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J Raptor Res. 29(4):265-267
¸ 1995 The Raptor Research Foundation, Inc.
Department of Biology, Nunez Community College, 3700 La Fontaine Street, Chalmette, LA 70043 U.S.A.
Department of Biochemistry, Louisiana State University Medical Center, 1100 Florida Avenue,
New Orleans, LA 70119 U.S.A.
KEY WORDS: Harris' hawk; group hunting; Parabuteo
unicinctus; Texas.
The degree of sociality appears to vary among Harris'
hawk (Parabuteo unicinctus) populations in the United
States, with group living being most frequent in the west-
ern part of the range. Mader (1975) found that 46% of
Harris' hawk nests he studied were attended by trios and
that groups varied in size from three to six hawks in
Arizona. Dawson and Mannan (1989) reported a mean
group size of 3.8 hawks per nest in Arizona, Bednarz
(1987) found 2.8 hawks per nest in New Mexico, and
groups of more than two hawks were rare at nests in Texas
(Griffin 1976, Brannon 1980). However, the Texas pop-
ulation of Harris' hawks has not been studied in detail,
and little is known of cooperative behaviors among Harris'
hawks nesting there. Group hunting in Harris' hawks has
been reported to occur in the deserts of Arizona (Mader
1975) and New Mexico (Bednarz 1987). This paper rep-
resents the first published accounts of group hunting be-
havior in Texas.
On 23 July 1994, at 2020 H, we observed an adult
male and female Harris' hawk (we identified sex of hawks
based on body size comparisons) perched on adjacent pow-
er poles approximately 60 m from each other along a
highway in Pecos County, 1.6 km north of Ft. Stockton,
Texas. The male initiated the hunt by flying high over
the road, and was followed closely by the female. Four
other adults (three males and one female), previously un-
seen, hppeared from low perches on the east side of the
road and followed the pair across the highway. The lead
male hovered briefly and then made a shallow dive, dip-
ping just above the ground cover at a desert cottontail
(Sylvilagus audubonii). The first adult female dove steeply
behind the male. Then the hawks executed a series of five
or six steep dives apparently missing the rabbit. Five of
the birds then landed on a single yucca (Yucca sp.). The
sixth hawk perched in a nearby mesquite (Prosopis juli-
flora) about 6 m away. After 1-2 rain, all six hawks chased
the rabbit, until they were lost from view in a low spot in
the landscape. No birds flew from this low area in 15 mln
of observation.
On 1 August 1994, at 0740 H, we again observed six
adult Harris' hawks roosting on power poles at the same
location described above. Two groups of two hawks were
perched on neighboring poles, a fifth hawk was perched
on an adjacent pole, and a sixth hawk (male) was perched
eight poles away (about 480 m). The fifth hawk soon joined
one of the perched pairs on a nearby pole. Then one
Harris' hawk flew to the next pole in line. Immediately
after it perched, another hawk flew toward it. As the
approaching hawk drew near, the first hawk vacated its
perch and flew to the next pole in line. The approaching
hawk then landed on the recently vacated perch. All five
hawks engaged in seven bouts of this "leap frog" behavior
(Bednarz 1988a) as they moved from perch to perch, ap-
parently group hunting. This method of hunting on the
move, or the move-search hunting tactic is often used by
Harris' hawks that are group hunting (Bednarz 1988a,
Dawson 1988). The "leap frog" behavior was briefly in-
terrupted two times when three Harris' hawks perched
side by side. At 0746 H, all five birds began pursuing a
cottontail and engaged in a series of stoops. One hawk
captured the rabbit, and the others landed on the ground
at the kill site.
We climbed a small hill to get a view of the kill site
and inadvertently flushed four of the five hawks from the
kill. One returned immediately to the kill while the re-
maining three perched on poles. Within about 5 min, these
three chased another cottontail. After making five stoops,
they perched together on a pole. Two of these hawks then
landed at the site of the rabbit kill, and one adult male
perched on a yucca under the power poles. At 0804 H,
an adult female carried the hindquarters of the cottontaft
to the adult male perched on the yucca. The female dropped
the hindquarters, and the male went down to it, presum-
ably to feed.
