ALTERRA Hans Schekkerman SCIENTIFIC CONTRIBUTIONS precocial problems Shorebird chick performance in relation to weather, farming, and predation 24 RIJKSUNIVERSITEIT GRONINGEN Precocial problems Shorebird chick performance in relation to weather, farming, and predation Proefschrift ter verkrijging van het doctoraat in de Wiskunde en Natuurwetenschappen aan de Rijksuniversiteit Groningen op gezag van de Rector Magnificus, dr. F. Zwarts, in het openbaar te verdedigen op maandag 26 mei 2008 om 13.15 uur door Hans Schekkerman geboren op 19 december 1963 te Alkmaar Promotores: Prof. dr. T. Piersma Prof. dr. G.H. Visser † Beoordelingscommissie: Prof. dr. F. Berendse Prof. dr. M. Klaassen Prof. dr. Å. Lindström precocial problems Shorebird chick performance in relation to weather, farming, and predation Colophon Photograpy Harvey van Diek: page 6, 22, 210 (left) Jan van de Kam: page 44, 68 Henk-Jan Ottens: page 204, 210 (right) Wolf Teunissen: page 152 Ingrid Tulp: page 212 (centre) All other pictures: Hans Schekkerman Figures Dick Visser Graphic Design Nicolet Pennekamp Printing Drukkerij van Denderen BV, Groningen ISBN: 978-90-9022979-9 1. Introduction 6 2. Prefl edging energy requirements in shorebirds: energetic implications 22 of self-feeding precocial development 3. Mechanisms promoting higher growth rate in arctic than in temperate 44 shorebirds. 4. Growth, behaviour of broods, and weather-related variation in breeding 68 productivity of Curlew Sandpipers Calidris ferruginea 5. Foraging in precocial chicks of the black-tailed godwit Limosa limosa: 90 CONTENTS vulnerability to weather and prey size 6. Abundance of invertebrates and foraging success of Black-tailed Godwit 112 Limosa limosa chicks in relation to agricultural grassland management 7. Can ‘mosaic management’ improve breeding success and halt the 134 population decline of Black-tailed godwits Limosa limosa in agricultural grasslands? 8. Mortality of Black-tailed Godwit Limosa limosa and Northern Lapwing 152 Vanellus vanellus chicks in wet grasslands: infl uence of predation and agriculture 9. Synthesis 172 10. Nederlandse samenvatting 204 Dankwoord 223 Author’s Addresses 227 Introduction 1 6 precocial problems the altricial-precocial spectrum in birds All birds have in common that their offspring hatch from eggs that develop outside the mother’s body, but the structural and functional state in which young birds hatch varies enormously between species. When megapode chicks emerge from their egg, buried in warm soil or decomposing litter, they are fully feathered and capable of dig- ging themselves to the surface, walking about, keeping warm and fi nding their own food without any help from their parents, and they can fl y within a day. At the other extreme, the chicks of most songbirds, owls and parrots hatch without any feathers, with closed eyes and poorly developed muscles, and incapable of doing much more than raise their heads and beg for food when something (a parent?) arrives at the nest, swallow, and digest. They are almost totally dependent on their parents for staying warm, detecting predators, and food acquisition. They remain so for an extended period in which they stay in the nest and, for some aspects like feeding, even beyond. Many other bird species fall at varying points in between these two extremes, both with respect to the state of the chick at hatching and to the subsequent developmental trajectory. This diversity includes multiple anatomical and physiological traits, behaviour, and parent-offspring relationships. These traits partly vary independently of each other, but there is suffi cient covariation among them to distinguish a single major axis of variation, which is known as the altricial-precocial spectrum (Nice 1962, Starck & Ricklefs 1998). Of the several classifi cations that have been proposed to sub- divide this gradient, that of (Nice 1962) has become the most used (fi g. 1.1). Naturally, it is of great interest to understand the selective factors that have led to the evolution of the altricial-precocial spectrum. Projection of the current diversity of developmental modes onto hypotheses about the phylogeny of birds does not allow fi rm conclusions on the avian ancestral state, although it seems more likely that it was precocial than altricial (Starck & Ricklefs 1998). Whatever the case, the difference between the two major developmental modes must have arisen in one of the basic splits in the avian phylogeny. Evolutionary reversals have occurred at least once, and the ‘middle ground’ of the spectrum – represented by semialtricial and semiprecocial species – has probably been occupied from both fully altricial and fully precocial roots (Ricklefs & Starck 1998). However, most of these transitions have taken place early in the