Percentage Of Nests Research Articles

Is Cooperative Breeding Associated With Bigger Brains? A Comparative Test in the Corvida (Passeriformes)

AbstractThe cognitive demands of a social existence favour the evolution of relatively large brains and neocortices in primates. Comparable tests of sociality and brain size/structure in birds have not been performed, despite marked similarities in the social systems of birds and mammals. Here, we test whether one aspect of avian sociality, cooperative breeding, is associated with an increase in brain size across 155 species of the passeriform parvorder Corvida. Using conventional and phylogeny‐corrected statistics, we examined the correlated evolution of relative brain size and: the presence/absence of cooperative breeding, percentage of nests that are cooperative and cooperatively breeding group size. Most of the comparisons yielded non‐significant results, which suggests that cooperative breeding is not related to relative brain size in this parvorder. There are a number of potential explanations for our findings. First, changes in brain region size may be correlated with cooperative breeding without affecting overall brain size. Secondly, cooperatively breeding birds might not possess more complex social behaviour than non‐cooperatively breeding birds. Thirdly, relatively large brains might be ancestral in this parvorder. This may predispose them to evolve the range of complex behaviours found in this group, including extreme sociality. Finally, ecological and/or developmental factors might play a more significant role than social behaviour in the diversification of avian brain size. Assessing these alternatives requires more information on the neural and cognitive differences between bird species.

Habitat Structure and Breeding Parameters of the White StorkCiconia ciconiain the Kolno Upland (NE Poland)

Abstract. An investigation of the habitat structure in nesting territories and the breeding success of the White Stork population in an agriculture landscape of the Kolno Upland adjoining the Biebrza river valley was conducted in 1994–1997. From 85.7% (1997) to 96.8% (1994) of nests were occupied by pairs of storks. The percentage of nests without nestlings was exceptionally low (0%–5.7%). Broods with three nestlings made up the highest proportion, c. 41.7–44.6 % of all the nests occupied by pairs. The average number of nestlings in nests with fledged young was lowest in 1997 (2.53); in 1994–1996 it had been significantly higher (2.84–3.06). Pairs with nests sited up to 100 m from the nearest wet meadows in the river valley have a higher average breeding success in comparison with the pairs whose nests are sited farther away. The White Stork population tended to inhabit the area near the edge of the river valley. In the nesting territories (an area of 1 km radius around the nest site) cereal crops, meadow...

Islands in a desert: breeding ecology of the African Reed WarblerAcrocephalus baeticatusin Namibia

The continental African Reed WarblerAcrocephalus baeticatus,like its relative the Seychelles WarblerAcrocephalus sechellensis,breeds in isolated patches. We studied the mating system of the African Reed Warbler to see whether this species, like the Seychelles Warbler, shows co‐operative breeding. The African Reed Warbler is not polygynous. The majority breed monogamously (88%,n= 65), however in 12% of the territories three adult unrelated birds (mostly males) were observed participating in the brooding and feeding of nestlings, suggesting a polyandrous breeding system. Multilocus DNA fingerprinting revealed that the helping bird was unrelated to the pair birds. The percentage of nests with helpers was low compared to rates found in the Seychelles Warbler or Henderson Reed WarblerAcrocephalus vaughani taiti.This could be due to the scarcity of potential helpers or to the fact that, although limited, birds still had the opportunity to disperse within a meta‐population structure in search of vacant territories. The presence of helpers was associated with increased hatching success due to lower predation rates, but not with increased fledging success. Another possible benefit of helping behaviour in this species could be improved predator detection and mobbing. Nest predation was high and warblers tended to build their nests in the highest, most dense reed patches available in their territory. There was no relation between habitat quality, measured as insect food availability, and the occurrence of helpers.

Arbovirus infection increases with group size.

Buggy Creek (BCR) virus is an arthropod-borne alphavirus that is naturally transmitted to its vertebrate host the cliff swallow (Petrochelidon pyrrhonota) by an invertebrate vector, namely the cimicid swallow bug (Oeciacus vicarius). We examined how the prevalence of the virus varied with the group size of both its vector and host. The study was conducted in southwestern Nebraska where cliff swallows breed in colonies ranging from one to 3700 nests and the bug populations at a site vary directly with the cliff swallow colony size. The percentage of cliff swallow nests containing bugs infected with BCR virus increased significantly with colony size at a site in the current year and at the site in the previous year. This result could not be explained by differences in the bug sampling methods, date of sampling, sample size of the bugs, age structure of the bugs or the presence of an alternate host, the house sparrow (Passer domesticus). Colony sites that were reused by cliff swallows showed a positive autocorrelation in the percentage of nests with infected bugs between year t and year t+1, but the spatial autocorrelation broke down for year t+2. The increased prevalence of BCR virus at larger cliff swallow colonies probably reflects the larger bug populations there, which are less likely to decline in size and lead to virus extinction. To the authors' knowledge this is the first demonstration of arbovirus infection increasing with group size and one of the few known predictive ecological relationships between an arbovirus and its vectors/hosts. The results have implications for both understanding the fitness consequences of coloniality for cliff swallows and understanding the temporal and spatial variation in arboviral epidemics.