TDC also observed group hunting by four Harris' hawks
on two occasions in Webb County, Texas, in the early
1980s in April or May. North and east of Laredo, an adult
male Harris' hawk that was perched on a power pole
executed a steep dive into the tall mesquite brush. Three
other hawks (also perched on that pole) followed, diving
in succession. Further observation was obscured by the
vegetation. On a second occasion, two adult Harris' hawks
perched on adjacent fence posts, while two more adults
ran around a large prickly pear cactus (Opuntia engel-
mannii). The two perched hawks then joined the others
in attempting to flush and ambush a prey animal in the
prickly pear. The group eventually flew off without cap-
turing anything.
The observations of cooperative hunting near Fort
Stockton may not be particularly surprising--because group
hunting is common in a nearby (approximately 225 km
away) population in New Mexico (Bednarz 1988a). How-
ever, the observations in Webb County were distant (720
km) from the New Mexico populations. Nevertheless, it
is likely that gene flow occurs between the Texas, New
Mexico, and Arizona populations. Bednarz (1988b) found
that based on morphology alone, P. u. superior and P. u.
harrisi could not be easily differentiated, that skins of New
Mexico Harris' hawks were morphologically intermedi-
ate, and that clinal variations exist between populations
in the United States and Mexico. Because Harris' hawk
populations do not appear to be geographically isolated in
the United States, behavioral propensities for sociality pos-
sibly occur throughout.
Ecological factors may contribute to the incidence of
group living and cooperative hunting. Dawson (1988) sug-
gested that both the dense and thorny nature of the brush
encourage group hunting in Arizona. These Harris' hawks
hve in a habitat characterized by a complex understory
with an abundance of thorny cover available to prey an-
imals. Groups are more successful than individuals when
hunting in this terrain (Dawson 1988). Group hunting
has also been proposed as a way for Harris' hawks to
exploit large prey (e.g., jackrabbits, [Lepus spp.], Bednarz
1988a), and prey that is active only for a short period of
time, dawn and dusk (e.g. cottontails, and woodrats, [Ne-
otoma spp.], Bednarz and Ligon 1988, Faaborg and Bed-
narz 1990).
It is unusual for all Harris' hawks in a group to be
adults (Dawson and Mannan 1989, 1991a), and it is par-
ticularly unusual for six adults to hunt together in the
summer when exclusive territories are maintained (Daw-
son and Mannan 1991b). We do not know if this group
of adults aggregated because of nest failure. No nest or
juvenile birds could be seen in the vicinity. However, groups
in New Mexico appear to compete with each other when
hunting (J. Bednarz pers. comm.). Alternatively, the group
observed in Pecos County could have been composed of
nonbreeding adult floaters (wandering adults looking for
breeding territories). Similar social aggregations are formed
by resident hawks and transients in Arizona in the fall
and winter during nonbreeding (Dawson and Mannan
1991b). In New Mexico, low prey years limit breeding in
Harris' hawks; under these circumstances, some adult males
remain with the parental group for up to 3 yr (J. Bednarz
pers. comm.). it is certainly possible that the group of six
adults we observed consisted of a breeding pair and four
adult offspring.
The Texas population of Harris' hawks appears to
consist primarily of pairs with no helpers (Griffin 1976,
Brannon 1980). While cooperative breeding (more than
two hawks per nest) may be rare in Texas, our observa-
tions suggest that cooperative hunting may be common
when hawks are not actively nesting, a situation similar
to that reported for New Mexico (Bednarz 1988a).
RESUMEN.--Caza cooperativa o grupal es realizada por
poblaciones de Parabuteo unicinctus en Arizona y New
Mexico. Observamos cuatro incidentes de caza grupal pro-
tagonizaddos por P. unicinctus en Texas, dos en el Condado
de Webb (principios de los aftos ochenta) y dos en el
Condado de Pecos (1994). E1 tamafio grupal vari6 de
cuatro aves a grupos de seis adultos (cuatro machos y dos
hembras). Es posible que el agrupamiento para la caza y
como forma de vida pueda ser caracterlstico de algunos P
unicinctus, a travis del rango total de la especie.
[Traducci6n de Ivan Lazo]
We are grateful to J.W. Dawson and w.J. Mader for
helpful comments on the earlier draft of this manuscript,
and to referees J. Bednarz, J.W. Dawson, and M.W.
Mannan for their critical reviews.
