Sitting ducklings: Timing of hatch, nest departure, and predation risk for dabbling duck broods

Abstract

For ground-nesting waterfowl, the timing of egg hatch and duckling departure from the nest may be influenced by the risk of predation at the nest and en route to wetlands and constrained by the time required for ducklings to imprint on the hen and be physically able to leave the nest. We determined the timing of hatch, nest departure, and predation on dabbling duck broods using small video cameras placed at the nests of mallard (Anas platyrhynchos; n = 26), gadwall (Mareca strepera; n = 24), and cinnamon teal (Anas cyanoptera; n = 5). Mallard eggs began to hatch throughout the day and night, whereas gadwall eggs generally started to hatch during daylight hours (mean 7.5 hr after dawn). Among all species, duckling departure from the nest occurred during daylight (98%), and 53% of hens typically left the nest with their broods 1-4 hr after dawn. For mallard and gadwall, we identified three strategies for the timing of nest departure: (a) 9% of broods left the nest the same day that eggs began to hatch (6-12 hr later), (b) 81% of broods left the nest the day after eggs began to hatch, and (c) 10% of broods waited 2 days to depart the nest after eggs began to hatch, leaving the nest just after the second dawn (27-42 hr later). Overall, eggs were depredated at 10% of nests with cameras in the 2 days prior to hatch and ducklings were depredated at 15% of nests with cameras before leaving the nest. Our results suggest that broods prefer to depart the nest early in the morning, which may best balance developmental constraints with predation risk both at the nest and en route to wetlands.

Keywords: Anas cyanoptera; Anas platyrhynchos; Mareca strepera; imprinting; nest depredation; nest exodus; predation.

Figure 1

The timing of the first duckling to hatch (left column; n = 55 nests), the last duckling to hatch (middle column; n = 29 nests), and duckling departure from the nest (right column; n = 52 nest) was determined using video cameras deployed at mallard (Anas platyrhynchos; top row), gadwall (Mareca strepera; middle row), and cinnamon teal (Anas cyanoptera; bottom row) nests. All times were standardized so that 05:00 hr local time is dawn in this figure, although statistics were conducted using time relative to nautical dawn. Daylight is shaded in yellow, and night is shaded in gray. Note that the y‐axis scale is different for cinnamon teal. This study took place at the Grizzly Island Wildlife Area (California, USA; 38.141°N, 121.970°W), within Suisun Marsh, 2015–2017

Figure 2

The duration of time at the nest between the first duckling to hatch and departure from the nest by mallard (Anas platyrhynchos; circle), gadwall (Mareca strepera; triangle), and cinnamon teal (Anas cyanoptera; square) ducklings, shown using model‐generated least squares means with 95% confidence intervals (sample sizes shown in light gray). The mean of all departures was generated from one model with the three species, whereas the mean values for each of the three departure strategies were generated from a model with the three strategies and two species (mallard and gadwall). Broods that left the nest the same day as hatch and before the next dawn are shown in blue, whereas broods that left after the next dawn are shown in yellow, and broods that left the nest after two dawns are shown in red. This study took place at the Grizzly Island Wildlife Area (California, USA; 38.141°N, 121.970°W), within Suisun Marsh, 2015–2017

Figure 3

(a) The time of day of the first duckling to hatch (first duckling fully emerged from the egg) related to the time of day that mallard (Anas platyrhynchos) and gadwall (Mareca strepera) ducklings departed the nest (n = 47 nests). Daylight (day and twilight) is shaded in yellow, and night is shaded in gray. All times were standardized so that 05:00 hr local time is dawn in this figure, although statistics were conducted using time relative to nautical dawn. Broods that left the nest the same day as the start of hatch and before the next dawn are shown in blue, whereas broods that left the nest after the next dawn are shown in yellow, and broods that left the nest after two dawns are shown in red. The dashed lines, color coded to correspond with the three departure strategies, indicate the timing of a potential 13‐hr threshold for imprinting relative to the start of hatch, and the stippled lines indicate a 16‐hr threshold for imprinting (Hess, 1959). Birds departing above/to the left of the line departed after the imprinting period relative to the start of hatch and those departing below/to the right departed prior to the end of the critical period for imprinting. (b) The time of day of the first duckling hatch related to the duration of time spent at the nest, color coded the same as in panel (a). This study took place at the Grizzly Island Wildlife Area (California, USA; 38.141°N, 121.970°W), within Suisun Marsh, 2015–2017

Figure 4

(a) The time of day of the end of hatch (last duckling fully out of the egg) related to the time of day that mallard (Anas platyrhynchos) and gadwall (Mareca strepera) ducklings departed the nest (n = 26 nests). Daylight (day and twilight) is shaded in yellow, and night is shaded in gray. All times were standardized so that 05:00 hr local time is dawn in this figure, although statistics were conducted using time relative to nautical dawn. Broods that left the nest the same day as the end of hatch and before the next dawn are shown in blue, whereas broods that left the nest after the next dawn are shown in yellow, and broods that left the nest after two dawns are shown in red. The dashed lines, color coded to correspond with the three departure strategies, indicate the timing of a potential 13‐hr threshold for imprinting relative to the end of hatch, and the stippled lines indicate a 16‐hr threshold for imprinting (Hess, 1959). Birds departing above/to the left of the line departed after the imprinting period relative to the start of hatch and those departing below/to the right departed prior to the end of the critical period for imprinting. (b) The time of day of the end of duckling hatch related to the duration of time spent at the nest, color coded the same as in panel (a). This study took place at the Grizzly Island Wildlife Area (California, USA; 38.141°N, 121.970°W), within Suisun Marsh, 2015–2017