NESTING ECOLOGY OF RESIDENT LOGGERHEAD SHRIKES IN SOUTHCENTRAL FLORIDA

I studied the reproductive ecology of Loggerhead Shrikes (Lanius ludovicianus) in southcentral Florida from 1991 through 1993. Pairs were sedentary and defended territories year-round. Completed nests were found from late December to mid-May. Nesting peaked during mid-March with second and third nestings attempted from late March to late May. Sixty percent of all nests were built in blackberry bushes (Rubus betulifolius), but cabbage palm (Sabal palmetto) and wax myrtle (Myrica cerifera) also were used frequently. Mean nest height was 1.6 m and mean clutch size was 4.3 eggs. A mean of 17 days was required for incubation and the mean fledging period was 15 days. Nest failure occurred more often during the incubation than the nestling stage. The majority of nest losses were due to predation and inclement weather (49 and 20 nests, respectively). Mean hatching success was 87%, and 81% of chicks fledged successfully. Nesting success (percentage of nests that fledged at least one young) was 55%, and an analysis of other studies that used this measure detected significant clinal variation in Loggerhead Shrike nesting success, with success rate positively correlated with latitude. Unlike conspecifics in northern latitudes where second broods are considered rare, 96% of breeding pairs in Florida attempted second broods.

Breeding Biology of Brant on Banks Island, Northwest Territories, Canada

The numbers of brant ( Branta bernicla ) in the Pacific Flyway are relatively small compared to other populations of arctic geese and have declined from historic levels. Little information is available on brant from Banks Island, although the size of the island and its location in the western Canadian Arctic make it a potentially important nesting area for this species. In 1992-93, we documented the distribution of nesting brant on the southern half of Banks Island through aerial surveys and carried out ground studies at the colonies to document nesting chronology and reproductive parameters. Ten colonies were found in 1992 (n = 159 nests) and 42 colonies (including seven colonies that had been active in 1992) and five solitary nests were found in 1993 (n = 514 nests). Two-thirds (67%) of the nesting locations supported 10 or fewer nests. Most colonies (36 of 45) were located on small islands (mean = 248 m²) in inland lakes or large ponds, and the remaining colonies (n = 9) were located on the mainland near active snowy owl (Nyctea scandiaca) nests. In 1993, when June temperatures were milder and snow melted sooner than in 1992, mean date of clutch initiation was significantly earlier (12 June vs. 20 June in 1992; p < 0.001) and mean clutch size was significantly larger (3.8 vs. 3.5 in 1992; p = 0.02). An index of productivity for the 21 414 km² area surveyed in both years was much higher in 1993 (1339 young) than in the very late spring of 1992 (347 young). The number of adult brant on the survey area was similar in both years, and the lower productivity in 1992 was due primarily to fewer pairs' nesting that year. Smaller clutch size and lower nesting success may also have lowered productivity in 1992, but their effects appeared to be secondary. No correlation was found between colony size and clutch size, mean number of goslings hatched, or the percentage of nests that proved successful.

The influence of fragment size and edge on nest predation in urban bushland

To test the effects of habitat fragmentation and edge on the rate of nest predation in an urban ecosystem, 20 artificial nests each containing 2 plasticine eggs were distributed in each of 24 bushland sites in Sydney, Australia. the eastern yellow robin Eopsaltria australis was adopted as a target species, and variables of nests, eggs and nesting behaviour were manipulated in experiments. Sites ranged in size from 3.8 ha to 14717 ha and were divided into three size classes: 1) 0–10 ha. 2) 11–100 ha and 3) ≥101 ha. Nests were positioned either around the edge of the fragment (within 50 m from the fragment boundary) or within the centre of the fragment (&lt; 50 m from the fragment boundary). The predation rate was calculated as the percentage of nests that had one or both eggs damaged or removed after 15 d of exposure. Nest predation rates were high (average 70.6%) but were not affected by patch size or distance from fragment edges. Predators were identified by marks of the beak or teeth left in the plasticine eggs. Nest predators identified were birds, black rats, brown antechinus and ringtail possum, with the majority of predation being by birds (61.7%), Our findings differ from those of most previous studies of nest predation, and perhaps reflect the ubiquity of generalist predators and the degree of habitat modification throughout remnants of bushland in the urban environment.