BEDNARZ, J.C. 1987. Pair and group reproductive suc-
cess, polyandry, and cooperative breeding in the Har-
ris' Hawk. Auk 104:393-404.
1988a. Cooperative hunting in Harris' hawks
( Parabuteo unicinctus ). Science 239:1525-1527.
1988b. Harris' hawk subspecies: is superior
larger or different than harrisi? Pages 294-300 in R.L.
Glinski, B. Giron Pendleton, M.B. Ross, M.N. Le-
Franc, B.A. Millsap and S.W. Hoffman [EDS.], Pro-
ceedings of the southwest raptor management sym-
posium and workshop. Natl. Wildl. Fed. Sci. Tech.
Ser. 11, Washington, DC U.S.A.
-- ^ND J.D. LIGON. 1988. A study of the ecological
bases of cooperative breeding in the Harris' hawk.
Ecology 69:1176-1187.
B•NNON, J.D. 1980. The reproductive ecology of a
Texas Harris' hawk (Parabuteo unicinctus harrisi) pop-
ulation. M.S. thesis, Univ. Texas, Austin, TX U.S.A.
DawsoN, J.W. 1988. The cooperative breeding system
of the Harris' hawk in Arizona. M.S. thesis, Univ.
Arizona, Tucson, AZ U.S.A.
-- ^ND R.W. Mt•NN^N. 1989. A comparison of two
methods of estimating breeding group size in Harris'
hawks. Auk 106:480-483.
--AND . 1991a. Dominance hierarchiesand
helper contributions in Harris' hawks. Auk 108:649-
-- AND -- 1991b. The role of territoriality
in the social organization of Harris' hawks. Auk 108:
FAABORG, J. AND J.C. BEDNARZ. 1990. Galfipagos and
Harris' hawks: divergent causes of sociality in two
raptors. Pages 357-383 in P.B. Stacey and W.D. Ko-
enig [EDs.], Cooperative breeding in birds: long-term
studies of ecology and behavior. Cambridge Univ. Press,
Cambridge, U.K.
GRIFFIN, C.R. 1976. A preliminary comparison of Texas
and Arizona Harris' hawk (Parabuteo unicinctus) pop-
ulations. Raptor Res. 10:50-54.
M^DV.R, W.J. 1975. Biology of the Harris' hawk •n
southern Arizona. Living Bird 14:59-85.
S^NDV. RS, R.R. ^ND W.J. G^BRmL. 1985. Soil survey
of Webb County, Texas. Natl. Coop. Soil Surv., U S
Gov. Print. Office, Washington, DC U.S.A.
Received 7 November 1994; accepted 17 May 1995
J Raptor Res. 29(4):267-269
¸ 1995 The Raptor Research Foundation, Inc.
Laboratory of Applied Zoology, Faculty of Agriculture, Hokkaido University,
Sapporo 060, Japan
Research Center, Wild Bird Society of Japan, 15-8 Nanpeidai, Shibuyaku, Tokyo 150, Japan •
Group for Biological Research of Falcons, 2269- 72, Shishiuchi, Toubetu,
Ishikarigun, Hokkaido 067-37, Japan
KEY WORDS: Accipiter gentilis; A. gularis; Japanese less-
er sparrowhawk; nestling predation; Northern goshawk.
The diet of Accipiter spp. has been investigated in var-
ious localities (e.g., Brown and Amadon 1968, Opdam et
al. 1977, Kenward 1982, Goszczynski and Pilatowski 1986,
Petty 1989, Hirano and Kimiziwa 1992, Ueta 1992). In
Japan the northern goshawk (Accipiter gentilis) preys on
medium- to small-sized birds (Yamashina 1941, Ishizawa
and Chiba 1967). The Japanese lesser sparrowhawk (A.
gularis) exclusively hunts small birds such as tree sparrows
and great tits (Parus major) during the breeding season
(Hirano and Kimizawa 1992, Ueta 1992). In addition,
hawks adjust their own fledgling periods to the season that
prey bird species fledge (Newton 1986, Ueta 1993). Some
previous reports that hawks hunt nestlings have been pub-
lished (Opdam et al. 1977, Newton 1986), but these au-
thors only observed prey delivered to hawk nests. There-
fore, they did not observe the hunting technique used to
capture nestlings. In this paper, we present observations
on nestling hunting by northern goshawks and Japanese
lesser sparrowhawks.
