DOI: 10.5061/dryad.h1893201k
title: Data from: Females are larger and less detected than males but experience similar annual survival in the lek-displaying <em>Eleothreptus anomalus</em> (Sickle-winged Nightjar)

description: We examined age- and sex- specific variation in body size, apparent annual
 survival, and recapture probability using morphometric measurements,
 molecular sexing, logistic regression, and Cormack-Jolly-Seber models on
 1006 captures of 370 Eleothreptus anomalus (Sickle-winged Nightjars) in
 northeastern Argentina (2012–2025). Adult females were larger than males
 in all measurements, with a dimorphism of 45% in length of secondary
 feathers, 30% in weight, 16% in tail length, and 10% in total length.
 Sexual size dimorphism (females larger than males) also occurred in
 juveniles, such that we were able to accurately determine the sex of
 juveniles by their measurements, especially the length of their
 secondaries. The best Cormack-Jolly-Seber models included age-specific
 survival (adults: 0.67 annually, CI: 0.6–0.73; juveniles: 0.58, 0.48-0.68)
 and a sex-specific capture probability for adults (females: 0.19,
 0.11–0.31; males: 0.64, 0.53–0.74), highlighting the need to account for
 intraspecific variation in avian demographic parameters. We propose that
 the larger size of females, not previously recorded in any nightjar
 species, is related to sexual or social selection for the males’
 extraordinary ‘sickle-shaped’ wings. The data and code are in two parts:
 (1) morphometric measurements and logistic regression in a Monte Carlo
 Cross Validation framework; (2) Cormack-Jolly-Seber models of sex-specific
 adult and juvenile survival.
description: Field, lab, and statistical analysis methods are described in
 Cockle et al. Females are larger and less detected than males but
 experience similar annual survival in the lek-displaying
 <em>Eleothreptus anomalus</em> (Sickle-winged Nightjar).
 Ornithology. Additional details are provided in the supplementary material
 to that article.
description: # Data from: Females are larger and less detected than males but
 experience similar annual survival in the lek-displaying *Eleothreptus
 anomalus* (Sickle-winged Nightjar) Dataset DOI:
 [10.5061/dryad.h1893201k](https://doi.org/10.5061/dryad.h1893201k) ##
 Description of the data and file structure Captures and measurements of
 Sickle-winged Nightjar at Reserva Natural Rincón de Santa María and a few
 other sites in northeastern Argentina, 2012-2025. The code and files come
 in two parts: (1) Morphometry, which includes the R script Morphometry.R
 and the two files Eleothreptus_measurements.csv and Eleothreptus
 months.csv, including captures at Reserva Natural Rincón de Santa María
 and other sites. (2) Survival, which includes the R script CJS_survival.R
 and the two files Eleothreptus_adult_capture_histories.xlsx and
 Eleothreptus_juvenile_capture_histories.xlsx. You can run these two
 sections independently from one another, although they are based on the
 same raw data. The morphometric sexing results of Part 1 were incorporated
 manually into the datasets for Part 2. ### Files and variables #### File:
 Morphometry.R **Description:** Code for morphometry analysis of
 Eleothreptus anomalus, including sex determination by logistic regression
 using Monte Carlo Cross Validation in a for loop. Author: Kristina Cockle.
