Effect of intraspecific interactions on seasonal decline in productivity of Common Terns Sterna hirundo

Capsule Kleptoparasitic activities of older chicks from earlier nests did not contribute to late reproductive declines.

Aims To determine whether intraspecific interactions, such as kleptoparasitism and aggression, were experienced more frequently by birds breeding late in the season as a result of exposure to breeders at a more advanced stage. If so, to investigate whether this was the cause of the observed seasonal decline in reproductive parameters observed at Bird Island, where nesting density is high and interactions are more probable.

Methods Plots were fenced within the colony, exploiting natural variability in distribution of early and peak breeders to create two treatments: plots with only late-laying terns and those with a mixture of early-, peak- and late-layers. Hatching success, productivity and the growth and survival of chicks were measured for all late-laying pairs. Intraspecific interactions, adult attendance and provisioning of chicks were recorded during 9600 minutes of nest observations made within two periods: a few days after hatching and one week later.

Results The frequency of intraspecific interactions was maintained by the kleptoparasitic activities of older chicks within the mixed-laying-date treatment and was significantly lower in plots containing only late breeders with chicks of similar ages (mean 11.0 days). The overall rate was rarely greater than two interactions per nest per hour and there was no corresponding reduction in the growth or survival of chicks from late nests or any change in the provisioning activities of late-breeding adults.

Conclusion Increased frequency of intraspecific interactions experienced by late breeders in the presence of early-breeding conspecifics resulted from the kleptoparasitic activities of older chicks but was not sufficient to contribute to the observed seasonal reproductive decline at this dense breeding colony.     

NESTING DENSITY AND BREEDING SUCCESS IN THE HERRING GULL LARUS ARGENTATUS

The relationship between nesting density and breeding success of Herring Gulls Larus argentatus was studied on the Isle of May, Scotland, in 1968. Herring Gulls nesting at the most common density started laying earlier in the season than those nesting at lower or higher densities. Therefore, although the overall spacing of nests was uniform, the nest density of birds laying later in the season progressively approached a random distribution. The onset of laying occurred in synchronized groups within the colony. Late-laid clutches were commonly situated on the periphery of the colony where the density of nests was lowest. When the laying period was divided into four time periods, in each period the tendancy was for birds nesting at the most common density to have the highest clutch-size, hatching and fledging success, and to rear the most chicks per pair to fledging. In addition, birds which spaced their nests most uniformly, presumably as a consequence of territorial behaviour, were the most successful parents.     

Behavioural ecology of the North Sulawesi Tarictic Hornbill Penelopides exarhatus exarhatus during the breeding season

Two nests of the North Sulawesi Tarictic Hornbill Penelopides exarhatus exarhatus were monitored for one breeding season (April-July). The females sealed themselves into the nest cavities and remained there for 70–90 days. Incubation was estimated at 16–19 days, and at both nests two offspring fledged. Tarictic Hornbills are cooperative breeders with up to three helpers at the nest and defend foraging territories of 72–139 ha. Food items delivered to the nest included fruits of 34 species (85% of diet items) and invertebrates. Provisioning by helpers allowed breeding males to reduce investment in parental care and may accelerate the development rates in chicks. Constraints on dispersal probably result from habitat saturation rather than living in an unpredictable environment.     

Nest-site characteristics and aspects of the breeding biology of the endangered Timneh Parrot Psittacus timneh in Guinea-Bissau

