Vegetation of New Zealand Shag Colonies

Transactions and Proceedings of the Royal Society of New Zealand, Volume 88, 1960-61, Page 363

Vegetation of New Zealand Shag Colonies By Mary E Gillham, Botany School, University of Melbourne * This work was done before and after a lecturing appointment at Massey College, University of New Zealand. [Received by the Editor, September 30, 1959.] Contents I Ground-Nesting Shags. II Scrub-Nesting Shags. III Tree Nesting Shags. IV Tissue Injury Induced by Guano. Summary An investigation of the flora of 28 shag colonies ranging from Stewart Island in the S. to Bay of Islands in the N. was carried out, and the habitats grouped in three categories according to the vegetation layer occupied by the shags. In colonies of ground-nesting shags the trampling and excreta of the birds eliminated all but the most halophytic of the indigenous plants, and much of the ground was bare. Thirty-three per cent of the species recorded were aliens, but the influx of winter annuals was not so marked as in many seabird rookeries because disturbance by the shags was more continuous throughout the year. Disphyma australe was the most characteristic species-as in shag roosts of Bass Strait, S. E. Australia. Where shags nested in low scrub the ground plants did not suffer from trampling or nest building activities, and the deposition of guano was slightly less concentrated. It was the rule rather than the exception for a fair plant cover to exist in the rookeries, but this was of specialised character, and less than half the species recorded were native to New Zealand. Nitrophilous annuals occupied most of the vegetated area beneath the partially dead shrubs, their introduction probably facilitated by gulls. The shrubs most favoured by the shags as nesting sites were Hebe elliptica in the S. and Coprosma repens in the N. In colonies of tree-nesting shags there was no trampling of the ground flora, and guano splashes were more diffuse. The indigenous flora suffered a certain amount of damage but not sufficient for it to be replaced by a specialised flora of coprophiles, and only 23% of the species recorded were aliens. The trees most favoured as nesting sites were Metrosideros lucida in the S. and M. excelsa in the N. Quite large trees died as a result of guano deposited at the roots by groundnesting shags or on the above-ground parts by shags nesting in the branches. Death was often localised, suggesting poor lateral translocation of solutes within the plant Damage resulting from light guano splashing of non-xeromorphic leaves sometimes failed to spread beyond the midrib, or withering occurred progressively downwards from the apices suggesting accumulation of toxic material in distal portions as with “salt scorching”. I. Ground-nesting Shags 1. Stewart Island. The bronze shag (Phalacrocorax chalconotus) interbreeds with the black and white Stewart Island shag (P. stewarts) on a number of small islets of the Stewart group. Many of the nesting areas seen were only a few metres above h.w.m. and the nests less than a metre apart so that few plants survived. Tillaea (Crassula) moschata appeared to be one of the most resistant species, and may have been the “Sedum” on Kan-te-toe referred to by Guthrie-Smith (1914).

Approximately 300 bronze and Stewart Island shags roosted on a corner of Tamihau Island in Paterson Inlet, their numbers having steadily increased over the past 40–50 years according to the local wild-life ranger. They were spreading gradually inland from the coastal rocks to the marginal scrub, and most of the older Olearia colensoi trees which dominated the scrub had been killed as a result of the guano at their roots. In a few only the lower branches had been killed and a sparse leafy crown persisted 4–5 m above the ground. (Plate 15, a.) Saplings of Olearia occurred on the inner margin of the shag roost, many of them dead, others with bare stems 1 m or more high topped by a depauperate cluster of leaves 15–30 cm across. The scarcity of lower branches may have been hastened by the shags breaking some of them off, as tree-nesting shags break off twigs about the nest to obtain a clear view (Oliver, 1930). Wherever a skin of peaty soil overlay the rocks of the roosting area it was occupied by an 80% cover of Tillaea moschata. This was heavily fouled with guano and much of it uprooted, but shoots were able to remain turgid if only one rootlet remained unsevered. The foliage was deep green, due presumably to the high nitrogen content, as it was a characteristic rusty red elsewhere. Atriplex hastata was the most abundant subordinate species, the plants of the roost, all of them damaged to some extent, being as follows. Tillaea moschata d. Chenopodium sp. Atriplex hastata a. Hebe elliptica Asplenium obtusatum Isolepis inundata Carex trifida Poa astonii The only important species of coastal rocks apparently unable to withstand the trampling and guano deposition was Selliera radicans The ground flora of the coastal bush adjacent to the roost appeared to be more resistant to disturbance by shags than was the dominant Olearia colensoi, and there was a rich growth dominated by Hebe elliptica 60 cm high under the half dead trees. Hebe was probably the most guano-tolerant shrub encountered in the S of New Zealand as well as one of the most salt-tolerant. Species of this marginal belt were as follows:— Hebe elliptica d. Nertera depresia Asplenium obtusatum Scirpus nodosus Blechnum durum Stellaria parviflora Carex trifida No nesting colonies of blue shags (Stictocarbo p. steadi, the Stewart Island sub-species of the grey or spotted shag) were visited, but the birds were frequent on coastal rocks of Goat Island, Tamihau Island, Tommy's Island and Ulva Island in Paterson Inlet. They were seldom present in large numbers and appeared to have little effect on the rock flora. 2 Otago A colony of bronze and Stewart Island shags occurred on the western slopes of Green Island, near Dunedin. The ground was saturated with guano, dry and very spongy, giving way underfoot, and no macroscopic plants survived. The remains of dead Hebe bushes were scattered through the colony, suggesting that the area had previously been part of the Hebe elliptica/H elliptica × salicifolia scrab which occupied the main part of the island. (Plate 15b.) Plants approaching closest to the shags were seedlings of Atriplex hastata and the fringe of vegetation on the landward side consisted of the two species of Hebe, Lavatera arborea and Solanum laciniatum. A colony of several hundred bronze and Stewart Island shags occurred on Taiaroa Head at the end of the Otago Peninsula, but it was not possible to make a landing there, so no floristic investigation was carried out. The neighbouring grass, bracken and shrubs had been killed out for 8–10 m back from the normal.

