Laying sequence and parasitized nests

Comma delimited file used to test whether daily parasitism of nests across the laying sequence differed between incubation temperature treatments

Sample sizes of Wood Duck nests and eggs and mean (± SE) incubation temperature and incubation period by temperature treatment.

<p>Sample sizes of Wood Duck nests and eggs and mean (± SE) incubation temperature and incubation period by temperature treatment.</p

Laying sequence interacts with incubation temperature to influence rate of embryonic development and hatching synchrony in a precocial bird

<div><p>Incubation starts during egg laying for many bird species and causes developmental asynchrony within clutches. Faster development of late-laid eggs can help reduce developmental differences and synchronize hatching, which is important for precocial species whose young must leave the nest soon after hatching. In this study, we examined the effect of egg laying sequence on length of the incubation period in Wood Ducks (<b><i>Aix sponsa</i></b>). Because incubation temperature strongly influences embryonic development rates, we tested the interactive effects of laying sequence and incubation temperature on the ability of late-laid eggs to accelerate development and synchronize hatching. We also examined the potential cost of faster development on duckling body condition. Fresh eggs were collected and incubated at three biologically relevant temperatures (Low: 34.9°C, Medium: 35.8°C, and High: 37.6°C), and egg laying sequences from 1 to 12 were used. Length of the incubation period declined linearly as laying sequence advanced, but the relationship was strongest at medium temperatures followed by low temperatures and high temperatures. There was little support for including fresh egg mass in models of incubation period. Estimated differences in length of the incubation period between eggs 1 and 12 were 2.7 d, 1.2 d, and 0.7 d at medium, low and high temperatures, respectively. Only at intermediate incubation temperatures did development rates of late-laid eggs increase sufficiently to completely compensate for natural levels of developmental asynchrony that have been reported in Wood Duck clutches at the start of full incubation. Body condition of ducklings was strongly affected by fresh egg mass and incubation temperature but declined only slightly as laying sequence progressed. Our findings show that laying sequence and incubation temperature play important roles in helping to shape embryo development and hatching synchrony in a precocial bird.</p></div

Relationship of incubation temperature to future reproductive success.

<p>Mean (± SE) numbers of breeding years, nest attempts and successful nests of female wood ducks that had been artificially incubated in 2008 at temperatures of 35°C (<i>n</i> = 1) and ≥35.9°C (<i>n</i> = 11). Nesting activity was monitored every four days in nest boxes (<i>n</i> = 110) at Par Pond and L Lake for four breeding seasons (2009–2012).</p

Means and least squares means (±SE) of incubation temperature (°C), incubation period (d), duckling mass (g), and tarsus length (mm) by temperature treatment of artificially-incubated wood duck eggs.

a<p>Least-squares means are from ANCOVAs using fresh egg mass as the covariate.</p>b<p>Means and least squares means within rows followed by different letters are significantly different (<i>p</i><0.05).</p

Wood Duck nests containing either 1 or > 1 egg during daily nest checks.

<p>Frequencies are displayed by egg laying sequence and incubation temperature (low, medium and high). Only data from active nests that were being checked daily are included.</p

Department of Energy's Savannah River Site.

<p>The study was conducted at the Savannah River Site (800 km²) in west-central South Carolina. Wood ducks used nest boxes that were erected at Par Pond (<i>n</i> = 80; 1120 ha) and L-Lake (<i>n</i> = 30; 450 ha).</p

Wood Duck eggs collected and successfully hatched.

<p>Frequencies are displayed according to laying sequence (1–12) and incubation temperature (low, medium and high).</p

Mixed models used to evaluate effect of egg laying sequence on length of the incubation period in Wood Ducks.

<p>Incubation temperature and fresh egg mass also were included as potential explanatory variables. We compared models using Akaike’s Information Criterion corrected for small sample size (AIC_c) and ranked models based on relative differences to the top model (ΔAIC_c). <i>w</i>_<i>i</i> = Akaike model weight and K = number of parameters.</p

Frequency that male and female wood duck ducklings fledged and left the nest after being incubated at high (≥35.9°C) and low (35.0°C) temperatures.

a<p>Includes ducklings from the mid and high temperature groups.</p