Northern Goshawk. A northern goshawk preying on
a nestling bull-headed shrike (Lanius bucephalus) was re-
corded on videotape in western Hokkaido, northern Japan.
The nest was being videotaped as a part of a study on
shrike ecology, and was positioned among vines (Vitis co•g-
netiae) about 1.2 m above ground. The four 14-d-old nest-
lings were recorded on videotape starting at 0800 H, 21
June 1992. The adult shrikes frequently brought prey to
their nest, but during their absence the nestlings were often
exposed to predators. Nest attack and subsequent behavior
of the hawk and shrikes were as follows: At 1648 H the
male shrike brought prey to the nest and left carrying a
fecal sac. At 1649 H the goshawk approached the nest
while parents gave alarm calls nearby. At 1650 H the
hawk grasped one nestling and flew away with it. At 1652
H one nestling left the nest. The other two nestlings also
left the nest at 1655 H and 1657 H, respectively. At 1700
H the parents again gave alarm calls. A few moments later
the hawk came back and searched the vacant nest for a
few minutes. The hawk remained in the vicinity and might
have been searching for the rest of the nestlings for several
minutes and then left the observation site. Even though
... The occurrence and seasonality of cooperative hunting varies within and among U.S. subpopulations (Bednarz 1987, Coulson and Coulson 1995, Dawson 1998. In Arizona, groups are largest and hunt together year round, whereas in New Mexico, groups are intermediate in size and hunt cooperatively mostly during the non-breeding season. ...
... In Arizona, groups are largest and hunt together year round, whereas in New Mexico, groups are intermediate in size and hunt cooperatively mostly during the non-breeding season. Groups are rare in Texas, and although studies at nests did not detect group hunting (Griffin 1976, Brannon 1980, it sometimes occurs (Coulson and Coulson 1995). Neither cooperative hunting nor cooperative breeding has been documented in Central or South America (Dwyer and Bednarz 2011), but see Santander et al. (2011). ...
... The occurrence and seasonality of cooperative hunting varies within and among U.S. subpopulations (Bednarz 1987, Coulson and Coulson 1995, Dawson 1998. In Arizona, groups are largest and hunt together year round, whereas in New Mexico, groups are intermediate in size and hunt cooperatively mostly during the non-breeding season. ...
... In Arizona, groups are largest and hunt together year round, whereas in New Mexico, groups are intermediate in size and hunt cooperatively mostly during the non-breeding season. Groups are rare in Texas, and although studies at nests did not detect group hunting (Griffin 1976, Brannon 1980, it sometimes occurs (Coulson and Coulson 1995). Neither cooperative hunting nor cooperative breeding has been documented in Central or South America (Dwyer and Bednarz 2011), but see Santander et al. (2011). ...
... In this way, Harris' hawk subgroups "leapfrog" throughout the group's home range, occasionally rejoining and splitting again, while moving in one general direction. This type of move-search hunting tactic was achieved by Harris' hawks during group hunting (Mader, 1975;Bednarz, 1988;Coulson and Coulson, 1995). ...