1 — Oleana colensot trees killed back by shags on Tamihau Island off Stewart Island Rank shrub layer of Hebe elliptica and ground layer of Tillaea moschata — Shag colony on edge of Hebe elliptica/H elliptica × salicifolia scrub on Green Island Otago showing branches of dead Hebe and bare guano-saturated soil

2a — Coastal grassland killed back by shaes on Taiaioa Head Otago 2b — Coastal Melrosideros lucida trees partially killed by shags nesting in their branches Glory Harbour Stewart Island

seaward margin of vegetation, and few if any angiosperms persisted in the rookery. (Plate 16, a.) Grey or spotted shags (Stictocarbo punctatus punctatus. or Phalacrocorax punctatus) also occurred on Taiaroa Head, sometimes nesting on Acaena anserinifolia (A. sanguisorbae) which died within two weeks of the shags' arrival according to the local wild-life ranger. A small colony of grey shags nested on a low stack off Portobello, in Otago Harbour. Some of the rookery area consisted of bare rock, some was covered by crisply erect, thalloid Prasiola sp. forming an algal mat 1 cm or more thick and some by a mat of Disphyma australe. Hebe elliptica occurred to either side, completely dead where most exposed to guano, taller and only partially dead where slightly more remote from the birds. The native Poa astonii occurred in the rookery together with three of the annual aliens so common in bird colonies of both Europe and Australasia (Poa annua, Hordeum murinum and Coronopus didymus). The native Senecio lautus and alien Sonchus oleraceus, two composites of widely dispersed seabird colonies in New Zealand and S. E. Australia, the Sonchus also in Britain, occurred a little further from the nests. Close behind these, and again characteristic of seabird colonies beyond New Zealand were Apium prostratum, Solanum laciniatum and the British Holcus lanatus and Sagina procumbens agg. 3 Cook Strait No nesting colonies of the king shag (Phalacrocorax carunculatus carunculatus) were visited, but birds were observed on the Disphyma australe, Salicornia australis, Senecio lautus, Coprosma repens communities of the chain of islands between Komakohua Island and Long Island and also on the S. of Little Brother Island. A group of grey shags were found roosting on a stack off the E. side of Motungarara Island beside Copiosma repens ½ m high. Poa caespitosa was colonising the soil of crevices not too fouled by guano. 4 Hauraki Gulf Five grey shag areas were visited in the Hauraki Gulf, one pair (a nesting colony and a roost approximately 3½ miles apart) about 26 miles E. of Auckland, another nest colony/roosting area pair in the Noises Group c. 15 miles N. E. of Auckland, and a further colony on cliffs of Bush Island, off the W. coast of the Coromandel Peninsula. In the first pair of habitats the shags nested on Tarakihi or Shag Island, to the N. E. of Pakatoa Island, and roosted on Ponui Island, to the S. E. of Waiheke Island. A “home roost” occurred on sloping rocks above the nesting colony on Tarakihi and several hundred birds were seen here, many taking off in the direction of the Ponui Island roost as the dinghy approached. The nests were of sticks, mostly in crevices or under ledges on almost vertical cliffs where there was no vegetation, but patches of very fouled Disphyma australe and Parapholis incurva? (Lepturus or Pholiurus) occurred where groups of unoccupied birds sat. The sloping rocks of the roost above were white with guano and dotted with patches of Disphyma with stunted Coprosma repens and Metrosideros excelsa less common. About 100 shags were seen on the Ponui Island roost before the general exodus in that direction from Tarakihi. Some of the birds were on the N. E. cliffs of the main island, others on a tidal stack forming part of an un-named reef to the N. of Scully's Reef. All repaired to an unvegetated offshore stack further S. when disturbed. Disphyma australe was dominant in both the cliff and reef roosts, heavily coated with guano but surviving well. Five other halophytes, also much fouled, occurred

