Different Temperature and Cooling Patterns at the Blunt and Sharp Egg Poles Reflect the Arrangement of Eggs in an Avian Clutch

<div><p>Incubation is an energetically demanding process during which birds apply heat to their eggs to ensure embryonic development. Parent behaviours such as egg turning and exchanging the outer and central eggs in the nest cup affect the amount of heat lost to the environment from individual eggs. Little is known, however, about whether and how egg surface temperature and cooling rates vary among the different areas of an egg and how the arrangement of eggs within the clutch influences heat loss. We performed laboratory (using Japanese quail eggs) and field (with northern lapwing eggs) experiments using infrared imaging to assess the temperature and cooling patterns of heated eggs and clutches. We found that (i) the sharp poles of individual quail eggs warmed to a higher egg surface temperature than did the blunt poles, resulting in faster cooling at the sharp poles compared to the blunt poles; (ii) both quail and lapwing clutches with the sharp poles oriented towards the clutch centre (arranged clutches) maintained higher temperatures over the central part of the clutch than occurred in those clutches where most of the sharp egg poles were oriented towards the exterior (scattered clutches); and (iii) the arranged clutches of both quail and lapwing showed slower cooling rates at both the inner and outer clutch positions than did the respective parts of scattered clutches. Our results demonstrate that egg surface temperature and cooling rates differ between the sharp and blunt poles of the egg and that the orientation of individual eggs within the nest cup can significantly affect cooling of the clutch as a whole. We suggest that birds can arrange their eggs within the nest cup to optimise thermoregulation of the clutch.</p></div

Effect of areas of an egg (sharp pole x equator x blunt pole) on temperature and effect of areas of an egg and initial temperature on cooling rates of Japanese quail eggs (n = 17).

<p>Eggs were heated to 38°C and subsequently cooled at ambient temperature of 12°C. Measurements were recorded at three time intervals (immediately after heating and 530.5 ± 9.8 and 1002.3 ± 4.1 s after heating).</p><p>¹ Controlled for egg mass and time of measurement</p><p>² Controlled for egg mass</p><p>³ Interaction between areas of an egg and temperature</p><p>Effect of areas of an egg (sharp pole x equator x blunt pole) on temperature and effect of areas of an egg and initial temperature on cooling rates of Japanese quail eggs (n = 17).</p

Temperature (a) and cooling rates (b) of arranged (n = 2) and scattered (n = 2) northern lapwing clutches at inner and outer parts of clutches.

<p>Means ± SE are given. Clutches were heated to 38°C and subsequently cooled in ambient temperature (20°C). Measurements were recorded at 71.5 ± 7.8 s intervals (mean ± SE) over a period of 15 min. Identical and different letters, respectively, inside the bars indicate non-significant and significant differences at P ≤ 0.05 (Tukey’s multiple comparisons).</p

Temperature (a) and cooling rates (b) of arranged (n = 2) and scattered (n = 2) Japanese quail clutches at inner and outer positions.

<p>Means ± SE are given. Clutches were heated to 38°C and subsequently cooled in ambient temperature (12°C). Measurements were recorded at 79.1 ± 3.6 s intervals (mean ± SE) over a period of 30 min. Identical and different letters inside the bars, respectively, indicate non-significant and significant differences at P ≤ 0.05 (Tukey’s multiple comparisons).</p

Results of Tukey’s tests for multiple comparisons of temperature and cooling rates between different areas of Japanese quail eggs and between internal (int) and outer (out) positions of arranged and scattered Japanese quail and northern lapwing clutches.

<p>¹ Controlled for egg mass and time of measurement</p><p>² Controlled for egg mass</p><p>³ Controlled for time of measurement</p><p>⁴ Controlled for initial temperature</p><p>Results of Tukey’s tests for multiple comparisons of temperature and cooling rates between different areas of Japanese quail eggs and between internal (int) and outer (out) positions of arranged and scattered Japanese quail and northern lapwing clutches.</p

Effects of egg arrangement (arranged or scattered) and clutch position (inner or outer part) on temperature and cooling rates of northern lapwing clutches (n = 2).

<p>Clutches were heated to 38°C and subsequently cooled in ambient temperature (20°C). Measurements were recorded at 71.5 ± 7.8 s intervals (mean ± SE) for a period of 15 min.</p><p>¹ Controlled for time of measurement</p><p>² Controlled for initial temperature</p><p>Effects of egg arrangement (arranged or scattered) and clutch position (inner or outer part) on temperature and cooling rates of northern lapwing clutches (n = 2).</p

Relationship between egg surface temperature and cooling rate of Japanese quail eggs (sharp and blunt poles).

<p>Relationship between egg surface temperature and cooling rate of Japanese quail eggs (sharp and blunt poles).</p

Dark or Short Nights: Differential Latitudinal Constraints in Nestling Provisioning Patterns of a Nocturnally Hunting Bird Species

<div><p>In diurnal bird species, individuals breeding at high latitudes have larger broods than at lower latitudes, which has been linked to differences in the daily time available for foraging. However, it remains unclear how latitude is linked with parental investment in nocturnal species. Here, we investigate nestling provisioning rates of male Tengmalm's owls in two populations at different latitudes (Czech Republic 50°N; Finland 63°N) with the help of cameras integrated into nest boxes. Clutch sizes were smaller in the Czech population (CZ: 5.1±0.1; FIN: 6.6±0.1), but given the higher nestling mortality in the Finnish population, the number of fledglings did not differ between the two populations (CZ: 3.5±0.3; FIN: 3.9±0.2). Nestling provisioning patterns varied within days, over the reproductive season and between the two sites. Males delivered most food at dusk and dawn, having peak delivery rates at sun angles of −11° to −15° at both sites, and males increased the prey delivery rates with higher nestling requirements. Given the longer nights during summer in the Czech Republic compared to Finland, Czech males only showed a small shift in their delivery peak during the night from −17° in April to −14° in July. In contrast, Finnish males shifted their peak of prey delivery from −11° in April to −1° in July. Consequently, Czech males had a longer hunting time per night around midsummer when feeding young (360 min) than Finnish males (270 min). This suggests that nocturnal owl species in northern populations are constrained by the short nights during the breeding season, which can limit the number of young they can raise. Moreover, owls in northern populations are additionally constrained through the unpredictable changes in food availability between years, and both these factors are likely to influence the reproductive investment between populations.</p> </div

Perching duration of (a) Finnish, and (b) Czech nestlings at the nest box entrance throughout the day. Individual columns show the mean number (± SE) of minutes per nestling, day and nest.

<p>Perching duration of (a) Finnish, and (b) Czech nestlings at the nest box entrance throughout the day. Individual columns show the mean number (± SE) of minutes per nestling, day and nest.</p

A Webcast of Bird Nesting as a State-of-the-Art Citizen Science - Fig 3

<p>An example of data collected from the nest of a great tit (<i>P</i>. <i>major</i>) during the nesting period (i.e., from April 19 to May 23) documenting (A) the structure of the diet delivered by tit parents to nestlings (the proportions and the number of items are shown); (B) the total number of arrivals (green area), feeding deliveries (grey area), and the removal of droppings (violet area) by bird parents, including the mean daily temperature outside the nest box (black line) and inside the nest box (red line); (C) the mean daily number of arrivals, feeding deliveries, and removals of droppings by bird parents in a 6-minute period between 5 am and 7 am, including the mean daily temperature outside and inside the nest box (box: mean; whiskers: SE). For detailed information, see <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2001132#pbio.2001132.s003" target="_blank">S2 Text</a> and <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2001132#pbio.2001132.s007" target="_blank">S4 Data</a>.</p