 #### File: Eleothreptus_measurements.csv **Description:** Morphometric
 measurements of Eleothreptus anomalus for input to Morphometry.R code. NA
 indicates missing values. Nestor Fariña took measurements on 86% of
 captures; Luis Pagano took 8%; Kristina Cockle and seven other
 collaborators took the remaining 6%. ##### Variables * ID_Final = aluminum
 leg band number (unique to each individual bird) * Localidad = Locality
 (RNRSM = Reserva Natural Rincón de Santa María, Corrientes, Argentina; CSJ
 = Campo San Juan, Misiones, Argentina; PPSanAntonio = Parque Provincial
 San Antonio, Corrientes, Argentina; ResDonLuis = Reserva Don Luis,
 Corrientes, Argentina) * codigo_salida = date (night) of capture
 (YYYY-MM-DD). For birds captured after midnight, codigo_salida is the date
 of the previous day, so that all birds captured in the same night have the
 same codigo_salida. * Year = year of capture * Sexo_plum = sex by plumage
 (M = male, H = Female, from the Spanish [hembra]). Birds were sexed
 primarily by Nestor Fariña and Luis Pagano based on plumage
 characteristics in the field. Juvenile birds could not be sexed by
 plumage, but we assigned their sex retroactively if they were recaptured
 in adult plumage. * Sexado_Mol = sex by molecular sexing (M = male, H =
 Female, from the Spanish [hembra]). Molecular sexing was performed by
 Cecilia Kopuchian and Simón Kraemer on a subset of juveniles. * Sexo_final
 = final sex (M = male, H = Female, from the Spanish [hembra]), as
 determined by plumage and/or molecular sexing. * Edad_final = age (A =
 Adult, I = intermediate, J = Juvenile, Pichón = nestling or recent
 fledgling [from Spanish]). Birds were aged by plumage or in some cases
 based on previous captures. Intermediates are approximately 1-year old
 birds in plumage that is transitioning from Juvenile to Adult. * Peso =
 weight in grams [from Spanish], measured with a spring balance (1 g). *
 Ala = wing chord in mm [from Spanish], measured with a wing rule. *
 Secundarias = length of secondary feathers in mm [from Spanish]. As
 described in Cockle et al. (in press, Ornithology): "Beginning in
 October 2018, we measured the length of the secondaries by extending the
 right wing, hooking the wing rule on the radius (leading edge of the
 wing), and measuring to the tip of the 4th secondary (Fig. S2). Although
 this measurement is not typical in ornithology, it gave us repeatable
 results within individual birds on different dates (Table S1)." *
 Cola = tail length in mm [from Spanish]. Measured using a ruler. * Tarso =
 tarsus length in mm to final leg scale before toes divide [from Spanish].
 This was not the measurement we used in the paper, as it was inconsistent,
 but it is included here because the Morphometry.R code assesses its
 usefulness. * Tarso_completo = complete tarsus length in mm to between
 toes [from Spanish]. From Cockle et al. (in press, Ornithology): "We
 used a caliper (0.1 mm) to measure the tarsus as follows: we rested the
 movable caliper jaw on the distal tibial epiphysis (bony protrusion
 posterior to the tibiotarsal joint), and the static jaw between the 2nd
 and 3rd toes, which we kept flexed toward the 1st toe (Fig. S2)." *
 Largo_total = total length from tip of beak to tip of tail [from Spanish].
 From Cockle et al. (in press, Ornithology: "Beginning in October
 2021, we measured the total length of each individual (from the tip of the
 bill to the tip of the tail) by lying them on their back on a wing rule (1
 mm) and holding the tip of the bill against the top of the ruler (Fig.
 S2)." #### File: Eleothreptus_months.csv **Description:** Captures by
 month of the year, to assess intra-annual variation. NA indicates missing
 values. ##### Variables * ID_Final = aluminum leg band number (unique to
 each individual bird) * Localidad = Locality (RNRSM = Reserva Natural
 Rincón de Santa María, Corrientes, Argentina; CSJ = Campo San Juan,
 Misiones, Argentina; PPSanAntonio = Parque Provincial San Antonio,
 Corrientes, Argentina; ResDonLuis = Reserva Don Luis, Corrientes,
 Argentina) * Night = date (night) of capture (YYYY-MM-DD). [Same as
 codigo_salida in other datasets]. For birds captured after midnight, this
 is the date of the previous day, so that all birds captured in the same
 night have the same value in this column. * Month = Month of capture (1 =
 January, 2 = February, ... 12 = December) * Lek_season = Was the
 observation in the lekking season when males display (August to December)?
 (1 = yes, 0 = no) * Year = Year of capture (YYYY) * Sexo_final = final sex
 (M = male, H = Female, from the Spanish [hembra]), as determined by
 plumage and/or molecular sexing. * Edad_final = age (A = Adult, I =
 intermediate, J = Juvenile, Pichón = nestling or recent fledgling [from
 Spanish]). Birds were aged by plumage or in some cases based on previous
 captures. Intermediates are approximately 1-year old birds in plumage that
 is transitioning from Juvenile to Adult. * Peso = weight in grams [from
 Spanish], measured with a spring balance (1 g). #### File: CJS_survival.R
 **Description:** Code for Cormack-Jolly-Seber models to estimate capture
 probability and survival of Eleothreptus anomalus by sex and age, based on
 data from Reserva Natural Rincón de Santa María, Corrientes, Argentina.