in the cliff roost, 1 halophyte and 7 non-halophytes in an adjacent area of similar size and aspect undisturbed by shags (Aliens in the subsequent lists are marked with an asterisk). Species of Cliff Shag Roost Species of Adjacent Cliff Disphyma australe *Avena fatua Rhagodia triandra? Coprosma repens Salicornia australis Danthonia sp. Senecio lautus Dichelachne crinita Sonchus oleraceus Muehlenbeckia complexa Spergularia media Nothopanax arboreum Scirpus nodosus *Vulpia sp. Disphyma formed a 75–80% cover on vegetated parts of the reef roost and with it three other halophytes, the annual Parapholis dead. On the seaward side of an adjacent stack unfrequented by shags the vegetation was more diverse. Species of Reef Shag Roost Species of Seaward Face of Unoccupied Coprosma repens Reef Disphyma australe Coprosma repens *Parapholis incurva Disphyma australe Salicornia australis Metrosideros excelsa Salicornia australis Scirpus nodosus Senecio lautus Stipa teretifolia The vegetation on the landward side of the shag reef was halophytic and resembled that on the seaward side;, that on the landward side of the unoccupied reef was less halophytic and more varied, including species from the grassland above. Species of Landward Face of Unoccupied Reef. Aira caryophyllea Muehlenbeckia complexa Anagallis arvensis Polycarpon tetraphyllum Deyeuxia forsteri Sonchus oleraceus Hypochoeris radicata Spergularia media Lagurus ovatus vulpia sp. The nests in the Noises Group of islands to the N. W. were in vertical niches of the cliffs of Otata Island and constructed mainly of seaweed. Disphyma was fairly frequent among the nests, Coprosma less so—both badly fouled but apparently thriving. Sixty to seventy birds were observed in the roost one mile to the E. on the S. and E. sides of the most southerly of the stacks forming David Rocks, and a few on the E side of the N. E. stack. In the main roost the ground was very foul and Disphyma the only surviving plant. As the boat approached the shags retreated up the cliff into the 1–2 m high Metrosideros excelsa scrub above. The soil there was saturated with guano, the ground vegetation had been eliminated and the Metrosideros was in poor condition with most of the lower branches killed back or broken off. 5 Summary of Vegetation in Colonies of Ground-nesting Shags Where seabirds are ashore for part of the year only, as in tern, gannet and gull colonies, there is an influx of winter annuals, most of them ahens, as the guano becomes diluted after the close of the nesting season (Gillham, 1959a). Shags are ashore for longer, some species seldom going far from the home area, throughout the year, so their suppressive effects on the vegetation are more continuous and the winter influx of annuals less noticeable. Table I summarises the vegetation of 10 of the more important shag areas visited and shows the number of native plants to be twice as great as the number

Table I — Plants in Ten Colonies of Ground-Nesting Shags, Proportion of Natives to Aliens % Occurrence Natives Aliens 60 Disphyma australe 40 Coprosma repens 30 Hebe elliptica and hybrids Metrosideros excelsa Poa astonu 20 Salicornia australis Atriplex hastata Senecio lautus Parapholis incurva Solanum laciniatum Sonchus oleraceus Tillaea moschata Apium prostratum Asplenium obtusalum Carex trifida Coronopus didymus Chenopodium sp. Holcus lanatus 10 Isolepis inundatus Hordeum murinum Olearia colensoi Lavatera arborea Poa caespitosa Poa annua Rhagodia triandra Sagina procumbens agg Spergalaria media No of spp. 18–67% 9–33% No of records 34–74% 12–26% of aliens. The three most characteristic species are indigenous to New Zealand and, if reckoned as individual occurrences, the introduced plants amount to only 26% of the total number of records. The indigenous plants are predominantly halophytic perennials, those able to withstand the greatest amounts of sea salt in the soil being also exceptionally resistant to high concentrations of guano. As in tern, gannet and gull colonies of Northern New Zealand, Disphyma australe is the most typical species and Coprosma repens the next, this shrub being replaced in the S. by Hebe elliptica, a species having similar growth form, leaf texture and habitat requirements. Disphyma australe is also the dominant species of roosts of black faced shags on Reef Island and Puncheon Head Reef in the Bass Strait, S. E. Australia. Other species of Bass Strait shag roosts which occur among ground nesting shags in New Zealand are Apium prostratum, Atriplex hastata, Lavatera arborea, Salicornia australis, Sonchus oleraceus and a Poa tussock.

II Scrub-nesting Shags 1. Stewart Island A small colony of white throated or little river shags (Phalacrocorax brevirostris or P. melanoleucos) occurred on Thompson's Nugget, a small sea-girt stack in Half Moon Bay. The birds had formerly nested in low Metrosideros lucida (M. umbellata) bushes (Traill in lit.) but these had been killed as a result of their presence, and they had now built in the Hebe ellipaca which was formerly the undershrub layer but now the dominant. This, too, was being killed back, and it seemed likely that the shags would migrate to another site when the bushes became untenable, giving the woody vegetation a chance to regenerate. The Hebe bushes were seldom more than 1 m high and some less than 1 m across supported as many as four nests. These were placed on top of the dense truncated branches so that the shags had no need to pluck off the surrounding twigs as in more diffusely branched trees. Sixty per cent of the species affected by guano were non-indigenous, a higher proportion than in the colonies of ground-nesting shags and no doubt due in large part to the presence of red-billed gulls (Larus novae-hollandiae) which nested between the Hebe bushes. (Gulls have a wide feeding range and are effective distributors of alien weed seeds). Both rock and soil bore a covering of the characteristically nitrophilous alga, Prasiola sp. On a nearby stack where the vegetation was unaffected by seabirds only 12½%of the plants were non-indigenous although the stack was close to the shore at a point where man-introduced weeds were abundant. The plant cover of this stack was closer, allowing room for fewer adventives, and consisted of only eight species, the one alien being very rare. Prasiola occurred on rocks below the seaward limit of macroscopic vegetation where Stewart Island shags rested. Spp. of Shag Rookery. Spp of Unoccupied Stack Hebe elliptica d. Hebe elliptica d Tillaea moschata 1d. Scirpus nodosus 1d *Holcus lanatus o. Poa astonii a -d *Poa annul o. Tillaea moschata 1f *Rumex crispus o. Asplenium obtusatum o -f *Sonchus oleraceus o. Dracophyllum longifolium o *Stellaria media o. Senecio puffinu o Asplenium obtusatum r. *Sonchus oleraceus v r *Crepis capillaris r. Solanum laciniatum r. Aliens marked with an asterisk. An earlier phase of the shag-induced Metrosideros Hebe. herb degeneration was observed on an offshore stack in Glory Harbour, Paterson Inlet. White-throated shags were nesting there in small Metrosideros lucida trees, their nests well in among the branches and not so obvious as those of the large pied shags (Phalacrocorax rarius) on the adjacent coast. Whole trees and individual branches of others had been killed by the shags but the undergrowth was still in fairly healthy condition. 2. Otago Only one specimen of Myoporum laetum a little under 2 m high overtopped the dominant Hebe scrub on the W. side of Green Island off the Otago coast, and this was occupied by the only three nests of white-throated shags seen on the island. The tree appeared to be suffering little harm, and although the plants beneath were white with guano, only the alien Lavatera arborea showed any signs of dying. The two other species present were Hebe elliptica and Solanum laciniatum. A number of large black shags (Phalacrocorax carbo) had built bulky nests of sticks in Hebe bushes ½–1 m high on the N. E. corner of the island. The bushes were on a steep slope so that the nests were at ground level on the upper side, but as much as 1 m above ground on the lower side.