Timneh Parrots Psittacus timneh are endemic to the moist forests of West Africa. Concerns over rapid declines in populations due to overharvesting for the pet trade and forest loss prompted the species’ categorisation as Endangered on the IUCN Red List of Threatened Species in 2016. Despite these threats, few data exist on their biology in the wild, impeding the development of effective conservation initiatives to protect populations. One of the few recorded breeding sites for this species occurs in the Bijagós Archipelago in Guinea-Bissau, where chicks have been historically harvested from nests and forest clearance for agriculture is common. We investigated the breeding ecology of Timneh Parrots in the Bijagós Archipelago focusing on two islands that harbour the densest populations. Specifically, we describe nest-site characteristics, breeding phenology and reproductive productivity. Timneh Parrots were found to use secondary nest cavities in 17 species of trees, predominantly nesting in trees between 20 m and 50 m in height. Nest cavities were generally aggregated, with a density of up to 14 nests ha^?1 in some areas, although nests also occurred in isolated large trees. The distribution of nests likely reflected a heterogeneous distribution of large trees containing suitable nest cavities, emphasising the importance of protecting mature trees. Nesting efforts were initiated between early January until late March, suggesting that nest surveillance efforts to deter poaching can be efficiently focused at a small number of key sites during February to May each year, when fledgling chicks are most likely to be present. These data further suggest that the population may be limited by the availability of suitable nest cavities and that the installation of artificial nest cavities could help increase the breeding population.     

Factors affecting the length of the breeding cycle and the frequency of nest attendance by Grey Herons Ardea cinerea

An investigation of the length of the breeding cycle and of the frequency of nest visits by Grey Herons at 3 heronries with different degrees of breeding success showed that the duration of reproduction, particularly the chickrearing period, decreased and the frequency of daily nest visits increased with increasing average breeding success of a colony. Successful pairs also seemed to spend less time displaying and incubating eggs. Herons arrived at their nests most frequently during twilight, especially in the morning. The mean time absent from the nest was greatest during incubation and smallest when feeding small chicks. The total reproductive period tended to be longer for those pairs whose periods of absence from the nest were longer.     

Competition with Egyptian Geese Alopochen aegyptiaca overrides environmental factors in determining productivity of Black Sparrowhawks Accipiter melanoleucus

We studied a population of Black Sparrowhawks Accipiter melanoleucus that has recently colonized the Cape Peninsula, South Africa. Black Sparrowhawks are winter breeders: over most of their range winters are dry, but the Cape Peninsula has a Mediterranean climate, with most rain falling in winter. The birds bred at an average density of 38 pairs/100 km². Monitoring of 70 breeding attempts by 26 pairs showed that the birds favoured large stands of trees for breeding. Birds breeding in smaller stands were more randomly spaced, dispersion being determined by habitat availability. Parameters related to climate, habitat and aspects of nest-site selection failed to predict the birds' productivity despite the fact that they had recently colonized a novel climatic window. Rather, productivity was best explained by the probability of nest usurpation by highly aggressive Egyptian Geese Alopochen aegyptiaca . Pairs encountering Goose usurpation problems raised an average of 0.76 chicks per breeding attempt, compared with 1.58 chicks for pairs without Geese. The only defence against nest usurpation by Geese appears to be the construction of multiple nests, an option most available to and most exploited by birds breeding in large stands of trees.     

Nestbox provisioning in a rural population of Eurasian Kestrels: breeding performance,nest predation and parasitism

The breeding biology of the Eurasian Kestrel Falco tinnunculusin nestboxes in farmland was studied to test for differences between artificial and natural sites. We report on the direct effect of nestbox provisioning on some life-history traits and how nestbox use affects nest predation and parasitism. Five types of nest-sites were available: nestboxes on poles and trees (artificial sites), stick nests on trees, stick nests on pylons and holes in buildings (‘natural’ sites). The Kestrel population increased from 23 pairs in 1993 (prior to nestbox installation) to 55 in 1998 as nestboxes were provided. In general, pairs breeding in trees started to lay later than those nesting in nestboxes on poles or in building holes, but this difference was probably associated with habitat quality rather than nest type. Differences in clutch size were found between nest-sites in some years, and were associated with laying date and, probably, with variation in territory quality. Using only data from successful nests, pairs breeding in nestboxes produce more fledglings than those in building holes or pylons. The frequency of nest predation was higher in natural sites than in nestboxes. The number of fledglings from pairs breeding in nestboxes was higher than from those breeding in old stick nests in trees when all nests were considered. Nestbox provisioning had no effect on the occurrence of the ectoparasite Carnus hemapterus, but chicks from nestboxes showed higher intensity of infection. Our results suggest that nestbox provisioning increases reproductive success and the frequency of nest predation or intensity of parasite infestation in Kestrels.     

