A New Equation for Calculating Reproductive Success of Clutches as a Function of the Day on Which Incubation Starts: Some Implications

Many species of birds start incubation before the last egg of a clutch is laid, which often results in asynchronous hatching and fledging. The incubation pattern favored by natural selection should lead to greater reproductive success than alternative patterns. Equations for calculating the reproductive success of a clutch as a function of the start of incubation have been proposed by Clark and Wilson (1981) and Hussell (1985). Both equations predicted a greater frequency of an earlier start of incubation than occurs in nature. Here, I present a new equation in which the relevant parameters determining reproductive success as a function of the start of incubation are (1) the probability of any young leaving a nest and (2) the post-first- fledging daily survival rates of the remaining nestlings. This equation is universally applicable and accounts for the greater frequency of incubation starting later, rather than earlier, in the laying sequence of most birds. I use the equation to evaluate various hypotheses regarding the evolution of incubation patterns. Una Nueva Ecuación para Calcular el Éxito Reproductivo de Nidadas en Función del Día en que Comienza la Incubación: Algunas Implicaciones

Nest-building Behaviour of the Asian Open Billed Stork Anastomus oscitans, in the Kulik Bird Sanctuary, Raiganj, India

A field study of the nest-building behaviour in the breeding season of the Asian Open-Billed Stork, Anastomus oscitans, was conducted in the Kulik Bird Sanctuary, Raiganj, Uttar Dinajpur, West Bengal, India. Observations were made throughout one complete breeding season (2007-2008) in the sanctuary. The open-billed stork comes in the last week of June at the Kulik bird sanctuary, stays there for 5 to 6 months and leaves the place in the month of December of every year. From the present observations it was noticed that about 58920 storks came to Kulik during 2008. Various types of behaviour were observed during this particular period. Coming to the Kulik, pairing of the individual storks start and mating display was observed within a day or two. Birds of a pair supplied the nest building materials to form the nest. To give a definite shape to the nest it took about 12-15 days before egg laying. The nesting territory consisted of a semicircle, some times circular and approximately with 30.21 ± 0.12 cm radius. The depth of the nest was about 6.9 ± 0.02 cm. The nest building materials consisted of fragments of old branches of trees, some soft green leaves and grasses. These branches helped in strengthening and the leaves and grasses helped in softening of the nest. During the incubation period both sexes were involved to incubate the eggs. Nest attendance of the breeding birds was continuous during the first 2-months period. From regular observation it was noticed that either of the pair took additional care by spreading their wings during the time of heavy sunshine or heavy rain. The main behavioral patterns examined were aerial displays, mating pattern, nest building, egg laying and incubation pattern, nest defense and nest protection. Diversity of nesting behavior in open-billed stork was pointed out and discussed.Key words: Asian Open-Billed Stork, Kulik Bird Sanctuary, Nest-building behaviorDOI: 10.3126/on.v7i1.2552Our Nature (2009) 7:39-47

Incubation and Nest-Building Behaviour of Black-Headed Gulls

Abstract(1) Parental behaviour, and its development from incubation behaviour during the reproductive season, is described. (2) Day to day observations of the natural situation showed that elements of the incubation pattern persist throughout the post-hatching period but progressively decline in quantity, duration and completeness. (3) Substitution of eggs for chicks also showed that the readiness to show incubation responses in a standard incubation situation declines progressively during the post-hatching period. (4) A certain amount of experience with hatched chicks renders Black-headed Gulls incapable of immediately returning to sustained incubation behaviour if the conditions of the incubation period are restored. (5) Failure of the eggs to hatch results in extension of the incubation behaviour period beyond the normal time. (6) Premature introduction of hatched chicks in the nests of incubating gulls can cause the gulls to switch to parental behaviour and so end the incubation behaviour period before the normal time. (7) The timing of the change from incubation to parental behaviour is thus mainly a matter of external control. (8) Certain of the relationships found to hold between responses having an incubation function and responses having a nest-building function in the earlier phases also hold in the post-hatching period.

Incubation and Nest Building Behaviour of Black-Headed Gulls. I: Incubation Behaviour in the Incubation Period

I. Descriptions are given of the elements of the behaviour performed by Black-headed Gulls on the nest during the time between laying of the third egg and hatching of the first egg. 2. With three eggs in the nest it is found that the majority of settling sequences are complete, the majority of sitting spells are relatively long, and the eggs are covered for almost all of the available time. Also most of the relatively long sitting spells are preceded by complete settling sequences and most of the short sitting spells are preceded by incomplete settling sequences; most of the complete settling sequences lead to long sitting spells and most of the incomplete settling sequences lead to short sitting spells. 3. The frequency of settling, the proportion of complete settling sequences, and the total amount of time spent sitting, are used in comparing the behaviour in different situations. It is found that more or less than three eggs in the nest, eggs of abnormal shape or size, fixed eggs, disturbed nest material, scaring stimuli near the nest, presence of the mate, and the early stage of the sitting bout, produce incubation behaviour which differs from the standard pattern; the birds rise and settle more often, spend less total time sitting, and, with the exception of the last two cases, complete less of their settling sequences. On the other hand different times of day, different stages of the incubation period, differences in weather conditions, eggs of abnormal colour or markings were not associated with differences in the incubation pattern in my observations. 4. It is concluded that stimuli relayed from the brood-patches are particularly important in determining the pattern of settling and sitting behaviour. 5. Some problems connected with the use of the concepts of incubation "drive" and incubation "tendency" are discussed. 6. Stimuli to the feet and legs probably play a part in the release of shifting. 7. Quivering while sitting is probably stimulated by disturbed or "novel" contact between brood-patches and eggs.