The Southern Crested Grebe -A Bird of Value

Forest and Bird, Issue 250, 1 November 1988, Page 26

The Southern Crested Grebe -A Bird of Value

by

Jim Ackerley

he southern crested grebe was once found throughout New Zealand but is now confined to lakes from Canterbury southwards. It is an endangered species with an estimated total population of a mere 250 birds, which are losing the struggle to survive in what has become a hostile environment. Their numbers are decreasing because of the destruction of their high country lake habitat. The first European to record the southern crested grebe (Podiceps cristatus) was Charles Heaphy in 1846 at Lake Rotoroa in the Nelson province. This was confirmed by others such as Governor George Grey and Julius Van Haast who added to the limited knowledge of these unusual birds. The Ashburton lakes at present provide habitat for the greatest number of grebes in the country but the lake with the largest individual population is Lake Alexandria which is adjacent to Lake Tekapo. My own studies of the birds have been at Lake Clearwater, about 60 kms from Ashburton in mid-Canterbury. I have been fascinated by their unique mode of living and their individual habits which are so different from other birds.

Mate for life The grebe is about the size of a mallard duck, darkly coloured on the back with a white breast, a long slender neck with two dark crests on their head and a chestnut coloured ruff that can be extended as a fan either in courtship or when facing an intruder. The male bird is stockier in build and is more dominant. They have a strong bond between them and they mate for life. Completely aquatic, they have legs which emerge at the extreme rear of their body, explained in the latin ‘‘Podiceps" (Podicis — rump, pes — foot). Their feet are not webbed like most other water birds but have three broad lobes which assist in diving and underwater swimming. Because of their physical build they cannot stand on land and must feed, mate, nest and live on the water. Grebes dive for their food of mainly nymphs and small fish, remaining underwater for a long time as they have an

amazing ability to navigate while they are submerged. Though reluctant fliers they move from lake to lake for food or in search of a new habitat. In flight they resemble a black shag but show their white breast and throat and have a rapid wing beat. Their nesting requirements are most specific and suitable sites are not plentiful. At Lake Clearwater we have had a pair of grebes nesting close to the holiday village for several years. They have an ideal site in a large willow which has extended over the water with its lower branches semi-sub-merged to a depth of about 60 cm. The grebes build their nest in a fork of these branches using weed plucked from the lake bed and lock the structure with twigs from the tree. Strongly Territorial They establish strong territorial claims and rigidly enforce their rights against all other

birds including other grebes. There is a definite boundary to their territory and all trespassers are attacked and driven away. I saw a black-backed gull alight on the water intent on eating some garbage it had scavenged. The male grebe immediately submerged, swam underwater and came up under the unsuspecting gull. Its reaction was swift: the startled bird shot into the air, dropped its food in the panic and rapidly disappeared while the victorious grebe quietly paddled back to its nest. The grebe’s courtship is complex. The birds come together with their ruffs extended, heads held high and beaks touching. They will hold this position for some time; then vary the procedure by solemnly presenting each other with a beakful of weed — a reminder to start nest building perhaps. At times they lift themselves up in the water, breast to breast, feet beating the water to a foam as they move back and forward. It is an intimate and touching scene. Nesting, which usually starts in December, is a serious and busy time. Both birds work very hard diving and carrying weed into the tree to build their nest, which is a large, dome-shaped structure raised above the water and securely anchored in place. They usually lay four chalky white-coloured eggs, which quickly become discoloured as the grebes always cover them with weed when they leave the nest. Incubation is shared by both birds and takes between three and four weeks. At change over at the nest, the grebe will approach below the surface and rise with enough force to slide onto the nest. To do this they must have a depth of water at the approach. It is a vulnerable time for the grebes. They are at the mercy of stoats and ferrets, and other grebes may raid their nest when they are absent.

Young at Home in Water The young grebes, coloured white with black markings, are at once at home in the water and start diving very quickly. They spend long rest periods on one parent's back, tucked under the feathers with only their heads protruding. While one parent is taking care of the family in this way, the other is working very hard diving for food which it feeds to the hungry infants on its mate’s back. At times they change roles: the carrying bird gently shrugs the chicks off while the other lowers its body well down into the water and the youngsters scramble aboard. It is hard, relentless work for both adults until the chicks are big enough to fend for themselves. The family stays together until the young are fully grown. How often they breed is unknown. I find it incredible that this bird which is so anti-social allows families of scaup or black teal to share the tree with them and raise their young in company of the young grebes. The grebes lead a quiet life but the scaup maintain large noisy groups of up to 20 adults and plenty of young that they are perpetually producing. They are the clowns of the waterfowl world and play as no other birds seem to do. The grebes tolerate their behaviour up to a point but if the scaup transgress beyond this they are punished for their sins and retreat, complaining loudly. I have.not seen any pattern of behaviour approaching this in any other lake or even anywhere else on Clearwater. The grebes most probably tolerate scaup because of the security offered by the extra number of birds present at any one time. Small grebes are very tempting targets for predatory gulls and hawks who are constantly on the lookout for an opportunity to seize one. In close proximity to the tree will be a good number of young scaup together with the young grebes, the parents of both in close attendance. If a predator flies over,

an alarm is given and the young ones scurry into the shelter of the tree until it is safe to emerge. Sometimes a hawk or gull is too fast and dives and takes a chick. Usually the large number of adults provides a warning system as they are constantly looking for danger in the sky. I have seen two adult scaup lure a hawk away from the area by simulating distress until they were well away from the others. A Wet and Wiser Hawk One hawk that dived on a solitary chick badly timed its flight and plunged into the lake. Unable to take off, it drifted helplessly, supported by its outstretched wings until it reached the bank some distance away. It crawled out and spent a long time drying out before it flew away — a wiser hawk no doubt. The key to the grebes survival lies in its habitat. The availability of suitable nesting sites is crucial to their existence. The nest must be in water and securely anchored, it must be protected from strong winds and have good and safe access. Fluctuating water levels are fatal to their future as the nest is either drowned or too high to reach. Suitable nesting sites in Lake Clearwater are few but we have managed to create a suitable place which was used last year — with no breeding success yet. Lake Emma and Lake Heron have good nesting sites in willows and raupo beds and there has been some successful rearing in the last three years. The number of grebes in any one lake varies from time to time as the birds move around the whole lake system. On a recent count we had a total of 75 grebes identified. Hopefully we can maintain these numbers and improve on them in the future before they join the growing list of creatures that have been sacrificed in the name of development and progress.