Sex-ratio of Skylark Alauda arvensis broods in relation to timing of breeding

Capsule Earlier broods tend to be more male biased than later broods     

Observer variation in estimates of Meadow Pipit Anthus pratensis and Skylark Alauda arvensis abundance on moorland

Capsule Counts least susceptible to observer effects were those within 25 m of a transect and the total number along a transect, with observer effects greater for distance sampling.     

Intraspecific Social Stimulation and Temporal Displacement of Songs of the Lesser Skylark,Alauda gulgula

Temporal patterning of flight song activity was examined in a population of Lesser Skylarks in Viet Nam. Onset and termination of songs were timed. Temporal dispersion of songs was analyzed from the distribution of intersong intervals, and the tendency of songs to be started prior to, shortly after, or long after cessation of a neighbor's song was examined. Skylarks tended to sing sequentially, clustering their songs in time after long periods of silence. However, they showed a strong tendency to avoid overlapping songs, perhaps because of the possibility of jamming by songs of neighbors. These two factors, intraspecific social stimulation and temporal avoidance, appear to be important determinants of singing behavior in this species.     

Factors affecting the territory distribution of Skylarks Alauda arvensis breeding on lowland farmland

The distribution of breeding Skylarks on lowland farmland was examined on a monthly basis on 13 farms in southern England in 1996. General linear models identified crop type and field area, shape and boundary characteristics as significant independent predictors of Skylark territory numbers in most or all months. Models predicted territory numbers best during the height of the breeding season and less well during territory establishment in March and abandonment in July. From March to May, crop height had no significant effect on Skylark territory distribution, but in June and July it had a highly significant quadratic effect, models suggesting an optimal vegetation height of around 0.55 m in these months. Set-aside held high territory densities, permanent pasture low densities. Spring cereals held higher territory densities than winter cereals. This could best be explained by differences between the two cereal types in crop structure. There was evidence of a positive correlation between crop height diversity and territory density at the farm scale. The results are discussed with reference to the species' recent severe population decline.     

Habitat selection by Skylarks Alauda arvensis wintering in Britain in 1997/98

The results of a national survey of wintering Skylarks Alauda arvensis undertaken by the British Trust for Ornithology (BTO) between November 1997 and February 1998 are reported here. Over three visits, volunteers counted Skylarks and mapped habitats in 541 1-km squares selected from the Skylark's winter range based on BTO Winter Atlas data and a stratified random sampling approach. Four landscape strata were defined from the Institute of Terrestrial Ecology landscape classification: arable, pastoral, marginal upland and saltmarsh. The survey counts underestimated Skylark abundance, but were good measures of relative abundance across habitat types. The two best predictors of Skylark presence–absence at the landscape scale were the availability of coastal and farmland habitats. Squares with saltmarsh had the highest densities and occupancy (80% of squares). At the patch scale crop stubbles, especially weedy cereal stubbles, were used significantly more than expected by chance. Oilseed rape was positively selected whereas cereal crops were used in proportion to availability and grazed grass was avoided. Skylarks avoided fields smaller than 2.5 ha and selected fields larger than 7.5 ha. We estimate that in midwinter there may be less than 1–2 ha of weedy cereal stubble per 1-km square. We recommend the retention of over-winter stubbles for the conservation of Skylarks and other farmland birds, and research on stubble management and effects on grain availability and arable weed regeneration on Skylark use.     

Habitat associations of Eurasian Skylarks Alauda arvensis breeding on Irish farmland and implications for agri-environment planning

Capsule Skylarks breeding in Ireland prefer extensive grassland habitats and almost completely avoid tillage habitats.

Aims To describe the distribution and habitat use of breeding Skylarks in Ireland, particularly in lowland agricultural habitats, and to use this information to inform conservation measures for this species.

Methods Countryside Bird Survey (CBS) and Farmland Bird Project (FBP) data were examined to determine large-scale (national) distribution and habitat selection, in addition to smaller-scale (farm- and field-level) habitat use. The CBS is a national breeding bird monitoring scheme involving 397 1-km squares. The FBP collected detailed bird and habitat data from 122 farms.

