Sex ratios of Mountain Plovers from egg production to fledging

Abstract

ABSTRACT. Skewed sex ratios can have negative implications for population growth if they do not match a species' life history. A skewed tertiary sex ratio has been detected in a population of Mountain Plover (Charadrius montanus), a grassland shorebird experiencing population declines. To study the cause of the observed male skew, we examined three early life stages between egg and fledgling in eastern Colorado from 2010 to 2012. This allows us to distinguish between egg production and chick survival as an explanation for the observed skew. We examined the primary sex ratio in eggs produced and the secondary sex ratio in hatched chicks to see if the sex ratio bias occurs before hatching. We also determined the sex ratio at fledging to reveal sex-specific mortality of nestlings. The primary sex ratio was 1.01 (± 0.01) males per female. The secondary sex ratio consisted of 1.10 (± 0.02) males per female. The probability of a chick surviving to fledging differed between males (0.55 ± 0.13) and females (0.47 ± 0.15), but the precision of these survival estimates was low. Sex ratios in early life stages of the Mountain Plover do not explain the skewed sex ratio observed in adults in this breeding population. Sex-ratios de la production d'oeufs à l'envol chez le Pluvier montagnardRÉSUMÉ. Des sex-ratios déséquilibrées peuvent avoir des effets négatifs sur la croissance d'une population si elles sont trop éloignées de la biodémographie naturelle de l'espèce. Une sex-ratio tertiaire déséquilibrée a été détectée chez une population de Pluvier montagnard (Charadrius montanus), un oiseau de rivage qui se reproduit dans les prairies et dont les populations sont en baisse. Dans le but d'étudier la cause du déséquilibre observé favorisant les mâles, nous avons examiné trois stades précoces des oeufs à l'envol, dans l'est du Colorado de 2010 à 2012. Cet examen nous a permis d'établir si la production d'oeufs ou la survie des jeunes pouvait expliquer la sex-ratio déséquilibrée. Nous avons examiné la sex-ratio primaire des oeufs et la sex-ratio secondaire des poussins éclos afin de déterminer si le déséquilibre de la sex-ratio était présent avant l'éclosion. Nous avons aussi déterminé la sex-ratio des jeunes à l'envol pour obtenir la mortalité spécifique au sexe des oisillons. La sex-ratio primaire s'élevait à 1,01 (± 0,01) mâle par femelle. La sex-ratio secondaire était de 1,10 (± 0,02) mâle par femelle. La probabilité qu'un oisillon survive jusqu'à l'envol était différente entre les mâles (0,55 ± 0,13) et les femelles (0,47 ± 0,15), mais la précision de ces estimations de survie était faible. La sex-ratio observée aux stades précoces n'explique pas le déséquilibre de la sex-ratio chez les adultes de cette population nicheuse de Pluvier montagnard.

Male‐specific mortality biases secondary sex ratio in Eurasian tree sparrows Passer montanus

“…For example, primary sex ratio can refer to the ratio at fertilization, (Aslam et al., ; DuRant et al., ; Eiby et al., ; Krackow, ), at laying (Alonso‐Alvarez, ; Czyż, Rowiński, & Wesołowski, ; Szász, Kiss, & Rosivall, ), or in the egg (Donald, ; Riordan, Lukacs, Huyvaert, & Dreitz, ). Secondary sex ratio can refer to the ratio after laying (DuRant et al., ; Szász et al., ), after hatching (Kilner, ; Riordan et al., ), at hatching (Eiby et al., ; Saunders & Cuthbert, ), at the chick stage (Czyż et al., ; Donald, ), or at fledging (Alonso‐Alvarez, ; Romano, Ambrosini, Caprioli, Bonisoli‐Alquati, & Saino, ), although there are distinct stages associated with the secondary sex ratio (i.e., embryo development, hatching, and fledging). To avoid semantic confusion on the difference of definition across studies, we need to define offspring sex ratio with respect to the major growth stages, which are at clutch, during incubation (embryo development), at hatching, and at fledging.…”

Age and performance at fledging are a cause and consequence of juvenile mortality between life stages

“…As a result, undetected individuals were assigned an unknown status. We included this unknown status as a third state in addition to live and dead and estimated survival using transition probabilities (Ψ) in a multistate model ( 37 ). We also estimated fledgling survival for gray-headed juncos using the multistate approach above but included treatment (control and enclosure), mass, and wing length as covariates to examine their influence on variation in fledgling survival.…”

Evaluating the Impacts of Headstarting on the Critically En-Dangered Spoon-Billed Sandpiper <em>Calidris pygmaea</em>

“…Liker et al [44] found that species with male-biased care usually have male-biased adult sex ratio. The ratio can also be biased already at hatching as it is shown for the mountain plover Charadrius montanus ( [45], but just within 10% of sex ratio difference. Heg et al [43] did not find any sexual difference in survival of chicks during the hatch-to-fledge period in eurasian oystercatshers Haematopus ostralegus.…”

“…Heg et al [43] did not find any sexual difference in survival of chicks during the hatch-to-fledge period in eurasian oystercatshers Haematopus ostralegus. Some higher hatch-to-fledge survival was shown for males of mountain plover chicks: 54.8% vs. 47.2% in females [45]. But Saunders & Cuthbert [46] found significant male-biased survival during pre-fledging in Ch.…”