The soil was less fouled than was usual in shag colonies, the guano being insufficient to kill the underlying vegetation, but sufficient to induce a very rank growth of coprophiles. Desiccation of the soft nitrogen-induced foliage was hindered by the close shade of the Hebe canopy and Poa annua, averaging 30 cm high, was the dominant ground species. This limiting of the guano to beneficial rather than toxic concentration was quite probably the result of the eggs or young having been taken from the nests early in the breeding season by fishermen who regarded the species as a pest. Six indigenous and eight non-indigenous plants occurred in the ground flora, the non-indigenous ones being much more robust and covering more ground.Tillaea moschata was again the most abundant indigenous species, and the Hebe was regenerating, small seedlings being scattered through the mat of introduced species. The high proportion of alien plants may well have been connected with the fact that scattered pairs of black-backed gulls (Larus dominicanus) nested on the edge of the scrub. Prasiola sp. was present, and the vascular plants were as follows, aliens marked with an asterisk. Hebe elliptica cd. Stellaria media 1.a. H. elliptica × salicifolia c.d. *Trifolium repens 1.a. *Poa annua sub. d. Asplenium obiusatum o. Tillaea moschata 1.s. d. Carex trifida o. *Bromus unioloides 1.a. Hebe seedlings o. *Dactylis glomerata 1.a Lepidium oleraceum o. *Hordeum murinum 1.a. Rumex sp. o. *Lolium perenne 1.a. Solanum laciniatum o. Three pairs of white-throated shags nested in a Hebe elliptica bush 1 m high on the cliff edge below the colony of royal albatrosses (Diomedea epomophora) on Taiaroa Head in 1956 (Sharpe in lit.). 3. Hauraki Gulf About 20 pairs of white throated shags and five pairs of little pied shags (Phalacrocorax melanoleucus) were found to be breeding on the innermost of three offshore stacks at the W. end of Motuihe Island with red-billed gulls and white-fronted terns (Sterna striata). The nests were in dense Coprosma repens scrub 30–100 cm high, and the ground flora consisted of Disphyma australe and the alien annual grass Avena fatua. 4. Summary of Vegetation in Colonies of Scrub-nesting Shags Most of the colonies of scrub-nesting shags investigated were in the S. of New Zealand and the shrub most favoured as a nesting site Hebe elliptica, its counterpart offering similar conditions in the N being Coprosma repens. Small specimens of Metrosideros lucida, a species also favoured by tree-nesting shags, were sometimes used as nesting sites in the S., the tendency being for these to die out and the shags to move to the Hebe understorey which in its turn died out causing the shags to move to other areas. The ground vegetation was spared most of the trampling suffered by that in colonies of surface-nesting shags, and some of the guano was prevented from reaching it by the dense leaf canopy of the shrubs and by the nests themselves. The plant habitat was thus much less rigorous and fewer areas were denuded of vegetation altogether. One of the commoner scrub-nesting species of shag, the white-throated, was characteristically associated with red-billed gulls which nested beneath the scrub to the detriment of the indigenous flora. Viable weed seeds ejected in pelletform by the gulls were able to germinate when the height of their nesting activity was over and the guano from the shags was insufficient to prevent this. There was, in fact, evidence that the shade provided by the nests and the diluted excreta

