.bird {
    background-image: url(../img/oiseau.svg);
    background-size: auto 100%;
    width: 88px;
    height: 125px;
    will-change: background-position;
    animation-name: fly-cycle;
    animation-timing-function: steps(10);
    animation-iteration-count: infinite;
}
.bird--one {
    animation-duration: 1s;
    animation-delay: -0.5s;
}
.bird--two {
    animation-duration: 0.9s;
    animation-delay: -0.75s;
}
.bird--three {
    animation-duration: 1.25s;
    animation-delay: -0.25s;
}
.bird--four {
    animation-duration: 1.1s;
    animation-delay: -0.5s;
}
.bird-container {
    position: absolute;
    top: 10%;
    left: -7.5vw;
    will-change: transform;
    animation-name: fly-right-one;
    animation-timing-function: linear;
    animation-iteration-count: infinite;
}
.bird-container--one {
    animation-duration: 15s;
}
.bird-container--two {
    animation-duration: 16s;
    animation-delay: 1s;
}
.bird-container--three {
    animation-duration: 14.6s;
    animation-delay: 9.5s;
}
.bird-container--four {
    animation-duration: 16s;
    animation-delay: 10.25s;
}

 @keyframes fly-cycle {
 100% {
 background-position: -900px 0;
}}

@keyframes fly-right-one {
 0% {
 left: -10%;
 transform: scale(0.3);
}
 10% {
 left: 10%;
 transform: translateY(2vh) scale(0.4);
}
 20% {
 left: 30%;
 transform: translateY(0vh) scale(0.5);
}
 30% {
 left: 50%;
 transform: translateY(4vh) scale(0.6);
}
 40% {
 left: 70%;
 transform: translateY(2vh) scale(0.6);
}
 50% {
 left: 90%;
 transform: translateY(0vh) scale(0.6);
}
 60% {
 left: 110%;
 transform: translateY(0vh) scale(0.6);
}
 100% {
 left: 110%;
 opacity: 1;
 transform: translateY(0vh) scale(0.6);
}}

@keyframes fly-right-two {
 0% {
 left: -10%;
 opacity: 1;
 transform: translateY(-2vh) scale(0.5);
}
 10% {
 left: 10%;
 transform: translateY(0vh) scale(0.4);
}
 20% {
 left: 30%;
 transform: translateY(-4vh) scale(0.6);
}
 30% {
 left: 50%;
 transform: translateY(1vh) scale(0.45);
}
 40% {
 left: 70%;
 transform: translateY(-2.5vh) scale(0.5);
}
 50% {
 left: 90%;
 transform: translateY(0vh) scale(0.45);
}
 51% {
 left: 110%;
 transform: translateY(0vh) scale(0.45);
}
 100% {
 left: 110%;
 transform: translateY(0vh) scale(0.45);
}}