Lessons from Old Eggs

Stella Bush to Pigeon Valley

It’s hard to believe that Pigeon Valley Nature Reserve, and the outstanding ~13 hectare Coastal Forest it protects, lies just a couple of kilometres west of Durban’s CBD. At this much-loved birding hotspot, visitors can see many resident species, regular non-breeding migrants like Spotted Ground-thrush and, if lucky, occasional exciting visitors like Knysna Warbler and Mangrove Kingfisher. Birds and birders alike have benefited from excellent work done to protect and restore the forest. For that we can be grateful to the Durban Parks Department, especially Geoff Nichols, and more recently to Crispin Hemson and the Friends of Pigeon Valley. What visitors may not know, though, is that Pigeon Valley was once part of a very large forest that extended from the Umbilo River in the south to the Umgeni River, and present day Burman Bush, in the north. This forest may have been ~1500 ha when Europeans first saw it! That’s more than twice the size of the Krantzkloof Nature Reserve. Sadly, less than 5% of the original forest cover remains.

A sense of what has been lost can be gleaned from early paintings of Durban, especially the piece by James B. West in 1856 which shows the western end of Stella Bush and a similar forest which grew at Montclair (Clairmont). The bay, associated grasslands, freshwater and estuarine wetlands, and the forests on the ancient red sand dunes beyond must have been a remarkable landscape.

The first aerial surveys of Durban were done in the 1930s. The fascinating photographs from these flights show that the forest, then known as Stella Bush, including present-day Pigeon Valley, was approximately 220 ha. Thus, although much-reduced, Stella Bush was then roughly twice as big as the current Hawaan Forest at Umhlanga. Thereafter, Stella Bush was gradually reduced as development engulfed it and only the small patch that we know today remained by the 1960s.

Some years ago, one of us (GD), discovered that a number of egg clutches had been collected at Stella Bush between 1899 and 1931. Sampling was sporadic in time and taxonomically, so only a portion of the breeding birds was sampled. Nonetheless, even this restricted sample grabbed our attention because some clutches came from birds that no longer breed at or are only scarce visitors to Pigeon Valley.

We then contrasted the old egg collections with more recent observations of Pigeon Valley’s birdlife, especially dissertation fieldwork undertaken by RB (Boon 1992). The basic questions were: what bird species were lost as Stella Bush was reduced? And what species survived and continued breeding even though the forest patch contracted by nearly 95% in approximately 30 years?

The following points emerged:

• Ninety-eight clutches from 39 species were collected at Stella Bush between 1899 and 1931.

• Clutches were collected from 12 bird species no longer resident at Pigeon Valley, including seven species that appear noteworthy: Lemon Dove (1 clutch), African Wood Owl (2), Green Malkoha (2), Gorgeous Bush-Shrike (1), Olive Bush-Shrike (1), Black-crowned Tchagra (1), and Brown Scrub-Robin (7).

• The remaining extirpated breeders were: Red-chested Cuckoo (1 clutch of Red-capped Robin-Chat parasitized), Burchell’s Coucal (1), African Pygmy Kingfisher (1), Little Bee-eater (2), and White-browed Scrub-Robin (1).

• We interpreted the above species to be ‘sensitive species’. In other words, they were able to breed in or on the margins of Stella Bush, but no longer breed at the smaller Pigeon Valley.

•Some of the ‘sensitive species’ occasionally visit Pigeon Valley, but in the last 35–40 years only as vagrants, wintering non-breeders or marginal incidental breeders that do not establish persistent populations.

•The number of Brown Scrub-Robin clutches is interesting. Nests of this robin are difficult to find (Oatley & Arnott 1998), thus seven clutches is noteworthy. The implication is that a flourishing population once existed at Stella Bush and the larger Berea forest.