Table II —Plants in Six Colonies of Scrub-Nesting Shags. Proportion of Natives to Aliens. % Occurrence Natives Aliens 83 Hebe elliptica 50 Solanum laciniatum 34 Asplenium obtusatum Poa annua Tillaea moschata Stellaria media Avena fatua Bromus unioloides Carex trifida Crepis capillaris Coprosma repens Dactylis glomerata Disphyma australe Holcus lanatus 17 Hebe elliptica × salicifolia Hordeum murinum Lepidium oleraceum Lavatera arborea Metrosideros lucida Lolium perenne Myoporum laetum Rumex crispus Rumex sp. Son hus oleraceus Trifolium repens No. of spp. 11–44% 14–56% No. of records 19–54% 16–46% seeping through during ram had a beneficial effect on those ruderals with high fertility requirements. In the Otago shag rookeries where gulls rested alongside but not within the shag area, the gulls were effective in bringing disseminules to the vicinity, but did not suppress the ground flora by their seasonal trampling and manuring. The resulting vegetation was very lush and predominantly alien. Table II shows that 56% of the total number of species recorded were nonindigenous and 46% of the total number of records were of non-indigenous plants Only 33% of the species of the ground flora beneath the shrubs were native to New Zealand. III Tree Nesting Shags 1 Stewart Island. The trees favoured by tree-nesting shags on the sea coast throughout New Zealand were species of Metrosideros, characteristically M. lucida in the S and M. excelsa in the N. Both species overhung the edge of the water in sheltered inlets and the configuration of their branches produced forks suitable for holding the

nests-bulky accumulations of sticks added to in successive years and sometimes attaining a depth of 1 m or more. Pied shags nested in Metrosideros lucida on the shores of Glory Harbour in Paterson Inlet, and were killing off the nesting trees branch by branch, some being completely dead. Death was hastered by the shags' habit of plucking leaves and twigs from about the nests and perches, but in some cases the birds roosted close to water level in low branches probably killed by the action of sea water (Pl. 2b). Some of the Stewart Island birds roosted in Podocarpus ferrugineus trees. 2. Marlborough Sounds. A few Metrosideros lucida trees at the edge of the mixed forest bordering Double Cove, Queen Charlotte Sound, were occupied by pied shags which occurred in none of the more abundant tree species. The largest Metrosideros tree was dead, others partially so but with unoccupied branches bearing a full complement of leaves. The vegetation beneath the trees was quite severely fouled by guano, but there was little alteration in the composition of the shrub and fern layers, only the ground layer being typically nitrophilous. Two of the most localised species of the forest floor beneath the shags were Stellaria media and Tillaea moschata, both lush and green. The fern layer was dominated by three species with tough, shiny leaves, probably fairly resistant to “scorching” by guano—viz, Asplenium lucidum and A. flaccidum with A. obtusatum downshore. With them were a Poa tussock (probably P. caespitosa) and Phormium colensoi? The shrub layer was a little more than 1 m high and included Brachyglottis repanda, Coprosma robusta, Olearia paniculata, Schefflera digitata, Solanum laciniatum and Suttonia (Myrsine) australis. Leptospermum scoparium, common in the vicinity, did not occur under the shag nests and the introduced Pinus radiata(P. insignis) trees were not being used as nesting sites as they were in an exotic plantation further N. where no Metrosideros trees were available. 3. Bay of Plenty. The exotic pine plantation occurred on the 27 mile long Matakana Island off Tauranga, trees on the sheltered southern side of the island forming nesting sites for pied and white-throated shags. The pines were in poor condition but had sea water lapping at their exposed roots where wave action had caused subsidence of the low sandy cliff, so this could not necessarily be attributed to the shags. Some of the trees had been completely undermined and fallen out across the water, where the dead branches were favoured as perches by the shags. Numerous white-throated shags, a few large black and a few pied shags, were found nesting in Metrosideros excelsa trees on the steep western cliffs of Motiti Island about 18 miles by sea from Tauranga. The Metrosideros leaves, protected by a woolly tomentum on the lower surface and a tough shiny cuticle on the upper, were extremely resistant to thick coatings of guano and sometimes did not fall from the tree until this was more than 1 mm thick. Some killing of terminal twigs after defoliation had occurred, but this was not very marked. No investigation was made of the flora of the steep rocks beneath the nesting trees. Pied shags habitually perched on Metrosideros excelsa trees on a stack W. of Opo Bay on Mayor Island 30 miles N. of Tauranga. The two horizontal branches which they used were dead and denuded of twigs. Defaecation was into the sea some distance below. Three colonies of this species occurred in Metrosideros trees by the crater lakes inland (Bailey in lit), two by the Black Lake and one by the Green Lake, the shags subsisting on the introduced carp.