evolutionary diversifi cation of birds. Developmental mode rarely varies within bird families and even less often within orders (the order Charadriiformes on which this thesis focuses forms an exception, see below). Apparently, it is an evolutionary con- servative trait, “not a characteristic of birds that responds readily to environmental factors” (Ricklefs & Starck 1998). This does not mean that selection on developmental mode is nowadays absent or inconsequential. Rather, if it is hard to change a mode once it has become established in a lineage, this character may itself become a factor shaping the success of that lineage under different environmental conditions. Develop- mental mode may thus shape a bird group’s ecological niche and evolutionary success by constraining choice of habitat, food type, or in other ways. Therefore, it is of interest to explore the ecological consequences of variation in developmental mode. 1 introduction 7 Although from a morphological-physiological point of view the most fundamental division along the altricial-precocial axis seems to be that between truly altricial (altricial-1) species and all other developmental groups (Starck & Ricklefs 1998), a major dividing point from a behavioural perspective is leaving the nest – so much that the term nidifugous (for chicks that leave the nest soon after hatching) is often equated with precocial, and nidicolous (for young that stay in the nest for some time) with altricial. The ability of the chicks to leave the nest, move around, hide upon alarm, or even follow the parents further away must have major consequences for predation risk and the economics of food acquisition of the family unit. According to Ricklefs & Starck (1998), the essence of this ability lies in the necessary neuromotor and sensory coordination in the higher centres of the chick’s brain, and differences among nidifugous taxa refl ect more the intensity of expression than the presence or absence of particular functional capabilities. From this point of view, semiprecocial birds can be seen as “precocials in which the parents gather food and deliver it to the chicks in a central place” (Ricklefs & Starck 1998). But while differences in demands on the functionality of various organ systems between young that merely wander about near the nest site and chicks that go out to fi nd their own food may indeed be a matter of degree, in a broader ecological sense the division between parental feeding and self-feeding represents another major transition in the spectrum. figure 1.1. Nice’s (1962) classifi cation of the altricial-precocial spectrum, with major characteristics distinguishing the classes, and examples of bird families belonging to each. Category Plumage Eyes Nest Parental Examples attendance care Precocial-1 contour none megapodes feathers Precocial-2 brooding ostriches, ducks & geese, leave vigilance plovers, sandpipers & allies Precocial-3 nest food pheasants, grouse, guineafowl open area showing Precocial-4 cranes, bustards, rails, grebes, down divers, oystercatchers, murrelets Semiprecocial leave nest gulls & terns, many auks stay near Semialtricial-1 feeding raptors, storks & herons, young crab plover Semialtricial-2 stay in pigeons, cormorants nest Altricial none closed songbirds, parrots, gannets 8 precocial problems self-feeding precociality The period of provisioning food to growing young is generally seen as one of the most demanding stages in the life cycle of adult birds (Drent & Daan 1980, Weathers & Sullivan 1993). When parent birds do not have to spend energy and time on fi nding and transporting food to their young, this will reduce the associated ‘cost of reproduc- tion’, with potentially important consequences for life-history trade-offs, and mating and parental care systems (Temrin & Tullberg 1995, Thomas & Szekely 2005). Simulta- neously, the burden of fi nding food is shifted to the chick. It must leave the shelter of the nest and exert a high level of activity, which is very likely to increase its energy expenditure and reduce the amount of growth achieved per unit energy metabolised, compared to altricial nestlings. This redistribution of effort from parent to chicks proceeds gradually from taxa in which chicks follow their parents to be fed (precocial-4) or shown food (precocial-3) on the feeding grounds, via groups in which parents provide no food but do warm and guard the young (precocial-2), to the totally independent megapodes (precocial-1), but it remains to be seen whether these steps are all of the same magnitude in an energetic sense. Some other potential consequences are particular to the self-feeding mode. First, the fact that incompletely developed chicks do not possess the same power and range of foraging skills that fully-grown and experienced