MU. Experimentally disentangling intrinsic and extrinsic drivers of natal dispersal in a nocturnal raptor. Proc Biol Sci 2019; 286:20191537. [PMID: 31480971 DOI: 10.1098/rspb.2019.1537] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Equivocal knowledge of the phase-specific drivers of natal dispersal remains a major deficit in understanding causes and consequences of dispersal and thus, spatial dynamics within and between populations. We performed a field experiment combining partial cross-fostering of nestlings and nestling food supplementation in little owls (Athene noctua). This approach disentangled the effect of nestling origin from the effect of the rearing environment on dispersal behaviour, while simultaneously investigating the effect of food availability in the rearing environment. We radio-tracked fledglings to quantify the timing of pre-emigration forays and emigration, foray and transfer duration, and the dispersal distances. Dispersal characteristics of the pre-emigration phase were affected by the rearing environment rather than by the origin of nestlings. In food-poor habitats, supplemented individuals emigrated later than unsupplemented individuals. By contrast, transfer duration and distance were influenced by the birds' origin rather than by their rearing environment. We found no correlation between timing of emigration and transfer duration or distance. We conclude that food supply to the nestlings and other characteristics of the rearing environment modulate the timing of emigration, while innate traits associated with the nestling origin affect the transfer phases after emigration. The dispersal behaviours of juveniles prior and after emigration, therefore, were related to different determinants, and are suggested to form different life-history traits.
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Affiliation(s)
- Julien Fattebert
- Swiss Ornithological Institute, CH-6204 Sempach, Switzerland.,Centre for Functional Biodiversity, School of Life Sciences, University of KwaZulu-Natal, Durban 4000, South Africa
| | - Marco Perrig
- Swiss Ornithological Institute, CH-6204 Sempach, Switzerland
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