Transactions 4. Hauraki Gulf. Numerous pied shags nested in Metrosideros excelsa on Little Barrier Island, 55 miles N. N. E. of Auckland. The trees, all damaged to some extent, were at the foot of a steep, heavily wooded slope on the brink of a cliff about 150ft (46 m)high. Almost all species of the ground layer immediately beneath had suffered as a result of guano deposition but not sufficiently for them to have died out and yielded place to a specialised flora of coprophiles. There were no alien plants present, and the only species likely to have appeared because of the guano was Parietaria debilis, which was very characteristic of gull colonies further N. Four of the shrubs, Brachyglottis, Coprosma, Corynocarpus and Macropiper,were flowering, although many of the leaves were badly damaged. It seemed probable that the soft-leaved shade forms suffered greater leaf injury than would more xeromorphic forms from the open and could not have survived much more than the diffuse sprinkling of guano which penetrated into the marginal bush zone. Three of the ferns, Doodia, Polystichum and Pteris, grew well away from the shags and were only lightly splashed by excreta, but were still damaged. Bush species beneath the inland and mostly unoccupied side of the nesting trees were as follows:- Spp. Suffering Little Damage Carex vacillan Peperomia urvilleana Parietaria debilis Pyrrosia (Cyclophorus) serpens Spp. Suffering Considerable Damage Shrubs Ferns Brachyglottis repanda Asplenium flaccidum Coprosma robusta A. lucidum Corynocarpus laevigata Doodia media Dysoxylum spectabile Hypolepis tenuifolia Macropiper excelsum Microsorium (Polypodium) diversifolium Pseudopanax lessonii Polystichum richardii Suttonia australis Pteris comans Astelia banksii Most of the guano from the shags was deposited on the plants of the cliff face below rather than on the bush species immediately beneath as the nesting trees overhung the brink of the cliff and the nests were mainly in the outer branches. This vegetation was a sparse Metrosideros scrub with Disphyma australe, Poa anceps and Rhagodia triandra co-dommant in the clearings. Most of the Poa shoots were dead but young ones were sprouting through the mats of old ones. Thirty-nine species were listed for the cliff face of the region as a whole, 25 of these occurring in areas subjected to guano and 33 in areas not so affected. Annual ruderals were present, the loose, eroding soil providing suitable habitats free from competition with established perennials. Of the nine alien species recorded all were present in the zone manured by the shags, only six in unmanured areas. Five species in the above list of bush plants were found on the open cliff only in areas unaffected by shags, being possibly able to withstand guano in the shelter of the bush or spray-bearing winds in the open, but not a combination of both. Species recorded on this stretch of cliffs are listed below, those subjected to guano deposition being marked “S”, those from areas not so affected “O” and aliens “*” *Agrostis tenuis? S.O. Metrosideros excelsa S.O. Arthropodium cirrhatum S.O. Microsorium diversifolium S.O. Arundo conspicua S.O. Muehlenbeckia complexa S.O. Asplenium flaccidum O. Olearia sp. O. A. lucidum O. Peperomia urvilleana O. Astelia banksii S.O. Phormium tenax O. *Bromus unioloides S.O. Phytolacca octandra S

Carex vacillans S.O. Poa anceps S.O. *Cerastium glomeratum S.O. Polystichum richardii O. *Cirsium vulgare S. Pseudopanax lessonii S. Coprosma repens S.O Rhagodia triandra S.O. C. robusta S.O Scirpus nodosus S. O Corynocarpus laevigata O. Senecio lautus S.O. Cotula australis O. ?*Solanum nigrum S. O. Deyeuxia sp. S.O. S. nodosum S. Disphyma australe S.O. Sonchus littoralis S. Hebe salicifolia O. *S oleraceus S.O. *Hypochoeris radicata S.O. Tillaeu sieberiana O. Leptospermum ericoides O. *Vulpia myruros S.O. Lobelia anceps O. *Vulpia myuros S.O. Pied shags nested in Metrosideros excelsa on a sheltered part of the coast S. of Coromandel. 5. Bay of Islands. About 20 small black shags (Phalacrocorax sulcirostris) and a few pied shags were seen roosting in Metrosideros excelsa by a sheltered arm of Crowell's Bay in the Bay of Islands. There were no nests and, although many of the leaves of the roosting-trees were invisible beneath a coating of guano there was less killing of branches than in the average nesting colony and little plucking of twigs. The following ground species were recorded, none very badly damaged. Spp. Splashed by Guano. Spp. Further from Shag Roost. Peperomia urvilleana d. Carex sp. Microsorium diversifolium a. Doodia media Solanum nodosum a. *Hypochoeris radicata *Sonchus oleraceus o-f Pteridium esculentum Asplenium lucidum o. Sophora microphylla Coprosma robusta o. Stipa teretifolia A fairly large nesting colony of pied shags and little pied shags with either whitethroated or small black shags occurred in more severely damaged Metrosideros excelsa trees in Manawaora Bay. When disturbed the birds flew inland to a much frequented hilltop perch on a partially dead Leptospermum scoparium tree. A diverse vegetation survived beneath the nesting trees, the species most severely “scorched” by the guano being Arthropodium, Microsorium, Olearia, Pteridium and Stellaria The following were recorded:- Spp. Splashed by Guano. Spp. Further from Shag Nests. *Anthoxanthum odoratum Adiantum hispidulum Arthropodium cirrhatum *Aira caryophyllea Asplenium flaccidum Asplenium lucidum Astelia banksii Brachyglottis repanda *Avena fatua Carex sp. Danthonia sp. Doodia media Dichelachne crinita Dysoxylum spectabile *Euphorbia peplus *Hypochoeris radicata Hebe salicifolia? Leptospermum ericoides Microsorium diversfolium Pyrrosia serpens Muehlenbeckia complexa Scirpus nodosus Olearia sp. *Sonchus oleraceus Peperomia urvilleana Suttonia australis Poa anceps? Pteridium esculentum Senecio laubus *Stellaria media Wahlenbergia gracilis agg. 6. Summary of Vegetation in Colonies of Tree-nesting Shags. The nesting trees, Metrosideros lucida in the S, M. excelsa in the N. and Pinus radiata where the native bush had been destroyed, possessed xeromorphic leaves