Full-text available
This thesis entitled “Hunting cooperation among predators: A mathematical study of ecological models” attempts to study the effect of hunting cooperation among predators in ecological systems. In nature, many predator species cooperate during hunting for a variety of reasons, such as (i) hunting and killing large prey, (ii) searching for food, (iii) increasing the ability to capture (or subdue) prey, (iv) attacking a herd of prey, (v) increasing vigilance and protection against other predators, (vi) preventing the theft of corpses by other hunters, (vii) reducing the distance of chasing, etc. Thus how predators enhance their biomass by group hunting, and as a result, how they impact prey biomass is a natural issue. Although, the study of cooperative behaviour during hunting is not new, in the mathematical modelling approach there are only a few studies. Thus the main objective of the study is to observe the dynamics of two-species predator-prey models in the presence of hunting cooperation among predators. In Chapter 1, first, we briefly described the evolution of mathematical models in ecology with the emphasis of two-species interaction and different types of functional response. Then characterize the cooperative hunting phenomenon in an ecological context. Here, we mainly concern with the following ecological issues: (1) why predators cooperate during hunting? (2) example of different cooperative hunting species and their strategies, (3) how to incorporate cooperative hunting phenomenon in ecological models? In Chapter 2, we consider a discrete-time predator-prey model with logistic type prey growth to study the impact of hunting cooperation. We investigate the basic analysis of the discrete model such as fixed points, stability, and bifurcation analysis, and explore that hunting cooperation has the potential to modify the well-known period-doubling route to chaos by reverse period-halving bifurcations and makes the system stable. Also, for an additional increase of the strength of hunting cooperation, the system exhibits chaotic oscillations via Neimark-Sacker bifurcation. However, very high hunting cooperation can be detrimental for the system and populations go to extinction. This is because of the overexploitation of the prey populations by their predators. The discrete system shows bistability behaviour between prey only fixed point and interior fixed point, and the basin of attraction of the interior fixed point increases with the strength of hunting cooperation. Moreover, hunting cooperation induces a strong demographic Allee effect in the discrete system, where predator populations persist due to cooperation during hunting and would go to extinction without hunting cooperation. In Chapter 3, we extend the continuous version of the model studied in the previous chapter, by incorporating predator induce fear in the birth rate of the prey population. We observe that without hunting cooperation, the unique coexistence equilibrium point is globally asymptotically stable. However, an increase in the hunting cooperation induce fear may destabilize the system and produce periodic solution via Hopf bifurcation. We explore very rich dynamics such as both supercritical and subcritical Hopf bifurcations, Bogdanov-Takens bifurcation, backward bifurcation, and different types of bistabilities. This model also generates strong demographic Allee effect in predator species. In Chapter 4, we study another type of model namely, the modified Leslie-Gower model with the same phenomena, hunting cooperation in predators and fear effect in prey. The main feature of Leslie-Gower model with compare to the Lotka-Volterra model is the logistic growth of predators, where the carrying capacity of the predator species is proportional to the prey biomass. We observe that the fear factor can stabilize the predator-prey system by excluding the existence of periodic solutions and makes the system more robust compared to hunting cooperation. This system also shows very rich dynamics such as Hopf bifurcation, Bogdanov-Takens bifurcation, and multi-type bistabilities. Chapter 5 is devoted to exploring the impact of time delay during cooperative hunting in a predator-prey model. Cooperative hunting predators do not aggregate in a group instantly but individuals use different stages and strategies such as tactile, visual, vocal cues/signals, or a suitable combination of these to communicate with each other. It is indeed plausible to add some time delay representing the delay in forming a group and ready for attack. Generally, delay has a destabilizing effect on predator-prey dynamics, but in our model, delay has both stabilizing as well as destabilizing effects. Also, for an increase in the strength of the delay, then system dynamics switch multiple times and finally become chaotic. We see that depending on the threshold of time delay, the system may restore its original state or may go far away from its original state and unable to recollect its memory. We also observe different kinds of multistability behaviours, coexistence of multiple attractors, and interesting changes in the basins of attractions of the system. We infer that depending on the initial population size and the strength of cooperation delay, the populations can exhibit stable coexistence, oscillating coexistence, or extinction of the predator species. Hunting cooperation has both stabilizing and destabilizing effects on the dynamics of the systems depending on the values of model parameters. It can mediate the survival of predators, where predators go extinct without cooperation. Mathematical models with hunting cooperation among predators may exhibit different types of bistabilities (node-node/node-cycle). This can be biologically interpreted as, depending on the initial population size, the populations can exhibit stable coexistence, oscillating coexistence, or extinction of the predator species (for the case of specialist predators). Predator-prey models with hunting cooperation among predators exhibit rich dynamical behaviours. We believe that, this research work will definitely enrich the existing knowledge about the impact of hunting cooperation in predators on various mathematical models in ecology.
... The existence, abundance and distribution of a species in an ecosystem are determined by whether the levels of one or more physical or chemical factors fall within the range tolerated by that species. The growth period and metabolic rates of insects significantly reduces as strident environmental conditions influence their survival including their altitudinal distribution range [9,10] . To gain a comprehensive understanding of species distributional patterns it is necessary to know the extent to which, species altitudinal distributions change among different taxa and across geographically separated areas [11,12] . ...