Breeding adaptations of Franklin's gull (larus pipixcan) to a marsh habitat

The behaviour and ecology of Franklin's gull were studied at Agassiz National Wildlife Refuge in northwestern Minnesota to determine the adaptations of the species for nesting in marshes. Two factors seemed to be important in colony site selection: cattail dispersion pattern and cattail density. Franklin's gulls prefer to nest in cattail areas closest to open water. The number of nests per unit area decreased as cattail density increased. Nest site selection is dependent on aggression and visibility. Visibility from nest level is the result of cattail placement and height. The distance between nests was directly correlated with visibility. Aggression by gulls on nests was lowered experimentally by decreasing visibility and raised by increasing visibility. Nest platforms were constructed of cattail material, and were attached to cattail stems. Nest material was added to the nests throughout the incubation and brooding period. Material was usually added following nest relief. The egg laying period was from 6 to 28 May. There was more synchrony of egg laying in sub-areas of the colony than in the colony as a whole. Successive eggs in clutches were laid at 24- to 48-hr intervals. The distance between nests decreased during the season as pairs filled in areas that were not defended. Territorial pairs defended an area up to 10 m from their stations prior to egg laying, but defended only the area within 3 m of their nests during incubation. Both members of pairs incubated the eggs and cared for the young. The incubation period was 24 days. The primary predators on adults and young were marsh hawk, great horned owl and mink. Franklin's gulls do not eat eggs or young of gulls. Adults fed on earthworms, insects and grain. Most marked adults fed within 16 km of the colony. Chicks were fed primarily on earthworms. The hatching period was from 30 May to 21 June. Chicks of all ages tested on a visual cliff apparatus were able to perceive the drop. Chicks tested on a 30-degree incline apparatus walked up it when 6 days old and younger, and walked down at 12 days of age and older. Brood mobility was less than in ground nesting species of gulls. In an undisturbed colony the chicks remained on the nest platforms until they were 25 to 30 days old although they were capable of swimming shortly after hatching. Individual recognition between parents and chicks appeared later in this species than in ground-nesting gulls. Adults accepted alien chicks (experimentally exchanged) that were younger than about 14 days old until their own chicks were over that age. Adults accepted larger and older broods than their own, as well as broods of mixed ages. Chicks began to react differently to strange adults at about 16 days of age. The breeding chronology of Franklin's gull is compressed when compared to that of other gulls. Possible selection pressures affecting this synchrony are discussed. The behaviour of the marsh-nesting Franklin's gull is compared with that of typical ground-and cliffnesting gulls; the possibility that the ancestral gull may have been a marsh nester is discussed.     

Nest orientation and hatching success of Black Kites Milvus migrans in Spain

An analysis of the orientation of 182 nest sites of the Black Kite Milvus migrans in two areas in south and central Spain found that orientations toward the east were preferred. In southern Spain an analysis of the relationship between nest orientation and hatching success showed that success was lower among the nests located in non-preferred orientations, with some inter-annual variation. The tendency to orientate nests toward the east was greater among the early nesting pairs and the effect that the orientation had on the hatching success was also greater than in late nesting pairs. The data suggest that rainfall and prevailing winds were the main factors conditioning nest orientation.     

Parental attendance and squatting in the Kittiwake Rissa tridactyla during the rearing period

Parental attendance was studied in 1991 in the Cap Sizun Kittiwake colonies (Brittany, France). After a period of continuous guarding lasting on average 22 days, parents left their chicks unattended. Thereafter, parental attendance decreased regularly until fledging. The chick age when first left alone was on average 3 days lower for large broods than for single-chick broods. Moreover, whatever the brood size, chicks from late nests were younger when left unattended. Parental age affected the initiation of first absence. Younger parents reduced their attendance sooner than older parents. About 80% of the nests with chicks were visited by other adults at least once during the absence of the parents, and 50% were visited in the 3 days following the first absence of the breeders. These squatters were mainly failed breeders and prebreeders looking for a future breeding site. The results are discussed in terms of costs and benefits of chick neglect and comparisons were made with data from other studies in North Atlantic and Alaskan colonies. This reflected the flexibility of adult behaviour in relation to brood size and food availability.     