Variability in Nest Survival Rates and Implications to Nesting Studies

-We used four reasonably large samples (83-213) of Mallard (Anas platyrhynchos) and Blue-winged Teal (A. discors) nests on an interstate highway right-of-way in southcentral North Dakota to evaluate potential biases in hatch-rate estimates. Twelve consecutive, weekly searches for nests were conducted with a cable-chain drag in 1976 and 1977. Nests were revisited at weekly intervals. Four methods were used to estimate hatch rates for the four data sets: the Traditional Method, the Mayfield Method, and two modifications of the Mayfield Method that are sometimes appropriate when daily mortality rates of nests are not constant. Hatch rates and the average age of nests at discovery declined as the interval between searches decreased, suggesting that mortality rates were not constant in our samples. An analysis of variance indicated that daily mortality rates varied with the age of nests in all four samples. Mortality was generally highest during the early laying period, moderately high during the late laying period, and lowest during incubation. We speculate that this relationship of mortality to nest age might be due to the presence of hens at nests or to differences in the vulnerability of nest sites to predation. A modification of the Mayfield Method that accounts for age-related variation in nest mortality was most appropriate for our samples. We suggest methods for conducting nesting studies and estimating nest success for species possessing similar nesting habits. Received 21 January 1981, accepted 1 July 1981. INVESTIGATORS have attempted to determine the nesting success of birds for many purposes and have used diverse methods as they studied species with different breeding strategies in a wide range of habitats. One characteristic common to most studies is the method used to calculate hatch rates: the percentage of nests in an observed sample in which at least one egg hatched (referred to as the Traditional Method in this paper). Several investigators (Lack 1954: 74, Coulson 1956, Hammond and Forward 1956, Peakall 1960) recognized that hatch rates calculated in this way were biased. Hammond and Forward (1956) warned, Neglect of consideration for the length of time nests are under observation as compared to the total period they are exposed to predation would lead to a recorded success higher than that actually occurring. Eggs found in older nests are more likely to hatch than those found in younger nests, because they have already survived a period of risk to which the latter have yet to be exposed. By following this reasoning to the ultimate, it is clear that only samples of nests found on the day they are initiated will yield an unbiased hatch rate. The bias will increase with the average age of nests at discovery. Mayfield (1961) proposed a method that accounts for bias related to the age of nests at discovery by introducing into the calculations the period of time nests are under observation. Mayfield's Method will greatly reduce the bias inherent in the hatch rate calculated by the Traditional Method if daily mortality rates are reasonably constant for all nests in the sampled population. Some progress has also been made in analyzing nesting data for which daily mortality rates are not constant. Mayfield (1961, 1975) and Johnson (1979) described a method of calculating nest success when daily mortality varies among laying, incubation, and nestling stages. Johnson (1979) also proposed a method to use when the daily mortality of nests varies between population components such as yearling and older nesters. These methods will be described later in this paper. The researchers who developed these methods often depended upon hypothetical population models or pooled samples from studies conducted over a period of years and sometimes in different areas. Our study is an attempt to evaluate these methods by applying them to four reasonably large samples of nests 77 The Auk 99: 77-87. January 1982 This content downloaded from 207.46.13.189 on Thu, 04 Aug 2016 04:31:18 UTC All use subject to http://about.jstor.org/terms 78 KLETT AND JOHNSON [Auk, Vol. 99 of two species, Mallard (Anas platyrhynchos) and Blue-winged Teal (A. discors), that were observed during 2 yr on a single study area. The specific purposes of this paper are (1) to evaluate the variation in daily mortality rates in four samples of nests, (2) to determine the importance of variation in estimating hatch rates by the methods listed above, (3) to discuss the appropriate methodologies for evaluating our data, and (4) to recommend methods to researchers studying species with similar characteristics.

