BRANTA — Kathleen M.C. Tjorve
From an egg to a fledgling: A perspective on shorebird breeding ecology and chick energetics
Institution: University of Groningen, the Netherlands
Details: Ph D 2006 (Completed)
Address: Lista Bird Observatory, Research Group, Fyrveien 6, N-4563 Borhaug, Norway (Apr 2006) Email
Species Keywords: shorebirds
Shorebirds form a diverse group of bird species exhibit a variety of growth rates, reproduction strategies and behaviours which enable them to survive in the different environments in which they live and breed. This variation makes this group of species an ideal subject to study latitudinal adaptations. During each life stage shorebirds are subject to selective pressures from these different environments. Adaptations to survive in these environments are not limited to specialised egg structure or large fat reserves to survive harsh conditions. There are other adaptations, also physiological, that enable shorebirds to survive in harsh climates; for example, metabolic adaptations in chicks. I discuss the adaptations of shorebird (Charadrii) chicks that enable them to grow and fledge successfully in their environment.
Although the breeding phenology, breeding success and population trends of African Black OystercatchersHaematopus moquini over three austral summers on Robben Island, South Africa, from the 2001-2002 to the 2003-2004 breeding seasons were discussed, the bulk of the thesis considers the prefledging growth and energetics of shorebird chicks; in particular, the Little Stint Calidris minuta (Scolopacidae), Kittlitz's PloverCharadrius pecuarius (Charadriidae), Blacksmith Lapwing Vanellus armatus (Charadriidae), Crowned Lapwing V. coronatus (Charadriidae), African Black Oystercatcher (Haematopodidae) and Spotted Thickknee Burhinus capensis (Burhinidae). These species were selected on the basis of different adult body masses, different modes of development and different timing of breeding. Together with data from the literature I could also investigate the influence of (adult) geographical breeding distribution on the growth and energy expenditure of shorebird (Charadrii and Lari) chicks.
Little Stint chicks at Medusa Bay, Siberia (73┬░N), grew relatively quickly; their growth rate coefficient was 14% greater than the prediction (from Beintema & Visser 1989) for a bird their size. Their total metabolisable energy, TME, over the 15-day prefledging period was 107% greater than the allometric prediction (from Weathers 1992) for a bird the size of a Little Stint. Therefore their small size and large surface area-to-volume ratio may have resulted in greater relative heat loss and thus impacted their energy expenditure and growth. To obtain the observed growth rates, chicks had to rely on a high rate of food intake.
Kittlitz's Plover, Blacksmith Lapwing and Crowned Lapwing chicks were studied in a warm, sub-tropical environment, in South Africa (34┬░S). Body size, timing of breeding, mode of development, and habitat all impacted the growth and energetics of the three species. Their small growth rate coefficients, low resting metabolic rates (RMR) and low daily energy expenditure (DEE) may be adaptations to low food availability and mild ambient temperatures. The three precocial species exhibited slower growth, longer fledging periods and lower daily energy expenditure than arctic and temperate zone relatives of similar size. African Black Oystercatcher chicks are semi-precocial; they are mobile soon after hatching but are parentally fed.
Growth rate influenced fledging success, the length of the prefledging period and mass at fledging. Chicks exhibited alarge variation in growth rate coefficients and chicks with comparatively slow growth rates were able to fledge. These chicks exhibited retarded growth of all body measures except wing length, thus enabling them to fledge in a shorter period of time than their slow growth would otherwise have allowed. Sibling rivalry occurs in African Black Oystercatchers and once a dominance relationship is established the larger chick remains so throughout the prefledging period. The larger sibling fledges earlier and at a heavier mass and may thus, have improved its chances of survival. Spotted Thick-knees are also semi-precocial shorebirds, feeding predominantly at night. The observed average growthrate coefficients of African Black Oystercatcher chicks on Robben Island (33┬░S) and Spotted Thick-knees in the Western Cape (34┬░S) were similar to that predicted from the Beintema & Visser (1989) allometric equation. Their relative (observed versus predicted) growth rate coefficient was closer to the predicted value for shorebirds than those of three precocial, self-feeding shorebird species in the Western Cape.
The growth rate coefficient of African Black Oystercatcher chicks was smaller than that of other oystercatcher species which may be a consequence of differences in body size and differences in climate and food availability. RMR, peak daily metabolisable energy (DME) and total metabolisable energy (TME) of African Black Oystercatchers and Spotted Thickknees were similar to those expected for the species (from Weathers 1992 and based on comparisons with the Eurasian Oystercatcher). African Black Oystercatchers spent less timeforaging and more time inactive than precocial species. The potential negative impact of nocturnal feeding on Spotted Thick-knee chick growth may be countered by parental feeding reducing chick energy expenditure on thermoregulation and activity and adults potentially extending their foraging time into the day as their chicks become larger. Therefore their mode of development enabled oystercatcher and thickknee chicks to reduce energy costs from thermoregulation and activity, enabling them to grow relatively faster than precocial shorebird species in similar climatic conditions.
Through a study of shorebirds (Charadrii) as a group and through comparing them with other Charadriiformes (Lari) we were able to investigate the importance of adult body mass, mode of development and latitude in shorebird growth and energy expenditure. Shorebird growth rate coefficients decreased whereas energy expenditure increased with increasing adult body mass. Semi-precocial shorebirds exhibited faster relative growth rates than precocial species at similar latitudes; e.g. comparing the growth of African Black Oystercatcher and Spotted Thick-knee chicks to that of precocial shorebirds in southern Africa. Habitat type and food availability are a consequence of latitude. The growth rate coefficients and metabolisable energy expenditure of shorebirds increased with increasing latitude, thus food availability and habitat type are influencing factors in shorebird growth and energetics. Shorebird chicks at higher latitudes spend their time brooding or foraging and spent little or no time in other activities whereas shorebird chicks in the Western Cape did not seem to be limited by time available for foraging but rather by food availability. Chicks at higher latitudes may be able to compensate for their greater energy expenditure due to greater thermoregulatory energy costs through greater food intake than chicks at lower latitudes.