Translocation of threatened New Zealand falcons to vineyards increases nest attendance, brooding and feeding rates

Anthropogenic landscapes can be rich in resources, and may in some cases provide potential habitat for species whose natural habitat has declined. We used remote videography to assess whether reintroducing individuals of the threatened New Zealand falcon Falco novaeseelandiae into a highly modified agricultural habitat affected the feeding rates of breeding falcons or related breeding behavior such as nest attendance and brooding rates. Over 2,800 recording hours of footage were used to compare the behavior of falcons living in six natural nests (in unmanaged, hilly terrain between 4 km and 20 km from the nearest vineyard), with that of four breeding falcon pairs that had been transported into vineyards and nested within 500 m of the nearest vineyard. Falcons in vineyard nests had higher feeding rates, higher nest attendance, and higher brooding rates. As chick age increased, parents in vineyard nests fed chicks a greater amount of total prey and larger prey items on average than did parents in hill nests. Parents with larger broods brought in larger prey items and a greater total sum of prey biomass. Nevertheless, chicks in nests containing siblings received less daily biomass per individual than single chicks. Some of these results can be attributed to the supplementary feeding of falcons in vineyards. However, even after removing supplementary food from our analysis, falcons in vineyards still fed larger prey items to chicks than did parents in hill nests, suggesting that the anthropogenic habitat may be a viable source of quality food. Although agricultural regions globally are rarely associated with raptor conservation, these results suggest that translocating New Zealand falcons into vineyards has potential for the conservation of this species.     

Philopatry and colony fidelity of Shags Phalacrocorax aristotelis on the east coast of Britain

Shag Phalacrocorax aristotelis colonies from the Firth of Forth south to the Fame Islands (SE Scotland and NE England) were surveyed in 1982 and 1983 for nesting Shags ringed as chicks or adults in the previous 20 years. On average, 5% of 863 Shags ringed as chicks were breeding away from their natal colony, and only 1% of 401 marked adults had left their breeding colony. The proportion p of chicks that settled at or beyond distance D from the natal colony followed the relationship p = 0.263D-^0.771, implying that more Shags moved 10 km or beyond to breed than expected from diffusion models or a constant-rate dispersal model; adjusted for birds that settled outside the study area, the relationship was p = 0.314D^-0771. There was no effect of colony size on emigration rate, but females showed a greater tendency to settle away from the natal colony than did males. At the natal colony, more males (69%) than females (47%) nested within 300 m of their birthplace. Two mechanisms appear to determine where a Shag settles to breed: a navigational one governing the return to the natal colony, plus the competitive process of nest-site establishment.     

Cooperative breeding, mate guarding, and nest sharing in two parrot species of New Caledonia

We provide evidence for cooperative breeding in two endemic parrot species of New Caledonia, the New Caledonian Parakeet (Cyanoramphus saisseti) and the Horned Parakeet (Eunymphicus cornutus). We intensively monitored 11 breeding attempts in two nests of New Caledonian Parakeets over 5 years, and noticed that two males of different size fed the female and the chicks in each nest. During one breeding attempt, the larger male guarded the female and the smaller male tried to copulate with her inside the nest. Genetic analyses showed that males shared paternity. During 17 breeding attempts in 11 Horned Parakeet nests, we observed two pairs sharing a nest on one occasion but we never saw feeding helpers.     

