The Chukar subspecies Alectoris chukar sinaica inhabits the Negev desert, which is characterized by hot, dry summers, and little winter rainfall. Vegetation is dry and dormant during the summer and autumn; green, succulent vegetation is available following winter rain. We studied whether or not and under what dietary conditions Chukars require drinking water. Four groups of Chukars in an outdoor aviary received either a dry ration + water, a dry ration + green vegetation, a dry ration + green vegetation + water, or green vegetation only.
The birds offered only greens lost 15% of their body mass in the first 8 days and 2.9% over the next 6 days, while birds on the other three treatments maintained body mass. The birds receiving only greens had the highest total body water to body mass ratio and the highest water influx. We concluded that the Chukars receiving only green vegetation met their water requirements but not their maintenance energy requirements. Chukars fulfilled both their water and energy requirements on a dry ration + green vegetation (without drinking water); the green vegetation comprised approximately 60% of their total fresh matter intake, or 26% of their total dry matter intake. Our analysis suggests that wild desert Chukars do not require drinking water from early winter to late spring, when succulent forage is available, but probably need free water during summer and autumn, when the bulk of their diet is seeds. Received 15 March 1983, accepted 8 July 1983.
Jacob Blaustein Institute for Desert Research, Ben-Gurion University of the Negev,
Sede Boqer Campus, 84990 Israel
BIRDS inhabiting deserts are often faced with
hot, dry environmental conditions as well as
sparse and unpredictable water and food sup-
plies. Diurnal, granivorous birds are most vul-
nerable to these harsh conditions, especially
those unable to fly great distances in search of
water or food. In addition, seeds, their princi-
pal food during the hot summer, yield little
preformed water at a time when their water
requirements for thermoregulation are great-
est. Although some small passerines are able to
maintain body mass (mb) when offered dry food
without drinking water, most seed-eating birds
must drink (Bartholomew and Cade 1963, Bar-
tholomew 1972, Dawson 1976). Some primarily
granivorous species can meet their water re-
quirements by adding succulent vegetation
and/or insects to their diet, however.
The desert subspecies of Chukar (Alectoris
chukar sinaica) is a primarily granivorous, diur-
nal phasianid and is a permanent resident of
the Negev desert, Israel (Nissani 1974). These
birds inhabit areas where annual rainfall may
be 90 mm or less and where surface water may
be unavailable year round (H. Mendelssohn, G.
Illani pers. comm.). Although Chukars have
relatively low water influxes (Degen et al. 1982),
previous reports have indicated that they de-
pend on surface water when succulent forage
is unavailable (Bump 1953, Christenson 1954,
McLean 1955, Harper et al. 1958) and that they
concentrate at open water sources during the
summer (Alcorn and Richardson 1951, Chris-
tenson 1958, Alkon 1974).
We examined whether or not and under what
conditions desert Chukars depend on the avail-
ability of drinking water. We measured the
body mass of Chukars caged in an outdoor avi-
ary during the summer and estimated their to-
tal body water, water influx, and food intake
when offered a dry ration and/or green, suc-
culent vegetation with and without drinking
water.
MATERIALS AND METHODS
Experimental design.--The study was made during
late summer at Sede Boqer (30ø52'N, 34ø46'E, 476 m
above sea level) in the central Negev highlands, Is-
rael. Chukars trapped near Sede Boqer were held in
an outdoor aviary, which was partitioned into four
similar cages (each 5 x 3 x 2.5 m) constructed of
chicken wire. The cages shared a common rear wall
and a sloping roof, which provided shade in parts of
the cage throughout the day, either on the ground
or on perches. Fresh tap water was available in open
troughs as required by protocol. Floor material was
gravel, and fine sand was provided to allow the birds
to dust bathe. For at least 6 weeks before experimen-
tation, all birds received a diet of a 1:1 mix of 15%
protein chicken chow and whole sorghum seeds (dry
ration) with occasional green vegetation. During the
experiment, green vegetation (greens) consisted of
both alfalfa seedlings (Medicago sativa) and 5- to 10-
day old wheat seedlings. The former were freshly
picked, while the latter were grown in styrofoam trays
(30 x 60 cm).
