Low Hatching Success Research Articles

Intraspecific variation in size and density of Avocet colonies: effects of nest‐distances on hatching and breeding success

In many colonial bird species there is considerable intraspecific variation in colony size and inter‐nest distance (colony density). Possible causes of this variation and its effects on hatching success (survival of eggs) and breeding success (probability of a pair raising chicks) were studied in 48 Avocet Recurvirostra avosetta colonies in Schleswig‐Holstein (Germany) between 1991 and 1996. Colony density was influenced by time of year and habitat (categories: island or mainland, close to or far from feeding grounds). Colonies on islands had the highest densities. When all available space at a colony site was used, colonies became very dense (mean nearest‐neighbour nest distance less than 1 m). Colony size (number of clutches) was influenced by time of year, but not by habitat. Hatching success was low in high density colonies and in very low density ‘colonies’ (single nests) and high over a broad range of intermediate nest densities. The low success rate of single nests was caused by a very high predation rate, whereas the low success rate in very dense colonies was caused by a high rate of nest abandonment. Nest abandonment in very dense colonies was associated with a high level of aggressiveness among Avocets during the egg‐laying period. Due to territorial behaviour, Avocets seemed to be expelled from the densest breeding sites. In very dense colonies, high frequencies of clutches of unusual size occurred due to conspecific nest parasitism. The number of Avocets taking part in attacks on potential egg predators was small and (in colonies of more than one clutch) depended neither on colony size nor on colony density. Despite a low hatching success in very dense colonies, individuals breeding in the densest colonies had significantly better chances of raising chicks than Avocets breeding in less dense colonies. Coloniality seemed to be obligatory for Avocets in order to ensure hatching success. The size and density of colonies seemed to be associated with the availability of suitable nesting habitats (islands).

Dynamics of a clinal hybrid zone and a comparison with island hybrid zones of flycatchers (Ficedula hypoleuca and F. albicollis)

AbstractBreeding data for pied flycatchers Ficedula hypoleuca and collared flycatchers F. albicollis, from 47 localities in the Czech Republic and Slovakia, were analysed. We show that co‐existence and hybridization were mainly restricted to a rather narrow, latitudinal cline. The distribution of the two flycatchers coincides with topography and habitat, collared flycatchers dominating in warmer habitats than pied flycatchers. Maintained co‐existence within the same locality was the exception rather than the rule and most matings occurred in allopatry. In sympatry hybridization occurred at a frequency that was much lower than expected from random mating. Hybrids had low hatching success but some hybrids were apparently fertile. Shortage of conspecific mates may explain why individual birds engage in mixed species pairs. The proportion of pied flycatchers that was involved in mixed pairs was high and increased with decreasing relative frequencies of pied flycatchers in the population. The proportion of collared flycatchers involved in mixed pairs was low, reflecting the higher relative frequency of this species in most mixed populations. Comparisons suggest that fewer hybrids are breeding in the Central European, clinal hybrid zone than in the isolated hybrid zones of the Baltic Isles. Moreover, hybrid fertility was apparently higher in the island zones than in the clinal zone. We suggest that more extensive introgression in the isolated island populations has resulted in an increase in hybrid fitness by an accumulation of fertile individuals of mixed ancestry (i.e. F2, F3 … Fn‐hybrids) acting as bridges for gene exchange. Differences in the dynamics of the two classes of hybrid zones, especially in pattern of gene flow, may explain these differences in frequency and fertility of hybrids.

Egg production and hatching success in the peri-Antarctic copepod Calanus simillimus

In situ rates of egg production and hatching success are reported for Calanus simillimus , one of the most abundant calanoid species in peri-Antarctic regions, during the Italian ‘Italics’ cruise in the Straits of Magellan in March-April 1995. Low fecundity (8.6 eggs female −1 day −1 ) and fecal pellet production (0.8 fecal pellets female −1 day −1 ) in this period indicate that the species was feeding very poorly. Sixty-six of the 126 females sampled did not produce eggs and 80 of these did not produce any fecal pellets during the 24 h period of incubation. Striking abnormal naupliar and embryonic development was recorded in 81.8% of the eggs spawned. Aberrant eggs did not undergo normal cleavage, and failed to develop to hatching. Deformed nauplii were asymmetrical and presented strong anatomical anomalies in the total body length and number of swimming appendages. These results are discussed in the light of recent findings on the causes of low hatching success in copepods.

