Mike Cullen

ST KILDA PENGUIN RESEARCH REPORT 1996-7

Visits by the Research Group continued fortnightly between 1 July 1996 and 30 June 1997. During the year 10 adults and 26 chicks were banded, bringing the total since 1986 to 342 adults and 243 chicks.

The previous year, 1995-6, was unusual because it included two potentially harmful effects for the penguins: (1) the pilchard crash of 1995 and (2) Phase 2 of the Breakwater reconstruction, which involved the penguin colony area substantially more than Phase 1. Thus comparison of 1996-7 with earlier years is particularly relevant in assessing their impact. Phase 3 of the reconstruction took place in Apr-May 1997 but its effect will not be evident yet.

Table 1 gives some statistics for fiscal years starting 1990. The number of adults recorded per visit this year averaged 27, compared with the 10-year mean of 30, but it represents a greater shortfall compared with 1992-94.   Over the whole year 98 different banded adults were identified, a further drop from last year. Absence of adults means they were not re-sighted by us but doesn't mean they are dead; about one-third of them normally reappear in a subsequent year. But of adults seen in 1994-5 an unusually large percent were not recorded in 1995-6 (59% vs a usual 20 - 40% (Table 1) - or at least failed to be seen.   Moving to another locality might seem an alternative explanation for disappearances but experience with most seabirds, including penguins, indicates that this very seldom happens once they have bred somewhere for the first time. In 1996 the survival rate of adults was 42%, as if returning to normal.

The number of St Kilda-banded birds found dead anywhere within Port Phillip Bay was up in 1995 but back to normal level in 96 (Table 1).    The high 95 mortality was most likely due to the pilchard crash, implying again that the St Kilda population has dropped (temporarily, it is hoped) as a result.

All this evidence indicates that there were fewer penguins using the breakwater in 1996 than before 1995.

Table 1. Some statistics on adult records and breeding at the Breakwater colony since 1990.

Year starting July	1990	1991	1992	1993	1994	1995	1996
Mean no. adults recorded per visit	28	32	42	43	42	26	27
No. new adults banded	21	22	38	34	41	19	10
No. individual adults recorded in year	85	105	131	168	189	131	98
% of adults in year x that had been seen in year x-1	28	38	22	28	34	59	42
no. birds found dead	6	3	2	2	4	9	4
No. breeding sites located	32	28	52	44	52	30	39
Earliest breeding record	20may	16jun	12jul	27jun	10jul	15oct	26may

Mean wt. ofchicks@ banding   1158 1220 1187 1175 1114 836 1206

The breeding picture in 1996 was more optimistic (Table 1). Earliest breeding evidence on the breakwater was 26 May, an earlier than usual date; the two eggs of the clutch hatched and one chick probably fledged successfully. Mean chick weight at banding 1206g (vs Phillip Island for the year 930 g). 39 breeding sites were recorded, with most pairs that laid first clutches before October going on to have second clutches.

In summary, start of breeding was back to normal following the very late onset in 95, with the number of breeding sites hardly down on recent years and chick weights back to a good level. But in contrast to the favourable breeding situation, adult numbers appear down.

Since this drop has followed Phase 2 of the breakwater operation as well as the pilchard crash, the question remains which of the two events (or both, or neither) might have been responsible for the reduction in adults. However some evaluation can be made by considering statistics for the section of the breakwater reconstructed in Phase 2 - called Section A (from the Fence to Marker 27) , and the outer, unreconstructed-part, called Section B.

Using the measure of adults known to have survived from one year to the next, Table 2 shows that survival from 1994 to 95 was very similar in the two sections, but was higher from 1995 to 96 in the unreconstructed Section B. This could be interpreted as saying: the drop in re-sightings from 94 to 95, due to the pilchard crash, affected A-birds and B-birds alike, but in the last year A-birds have survived less well or been less visible.

Table 2.  The survival rate of banded adults from 1994 and 1995 in Sections A and B. (In brackets the numbers on which percentages based.)

 

	1994 to 95		1995 to 96
Section A	38%	(39)	42%	(33)
Section B	41%	(145)	62%	(90)

Table 3. The percentage of banded birds and breeding sites recorded in Section A in years since 1990.

Year starting July             1990   91     92      93     94       95      96
% of records of

banded birds in Section A               23    25  23      26     26       29     17

% of breeding sites in A                    19     18  12      27     21        23      17

Table 3 confirms that there has been a relative drop in sightings of banded birds and of recorded breeding sites in Section A since it was reconstructed. An important finding has been that, with one exception, a female, the birds formerly reported from Section A have not relocated elsewhere on the breakwater after the reconstruction.

It is quite possible that at least part of this drop in sightings in Section A is because the arrangement of the new rock in Phase 2 makes any penguins that are present much more difficult to detect and reach than before. Often, our attention is first drawn to new penguin locations by droppings and/or calls, and the bird(s) may even then be out of sight between the sizeable boulders that now make up the breakwater. And if we can't reach the bird to read its band number, we can't establish its identity, but we do record it as an unreachable bird.

If this were the correct explanation of the decrease in Section A, then the percentage of birds recorded in A that could not be reached should be higher in 1996. But this percent has remained remarkably constant in both sections back to 1993 at least (Table 4). So this evidence offers no support for the explanation of unreachability as responsible for the decline in numbers in A. This is reinforced by the observation that there has been since 1995 a general absence of penguin droppings in A.

Table 4. The percentage of unreachable birds in Sections A andB. Year starting July               1993     94     95     96

% unreachable birds in Section A         49     46     42     48

       B         60     59     61     64

We may conclude that there has been a decline in the numbers of penguin using the section of the breakwater reconstructed in 1996, over and above any decline due to the pilchard crash of 95. As this section only constituted about one-quarter of the breeding sites (Table 3), the drop is probably not serious, but reinforces our recommendation for more sensitive treatment of Section B, made in The Breakwater Committee meeting of 29 Jan 1997.   There was a good response to this request from Parks Victoria (see Neil Blake's report), and provisionally it seems that the birds have been less disturbed by the 1997 operation than in the previous year.

The good news. Phase 1 of the breakwater operation, in May 1995, reconstructed the section from the kiosk to the fence, which we call the Judges Box (JB) section. There were only two pairs of penguins using that section prior to 94 but the number of records has been growing, and in 1994 and 96 chicks were hatched and, at least in 94, probably fledged successfully.

Year starting July               1990     91     92     93     94     95     96

Number of banded birds