Full-text available
Analyzing the changes in eco system co-related with species diversity across different altitudinal and latitudinal gradients are essential in understanding the complex nature of biodiversity. Four different eco systems was selected and analyzed to examine the altitudinal and latitudinal variations in the distributional pattern of Drosophila (Diptera: Drosophiladae) Population in Kodachadri Hills, Kath lekhan, Gopal Swamy Hills and Nandi Hill regions of Karnataka state, India. Cluster analysis, constancy methods, Simpson's, Berger-Parker's, and Shannon-Weiner indices were used to analyze the species occurrence qualitatively. We hypothesized that the Gause's competitive exclusion principle still remains to be questionable and have used 4 sets of environmental data to build a model using Venn's 4 set diagram illustrating the common species accommodated at differing eco systems and have characterized species-environment relationship. We recorded 13 species from 8 different altitudes varying between 530m and 1478m and evaluated clinal trends in species distributional pattern among different ecological niche. The result indicates that Drosophila community was significantly affected by elevation as the density of Drosophila decreased with increasing altitudes. Drosophila ananssae, Drosophila bipectinata, Drosophila malerkotliana, Drosophila nasuta and Phorticella striata were the 5 common dominant species, further, Drosophila bipectinata and Drosophila malerkotliana being the two competing sympatric species was co-existed in all the four different eco systems. These data indicate there is a positive correlation between species diversity and elevation and also there is an emphatical interaction between competing species to co-exist in the same niche.
... Parabuteo unicinctus is a relative habitat specialist, with some preference for little disturbed habitats for breeding, although it is not exclusive to these environments. It predates mainly on lagomorphs, but also on some other small mammals (Bednarz and David 1988;Coulson and Coulson 1995;Johnsgard 1990;Rodríguez-Estrella 1997;Partida 2015). Caracara cheriway is a habitat and diet generalist, its diet consists of both carrion and living preys such as small mammals, reptiles, birds and invertebrates (Preston and Beane 1993;Rodríguez-Estrella and Rivera 1997). ...
Full-text available
Prioritizing biodiversity conservation strategies is urgently needed. Surrogate species have been used for that purpose as a means to lower costs/effort to assess representation of other species important for conservation planning. Such strategy should include multiple species and habitats within a given landscape or geographic area. The use of surrogates provides an appealing shortcut to monitoring biodiversity as it enables an efficient use of limited resources. As a group, raptors feed on a very wide range of prey sizes and, therefore, on a high diversity of prey species, which should improve their surrogacy complementarity. The aim of this paper is to identify a suitable approach that can be used as an efficient surrogate of regional diversity in desert ecosystems. First, through assemblage concordance analysis we tested two alternative approaches either using: (a) a single raptor species or (b) the entire group of raptor species as surrogates of biodiversity. Second, through correlation analysis we also tested whether the species richness of single target groups (raptors, other birds, reptiles, mammals and plants), or of two-group combinations, was correlated with the pooled species richness of the remaining groups, and then determine each of the taxonomic groups as surrogates of the entire biodiversity at the regional scale. Four single raptor species showed significant concordance with the entire bird community but, overall, most comparisons between single raptor species and other taxonomic groups failed to show any consistent correlation. A remarkable finding from the single species approach was that the strongest significant positive association was that found between caracara C. cheriway and bird species richness. This raptor is a habitat and diet generalist, thus contradicting the hypothesis that specialist species make the best bioindicators. Raptor species were significantly associated with non-raptor birds, vegetation and rodents, but not with the mammal or reptile communities. Plant species richness showed a statistically significant concordance with most of the other groups except for reptiles. Reptiles were the group that showed less concordance with the others. Between-groups comparisons showed that the species richness was strongly correlated between birds and plants, followed by between raptors and birds; correlations between birds and mammals, reptiles and mammals and raptors and plants were weak albeit statistically significant. Species richness of some individual groups, namely other birds, plants and mammals, were significantly correlated with their corresponding remaining richness values. The pooled species richness of two-group combinations were strongly correlated for raptors and other birds, raptors and plants, other birds and mammals, and reptiles and plants, and their corresponding remaining richness. We propose an approach using the combined species richness of two taxonomic groups given the high, statistically significant correlation with their corresponding remaining richness in the Baja California peninsula and possibly in other desert ecosystems too.
