Consideraciones éticas

Generally, the offspring began to call within an egg one day before it pecked an air hole in the egg shell. One egg weighed 28 g when pipping (50.1 x 35.5 mm), another 25 g (45.2 x 34.8 mm). The weights of another four pipping eggs were 28, 29, 29 and 30 g and their progress, suggested that these are pre-hatching weights for the Little Shearwater eggs. Once a small hole had been made in the shell by the nestling, hatching occurred slowly. The process from pipping to hatching occurred over intervals of 2, 4, 2 and 2 days respectively. The nestling that hatched over a period of 4 days was still viable, although, some nestlings became stuck to the egg membrane and died if they took too long to hatch. An adult was usually present while the nestling was hatching.

One egg weighed 24 g when pipping with an air hole and the nestling weighed 21 g once hatched. Another weighed 24 g in the egg and 20 g the next day outside the egg. In 2000 and 2001, 15 nestlings were weighed and measured at hatching had a mean weight of 21 ± 1.7 g (range 18-24 g). These nests had not been disturbed prior or during hatching. The hatched nestling was wet, with poor motor control and the head often poorly supported. It often curled up, as if still within the egg, and the eyes were closed. On day two, the nestling was no longer wet, not curled up and the eyes were still half closed, the head was floppy, egg tooth prominent (it persisted for

approximately one to two weeks) and, overall, the nestling was more active. On day three, motor skills had improved and the nestling was often able to support its head. The eyes were usually open and overall a more robust image was presented.

The mortality rate of unattended nestlings that had recently hatched was high. After hatching, the nestling lives off its yolk reserves, but weight increased during the day, suggesting that attending adults supplementarily fed the nestling if able to do so. A nestling that hovered below 30 g for several days did not thrive and one in the vicinity of 20 g for three to four days was unlikely to survive (Figure 3.11). Nestlings that were of low weight and subsequently died were much cooler and less active than viable nestlings. Once a nestling had reached an afternoon weight above 30 g, it had a good chance of surviving a missed meal without dropping towards a critical weight (Figure 3.12) and was more likely to survive to fledging.

Upon the researcher’s arrival at Beacon Island on 5 September in 2000, some nestlings were already approximately one to two weeks old and hatching continued until 18 September. The ensuing size difference between nestlings prevailed throughout the nestling period. This suggested that hatching is asynchronous in this species and this was investigated in subsequent years.

In 2001, the 39 nestlings monitored hatched over 22 days between 29 August and 19 September (Figure 3.13). Hatching appeared to be spread evenly throughout the whole period, with a slight, but not significant (Χ2 = 2.18) tendency for nestlings to hatch in the first half of the hatching period. The highest number of nestlings to hatch in a day was four (or 10 %) and this occurred on three days. Overall, 44 % of

nestlings hatched within the three days either side of the median of 05 September 2001.

Figure 3.11 The morning and afternoon weight changes of Little Shearwater nestlings belonging to one of two categories, viable and not viable nestlings, during their first 12 days outside the egg.

Figure 3.12 Individual nestlings could afford and those that could not afford to be fed for a night.

In 2002, 34 nestlings monitored hatched over 23 days from 28 August until 19 September (Figure 3.13). The greatest number of nestlings to hatch on a single day was 12 %. The median hatch date was 07 September 2002, very similar to the previous year, and 47 % of nestlings hatched within three days of this date. The laying period was calculated to extend from 5 to 27 July based upon an incubation period of 55 days, but may occur slightly earlier, as the recorded

incubation period ranges from 52 to 58 days (Glauert 1946). This is in keeping with observations that in late June, at the end of the crayfishing season, no eggs were present in burrows on Beacon Island.

In 2001 and 2002, the attendance of adults was monitored at burrows where a nestling had recently hatched (Figure 3.14). The period monitored in 2001 was shorter than in 2002 and only ran for 13 days, owing to logistical constraints. On the first day that the nestling was outside the egg, an adult was present in all cases in all years. Diurnal attendance at the burrows was high for the first three days of nestling life, although in some instances the nestling remained deserted after the first night (Figure 3.14).

Although, sample sizes were inadequate to test, those adults that left their hatchlings early during the guard period had been incubating for a prolonged period of time and, when handled, expelled faeces that contained green (bile) streaks, rather than the black material indicative of digested prey. In contrast, nestlings attended during the day by adults gained weight, suggesting that supplementary feeding occurred. It is possible that adults depart to forage for a day, during the guard period in order to be able to feed the nestling to ensure its viability.

Figure 3.13 The hatching dates of 38 Little Shearwater eggs on Beacon Island in 2001 and 34 eggs in 2002 monitored from 28 August to 19 September.

Figure 3.14 The post-hatching, diurnal attendance of adult Little Shearwaters at the burrow was monitored in relation to nestling age.

Adult absence during the guard period comes at a cost, as two unattended hatchlings were found in bush burrows pecked to death. However, Little Shearwater adults guarding a nestling reacted passively to burrow intrusions from the researcher. Indeed, defence of the nestling is short-lived and often absent, with the adult often scurrying to the depth of the burrow, leaving the nestling exposed to the potential predator.