Incubation parameters, offspring growth, and behavioral adaptations to heat stress of Black Skimmers (Rynchops niger) in a Neotropical inland colony (Aves, Charadriiformes, Laridae)

Abstract

This study focuses on incubation parameters, egg morphometrics, and body mass development, hatching, and behavioral adaptations to heat stress within a colony of freshwater-breeding Black Skimmers (Rynchops niger) located in the private nature reserve of Serviço Social do Comércio (SESC) in the northern Pantanal, Mato Grosso, Brazil. Temperatures of nest, eggs, and surface substratum, as well as the development of embryos, were surveyed using thermal imaging, a method allowing digital recording from a distance and in a fraction of the time of traditional measuring techniques. The mean egg dimensions (n = 71) were 4.48 (± 0.13) × 3.27 (± 0.07) cm; the mean mass at hatching was 24.3 (± 1.9) g, with a significant decrease over incubation time. The mean surface temperature of eggs varied from 30.9℃ to 39.7℃, while the sand surface temperature was 20℃ at 06:00 h, rising to 47.7℃ at 11:00 h. There was a significant increase (7%) in egg surface temperature throughout incubation. Incubation-bout durations (n = 2108) were correlated with the microclimatic conditions of the substratum, becoming shorter with increasing sand-surface temperature around midday. Egg hatching lasted one day, and siblings hatched no more than 24 h apart. The mean body mass on Day 1 after hatching was 16.8 (± 1.6) g (n = 6). Three days after hatching, chicks moved to new sand depressions provided by parents near the original nest, where they remained motionless or tried to hide under riparian vegetation. The single chick that fledged had a growth rate of K = 0.117 and a t₁₀₋₉₀ value of 37.3 days. On Day 7, dorsal pintail feathers and primaries appeared, which were open on Day 15. After 14 days, the chick was able to regulate its body temperature, and no more feeding by parental birds during the daytime was observed. On Day 21, the immature plumage was fully developed. Fledging was completed on Day 27. Our study demonstrates that thermal imaging is a useful method of surveying egg and embryo development in the Black Skimmer, reducing nest disturbance and observation efforts.

Biparental incubation behaviour under temperature extremes in sandbank nesting black skimmers

“…The use of 1‐min time‐lapse images meant that certain behaviours such as any incubation bouts shorter than 1‐min or the same bird leaving the nest within a minute might have gone undetected. However, mean bout length in this study was very similar to one using video recordings (Schuchmann et al., 2022 ), showing that time‐lapse cameras can be as reliable but probably more efficient than video recorders.…”

“…We found highly shared biparental incubation in Amazonian black skimmers across the diel cycle. Overall, males were found to incubate slightly less than females, complementing results from the Brazilian Amazon using only diurnal observations (Schuchmann et al., 2022 ). Incubation was shared most equally between 10:00 to 14:00 h, in contrast to larger variations in contribution during other parts of the diel period (Figure 3 ).…”

“…Incubation behaviour, especially in the Amazon breeding range of black skimmers, is poorly studied (Vieira et al., 2018b ). Generally, females were found to incubate more than males (Quinn, 1990 ; Schuchmann et al., 2022 ), but one study from a North American population found higher male incubation rates (Burger, 1981b ). However, the limited observation time in these studies, mainly constrained to daylight hours, means we know very little about the incubation behaviour across the entire diel cycle, especially nocturnal time allocation to incubation (Vieira et al., 2018b ), which might conflict with foraging requirements (Bulla et al., 2015 ; Erwin, 1977 ).…”

An Evaluation of Morphological Methods for Sex Determination of Black Skimmers (Rynchops niger) in the Pre-Fledgling Stage

“…Few studies have measured Black Skimmer chick growth over time, but a recent study conducted by Schuchmann et al . (2022) discovered that the growth rate constant of Black Skimmers in Brazil was c. 30% lower than studies on skimmers in Virginia, USA (Erwin 1977; Gordon et al . 2000).…”

“…Few studies have measured Black Skimmer chick growth over time, but a recent study conducted by Schuchmann et al (2022) discovered that the growth rate constant of Black Skimmers in Brazil was c. 30% lower than studies on skimmers in Virginia, USA (Erwin 1977;Gordon et al 2000). It is important to consider that Black Skimmers in southwest Florida and Brazil are both non-migratory, while skimmers in California and Virginia migrate south after the breeding season (Gochfeld et al 2020).…”