Full-text available
The Harris's Hawk (Parabuteo unicinctus), a social raptor species, often breeds and hunts cooperatively in groups typically consisting of a dominant breeding pair and one or more auxiliary group members. Why these birds form social groups is not completely understood, but one hypothesis is that the ability to hunt cooperatively may benefit groups with a higher hunting success rate or facilitate the capture of larger prey than an individual hawk could catch on its own. To test the hypothesis that group hunting affects patterns of prey delivery and the types of prey delivered to nests, we recorded videos of prey deliveries in May and June at nests of five breeding groups and five breeding pairs in Cameron County and Willacy County, Texas. In contrast to the diets of Harris's Hawks in New Mexico and Arizona that depend heavily on lagomorphs, we documented mostly avian prey items (39.1% of prey deliveries) and rodent prey items (39.1%), and only 0.7% lagomorphs (n = 284 prey items recorded). Significantly more prey items per day were delivered to nests with more nestlings. Importantly, and contrary to our hypothesis, pairs delivered more prey items per day on average than groups; this pattern was not significant, but this may be attributable in part to a small sample size of nests. These results suggest that the presence of auxiliaries may not necessarily provide direct benefits to offspring during the nest provisioning stage at late spring and summer nests in south Texas.
Birds of prey are highly complex and intelligent species with many of their activities deeply rooted in modal action patterns, such as foraging, courtship and nest building, migration, bathing, or preening. Raptors in managed care are susceptible to presenting undesired behavior when the environment provides antecedents for these behaviors and consequences to maintain them. This article aims to describe concepts of behavior in birds of prey in managed care, with inferences from their wild counterparts, to assist in understanding the etiologies and management of undesired behaviors.
Swarm intelligence is a modern optimization technique, and one of the most promising techniques for solving optimization problems. In this paper, a new swarm intelligence based algorithm namely, Harris’ Hawk Optimizer (HHO) is proposed. The algorithm mimics the cooperative hunting behaviour of Harris’ hawks. The algorithm is analysed for twenty five well known benchmark functions. Performance of HHO is compared with Particle Swarm Optimization (PSO), Differential Evolution (DE), Grey Wolf Optimizer (GWO) and The Whale Optimization Algorithm (WOA). HHO is implemented and results present HHO as one of the efficient optimization methods.
Full-text available
El Gavilán Mixto es una de las rapaces más frecuentemente obervada en la ciudad de Buenos Aires, habiéndose registrado principalmente en espacios verdes. En este trabajo estudiamos la dieta del Gavilán Mixto durante el período reproductivo a partir de restos de presas registrados en la Reserva Ecológica Costanera Norte, Ciudad Autónoma de Buenos Aires, Argentina, identificando las presas a nivel de especie y calculando el aporte de biomasa de cada una. Los resultados que reportamos admitirían catalogar a esta especie como parte del gremio de consumidores de mamíferos, con predilección por presas de tamaño medio. La amplitud y variedad de su dieta en diferentes regiones y diversos ambientes indican cierta flexibilidad en sus hábitos de alimentación y en sus tácticas de caza. Esto se refleja también en el aprovechamiento de presas alternativas temporal o regionalmente abundantes, como el caso de los anfibios que reportamos. Por lo tanto, estas observaciones sugieren que el Gavilán Mixto presenta una dieta generalista y una conducta de caza oportunista, tal como ha sido propuesto para muchas otras rapaces.
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Zelus annulosus is an assassin bug species mostly 28 noted on Hirtella physophora, a myrmecophyte specifically associated with the ant Allomerus decemarticulatus known to build traps on host tree twigs to ambush insect prey. The females lay egg clutches protected by a sticky substance. To avoid being trapped, the first three instars of Z. annulosus nymphs remain grouped in a clutch beneath the leaves where they hatched, yet from time to time they climb onto the upper side to group ambush prey. Long-distance prey detection permits these bugs to capture flying or jumping insects that alight on their leaves. Like for some other Zelus species, the sticky substance of the sundew setae of their forelegs aids in prey capture. Group ambushing permits early instars to capture insects that they then share or not depending on prey size and the hunger of the successful nymphs. Fourth and fifth instars, with greater needs, rather ambush solitarily on different host tree leaves, but attract siblings to share large prey. Communal feeding permits faster prey consumption, enabling small nymphs to return sooner to the shelter of their leaves. By improving the regularity of feeding for each nymph, it likely regulates nymphal development, synchronizing molting and subsequently limiting cannibalism.
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