Results CBS and FBP data both showed significant regional differences in breeding Skylark densities, with the highest relative abundances in the northwest and west. Dry grassland/grass moor habitats supported the highest densities of breeding Skylarks in the CBS, which were significantly higher than in improved grassland or tillage. At the farm-level, Skylark numbers were positively related to wetland habitats but negatively associated with trees in field boundaries, dense ground vegetation and overall density of farm boundaries. At the field-scale, larger fields and unimproved grasslands were preferred.

Conclusion Agri-environment measures tailored to region-specific requirements and to the relatively local habitat preferences of target species are required if population declines of species of conservation concern, including Skylarks, are to be reversed.     

Population declines and reproductive performance of Skylarks Alauda arvensis in different regions and habitats of the United Kingdom

Declines in the number of breeding Skylarks Alauda aruensis and changes in their reproductive performance were analysed using data from two long-running surveys co-ordinated by the British Trust for Ornithology: the Common Birds Census and the Nest Record Scheme. In the UK, the number of breeding Skylarks declined by approximately 55% between 1975 and 1994. This decline was steepest in agricultural habitats and in regions associated with intensive agriculture. In contrast, Skylark reproductive performance per nest, in terms of clutch size, brood size and post-hatching survival rate of nests, showed a general improvement over time. This improvement was greatest in intensively farmed agricultural habitats. Therefore changes in reproductive performance per nesting attempt were probably not responsible for the decline in numbers. It is inferred that possible causes of the decline of the Skylark are: reductions in the number of breeding attempts per pair per season, reductions in the proportion of birds attempting to breed, and increased mortality outside the breeding season.     

Effect of the moon on the nocturnal postnuptial migration of the skylark Alauda arvensis L. in France

Night-migrating skylarks (Alauda arvensis) were captured during four successive autumns in France. The study aimed at detecting a possible influence of the lunar cycle on the nocturnal migration of this species. Though nocturnal postnuptial migration of the skylarks can occur during every phase of the moon, main nocturnal movements occurred when the moon was in its waxing gibbous phase. This phase gives the best conditions for migration because from the very beginning of night, it provides the necessary horizon for individuals to navigate and its light allows the use of topographic cues. In addition it allows the species to benefit from optimal conditions of illumination for almost a week.     

Comparative nesting and feeding ecology of skylarks Alauda arvensis on arable farmland in southern England with special reference to set-aside

1. A study of skylark Alauda arvensis L. breeding ecology in relation to crop type was carried out from April to August 1992 on arable land in southern England. Set-aside land was included in this comparative study.
2. Territory density averaged 0·15 ha⁻¹. It was 2–3 times higher in fields of set-aside and grass, especially permanent pasture, than in winter and spring-sown cereals.
3. Territory size was nearly twice as large in fields of winter cereals (4·5 ha) than in other crop types (2·5 ha). Where set-aside was present on one farm, territory size in set-aside (1·7 ha) was a third lower than in cereals and grass.
4. Nesting began in set-aside and permanent pasture in April and peaked in late May. Nesting was not detected in spring barley until late May and in silage grass until early June. The density of successful nests in set-aside fields was more than double that in any of the arable crop types.
5. Average clutch size at hatching was 3·91 eggs in fields of set-aside, over 15% higher than in silage grass (3·40) and in spring barley (3·27).
6. Fledging success did not differ according to crop type, but productivity, expressed as the number of fledglings produced per hectare, was 0·50 in set-aside, 0·13 in silage grass, and 0·21 in spring barley. Nests with chicks were not found in fields of winter cereals. The causes of chick death were thought to be predation in set-aside fields, farming practices in silage grass fields, and suspected starvation in spring cereals.
7. The potentially high nesting success of skylarks in set-aside implies that sympathetic set-aside management could play an important part in reversing its decline across the European Union.     