Table III —Plants in Eight Colonies of Tree-Nesting Shags. Proportion of Natives to Aliens % Occurrence Natives Aliens 63 Metiosideros excelsa Asplenium flaccidum Asplenium lucidum 38 Coprosma robusta Microsorium diversifolium Peperomia urvilleana Arthropodium cirrhatum Astelia banksii Brachyglottis repanda Metiosideros lucida Sonchus oleraceus 25 Olearia spp. Stellaria media Poa anceps Senecio lautus Solanum nodosum Suttonia australis Arundo conspicua Carex uacillans Coprosma repens Corynocarpus laevigata Danthonia sp. Deyeuxia sp. Dichelachne crinita Disphyma australe Doodia media Dvsoxylum spectabile Agrostis tenuis Hebe salicifolia Anthoxanthum odoratum Leptospermum scoparium Avena fatua Hypolepis tenuifolia Bromus unioloides Macropiper excelsum Cerastaum glomeratum 13 Muehlerbeckia complexa Carsium vulgare Parietaria debilis Euphoria peplus Phormium colensoi Hypochoeris radicata Poa caespitosa? Phytolacca octandra Podocarpus ferrugineus Pinus radiata Polystichum richardii Solanum nigrum Psedopanax lessonii Vulpia myuros Pteridium esculentum Pteus comans Pyrrosia serpens Rhagodia triandra Scheffleria digitata Scirpus nodosus Solanum laciniatum Tillaea moschata Wahlenbergia gracilis agg No. of spp. 46–77% 14–23% No of records 69–81% 16–19%

very resistant to damage by shag guano. Both leaves and twigs were often broken off, braches were killed back and sometimes the entire tree had died. Trees used only for roosting had usually suffered less damage. The configuration of the branches was not as important as where suitable sites were required for nestbuilding and other species were utilised (e. g., Podocarpus ferrugineus and Leptospermum scoparium) Coastal forest occurred only where there was a reasonable degree of shelter from wind-borne spray (Gillham, 1959b) and the vegetation as a whole was less halophytic. The nesting trees frequently overhung the water so that much of the excreta was deposited in the sea or on the Hormosira, etc., of the mtertidal zone. Distribution of Native and Alien Plants in 28 Shag Colonies

Table IV —Relative Percentage Occurrence of Native and Alien Plants in 28 Shag Colonies in Open Cliff Habitats, Coastal Scrub and Coastal Forest. % Occurrence Natives Aliens 36 Hebe elliptica and hybrids Metrosideros excelsa 32 Disphyma australe 25 Coprosma repens 21 Solanum laciniatum 18 Senecio lautus Sonchus olerarceas Tillaea moschata 14 Stellaria media Asplenium flaccidum Asplenium lucidum Asplenium obtusatum Coprosma robusta 11 Metrosideros lucida Poa annua Microsorium diversifolium Olearia sp. Peperomia urvilleana Salicornia australis Arthropodium cirrhatum Astelia banksii Brachyglottis repanda Atriplex hastata Carex trifida Avena fatua 7 Poa anceps Bromus unioloides Poa astonii Holcus lanatus Poa caespitosa? Hordeum murinum Rhagodia triandra Lavatera arborea Solanum nodosum Parapholis incuroa Suttonia australis 4 or less 34 other species 18 other species Total No. of spp. 60 28

Even where this was not the case, deposition was more diffuse than in colonies of ground-nesting or scrub-nesting shags and had a less deleterious effect on the ground flora. Comparison of Tables I, II and III shows more than twice as many species to have been recorded in colonies of tree-nesting shags as in the other two types of colony, although ground flora was listed in only four localities, defaecation being into the sea in most of the others. The ground flora was composed largely of indigenous plants differing little from those of the surrounding territory. Many were damaged, often quite severely, but were usually able to survive without yielding place to more nitrophilous alien species as in colonies of scrub-nesting shags or to practically bare soil as in colonies of ground-nesting shags. The remoteness of the source of guano and absence of trampling were of undoubted importance in minimising the modification of the ground flora, but the often diffuse light was another. Most of the adventive species of the coast were plants of open habitats which seldom penetrated far into the shade of the forest, even where bare soil was available for colonisation. Another factor contributing to the relative paucity of aliens (only 23% of the 61 species recorded) was the almost complete absence of gulls in the bush habitat. Table IV summarises the flora of 28 coastal shag rookeries in which 88 species were recorded, 28 of them not indigenous to New Zealand. In spite of the diversity of the habitats investigated, the most characteristic plants were the same as in other types of seabird colonies in New Zealand, the commonest indigenous ones being markedly halophytic and Sonchus oleraceus the most widely dispersed alien. IV. Tissue Injury Induced By Guano Prolonged deposition of guano whether at the roots of plants or on the leaves and branches of either trees or herbs eventually caused death of the entire organism. Smaller depositions caused localised death, parts of the plant, or even of individual leaves not coming into direct contact with the guano remaining undamaged. Where birds congregated only beneath one side of a tree the branches above but not those on the opposite side died, suggesting that toxic solutes from the guano were carried vertically upwards with little lateral translocation. The same localisation of effect occurred where shags nested in some branches and not others. Where defaecation was on to the soil directly beneath it was likely that there was absorption of solutes by roots on that side of the tree only and the solutes were carried back to the nesting branches internally. Death also occurred, however, where the branches overhung the sea or a beach from which the excreta would be periodically leached by the tide. It seemed evident in such cases that guano was entering the branches direct and killing the tissues, its entry probably facilitated by mechanical damage to the bark by perching birds. Defoliation by the shags and the plucking of twigs for nest material would hasten the degeneration. The pattern of damage to individual leaves could best be observed where guano deposition was quite diffuse beneath colonies of tree-nesting shags because elsewhere all but the most resistant leaf types were killed. Xeromorphic leaves were the most resistant, the characters which served to prevent the exit of excess water serving not only to prevent the entry of soluble material from excreta deposited on the leaf surface but also to minimise mechanical damage by wind and shags giving abrasions through which passage of solutes was unrestricted. The highly resistant leaves of the commonest nesting tree, Metrosideros excelsa,demonstrated the efficacy of both the woolly tomentum and glabrous shiny cuticle in this respect.