A comparison of Herring Gull Larus argentatus and Lesser Black-backed Gull Larus fuscus nest sites: their characteristics and relationships with breeding success

Nest sites used by Herring Gulls and Lesser Black-backed Gulls in a mixed colony were compared. Correlations between features surrounding a nest and breeding success at different stages of the breeding cycle are presented. Lesser Black-backed Gulls nested on more vegetated and flatter areas than did Herring Gulls, even though the latter species had a lower hatching success at less vegetated sites. The difference in the general topography of nest sites between the species suggests that the Lesser Black-backed Gull, through an individual defence strategy, may be better adapted to use sites which are accessible to ground predators than the Herring Gull. The fledging success of Lesser Black-backed Gulls tended to increase with an increased proportion of relatively tall vegetation close to the nest. The Lesser Black-backed Gull may therefore be able to leave its young unattended and rely on their concealment for protection against predators. In contrast, the Herring Gull may rely more on parental vigilance to protect young. More frequent attendance by adult Herring Gulls at the nest site during chick rearing compared with Lesser Black-backed Gulls supports this hypothesis.

Shark and skate egg-cases cast up on two South African beaches and their rates of hatching success, or causes of death

Collections of chondrichthyan egg-cases cast ashore at two sites along the South African coastline were identified and examined for cause of mortality. A total of 574 egg-cases collected from False Bay could be attributed to five species of scyliorhinid shark, two skates and the elephantfish or chimaera, while the 538 egg-cases collected from Port Alfred belonged to four scyliorhinid sharks and two skate species. At both sites eggs of shy-sharks of the genus Haploblepharus made up more than 70% of the samples, followed by skates (5% in False Bay and 19% in Port Alfred) and then catsharks of the genus Poroderma (1 and 7% respectively). Haploblepharus egg-cases generally displayed relatively high rates of hatching success of over 60% and predation rates of 18-30%. Haploblepharus fuscus was the exception with a low hatching success of 37% and a predation rate of 40%. Poroderma egg-cases suffered predation losses of 43%, and had a hatching success of 47%. Skate egg-cases displayed non-predator induced egg mor...

Interactive effects of food shortage and predation on breeding failure of black-legged kittiwakes:indirect effects of fisheries activities and implications for indicator species

We investigated the roles of food shortage and predation in anticipated breeding failure of black-legged kittiwakes Rlssa trldactyla at Great Island, Kr~tless Bay, Newfoundland, Canada In 1992 and 1993, following widespread failure in 1991 Reduced and delayed availability of capelin Mallotus villosus, plus elimination of previously plentiful fish offal and discards following an eastern Canadian groundfish moratorium in 1992, induced food-stress on kitt~wakes and on large predatory Larus gulls. Breeding was late, a low proportion of pairs laid eggs, and egg and clutch sizes were small, indicating that feeding condlt~onsfo r kittiwakes were poor early in the season. Extreme food-stress resulted in low breed~ng success of Larns gulls that turned to kittiwake eggs as an alternate food source. Forced egg predation by great black-backed gulls Larus marinus was the primary cause of low hatching success (10 to 11 %) in both years. Durations of incubation and chick-rearing shifts decreased following the inshore arrival of capelin, and chicks that hatched after capelin arrival survived longer than earlier hatched chicks. Unattended nests were uncommon, probably in response to predation. In 1992, earlier hatching, later capelin arrival, and apparent lack of alternate prey resulted in many chicks starving and poor fledging success (7%). In 1993, food appeared to be more available both before and after capelin arrival, parents were able to provision chicks, and fledging success was normal (68%) The interactive effects of food shortage and predation have important linplications for the use of kittiwakes as indicator species and for the indirect effects of fishery activities on seabird interactions. Kittiwake productivity also reflects the resource base of their predators and caution is required when linking kittiwake breeding success to prey abundance. Moreover, fishery activities, such as the eastern Canadian groundfish morator~umth at eliminated fish discards and offal for large scavenging gulls, can have profound second-order effects on other seabird species that are preyed on by scavengers.