A Population Study of Spergula arvensis: II. Genetics and Breeding Behaviour

Genetical work has shown that one locus and two alleles areinvolved in the inheritance of a seedcoat character of Spergulaarvensis and that the hetero-zygous plants are intermediatebetween the two types of homozygous plants. It is thus possibleto translate directly the observed geographical distributionof plant frequencies into distribution of gene frequencies.The inheritance of a hairiness character is less straightforward,but in this case also there is a close relation between phenotypefrequency distribution and gene frequency distribution. Using the fact that plants heterozygous for the seedcoat characterare easily recognizable, it is possible to make an estimateof the amount of outbreeding in nature. The values obtainedrange from o to 3 per cent.     

Sustainable Arable Farming For an Improved Environment (SAFFIE): managing winter wheat sward structure for Skylarks Alauda arvensis

Research has shown a close correlation between the decline of the UK Skylark Alauda arvensis population and the replacement of spring-sown cereals with winter-sown varieties, in which advanced sward development prevents successful multiple nesting attempts and reduces access for foraging. Widescale reversal of sowing times is unlikely for commercial reasons, so research has recently focused on ways of manipulating the sward structure of winter wheat to prolong access to nest-sites and food. An RSPB pilot study investigated leaving small 'undrilled patches' in otherwise conventionally managed winter wheat crops. This option was later incorporated into a fully replicated experimental design, as part of the Sustainable Arable Farming For an Improved Environment (SAFFIE) project. This large consortium-led project aims to test solutions for improving biodiversity within winter-cereal-dominated rotations. The experiment described here ran over 2002–3, with three field-scale 'treatments' on 15 sites in the first year. The treatments compare (1) conventional winter wheat, (2) winter wheat sown in double-normal width (25 cm) wide-spaced rows (WSR) and (3) winter wheat with two 4-m by 4-m undrilled patches per hectare (UP). Results from the 2002 breeding season showed that undrilled patch treatments supported more breeding Skylarks for longer, most likely by aiding accessibility of food. WSR rows were little used by Skylarks and did not improve the abundance of favoured seed and invertebrate food items over conventional crops. Nesting performance and foraging patterns are discussed with reference to invertebrate food abundance and its accessibility, as determined by sward structure.     

Multiple patterns of parental care

Many animals show multiple patterns of parental care, where more than one of the four basic patterns (biparental care, uniparental care by males or females, or no care) is present within a single population during a single breeding season. We consider three reasons for the existence of multiple patterns of parental care: (1) mixed-strategy behaviours; (2) time-dependent behaviour with parents changing their care decision during the breeding season; and (3) quality differences between individuals leading to different care decisions being made depending on the qualities of both parents. The basic framework we use to investigate these is a two-stage game-theoretical model, and we highlight the importance of including feedback between the parental care decisions made by population members and the probability that a deserting individual will find a new mate. Including this feedback may introduce a nonlinear dependence of the fitness payoffs on the frequencies with which the pure strategies ('care' and 'desert') are played by each of the sexes. This can have important consequences for the existence of evolutionarily stable strategies (ESSs). For example, mixed-strategy ESSs may exist (an outcome forbidden if the feedback is not included) and, in one model, the feedback also prevents uniparental care by either sex from being evolutionarily stable. We also point out that decisions made by animals without dependent offspring can have important consequences for observed parental care behaviour. Copyright 1999 The Association for the Study of Animal Behaviour.     

The evolution of parental care

Our understanding of parental care behavior can be significantly advanced through the application of Williams's Principle, which states that reproduction has not only a benefit but also a cost to lifetime fitness. My laboratory has formalized Williams's Principle into the relative value theorem and found that its application to fishes, the taxa with the most diverse patterns of parental care, can help to explain which sex provides care and how much. In fishes, it is often the male that provides parental care, not because the male obtains greater benefits from this care, but probably because he pays fewer costs. Fish dynamically adjust their investment into parental care according to the number of offspring in their brood, past investment, genetic relatedness, and alternative mating opportunities, all of which affect the value of current offspring relative to potential future offspring. These results may also help us understand the joy and the challenges of parental care in humans.     

