Do uniparental sanderlings Calidris alba increase egg heat input to compensate for low nest attentiveness?

Abstract

Birds breeding in cold environments regularly have to interrupt incubation to forage, causing a trade-off between two mutually exclusive behaviours. Earlier studies showed that uniparental Arctic sandpipers overall spend less time incubating their eggs than biparental species, but interspecific differences in size and ecology were potential confounding factors. This study reports on a within-species comparison of breeding schedules and metal egg temperatures in uni- and biparental sanderlings (Calidris alba) in Northeast Greenland in relation to ambient temperature. We recorded incubation schedules with nest temperature loggers in 34 sanderling clutches (13 uniparentals, 21 biparentals). The temperature of a metal egg placed within the clutch of 17 incubating birds (6 uniparentals, 9 biparentals) was measured as an indicator of the heat put into eggs. Recess frequency, recess duration and total recess time were higher in uniparentals than in biparentals and positively correlated with ambient temperatures in uniparentals only. Uniparental sanderlings maintained significantly higher metal egg temperatures during incubation than biparentals (1.4°C difference on average). Our results suggest that uniparental sanderlings compensate for the lower nest attendance, which may prolong the duration of the incubation period and negatively affect the condition of the hatchlings, by maintaining a higher heat flux into the eggs.

Figure 1. An individually color-ringed sanderling Calidris alba tries to lure away a researcher from its nest.

Note the antenna loop around the clutch of four eggs in the background. The PIT is glued to the side of the extended green color-ring that is not visible on this photograph. Photo by Jeroen Reneerkens.

Figure 2. Two examples of an incubation pattern of 48 hours as registered by a temperature probe and by the PITs.

Measured temperatures are depicted as a solid line, the presence of a PIT tagged male (black) and female (grey) as horizontal bars on top. The difference in incubation schedules with more recesses by the uniparental than the biparental clutch is clearly visible. Note that the PIT was not always detected when the temperature logger suggested an incubating bird (constant temperature around 40°C).

Figure 3. Metal egg temperature measurements in uni- and biparental clutches.

Examples of temperature profiles during which a temperature plateau was or was not reached are shown in (A) and connected with a dashed line to the corresponding data point in (B). The final data are depicted in (B) where black solid circles indicate values of temperature profiles during which a plateau temperature was reached and the open circles where it was not.

Figure 4. Average percentage of time that clutches were left unattended, recess frequency and recess duration of uniparentals and biparentals.

Uniparentals are indicated by grey boxes, biparentals by white boxes. For presentation purposes the hourly ambient temperatures are catagorized per 5°C. The graphs are based on the raw data. The dots indicate the average, the boxes encloses 50% of the data and the error bars 95%.

Figure 5. Relationship between daily mean ambient temperature and the average dry weight of arthropods collected per pitfall trap.

The linear regression is statistically significant (F₁ = 31.2, P<0.0001, R² = 0.486).