Blue penguin (Eudyptula minor) nest distribution and breeding success on Otago Peninsula, 1992 to 1998

Abstract

Annual counts of nests with eggs or chicks (known nests) were made at blue penguin (Eudyptula minor) breeding sites on the Otago Peninsula in each November from 1994 to 1997. Although the population has doubled to an estimated 600 known nests over this period, the number of breeding sites on the Otago Peninsula has reduced since the 1970s. Breeding success at three areas at Taiaroa Head were monitored by regular nest checks in the breeding season from 1992 to 1998. At Taiaroa Head reproductive success ranged from 41 to 78% at the three sites during the seven‐year study and was generally higher for pairs nesting in nest boxes than for those in burrows. The percentage of breeding pairs that laid a second clutch after fledging at least one chick from their first clutch (double brooded) varied between seasons (0–48%) and was correlated with the date of the onset of breeding. Egg loss, possibly through predation by Norway rats (Rattus norvegicus), influenced the significantly lower reproductive success at one area (Area A) at Taiaroa Head during the 1996 season.     

Survival and non-breeding of adult Common Guillemots Una aalge

Annual survival of colour-ringed Common Guillemots Uria aalge with at least 1 year of breeding experience was measured in five study areas on the Isle of May, southeast Scotland from 1982 to 1993. Annual survival averaged 94.9%. There were no significant sex, year or area differences. Between 5% and 10% of the birds known to be alive in any year did not breed, and on average such birds appeared to survive less well (87%) than breeders (95%). Non-breeding did not occur randomly within the population, and 6% of birds accounted for 47% of the cases of non-breeding. It appeared that non-breeding in Common Guillemots on the Isle of May was socially induced with most cases occurring after an individual had lost its site.     

Breeding biology and breeding success of the Lesser Grey Shrike Lanius minor in a stable and dense population

The Lesser Grey Shrike Lanius minor is highly endangered throughout Europe, having declined markedly in abundance and range. Long-term changes in climate and agricultural practices have been identified as the main reasons for its decline. To determine which factors influence short-term changes in breeding success, we examined several aspects of its breeding biology. Our investigation revealed that our study area bears a large and stable population of this species. In 1996 and 1997, we recorded 84 and 77 breeding pairs in an area of 20 km², with an average of 4.20 and 3.85 pairs/km² respectively. Data on breeding density, clutch size and fledging success from 1989 to 1997 (excluding 1992) indicate a stable breeding population with a constant high breeding success. Reproductive success declined through the season, mainly through seasonal variation in clutch size rather than chick mortality. However, breeding success was generally high (69% and 79% of the nests produced chicks], with low hatching failure and few nest losses. The main cause of breeding failure was nest predation (at least 50% of nest losses), mainly by magpies (at least 66% of depredated nests). Although in this population the Lesser Grey Shrike tends to aggregate in clusters, breeding density had no obvious effect on breeding success and nest predation.     

Fitness consequences of helping behavior in the western bluebird

We examined the fitness consequences of helping behavior inthe western bluebird (Sialia mexicana) at Hastings Reservationin Carmel Valley, California, USA, and tested hypotheses forhow helpers benefit from engaging in alloparental behavior.Both juvenile and adult western bluebirds occasionally helpat the nest During a 12 year period, all adult helpers and mostjuvenile helpers were male. Helpers usually fed at nests ofboth their parents and rarely helped when only one parent waspresent. The frequency of pairs with adult helpers was only7%, but nearly one-third of adult males helped among those withboth parents on the study area. At least 28% were breeders whosenests failed. The propensity to help appears to depend uponparental survival, male philopatry, and the breeding successof potential helpers. Feeding rates were not increased at nestswith juvenile helpers, apparendy because breeding males reducedtheir feeding rates. In contrast, adult helpers increased theoverall rates of food delivery to the nest in spite of a reductionin the number of feeding trips made by both male and femaleparents. Helpers did not derive any obvious direct fitness benefitsfrom helping, but they had greater indirect fitness than nonhelpersdue to increases in nestling growth rates and fledging successat their parents' nests. Helpers fledged fewer offspring intheir first nests than did nonhelpers, suggesting that theywere birds with reduced reproductive potential. Although wehave not yet measured the effect of extrapair fertilizationson the fitness benefits of helping, we calculated the differencein fitness between helpers and nonhelpers as a function of thepotential helper's paternity when breeding independently andhis father's paternity in the nest at which he might help. Inconjunction with constraints on breeding and indirect fitnessbenefits, we predict that relatedness of males to the youngin their own as well as their parents' nests will influencehelping behavior in western bluebirds.     