The diatom Thalassiosira rotula affects reproductive success in the copepod Acartia clausi

Fecundity, egg viability and fecal pellet production are reported for Acartia clausi females collected in the Bay of Naples, Italy, from April to October 1992 and fed either with a diatom (Thalassiosira rotula) or dinoflagellate (Prorocentrum minimum) diet, at food saturated conditions. The diatom diet significantly reduced both egg and fecal pellet production as well as hatching success. Blockage of egg development occurred with both axenic and non-axenic cultures of T. rotula, suggesting that inhibitors were provided by the diatoms and not by the bacteria associated with diatom cultures. Low hatching success was also artificially induced by exposing newly spawned A. clausi eggs to high concentrations of diatom extracts, indicating the presence of deleterious, inhibitory compounds blocking copepod embryogenesis. Fecundity and hatching success diminished significantly with female age. In contrast, female longevity was not significantly modified by food type. The presence of males did not significantly alter fecundity or egg viability. Females continued to produce viable eggs throughout the period of incubation, with and without males, in both food conditions, indicating that remating is infrequent and not necessary to sustain viable egg production in this species. The succession in low and high population densities may therefore be the outcome of variations in survival rates of eggs, rather than reproductive protential perse; such variations may strongly depend on the adult copepod diet.

The effect of multiple mating on female reproductive success in the simultaneously hermaphroditic land snail Arianta arbustorum

The simultaneously hermaphroditic land snail Arianta arbustorum mates several times in the course of a reproductive season. Repeated matings might be adaptive for the male function of A. arbustorum to inseminate several "females." We designed an experiment to evaluate the effects of repeated mating on the female reproductive success of this hermaphrodite. Reproductive traits and survival were examined over 2 years in individuals that copulated several times per year (snails were kept in pairs), in individuals that copulated twice (once at the beginning of each year) or once (at the beginning of the first year only), and in individuals prevented from copulating (they were kept isolated). Copulations were not always reciprocally successful: 3 of 57 snails (5.3%) failed to produce fertile eggs, although their mates reproduced successfully. Similarly, 2 of 15 pairs (13.3%) failed to reproduce successfully. Snails allowed to mate repeatedly within each season tended to lay more eggs than snails that mated once per year. However, the numbers of hatchlings did not differ significantly between the two treatment groups, because eggs laid by snails allowed to mate repeatedly had a lower hatching success. Snails that remated in the second year laid more eggs that had higher hatching success, and thus produced more hatchlings than snails that mated once at the beginning of the first year only. Snails that were prevented from mating produced a few hatchlings (by self-fertilization) in the second year; their reproductive success was less than 1% of that of mated snails. Our results suggest that multiple mating is also adaptive for the female function of A. arbustorum by increasing female fecundity and fertility and serving as a hedge against unsuccessful copulations.

Contaminant Levels of Osprey Eggs and Prey Reflect Regional Differences in Reproductive Success

To determine if contaminants contributed to low hatching success of ospreys (Pandion haliaetus) nesting near Delaware Bay, we compared levels of organochlorines, mercury, and lead in addled and randomly collected eggs and potential prey from Delaware Bay to a successful population along the Atlantic Coat (<80 km from the Bay colony), a tributary of Delaware Bay. Eggs from Delaware Bay contained significantly higher levels of DDE, DDD, PCB's, dieldrin, and heptachlor epoxide than did Atlantic Coast eggs (P<0.008) and also had thinner eggshells (P=0.04); eggs from Maurice River had intermediate contaminant levels and eggshell thickness. Contaminant levels in potential prey from each region reflected levels found in eggs, suggesting that ospreys accumulated contaminants on their breeding grounds

Distribution, reproductive success, and population trend in the Dunlin Calidris alpina schinzii on the Swedish west coast