Interspecific nest parasitism by redheads on islands in southeastern Alberta

I studied interspecific nest parasitism by redheads (Aythya americana) from 1976 to 1978 in a population of upland nesting ducks on artificial islands in southeastern Alberta. Of 685 duck nests, 19% were parasitized by redheads with a mean of 2.68 parasitic eggs per host nest. The proportion of nests parasitized increased with the density of host nests on the islands. There is also some evidence that the rate of parasitism was influenced by the nesting density of redheads. Mallards (Anas platyrhynchos) had the greatest percentage of nests parasitized by redheads whereas lesser scaup (Aythya affinis) had the largest number of parasitic eggs per nest. Redhead parasitism affected reproductive output of hosts by increasing nest desertion. Finally, the parasitic activity of redheads was reduced during a season characterized by drought conditions.

FORAGING, SEASONALITY AND NESTING OF SEYCHELLES SUNBIRDS NECTARINIA DUSSUMIERI

SummaryForaging and breeding behaviour of Seychelles Sunbirds Nectarinia dussumieri was studied for a total of four months on six islands in the Seychelles.Birds obtained nectar from indigenous and introduced plants directly (inserting the bill into the corolla‐tube), perched or hovering, or indirectly (piercing the corolla). Direct methods were used in plants with corolla‐tubes less than 20 mm (the length of birds' bills) and indirect methods in most longer flowers. Flowers with longer corolla‐tubes appeared to be preferred. In feeding groups, birds fed more rapidly if not involved in aggressive interactions, which may reflect defence of feeding areas.Insects were taken from the foliage of indigenous and introduced trees, using a variety of techniques. Flycatching was most prevalent in small‐leaved species, and upright probing in large‐leaved species. In Calophyllum inophyllum, which held very high densities of insects, hovering was used only in saplings, while other methods were used in both mature trees and saplings.The percentage of nests that were active declined from September to December‐January, suggesting a peak of breeding during this period, the first part of the northwest monsoon season. Examination of live birds and museum skins showed that wing‐moult occurs chiefly from January‐May, but males on Praslin also moult in August‐September.Nests varied in conspicuousness, being best hidden on Mahé and Silhouette, the only islands with populations of Seychelles Kestrels Falco araea. Males contributed to the earliest stages of nest building, but all later building, as well as all incubation and most feeding of young was done by females. Both sexes defended the nest area against other birds, especially those attempting to steal nest material. Males advertized by song from prominent perches near nests; females also sang occasionally.Males are larger in most dimensions than females, but no inter‐island differences were found. The species may have evolved duller plumage and larger size than related species, but this remains uncertain without further evidence on its origins. The clutch of one egg only represents a reduction from the normal clutch size of local mainland congeners.

Optimal Niche Space of the Redwinged Blackbird: Spatial and Temporal Patterns of Nesting Activity and Success

Nesting colonies of redwings in marshes are larger and tend to be more synchronous than colonies in upland habitats of comparable area, but the duration of nesting activity is longer in large colonies. These variations in timing are probably correlated with the phenology of the vegetation in nesting habitat and not with the size of the breeding colony. Earlier nesting may be selectively advanageous because of a seasonal trend of increasing predation. The survival value to redwings of large colony size and synchronous nesting, in the colonies studied, was a reduced predation rate on a percentage basis. In most large and small colonies, the percentage of nests predated was lower during the peak of nesting activity than later. The Holling predation model is applied as a possible interpretation of predation rates on different—sized nesting colonies. Larger colonies in uplands might reduce predation on individual nests, but colony size is probably limited by the abundance of certain resources, such as availability of suitable nest—sites or food supply. Solitary pairs of smaller colonies might also suffer less predation, but genetic exchange with marsh populations, where colonial nesting is advantageous, may prevent their occurrence.

A Colony of Sandhill Cranes in Mississippi

The small isolated colony of Florida sandhill cranes (Grus canadensis pratensis) in southeastern Mississippi was studied during 1963 through the spring of 1970. The important feeding and nesting habitats are boggy savannas and swamps. The total estimated population is between 38 and 40 birds. The egg-laying period was between April 4 and May 20. Thirty nests were found containing an average of 1.7 eggs per completed set. From a total of 51 eggs, 22 were collected for propagation purposes; 29 were left in the nests and 18 successfully hatched. Four nests were abandoned and none was destroyed by predation. The colony is endangered by pine plantations, drainage, an interstate highway, and increasing housing developments. The establishment of state, federal, or private refuges is recommended if the colony is to survive. SANDHILL CRANES IN MISSISSIPPI * Valentine and Noble 761 Variations in clutch size) hatchability, and weather prior to oviposition are unlikely to significantly affect the mean numbel of ruffed grouse per brood at hatching in southern Ontario. It will be necessary to account for gross variations in observed age ratios among years by other variables such as percentage of nests that are destroyed, phenology of nest destruction, renesting rate, and immature mortality rate.