Twenty-four adult Chukars of both sexes were
weighed (initial rnb) and randomly separated into four
groups. Each group was placed in a cage on one of
the following dietary regimes for 14 days: Cage I--
dry ration + water; Cage II--dry ration + greens;
Cage III--dry ration + greens + water; Cage IV--
greens. Food was available ad libiturn throughout the
day, and fresh food was placed in the cages between
1600 and 1700 daily. Old wheat trays were usually
replaced with new trays, but on occasion it was nec-
essary to use wheat from a previous day, which had
regrown to some extent. Samples of all feed were
dried at 70øC to constant mass for moisture determi-
nation. On day 11, birds offered only greens were
visibly weak, and, consequently, they were given
younger wheat seedlings with a larger amount of
endosperm, i.e. a more digestible and concentrated
source of energy, until the end of the experiment.
Birds in other cages did not receive this food.
Using tritiated water (TON) in accordance with
Degen et al. (1981), we estimated total body water
(TBW) for all birds on day 8. The birds were weighed
(to the nearest 0.1 g) and injected intramuscularly
with 0.1 mCi/kg rnb of TON in approximately 1 ml
(weighed to 0.1 mg, assuming 1 ml weighs 1 g) sterile
avian saline. After 45 to 60 min, to allow TON equil-
ibration with body fluids, birds were reweighed, and
blood samples were taken from the basilic vein for
TBW estimation (as TON space). The mean of the two
body masses, that is before TON injection and after
blood sampling, was used in subsequent calculations.
Six days after injection, birds were weighed, and
blood samples were collected to estimate water in-
flux. We assumed that maintenance of constant body
mass over the 6-day period, as in Cages I, II, and III,
indicated constant TON space. When body mass
changed, as in Cage IV, we assumed the ratio of TON
space to body mass was constant and that changes
were linear with time (Nagy and Costa 1980).
Serum samples of 0.05 ml were added to 5 ml Bray's
solution and specific activity of tritium was measured
in duplicate samples in a liquid scintillation counter
(Packard Tri-Carb, model PLD). Counts were cor-
rected for 6% dry matter content of the serum and
for quenching, which was estimated by use of
quenched standards (Packard).
Calculation of food intake.--The daily, dry-ration in-
take of birds in Cage ! (dry ration + water) was cal-
culated as:
rnb x EE
D ME x F' (1)
where D = fresh mass of dry ration (g); rnb = body
mass (g); EE = existence energy (kJ/g rob); ME =
metabolizable energy of D (kJ/g dry matter); and
F = fractional dry matter content of D.
Using the same dry ration, we had previously es-
timated that the daily existence energy of caged Chu-
kars was 0.438 kJ/g rnb, and that 1 g of the dry matter
had a metabolizable energy content of 13.8 kJ and
yielded 0.5 g of metabolic water (Pinshow et al. 1983).
FD was 0.879 in the present study.
Greens (G) had a moisture content of 80.0%, and
we assumed that 1 g of dry matter had a metaboliz-
able energy content of 15.4 kJ and yielded 0.5 g of
metabolic water (Hill 1964).
For birds in Cage I! (dry ration + greens), the daily
energy obtained from the dry ration was 13.8 (kJ/
g) x 0.879 D (g) and from the greens was 15.4 (kJ/
g) x 0.2 G (g). Therefore:
12.13 D + 3.08 G = rnb x 0.438, (2)
where G = fresh mass of greens (g).
Preformed water from the dry ration was 0.121 x
D (g), and metabolic water was 0.5 x 0.879D (g),
whereas for the greens these values were 0.8 x G (g)
and 0.5 x 0.2G (g). Therefore:
0.56D + 0.9G = WI, (3)
where WI = water influx (g).
Solving for D and G in equations (2) and (3), we
calculated the dry ration and greens consumed by
birds in this treatment.
Our casual observations indicated that the birds in
Cage II! (dry ration + greens + water) ate the same
amounts of dry ration and greens as did the birds in
Cage I! (dry ration + greens). We therefore assumed
that the difference between their water influxes was
a result of water drunk.
The greens intake of the birds in Cage IV (greens
only) was calculated as:
0.8G + 0.5 x 0.2G = WI. (4)
In all four cages, water obtained from food (pre-
formed and metabolic) was calculated, and, in Cages
! and III, water drunk was calculated as the difference
between water influx and water from food.