Stimulus features of chicks and other factors evoking parental protective behaviour in ring-billed gulls

We examined the role of certain stimuli in parental approach and protection of ‘straying’ chicks by noting the response of ring-billed gulls, Larus delawarensis, to different stimuli placed within their territories. Playback of chick calls and presentation of surgically devocallzed chickes each elicited and oriented parental approach and protective behaviour, although a combination of the two was more effective. Other factors affecting a parent's reaction included the parent's reproductive state whether other offspring were present, the chick's location, and the chick'ssize relative to the parent's own chicks. These response tendencies should increase a gull's probability of responding selectively toward its own chicks before it can individually recognize them, while rejecting foreign chicks.     

The evolution of avian parental care

A stage model traces key behavioural tactics and life-history traits that are involved in the transition from promiscuity with no parental care, the mating system that typifies reptiles, to that typical of most birds, social monogamy with biparental care. In stage I, females assumed increasing parental investment in precocial young, female choice of mates increased, female-biased mating dispersal evolved and population sex ratios became male biased. In stage II, consortships between mating partners allowed males to attract rare social mates, provided a mechanism for paternity assessment and increased female ability to assess mate quality. In stage III, relative female scarcity enabled females to demand parental investment contributions from males having some paternity certainty. This innovation was facilitated by the nature of avian parental care; i.e. most care-giving activities can be adopted in small units. Moreover, the initial cost of care giving to males was small compared with its benefit to females. Males, however, tended to decline to assume non-partitionable, risky, or relatively costly parental activities. In stage IV, altriciality coevolved with increasing biparental care, resulting in social monogamy. Approaches for testing behavioural hypotheses are suggested.     

Paternity and the evolution of male parental care

It is generally believed that level of paternity (the proportion of zygotes in a brood that were fertilized by the male providing parental care) has an important role in the evolution of parental care. We have used population genetics models to investigate this role. The models indicate that only in mating systems where a parental male “sacrifices” promiscous matings can paternity influence the evolution of male parental care. This is because level of paternity can reflect the number of opportunities for these promiscuous fertilizations. For example, high paternity can mean few opportunities and therefore a low cost for paternal care.Certain behaviors may preadapt a species for the evolution of male parental care because they decrease the costs of providing care. For example, in fish species where male care has evolved from spawning territories, the very establishment of territories may have precluded males from gaining promiscuous matings, thereby eliminating the promiscuity costs and facilitating the evolution of care. Without a promiscuity cost, level of paternity will not have influenced the evolution of male care in fishes.Because paternity has limited influence in the evolution of male care, differences in reliability of parentage between males and females are unlikely to explain the prevalence of female care. Our analysis suggests that paternity differences between species cannot serve as a general explanation for the observed patterns of parental care behavior.     

Skylark optimal flight speeds for flying nowhere and somewhere

Flight is energetically very costly. For birds the mechanicalpower in relation to airspeed is characterized by a U-shapedfunction. From this function we can derive optimal flight speedsassociated with minimum power (V_mp), minimum cost of transport(V_mr) and minimum overall time of migration (V_mt). Since flightis energetically so costly, aerial displays and song flightcan potentially serve as signals reliably indicating the individualquality or resource potential of the signaler. In order to maximizethe amount of song flight produced, we expect V_mp during songflight, while during migration we rather expect V_mr or V_mv Wecompared flight speeds of skylarks (Alauda arvensis) duringsong flight and migration flight, respectively. In this speciespredicted V_mp = 5.5 m/s, V_mr = 10.5 m/s, and V_mt = 12.1 m/s.The preferred airspeed during song flight did not differ significantlyfrom the predicted V_mp, while airspeed during migration wassignificantly higher than V_mr and Vmp indicating that flightspeed is a flexible trait that birds adjust to different situations.Why the skylarks speed up so much on migration is still unclear,but it may be that due to the shape of the predicted power curve,variation in cost of transport at high speeds is relativelysmall.