Leaf Necrosis Caused by Guano

Leaves of succulent halophytes such as Disphyma australe and Peperomia urvilleana were also very resistant to guano, as to sea salt, and undamaged Metrosideros and Peperomiay leaves from beneath shags' nests are illustrated in the top left hand corner of Fig. 2. The figure shows guano-induced necrosis in leaves of 16 bush species from beneath the tree-nesting shags on Little Barrier Island. Leaves showing only partial damage were chosen for illustration, but many of the softer leaves of ferns and non-xeromorphic shrubs such as Macropiper were completely withered. Three main features were observed in the necrosis patterns:-(a) Translocation of toxins to the apices of leaves and leaf lobes causing die-back from the tips as seen commonly with salt necrosis. (b) Translocation of toxins only as far as the leaf midrib, one side of the lamina remaining undamaged whilst the other was almost completely dead. (c) Little or no radial translocation from the point of contact, the leaf tissue dying and disintegrating beneath the guano splashes to give small round holes ringed by a narrow circle of necrotic cells. Type (a) was that most commonly seen in the ferns and monocotyledons (Polystichum richardii, Doodia media, Pteris comans, Asplenium lucidum, A. flaccidum, Pyrrosia serpens, Microsorium diversifolium, Carex vacillans and Astelia banksii) and was also shown by some of the shrubs (Dysoxylum spectabile, Sattonia australis, Pseudopanax lessonii, Coprosma robusta and Macropiper excelsum). This tip necrosis has been induced experimentally with sea salt solutions (Boyce, 1954, and Gillham, unpublished data) and Boyce found the usual necrosis pattern to be in the form of an inverted V extending down the leaf margins. This pattern was seen also with guano, but there were instances, as illustrated in Macropiper, where the midrib area most likely to be concerned with translocation of toxins to the distal part of the leaf died first and the pattern was inverted. Brachyglottis repanda showed marginal necrosis, the leaf margins rolling up over the adaxial surface as they withered. Restriction of damage to one side of the midrib was commonly seen in the large leaves of Corynocarpus laevigata. In some instances there was no evidence that guano had passed into or beyond the midrib area, in others unilateral damage was associated with tip necrosis, suggesting that any toxins entering the midrib had been carried up to the apex and not passed to the other side of the leaf. Side veins also functioned as checks to lateral movement in leaves of plants such as Dysoxylum, Suttonia, Pseudopanax, Pteris, Asplenium and Microsorium. In the compound Dysoxylum leaf illustrated four of the terminal leaflets had been exfoliated. The remaining leaflet on the left showed two stages of unilateral necrosis, the more advanced in the distal half where the right hand side of the lamina had disintegrated and the left hand side was dead but still in situ, the carlier stage in the proximal half where the right hand portion was dead and the left hand portion still living. Extreme localisation of damage causing holes to appear in the lamina beneath small guano splashes was well seen in Dysoxylum, Pseudopanax, Macropiper, Asplenium and Microsorium. Damage extended radially from a central focus and in intermediate stages the central area had disintegrated and was ringed by dying tissue which eventually disappeared right to the margin of the living tissue. Formation of numerous holes was often associated with tip necrosis, the tissue between through which translocated toxins must have passed remaining undamaged. Accumulation of toxins from only a few hole-forming guano splashes was often insufficient to cause tip necrosis.

Acknowledgments My thanks are due to the University of New Zealand for a grant towards travelling expenses, the Government Marine Department and Captain Black of Dunedin for the provision of boat transport and the D.S.I.R., Botany Division, for the identification of specimens. Also to Mr. Aukaha for hospitality in the Maori village on Motiti Island, Mr. and Mrs Parkin, wild-life wardens, for hospitality on Little Barrier Island, Mr. Fraser, fisheries officer, for organising boat transport in Bay of Plenty and accommodation in the Mayor Island Big Game Fishing Camp, Messrs Traill and Sharpe, wild-life rangers, for conducted tours of the Stewart Island and Otago Peninsula habitats, and Mr. Bailey, for information relating to shags on Mayor Island. References Boyce, S. G., 1954. The Salt-spray community Ecol Monog 24 1 pp. 29–67. Gillham, M. E., 1959a Vegetation of tern and gannet colonies in Northern New Zealand. Trans. Roy Soc. NZ. ——1959b Vegetation of Little Brother Island, Cook Strait, in relation to spray-bearing winds, soil salinity and pH Trans. Roy Soc. N. Z.. Guthrie-Smith, H, 1914. Mutton birds and other birds, Christchurh. Oliver, W. R. B., 1930. New Zealand Birds, Wellington.