Aspects of the breeding biology of the Chinspot Batis Batis molitor in Acacia savanna in Swaziland

Some aspects of the breeding ecology of the Chinspot Batis (Batis molitor) were studied in Mlawula Nature Reserve, north-eastern Swaziland. Nests were predominantly built in thorny bushes or trees. Eggs were laid between 20 September and 2 January. However there was a definite peak in November, during which the majority of eggs were laid. Nesting success in the Chinspot Batis was over 30%, while fecundity was 0.65 fledglings/pair/annum. Except for a single occasion, pairs did not double brood unless breeding failed or fledged chicks disappeared. Replacement nests, however, were the norm where a previous nest had failed. Adult batises were observed to feed predominantly on caterpillars and moths. Observations at the nest confirmed that batises fed predominantly moths and caterpillars to their nestlings. The rate at which nestlings were fed depended on their age, older chicks being fed more frequently than younger ones. The correlation between feeding rate and nestling age, and between feeding rate and fledgling age, was significant. In contrast to nestlings, younger fledglings were fed at a higher rate than older ones.     

Load Lightening in Southern Lapwings: Group‐Living Mothers Lay Smaller Eggs than Pair‐Living Mothers

Females of some cooperative‐breeding species can decrease their egg investment without costs for their offspring because helpers‐at‐the‐nest compensate for this reduction either by feeding more or by better protecting offspring from predation. We used the southern lapwing (Vanellus chilensis) to evaluate the effects of the presence of helpers on maternal investment. Southern lapwings are cooperative (some breeding pairs are aided by helpers), chick development is precocial, thus adults do not feed the chicks, and adults offer protection from predators through mobbing behaviors. We tested whether southern lapwing females reduced their reproductive investment (i.e. load‐lightening [LL] hypothesis) or increased their investment (i.e. differential allocation hypothesis) when breeding in groups when compared with females that bred in pairs. We found that increased group size was associated with lower egg volume. A significant negative association between the combined egg nutritional investment (yolk, protein, and lipid mass) and group size was observed. Chicks that hatched from eggs laid in nests of groups were also smaller than chicks hatched in nests of pairs. However, there was no relationship between the body mass index of chicks, or clutch size and group size, which suggests that such eggs are, simply, proportionally smaller. Our results support the LL hypothesis even in a situation where adults do not feed the chicks, allowing females to reduce investment in eggs without incurring a cost to their offspring.     

Prolactin and parental behavior in Adélie penguins: effects of absence from nest, incubation length, and nest failure

Adélie penguin (Pygoscelis adeliae) males and females, nesting in Antarctica, alternate attendance at the nest with absences of many days to forage at sea. We investigated the importance of tactile input from egg and chicks on prolactin levels by observing nest attendance patterns and obtaining blood samples (1) during the first nest exchange of the incubation stage, (2) from birds whose incubation period was artificially increased or decreased by about 10 days, and (3) from birds whose nests had failed. Prolactin levels in females after 8 to 11 days of absence from the breeding colony did not differ from those in incubating males and did not change after females resumed incubation. Moving eggs between nests resulted in nests in which chicks hatched after about 26, 36 (normal), or 46 days. Duration of incubation did not affect prolactin levels in the parents measured during incubation, at the pip stage, hatch stage, or early brood stage. Adults first left their chicks unguarded on about the same calendar date, regardless of chick age. However, chicks from long incubation nests averaged 8 days younger when they were left unguarded than chicks from control or short-incubation nests. In females, there was no effect of nest failure on prolactin levels. In males, prolactin levels were slightly lower after nest failure than in males tending nests. Testosterone was significantly higher in males after nest failure than in males still tending nests. Prolactin is elevated in Adélie penguins as part of the program of cyclical hormonal changes that accompany the lengthy reproductive season and is relatively independent of tactile input. Sustained prolactin secretion is probably required for the maintenance of parental behavior in offshore feeding species that must be absent from the nest for many days at a time.