Data analysis.--Upon comparison of initial body
mass of the Chukars among the four cages, we found
that the mean body mass of the birds in Cage IV was
significantly different from those in the other three
cages. Therefore, subsequent mass-specific statistical
comparisons of TBW and water influx were made.
Analysis of variance was used to test whether or not
means were different among treatment diets. A level
of P < 0.05 was chosen as significant, and means were
separated by a Student Neuman-Keuls test (Steel and
Torrie 1960).
RESULTS
The average minimum and maximum air
temperatures in the aviary were 16.5øC and
35.9øC, respectively, and water vapor pressure
varied between 17.8 and 20.8 mbars. Relative
humidity varied from approximately 35% at
midday to 95% between 0200 and 0600 over the
same period (Meteorology Unit, Jacob Blau-
stein Institute for Desert Research). No rain fell
during the study.
Birds fed mostly at first light. Feeding in late
afternoon was observed on two occasions, when
birds in Cage IV (greens only) were given
younger wheat seedlings. All birds, except those
receiving only greens, maintained their mb
throughout the experimental period. Birds giv-
en only greens lost 15% of their initial body
mass after 8 days and a further 2.9% in the fol-
lowing 6 days (Table 1).
On day 8 of treatment, the total body water
volumes (TBW) of the birds ranged from 64.4%
of body mass for birds receiving dry ration +
greens + water to 68.1% for birds receiving
greens only (Table 1). Daily water influx be-
tween days 8 and 14 ranged from 50.2 + 9.9
ml.kg - .day - for birds receiving dry ration +
greens to 103.1 + 20.9 ml-kg--day - for birds
receiving greens only. Differences in TBW and
water influx among treatments were significant
(Table 1).
It was calculated that the dry matter intake
of the birds fed only greens was 22.6 g/kg mb,
29% less than that of the other three treatments
(Table 2). The birds on the dry ration + greens
diet consumed 11.0 g dry ration and 15.8 g
greens. Thus, greens comprised 60% of the total
fresh matter intake or 26% of the total dry mat-
ter intake (Table 2).
DISCUSSION
Most seed-eating birds inhabiting deserts de-
pend on drinking water in the absence of suc-
culent vegetation and/or insects (Fisher et al.
1972, Bartholomew 1972, Dawson 1976), as the
&
+1 +1 +1
+++
TABLE 2. Calculated daily mean food and water intakes for Chukars on 4 different diets (see text for details
of diet).
Fresh mass intake (g)
Dry mass intake,
DMI (g)
Dry Dry
Cage Diet ration Greens Total ration Greens Total
Water influx
(ml)
Pre-
formed
DMI/mb + meta-
(g/kg) Drunk bolic
! Dry ration + water 15.1 -- 15.1 13.3 -- 13.3 31.6 22.1 8.5
II Dry ration + greens 11.9 17.0 28.9 10.4 3.4 13.8 31.7 -- 21.9
III Dry ration + greens 11.0 15.8 26.8 9.7 3.2 12.9 31.7 3.8 20.3
+ water
IV Greens -- 35.9 35.9 -- 7.2 7.2 22.6 -- 32.3
preformed and metabolic water obtained from
dry food is insufficient to meet their water re-
quirements. Many of these birds, however, do
not have to drink when succulent, green vege-
tation is available in addition to the dry food.
This is the case with a number of quail species
such as California Quail (Callipepla californica;
Bartholomew and MacMillen 1961), Gambel's
Quail (C. gambelii; Gullion 1960), and Monte-
zuma Quail (Cyrtonyx montezumae; Leopold and
McCabe 1957).
We have observed Chukars drinking surface
water in the summer months when their diet
is principally dry seeds. In addition, we have
shown that in the laboratory (Pinshow et al.
1983) and in the field (Degen et al. 1983) they
must drink when dry food alone is available.
When succulent vegetation is their principal
food component, the water influx of Chukars
can increase four-fold when compared to Chu-
kars eating primarily seeds, but this may be
accompanied by an initial decrease in body mass
and body solids. In this situation, water influx
clearly exceeds the birds' water requirements,
while energy intake is below that required for
maintenance (Alkon et al. 1982).