In 1989, the breeding population of the Dunlin in the provinces of Bohuslän and Halland on the Swedish west coast was surveyed. The total population size was estimated at a maximum of 44 pairs. The number of breeding pairs has declined during the 1980s and the population has been restricted to about 10 localities; 55% of the total population occurred at two sites. At two of the surveyed localities, hatching success varied considerably among years, reflecting variation in nest predation rate. An experiment with dummy nests suggested that vegetation height, and thus protective cover, does not influence the probability of predation. On average, 0.8 and 1.0 fledglings per pair were produced at the two localities. Estimates of maintenance of population size in one study area indicated that this subpopulation was not self-supporting, apparently due to low hatching success. No clear relationship was found between moderately decreased grazing intensity and the decline of the population during the last decade. In addition to habitat alterations, other factors seem to affect the population trend of the Dunlin on the Swedish west coast. The small population is vulnerable to unpredictable events, such as temporarily increased nest predation.

Population, productivity and DDT contamination trends of Northern Gannets (Sula bassanus) at Bonaventure Island, Quebec, 1967–1984

A comparison of the results of recent surveys of Northern Gannets on Bonaventure Island shows that the population increased from 16 400 pairs in 1976 to 21 100 pairs in 1984, which represents an annual increase of 3.2%. Hatching success was only 36–40% between 1966 and 1970, after which it increased to 58% in 1974 and then varied from 78 to 89% during 1976–1984. Net productivity now exceeds the level necessary to maintain zero population growth. The marked increase in breeding performance coincided with a significant decline in DDT and dieldrin residues in eggs, which suggests that toxic chemical contamination was responsible for the low hatching success between 1966 and 1970.

Toxicological investigations of pollutant-related effects in Great Lakes gulls.

Reproductive failure of a number of fish-eating birds was observed on the Great Lakes in the mid-1960s to mid-1970s. The herring gull (Larus argentatus) has been used as the primary monitoring species. The low hatching success observed in this species on Lake Ontario in the mid-1970s was due to loss of eggs and failure of eggs to hatch. Egg exchange experiments demonstrated that this was due both to the incubation behavior of adults and to direct embryotoxic effects. Decrease of nest attentiveness was demonstrated using telemetered eggs, but attempts to reproduce the embryonic effects by injection of pollutant mixtures into eggs were not successful. Reproductive success improved rapidly during the late 1970s and was normal by the end of the decade. Recent studies have focused on cytogenetic and biochemical changes and detailed analytical chemistry of residues. No changes in the rate of sister chromatid exchange over values determined in coastal colonies were observed. Elevation of hepatic aryl hydrocarbon hydroxylase activity, levels of highly carboxylated porphyrins, and changes of thyroid function have been found. The geographic pattern of these changes indicates that they are caused by xenobiotics, but it has not been possible to relate the changes to a specific chemical.

Artificial incubation of eggs of the green iguana (Iguana iguana)

AbstractSuccessful hatching of large numbers of artificially incubated eggs from the green iguana, Iguana iguana, are reported. Gravid females were captured at a nesting site in Summit Gardens, Soberania, Parque Nacional, Panama, and released into an enclosure with an artificial nesting area. Females dug their own tunnels and nest chambers or used artificial nest chambers for egg deposition. Eggs (n = 829) from 21 clutches were removed from the nests and artificially incubated. Average hatching success per clutch was 94.6% and the mean clutch incubation time was 92.1 days. A distinct odor was noticed in the incubation containers several days before the eggs began to hatch. At this time, the substrate layer was removed exposing the top surface of all eggs, and the eggs desiccated to some degree prior to hatching. High incubation temperature, hydric conditions, and egg arrangement are all implicated as contributing factors in low hatching success in previous studies using artificial incubation techniques.

The pair bond and divorce among Oystercatchers Haematopus ostralegus on Skokholm Island, Wales

Mate changes of Oystercatchers were followed over a 15‐year period. In 8.0% of instances, the pair split up between breeding seasons even when both members bred the second season. The likelihood of divorce was highest for birds aged five years, the modal age of first breeding. After divorce birds did not select an older or younger mate when re‐pairing. Low hatching success increased the chances of divorce. Divorce was not followed by significant changes in clutch‐size, laying date or nesting success (although females tended to be more successful).