•Clutches were also collected of species that still breed at Pigeon Valley and the broader Berea Ridge: African Goshawk (1 clutch), Buffspotted Flufftail (2), Tambourine

Dove (1), Red-eyed Dove (1), Speckled Mousebird (1), Cardinal Woodpecker (1), Black-backed Puffback (2), Southern Boubou (5), Southern Fiscal (1), Fork-tailed Drongo (2), Square-tailed Drongo (4), African Paradise Flycatcher (7), Dark-capped Bulbul (2), Sombre Greenbul (3), Terrestrial Brownbul (4), Yellow-bellied Greenbul (1), Green-backed Camaroptera (2), Tawny-flanked Prinia (1), Barthroated Apalis (3), Red-capped Robin-Chat (9), Southern Black Flycatcher (2), Collared Sunbird (16), Olive Sunbird (1), Grey Sunbird (2), Cape White-eye (1), Dark-backed Weaver (1) and Village Weaver (1).

•The species listed in the last point we interpreted as ‘resilient species’. Despite a massive decline in forest cover, they were able to persist as breeding populations (sometimes small) within a radically-transformed landscape. These resilient species also formed most clutches from the old egg collections.

•The resilient species are today often found in gardens and parks of the adjoining suburbs and have also been found along the narrow corridors of natural vegetation, especially on the Howard College campus of the University of KZN, which connect Pigeon Valley to the nearby Msinsi Nature Reserve and Umbilo Valley.

In summary, the findings show that most of the birds breeding at Stella Bush in the early part of the 20th Century survived to modern times at Pigeon Valley. Evidently, the significant fragmentation did not condemn them to local extinction. Thus even small remnant patches of coastal forest can support many bird species.

But many of the original breeding bird species did not endure the changes. Their demise as Stella Bush shrank raises fascinating ecological questions of why some species were more sensitive to landscape modification than similar species of broadly equivalent life histories.

This is especially stark when one contrasts, say, Brown Scrub-Robin against Red-capped Robin-Chat. Both are largely ground-dwelling insectivorous robins of thick cover and of approximately similar body mass. Yet their fates at Pigeon Valley were very different!

Similarly, the disappearance of the Gorgeous Bush-Shrike contrasts against the Southern Boubou, which continues to prosper at Pigeon Valley. These are both understorey shrikes with comparable body masses and diets, but their fortunes have been radically divergent.

Can the conclusions from this Stella Bush–Pigeon Valley dataset be extrapolated to other areas of the eThekwini Municipality, the KwaZulu-Natal coast or an even wider area?

Certainly, elsewhere, birds do different things and even have opposite status trends. For example, Brown Scrub-Robin is apparently a garden bird in Anerley and Umtentweni on the South Coast of

KZN, and it reportedly occurs in ‘very small forest patches’ in the Eastern Cape (Oatley 2005). Such facts are in sharp contrast to our Durban findings!

On the other hand, some evidence aligns with our results. For instance, the development of the Zimbali housing estate near Ballito resulted in the populations of Brown Scrub-Robin and Gorgeous Bush Shrike suffering notable declines (Nichols 2011). And, in southern Mozambique, Brown Scrub-Robin is reported only in sand forest patches above 70 hectares in size (Wilson et al. 2007), which indicates that it is sensitive to forest patch size.

In conclusion, we suggest that, within the eThekwini area, African Wood Owl, Green Malkoha, Brown-Scrub Robin, and Gorgeous Bush Shrike are especially sensitive to forest loss and species to watch within the municipal boundaries. Other species not included in the egg collections, like African Broadbill and Narina Trogon, may also be vulnerable to forest change. Forests on the KZN coast south of the Tugela River that boast resident breeding populations of these species are probably ‘healthy’ and worthy of heightened ecological and conservation interest. These forests should not be developed or disturbed.

Full references and further details were published in Davies & Boon (2020). If you would like a copy of the paper, please email Greg Davies at seicercus@gmail.com. It can also be downloaded from ResearchGate.

Greg Davies and Richard Boon

Further Reading: DAVIES, G.B.P. & BOON, R.G.C. 2020. Medium- and long-term avifaunal changes of a coastal forest and its resultant fragment: Stella Bush and Pigeon Valley Park, eThekwini Municipality, South Africa. Durban Natural Science Museum Novitates 40: 1–23.