This study showed that Chukars faced with
an abrupt shift to only greens from a diet of
dry ration + greens + water increased their
water influx substantially, but their energy in-
take for maintenance was insufficient. In ad-
dition, the birds fed only greens had the larg-
est TBW to body-mass ratio, indicating that they
had the lowest body-solid and, presumably,
lipid content to body-mass ratio. Chukars
maintained body mass on a dry diet supple-
mented by greens, however. We calculated that
if greens that are 80% water (26% of the total
dry matter content) comprise some 60% or more
of their fresh food, then Chukars can obtain
sufficient water to maintain their water bal-
ance.
Chukars fed only greens had the highest
water influx, a consequence of the high water
content of the greens. The water influx of these
birds was lower, however, than that of free-
living Chukars feeding mainly on green vege-
tation during the winter (Alkon et al. 1982).
The fractional moisture content (0.80) of the
greens during this summer study was lower
than that of the winter green vegetation that
Chukars eat in the wild (unpubl. data), and this
could explain the difference in water influx.
Birds that received a dry ration + water had a
higher water influx than the two groups that
received a dry ration + greens (Cages II and
III). This is a possible result of the higher pro-
tein and electrolyte contents of the former diet,
necessitating more water for nitrogenous and
electrolyte waste excretion (McNabb et al. 1972).
Ecological implications.--The Negev highlands
are characterized by hot, dry summers with 250-
300 biologically "dry" days per year (UNESCO
1963). Annual precipitation averages 90 mm,
with all rain falling during the winter months.
Temperatures are highest in August, with a
daily mean of 25.3øC, and are lowest in January,
with a daily mean of 9.7øC (Desert Meteorology
Unit, Jacob Blaustein Institute for Desert Re-
search).
The onset of germination and the growth of
annual and perennial plants are linked to the
timing of winter rains. The major period of
plant growth is in winter and early spring, i.e.
usually from mid-January to mid-April, and
most herbaceous vegetation is dry and dormant
IO0
20 4 20 19
90
80
70
60
oJ
50
40
oJ
E 30
o
L)
c 20
o
IO
o
June Aug, Jan, Feb, Mar,
1981 1982
-] seed s arthropods
fruits .'.:green vegetation
[Ill. germinating seeds & bulbs
Fig. 1. Fresh matter components of Chukar crop
contents during summer (June, August), winter (Jan-
uary, February) and spring (March). Crop contents
were separated into items of high (green vegetation,
germinating seeds and bulbs, fruits, and arthropods)
and low (seeds) moisture content. The number of
crops analyzed each season is given at the top of each
column.
by mid-May. Large variations in primary pro-
duction, especially of annual plants, are char-
acteristics of the study region (Evenari 1981).
In a separate study (P. U. Alkon et al. MS),
the crops of 76 Chukars, collected during dif-
ferent seasons, were examined for food types
and quantities. Crop contents were categorized
into items with high (green vegetation, sprout-
ing seeds, fruits, and arthropods) and low
(seeds) moisture content. In general, the ratio
of high- to low-moisture-content food (Fig. 1)
followed the seasonal availability of green
vegetation. It is apparent that captive Chukars
can fulfill their water requirements if approx-
imately 60% of their fresh-matter intake is green
vegetation. If we assume that the ratio of water
to dry matter intake is the same in caged and
free-living birds, then free-living Chukars may
be independent of drinking water from early
winter to sometime in late spring. During the
summer and autumn, however, when seeds
form the bulk of their diet and vegetation is
dry, Chukars must drink. Because Chukars have
been observed in areas where surface water is
unavailable in the summer and autumn (H.
Mendelssohn, G. Illani pers. comm.), we as-
sume that either these birds have access to suc-
culent vegetation all year, or they migrate pe-
riodically to surface water.
ACKNOWLEDGEMENTS
We thank Philip U. Alkon for helpful comments
on the manuscript. The study was done in the Lady
Edith Wolfson Laboratory for Environmental Physi-
ology and was supported by United States-Israel Bi-
national Science Foundation grants 2496/81 and 2911/
82. Berry Pinshow is a Bat-Sheva de Rothschild Fel-
low.
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