 Author: Alejandro Pietrek. #### #### File:
 Eleothreptus_adult_capture_histories.xlsx **Description:** Captures of
 adult Eleothreptus anomalus to use as input for Cormack-Jolly-Seber models
 of capture probability and survival (by sex). NA indicates missing values.
 ##### Variables * ID_Final = aluminum leg band number (unique to each
 individual bird) * Codigo_salida = date (night) (YYYY-MM-DD). For birds
 captured after midnight, codigo_salida is the date of the previous day, so
 that all birds captured in the same night have the same codigo_salida. *
 Sexo_final = final sex (M = male, H = Female, from the Spanish [hembra]),
 as determined by plumage and/or molecular sexing. * Edad_final = age (A =
 Adult). Birds were aged by plumage or in some cases based on previous
 captures. Intermediate-plumaged birds (approximately 1 year old,
 transitioning from juvenile plumage to adult plumage) were included here
 as adults. #### File: Eleothreptus_juvenile_capture_histories.xlsx
 **Description:** Capture histories of juvenile Eleothreptus anomalus at
 Reserva Natural Rincón de Santa María, Corrientes, Argentina, for
 Cormack-Jolly-Seber models estimating capture probability and survival. NA
 indicates missing values. ##### Variables * ID_Final = aluminum leg band
 number (unique to each individual bird) * ch = capture history, a series
 of seventeen 0s and 1s indicating whether the bird was captured (1) or not
 (0) in each of seventeen 6-month periods, starting on 21 September 2016.
 We assigned a 1 if the individual was captured at least once in the
 6-month period, and a 0 if it was not captured during the 6-month period.
 * sex = sex of the captured bird (M = male, H = female [from the Spanish,
 hembra]. For this dataset, we assigned sex based on (1) recaptures of the
 same individual in adult plumage (easy to distinguish the sex of adult
 birds by plumage), (2) molecular sexing (performed by Cecilia Kopuchian
 and Simón Kraemer at CECOAL-CONICET), or (3) - last option - morphometry.
 When assigning sex by morphometry, we used the output of our Monte Carlo
 Cross Validation logistic regression models with length of secondaries as
 the predictor variable. This latter approach is described by Cockle et al.
 (in press): "We used the following criteria to classify 45 juvenile
 individuals as female, male, or unknown sex. If 75% or more of the model
 iterations produced predictions (probability of being female) above 0.8,
 we assigned the individual the sex "female". If 75% or more of
 the model iterations produced predictions below 0.2, we assigned the
 individual the sex "male". In all other cases, we assigned
 "unknown sex" and excluded the individual from the analysis of
 survival and probability of recapture." * age = age of the bird
 (categorical) when first captured. Age was determined by plumage and time
 of year. Age classification was performed by Nestor Fariña and Olga
 Villalba in consultation with Kristina Cockle and Luis Pagano. under6 =
 less than 6 months old when first captured. 6to12 = 6 to 12 months old
 when first captured.  ## Code/software We have included two R scripts. The
 first script, Morphometry.R (by Kristina Cockle), uses as input the files
 Eleothreptus_measurements.csv and Eleothreptus_months.csv. This script
 summarizes the morphometric measurements, runs logistic regression models
 under a Monte Carlos Cross Validation approach, predicts sex from juvenile
 measurements, and produces the morphometric figures included in Cockle et
 al. (in press, Ornithology) and its supplementary material. The second
 script, CJS survival.R (by Alejandro Pietrek), takes as input the files
 Eleothreptus_adult_capture_histories.xlsx and
 Eleothreptus_juvenile_capture_histories.xlsx, models survival and
 recapture rate (Cormack-Jolly-Seber models) separately for adults and
 juveniles, and produces the survival and recapture-related figures in
 Cockle et al. (in press, Ornithology).