Temperature and Other Factors That Regulate the Composition and Infrapopulation Densities of Bothriocephalus acheilognathi (Cestoda) in Gambusia affinis (Pisces)

Changes in mean infrapopulation densities of Bothriocephalus acheilognathi in Gambusia affinis followed a clear seasonal pattern in the ambient and thermally altered areas of Belews Lake, a North Carolina cooling reservoir that is devoid of piscivorous fish except in the headwaters. Highest infrapopulations occurred during fall and winter and lowest in mid to late summer. The composition of the infrapopulations varied seasonally. From late spring to late summer, the majority of worms were segmented (maturing) or gravid; this period coincided with time of recruitment. Beginning in October and continuing into May, nearly all (> 98%) of the worms were nonsegmented. The major shifts in composition occurred when surface water temperatures increased above 25 C in the spring and fell below 25 C in the fall. Laboratory studies showed conclusively that growth and development were stimulated at water temperatures above 25 C. Moreover, at temperatures above 25 C, mean infrapopulation densities declined significantly. It is suggested that the decline in mean infrapop- ulation densities could result from a temperature-dependent rejection response, selective mortality or an immune response. However, the best evidence points to competition for limited space or nutrient resources within the intestine of mosquitofish as the most probable cause for decline in parasite density. Egg maturation and hatching, and coracidium motility, were all found to be temperature dependent, with maximum activity occurring at 25 and 30 C; at 20 and 35 C, activity was depressed. The lower hatching success and briefer period of coracidium motility at 35 C may, in part, explain differences in the population biology of the cestode at the thermally altered and ambient temperature sites during part of the summer months.

Cytopathology of the brain and retina of embryonic surf smelt ( Hypomesus pretiosus) exposed to crude oil

In laboratory experiments, surf smelt ( Hypomesus pretiosus) embryos were exposed to 54 or 113 ppb of the seawater-accommodated fraction (SWAF) of Cook Inlet crude oil (CICO) for 3 hr per day, beginning 6 days after fertilization. Embryos 21 and 27 days old (just prior to hatching) exposed to CICO were examined for morphological abnormalities. The only tissues that showed morphological changes in both the 21- and 27-day-old CICO-exposed smelt were the forebrain and the neuronal layer of the retina: both contained numerous necrotic neurons. The retinal receptor cells appeared normal in 21-day-old exposed smelt; in contrast, in 27-day-old treated embryos the ellipsoid and myoid regions of the receptor cell inner segments were severely damaged. Further impact from the SWAF of CICO on developing smelt was indicated by a lower hatching success: approximately 10% in the exposed groups as compared to 50% in the controls.

Some Factors Affecting the Laying Date, Incubation and Breeding Success of the Manx Shearwater, Puffinus puffinus

SUMMARY (1) The breeding success and timing of laying of manx shearwaters breeding on Skokholm Island, Wales, are discussed. (2) Newly formed pairs have a lower hatching success (66-2%) than established pairs (79'1%). This is due to the fact that new pairs include birds without prior breeding experience and not to the newly formed pair bond per se. (3) When forming new pairs experienced breeding birds tend to mate with other experienced breeding birds rather than new breeders. (4) Divorce and burrow movement are both more likely after breeding failure than after success. (5) The timing of laying and the size of eggs laid are very constant from year to year, both for the population as a whole and for individual females. (6) The relationship of laying date and egg size to female age is described. (7) It is suggested that birds do not lay earlier than they do because, early in the season, the food supply would be inadequate to enable the adults to maintain continuous incubation. (8) Circumstantial evidence is presented suggesting that conditions for incubation improve during the incubation period.

Embryonic Mortality and Chromosomal Alterations Caused by Aroclor 1254 in Ring Doves

The breeding success of Ring Doves (Streptopelia risoria) fed Aroclor 1254 at 10 ppm was determined over two generations. Six pairs of birds were fed PCBs for three months, then allowed to incubate their clutch of two eggs. Eggs were then collected again for six months, at which time the birds were allowed to incubate another clutch. Results are given in Table 1. The low-hatching success of the second generation was due to heavy embryonic mortality. The age of embryonic death varied considerably but was mainly in the range of 3-8 days. This finding is at variance with that of Scott et al. (1), who found a significant decrease in hatchability of chicken eggs in the first generation with 10 ppm Aroclor 1248 for eight weeks and almost complete failure at both four and eight weeks at 20 ppm Aroclor 1248. In this case mortality occurred immediately before hatching. Eggshell thinning was not observed in either the first or second generation (2, 3). This is in agreement with the findings of Dahigren and Linder (4) for the pheasant (Phasianus colchicus) and Heath et al. (5) for the Mallard (Anas platyrhynchos). Cytogenetic studies were performed on 24 dove embryos at 3-6 days of incubation. Six embryos were from dove pairs not fed PCBs (control), 17 embryos were from PCB-fed (10 ppm in diet) pairs and one embryo was irradiated with 155

CLUTCH‐SIZE, INCUBATION AND HATCHING SUCCESS IN THE HOUSE SPARROW AND TREE SPARROW PASSER SPP. AT OXFORD

SummaryClutch‐size, incubation and hatching success were studied in P. domesticus and P. montanus in 1961 and 1963–64 at Oxford. The most frequent clutch‐size was four eggs in P. domesticus and five eggs in P. montanus. With one exception, colonies of P. domesticus showed no significant annual or local variations in its mean clutch‐size; in P. montanus, however, there were significant annual variations in the mean clutch‐size. Both species showed a seasonal increase followed by a decrease in their mean clutch‐sizes.Partial incubation occurred during the laying period of the clutch; sufficient incubation for continuous development of the embryo was apparently achieved when the last egg had been laid in clutches of two and three eggs in P. domesticus and in clutches of four eggs in P. montanus, but when the penultimate egg had been laid in larger clutches of both species. On average, hatching in P. domesticus occurred more or less synchronously in all eggs in clutches of two and three eggs, and in all eggs except the last one laid in larger clutches; the last egg in the larger clutches hatched up to a day after the others. It is suggested that this pattern of hatching was brought about by the pattern of incubation during the laying period.P. domesticus had a lower hatching success than P. montanus, probably because fewer of its eggs were fertile.

BREEDING SUCCESS AND POPULATION GROWTH IN A COLONY OF HERRING AND LESSER BLACK‐BACKED GULLS LARUS ARGENTATUS AND L. FUSCUS

SummaryThis paper describes the results of investigations into the factors affecting breeding success of the Herring and Lesser Black‐backed Gulls Larus argentatus and L. fuscus, in the large colony on Walney Island, northwest Lancashire, between 1962 and 1965. These investigations were concerned with the incubation period, and the first ten days after hatching.The survival of chicks to ten days is 67% in Herring Gulls, and 56% in Lesser Black‐backs. Most of these losses occur in the period just after hatching and are due to “cannibalism” by other gulls. This form of predation does not appear to be masking any effects from starvation or disease.The following factors contribute to egg or chick mortality:breeding too late (and, to a much smaller extent, too early); breeding in the open, as opposed to amongst cover; the facts that eggs in small clutches have a lower hatching success than those in large ones and that Herring Gull (but not Lesser Black‐back) chicks in small broods are less likely to survive to ten days than are those in large broods.Chick mortality after the first ten days is not certainly known. About 30% of the eggs laid gave rise to fledged young— or about one fledged chick per pair.In the Herring Gull, the average clutch size (2.56) is lower than that of the Lesser Black‐back (2.76). Both species show a seasonal decline in clutch size—this occurs earlier in the Herring Gulls than in the Lesser Black‐backs.The Walney population, which stood at about 700 pairs in 1950, had reached 12,000 in 1957, and is at present about 18–19,000 pairs. It is suggested that this increase may be linked to the greater availability, or exploitation, of human garbage in the Morecambe Bay area. The population explosion between 1950 and 1957 must have been partly due to massive immigration and could not have come about through natural increase alone.The possible influences of the gulls' behaviour on the population growth are discussed. There is no evidence of any “shock disease”, although the Walney colony is very crowded. “Cannibalism” is regarded, not as evidence of a failing food supply, but as an extension of the normal hunting behaviour of these omnivorous gulls; it will be an economical means of obtaining food only in a large, dense colony, such as Walney. It may be offset by increased breeding efficiency due to social factors.